Radiofrequency ablation annotation algorithm reduces the incidence of linear gaps and reconnection after pulmonary vein isolation Elad Anter, MD, Cory M. Tschabrunn, CEPS, Fernando M. Contreras-Valdes, MD, Alfred E. Buxton, MD, Mark E. Josephson, MD From the Harvard-Thorndike Electrophysiology Institute, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts. BACKGROUND A common mechanism of atrial fibrillation recurrence after catheter ablation is resumption of pulmonary vein (PV) conduction due to gaps in the ablation line. These gaps may go unrecognized owing to inadequate ablation lesion annotation. OBJECTIVE To examine the utility of an automated radiofrequency (RF) ablation annotation algorithm for the detection and treatment of ablation gaps during pulmonary vein isolation (PVI). METHODS Eighty-four patients with paroxysmal atrial fibrillation underwent PVI. In 42 patients (group A), RF ablation was guided by an automated algorithm with predefined criteria of catheter stability range of motion r2 mm and impedance decrease Z5% for individual ablation applications. In 42 control patients (group B), ablation was guided by the operator. Successful PVI, conduction recovery, and dormant conduction with adenosine were compared between the groups. RESULTS Ipsilateral PVI at the completion of the initial anatomical line was obtained in 90.5% of group A patients (76 of 84 ipsilateral pairs of PVs) but only in 66.7% of group B patients (56 of
Introduction Pulmonary vein isolation (PVI) is an effective therapy for patients with symptomatic atrial fibrillation (AF) and is the cornerstone of ablation. However, arrhythmia recurrence is common and often related to the resumption of conduction between the pulmonary vein (PV) and the left atrium (LA).1,2 The mechanism of recovered conduction is usually partialthickness lesion formation that causes temporary electric uncoupling but not cell death.3 Thus, lesion gaps can go undetected during the index procedure only to recover conduction after the procedure.4–6 The real-time detection of ablation gaps may be facilitated by reviewing the annotated ablation lesions on the Dr Anter has received research grants from Biosense Webster and Boston Scientific. Dr Josephson has received research grants and speaking honoraria from Medtronic. Address reprint requests and correspondence: Dr Elad Anter, Harvard-Thorndike Electrophysiology Institute, Beth Israel Deaconess Medical Center, Harvard Medical School, 185 Pilgrim Rd, Baker 4, Boston, MA 02215. E-mail address: [email protected].
1547-5271/$-see front matter B 2014 Heart Rhythm Society. All rights reserved.
84 ipsilateral pairs of PVs) (P ¼ .0001). Ineffective energy delivery was detected in 23% (1005 of 4362) of group A applications but only in 9% (368 of 4071) of group B applications (P ¼ .0001). The frequency of conduction recovery was lower in group A than in group B (5.9% vs 25%; P ¼ .001). Arrhythmia-free survival at 6 months trended higher in group A (38 of 42 [90%]) than in group B (32 of 42 [76%]; P ¼ .07). CONCLUSION Automated ablation lesion annotation provides real-time feedback of RF ablation that may improve effective energy delivery. KEYWORDS Atrial fibrillation; Acute reconnection; Pulmonary vein isolation; Catheter ablation; Recurrence ABBREVIATIONS AF ¼ atrial fibrillation; LA ¼ left atrium; PV ¼ pulmonary vein; PVI ¼ pulmonary vein isolation; RF ¼ radiofrequency (Heart Rhythm 2014;11:783–790) I 2014 Heart Rhythm Society. All rights reserved.
electroanatomical map. However, this method is subjected to significant limitations: (1) annotation of ablation lesions is performed subjectively in terms of the precise location and carries significant intra- and interoperator variability; (2) ablation tags are annotated in an “all or none” fashion, lacking the biophysical parameters of individual ablation lesions (ie, temperature, power, impedance change, stability, and contact force). Thus, the current annotation of ablation lesions on electroanatomical mapping systems is insufficient for the detection of sites potentially subjected to insufficient ablation. The objective of this study was to determine the utility of an automated ablation annotation algorithm for the detection of gaps during PVI and its effect on acute PV reconnection and dormant conduction.
Methods Patients We prospectively studied 84 patients with symptomatic paroxysmal AF undergoing index PVI. In 42 patients (group http://dx.doi.org/10.1016/j.hrthm.2014.02.022
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Heart Rhythm, Vol 11, No 5, May 2014 Clinical characteristics of patients
Variable
Study group A (n ¼ 42)
Control group B (n ¼ 42)
P
Age (y) Sex: male Hypertension Diabetes CAD LVEF (%) LAD (mm) OSA
56.6 ⫾ 5.1 27 (64) 9 (21) 3 (7) 5 (12) 56.6 ⫾ 5.0 46.6 ⫾ 5.8 7 (16.6)
58.6 ⫾ 8.4 27 (64) 11 (26) 4 (9) 6 (14) 59.0 ⫾ 8.2 48.4 ⫾ 10 5 (11.9)
.19 1.00 .72 .26 .18 .10 .32 .21
Values are presented as mean ⫾ SD and as n (%). CAD ¼ coronary artery disease; LAD ¼ left atrial diameter; LVEF ¼ left ventricular ejection fraction; OSA ¼ obstructive sleep apnea.
A), ablation was guided by an automated ablation annotation algorithm with predefined ablation parameters. We compared these 42 patients with the preceding 42 patients (group B) in whom ablation was performed by using the same strategy; however, the annotation of ablation tags was guided by the operator by using the conventional method. Table 1 summarizes the clinical characteristics of patients. The study protocol was approved by the Institutional Review Board of the Beth Israel Deaconess Medical Center.
Ablation annotation method The ablation annotation system (CARTO 3 System, VISITAG Module, Biosense Webster, Inc, Diamond Bar, CA) uses an algorithm for the automated annotation of radiofrequency (RF) ablation applications based on objective, predefined parameters. These are user-defined and include the following: (1) catheter stability range of motion r2 mm
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throughout the RF application, (2) catheter stability duration 415 seconds, and (3) impedance decrease 45% (47–8 Ω). Ablation parameters are recorded and updated 60 times/s throughout each energy application, and ablation tags are displayed accurately on the electroanatomical map on the basis of the locating coordinates of the catheter at each individual stable ablation site. In addition, the tags are color coded to provide the biophysical information of each individual ablation site. Figure 1 compares the 2 annotation methods in the same patient. In group A, ablation was guided by the automated annotation system by using the above ablation criteria. If any of these criteria were not met, ablation energy was terminated within the first 15 seconds, the catheter and supporting sheath were repositioned to improve catheter contact, and atrial pacing with or without apnea were used to further improve catheter stability. Ablation was repeated at the same location until parameters were met. Contact force criteria were not applied to the algorithm as contact force catheter technology was not commercially available in the United States during the study period. In group B, the strategy of ablation and energy settings were similar; however, the annotation of ablation tags, determination of effective vs ineffective application, and repeat energy applications were at the operator’s and technician’s discretion who use conventional modalities that included fluoroscopy, intracardiac echocardiography, and review of changes in tissue impedance and local electrogram. Ablation was defined as ineffective in the case of catheter instability visualized by using fluoroscopy or intracardiac echocardiography, lack of adequate change in local electrogram, or impedance decrease over the initial 15 seconds of energy application.
Figure 1 Radiofrequency ablation annotation techniques: standard vs automated. A:A contiguous line of ablation in a patient who underwent circumferential pulmonary vein isolation by using a standard ablation annotation method. B: The annotation of ablation tags from the same patient by using the automated algorithm with predefined criteria: annotation of ablation tag required catheter stability range of motion r2 mm for at least 15 seconds. Ablation tags are color coded according to the decrease in impedance (red represents impedance decrease 410 Ω, white represents impedance decrease o6 Ω, and pink represents an intermediate impedance decrease). In this patient, the automated annotation method revealed inadequate ablation at both the right and the left posterior line that correlated with the bilateral sites of acute reconnections.
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Ablation Annotation Algorithm to Improve Electrical Contiguity During PVI
The energy settings were similar between the groups: ablation in the anterior and septal aspects of PVs was performed by using a power of 30–40 W for a duration of 30–40 seconds in an attempt to achieve an impedance decrease of at least 5% (47–8 Ω). Ablation at the posterior wall was performed by using a power of 15–20 W for 15–20 seconds.
Study procedure Our approach to AF ablation has been previously described.7 In brief, antiarrhythmic drugs (were discontinued for Z5 half-lives (amiodarone was discontinued for Z4 weeks) before the ablation procedure and all patients were anticoagulated for Z1 month. All procedures were performed under general anesthesia with the use of jet ventilation. PVI was performed by isolating the left and right pairs of veins en bloc by using a point-by-point ablation approach. A cavotricuspid isthmus line was created in patients with documented or induced typical atrial flutter; however, no additional LA ablation lines were made. All procedures were performed with the use of an electroanatomical mapping system (CARTO 3 System) and a dual transseptal approach by using an open-irrigated catheter (ThermoCool, Biosense Webster) and a circular mapping catheter (Lasso, Biosense Webster; adjustable circumference 15–25 mm; interelectrode spacing 1–2 mm). A long steerable sheath (Agillis, St Jude Medical, Minneapolis, MN) supported the ablation catheter and a second fixed-curve long sheath (SL1, St Jude Medical) supported the circular mapping catheter. Successful PVI was defined by the loss of PV potentials (entrance block) and failure to capture the LA during pacing from all bipoles of the circular multielectrode mapping catheter when positioned at the PV ostium (output 10 mA; pulse width 2 ms; exit block). Persistent isolation (entrance and exit block) for each PV was confirmed after a waiting period of Z30 minutes. If persistent isolation was documented, dormant conduction was then evaluated separately for each ipsilateral pairs of PVs with intravenous adenosine at a dose producing temporary atrioventricular conduction block during coronary sinus pacing. If adenosine revealed dormant conduction, further ablation was delivered at areas in which the earliest activation was transiently observed on the circular mapping catheter. In all cases of dormant conduction, challenge with adenosine was repeated until dormant conduction was no longer present.
Ablation data analysis RF ablation applications were analyzed for duration and change in impedance. Temporal and spatial catheter stability was also determined in group A. The detection of ineffective energy application lesions was determined by the automated annotation system in group A using the above-mentioned criteria and by the operator in group B. For the purpose of analysis, the isolation line around each ipsilateral pair of PVs was divided into 8 distinct segments (Figure 2A).
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6 months (⫾3 weeks) after the procedure. A 12-lead electrocardiogram was assessed at every follow-up clinic visits at 1, 3, and 6 months. Additional monitoring was performed on the basis of symptoms. Antiarrhythmic drugs, if used, were discontinued 1 month after the procedure in the absence of any atrial tachyarrhythmia. Freedom from atrial tachyarrhythmia was defined as the absence of AF, atrial flutter, or atrial tachycardia lasting more than 30 seconds and without a blanking period.
Statistical analysis Descriptive statistics are reported as mean ⫾ SD for continuous variables and as absolute frequencies and percentages for categorical variables. Continuous variables were compared by using the unpaired Student t test and categorical variables by using the Fisher exact test. Event-free survival was reported as crude event rates and estimated by using the Kaplan-Meier survival function. Pairwise comparisons of survival rates were made by using the log-rank test. Statistical analyses were performed with JMP Pro 11.0.0 (SAS Institute Inc, Cary, NC, 2007).
Results The acute procedural effectiveness was 100%, with all PVs successfully isolated in both groups. There were 4362 ablation application records in group A and 4071 ablation application records in group B. An analysis of the ablation records was divided into applications required for initial PVI and additional ablation applied for the treatment of PV reconnection including dormant conduction.
Initial PVI Following the completion of the initial anatomical line of ablation, successful PVI was achieved in 90.5% of group A patients (76 of 84 ipsilateral pairs of PVs) but only in 66.7% of group B patients (56 of 84 ipsilateral pairs of PVs) (P ¼ .0001; Figure 3A). The mean number of ablation applications per patient applied to complete the initial anatomical line of ablation was higher in group A than in group B (96 ⫾ 7 vs 78 ⫾ 8; P ¼ .0001). This increased number of ablation applications in group A was largely the result of more frequent detection and treatment of ineffective applications guided by the automated lesion annotation algorithm. In group A, 23% of all ablation applications (23.9 ⫾ 7.6 per patient) were detected as ineffective compared with only 9% (8.7 ⫾ 4.8 per patient) of group B applications (P ¼ .0001). In both study groups, incomplete PVI following the initial anatomical line was similarly distributed between the right and left ipsilateral PVs. In group A, 4 of 8 incompletely isolated ipsilateral PVs were left sided, while in group B, 16 of 28 incompletely isolated ipsilateral PVs were left sided.
Distribution of ineffective ablation applications Follow-up Patients were monitored by 14-day Holter recordings immediately after the procedure and at 3 month (⫾2 weeks) and
The topographical variability in the distribution of ineffective energy applications was analyzed and is depicted in Figure 2B. The most common anatomical sites of ineffective
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Figure 2 Anatomical subdivision of pulmonary veins (PVs). A: Anatomical subdivision of each ipsilateral pair of PVs into 8 sites for a detailed analysis of ablation data. B: Anatomical distribution of sites with ineffective energy applications. In 42 group A patients, a total of 1003 (23%) energy applications were determined as ineffective by the ablation annotation algorithm (522 in the left PVs and 481 in the right PVs). The sites that were difficult to obtain adequate ablation were the left anterior ridge (L2–L4), the right anterior superior (R8), and the right posterior carina (R3). LIPV ¼ left inferior pulmonary vein; LSPV ¼ left superior pulmonary vein; RIPV ¼ right inferior pulmonary vein; RSPV ¼ right superior pulmonary vein.
ablation applications were the left anterior ridge (L2-L4; 27.3%), followed by the right posterior carina (R3; 8.5%) and the right anterior superior (R8; 8.2%), while the most consistent site of effective ablation application was the right anterior inferior (R6). The topographical distribution of ineffective ablation applications correlated well between the groups; however, the frequency of detection and therapy was significantly higher in group A.
Relationship between ineffective ablation applications and gaps We examined the relationship between sites of ineffective ablation applications and linear gaps. In order to do so, we analyzed the data from all veins that were not isolated following the initial anatomical line (presumably due to remaining gaps) and correlated these sites with the efficacy of ablation as determined by the automated ablation algorithm. In group A, 8 of 84 PVs were not isolated following
the initial anatomical line. In 2 of 8 (25%) PVs, the gap was mapped and successfully ablated at the circumferential line (L3 and R3); however, 6 of 8 (75%) PVs had no detectable gaps over the line and were mapped and successfully ablated at the carina between the veins, presumably owing to epicardial connections. In group B, 28 of 84 PVs were not isolated following the initial circumferential PVI. In 20 (71.4%) PVs, the gap was mapped and ablated at the circumferential line. Of these 20 gaps in the circumferential line, 17 (85%) were mapped and ablated at the sites of low ablation efficacy as detected in group A: 9 gaps were mapped to L2-L4, 5 gaps were mapped to R8, and 3 gaps were mapped to R3.
Acute PV reconnection The frequency of conduction recovery between the LA and the PV in response to 30-minute waiting period and intravenous adenosine was examined in each ipsilateral pair of
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Figure 3 Success rate of acute pulmonary vein isolation (PVI). A: Comparison of the success rate of PVI following the completion of the initial anatomical line in the 2 groups. In group A, the annotation of ablation lesions was performed by using the automated algorithm, while in group B, the annotation of ablation was performed manually by the operator. B: Comparison of the incidence of acute pulmonary vein (PV) reconnection and dormant conduction between the groups.
PVs. The rate of reconnection was lower in group A patients with 5 of 84 (5.9%) ipsilateral PVs that recovered conduction than in group B patients with 21 of 84 (25%) ipsilateral PVs (P ¼ .001; Figure 3B). The conduction recovery was in response to waiting time alone in 4 of 5 group A PVs and in 13 of 21 group B PVs. Dormant PV conduction in response to adenosine was detected in 1 of 5 group A veins and in 8 of 21 group B veins. Figure 4 demonstrates acute reconnection in a site of linear gap as depicted by the automated annotation algorithm but missed by the conventional annotation method.
(P ¼ .07; Figure 5). The recurrent arrhythmia was AF in 3 of 4 patients in group A and in 8 of 10 patients in group B.
RF ablation time
Discussion
Although the mean RF time for the completion of the initial anatomical line of ablation was higher in group A (2873 ⫾ 264 seconds vs 2513 ⫾ 211 seconds; P ¼ .0001), the mean total RF time trended higher in group B owing to a higher rate of incomplete isolation following the initial circumferential line and the additional ablation required for the treatment of reconnection and dormant conduction (2992 ⫾ 271 seconds vs 3013 ⫾ 287 seconds; P ¼ 0.76). Similarly, the procedure time to complete the initial circumferential PVI line of ablation was longer in group A; however, the total procedural time (defined from the initial to the last ablation application) trended higher in group B owing to a higher rate of incomplete isolation and addition ablation required for the treatment of reconnection and dormant conduction (97 ⫾ 17 minutes vs 113 ⫾ 22 minutes; P ¼ NS).
Major findings
Clinical recurrence of arrhythmia The recurrence of atrial arrhythmia during a follow-up period of 6 months was higher in 10 of 42 (23.8%) group B patients compared with only 4 of 42 (9.5%) patients group A patients
Procedural complications One patient from group A developed atrioventricular fistula that resolved spontaneously after a month. A single patient from group B developed venous pseudoaneurysm that required thrombin injection. There were no pericardial effusions, strokes, phrenic nerve paralysis, atrioesophageal fistulas, or other complications.
This study examined the utility of an automated RF ablation annotation algorithm for the detection and treatment of ablation gaps during PVI. We report the following findings: (1) the automated assessment of RF ablation increased the success rate of acute circumferential PVI, (2) its application led to a dramatic reduction in acute PV reconnection and dormant conduction, (3) the topographic distribution of inadequate ablation applications correlated well with the anatomical distribution of ablation gaps detected in the control arm. Acute PVI can be achieved after the partial circumferential line of ablation, irrespective of intervening ablation gaps. This is thought to result from a combination of irreversible and reversible atrial injury.5 Reversible tissue injury stems from the incomplete lesion formation, resulting in temporarily electric uncoupling without cell death.3 Thus, ablation gaps often go unrecognized only to resume conduction after the procedure. Permanent conduction block across linear lesions requires transmural linear lesions. The real-time assessment of lesion
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Figure 4 Correlation between linear gap and conduction recovery. A: A contiguous line of ablation in a patient who underwent circumferential pulmonary vein isolation as annotated by the standard method. B and C: A linear gap in the right posterior carina (R3, yellow star) as noted by the lack of catheter stability and inadequate impedance decrease, respectively. D: Following the initial successful isolation, acute pulmonary vein reconnection occurred at this site. A single ablation lesion (pink tag) resulted in the re-isolation of the vein.
formation with the confirmation of electrical contiguity and transmural tissue injury is desirable, but is clinically unavailable. Emerging technologies that hold promise include lesion thermography, intraprocedural high-resolution magnetic resonance imaging, and near-field ultrasound.
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Figure 5 Arrhythmia-free survival. Kaplan-Meier survival curve showing freedom from any atrial tachyarrhythmia after pulmonary vein isolation in each group at a follow-up of 6 months.
In clinical practice, mapping of ablation gaps is usually performed by the detection of residual electrical signals or pacing along the circumferential PVI line.8 Although these methods are effective, certain limitations exist, as ablation gaps are often electrically silent owing to edema and can therefore be missed while the additional ablation required to achieve loss of tissue excitability is often substantial and may be associated with significant procedural prolongation. Another method to detect incomplete lesion formation is the presence of dormant conduction in response to adenosine that hyperpolarizes atrial cell membranes, permitting transient conduction at sites with incomplete cell destruction.9 Although further ablation at these sites may reduce arrhythmia recurrence, it also identifies patients with a greater likelihood of arrhythmia recurrence despite additional ablation.7,10,11 A possible explanation might be the presence of tissue edema at sites with incomplete cell death, potentially limiting additional effective ablation. In this regard, the use of reliable and easily reproducible methods for the real-time assessment of ablation energy delivery may improve effective tissue injury and lesion completeness. A recent technology aimed to improve
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Ablation Annotation Algorithm to Improve Electrical Contiguity During PVI
effective ablation is contact force–sensing catheters. The use of this technology, although not presently available in the United States, has been shown to improve lesion efficacy and reduce recovery of conduction and recurrence of arrhythmia.12 The use of contact force was of particular added value in ablation at difficult anatomical sites of low contact force.12,13 Low contact force was prevalent in 35%–40% of all ablation sites and appeared to have a particular topographical distribution. Interestingly, in the present study, we observed a prevalence of 23% ineffective ablation applications at a similar topographical distribution seen with contact force–sensing catheters. The most common anatomical sites of ineffective ablation applications were the left anterior ridge (L2-L4), the right anterior superior (R8), and the right posterior carina (R3). We also found that effective ablation application was most consistently achieved at the right anterior inferior (R6). The association between impedance decrease during RF ablation and tissue contact force has been assessed in both animals and humans.14–18 While animal studies have found a direct correlation between impedance decrease and contact force, with the magnitude of impedance decrease strongly correlating with the imparted contact force, lesion depth, diameter, and volume, human data have shown conflicting results.19,20 Reichlin et al19 found that a median impedance decrease of 6%–8% (8–10 Ω) was a surrogate for good catheter contact in a group of 49 patients undergoing PVI, while Kumar et al20 found only a modest correlation, with significant overlap between contact force and impedance decrease during RF ablation. While discrepancy between these studies could potentially be attributed to variability in procedural strategy, impedance decrease alone may be a simple, but insufficient, marker for lesion formation. In our study, we found that the combination of impedance decrease 45% (47–8 Ω) coupled with catheter stability range of motion r2 mm correlated with a reduced incidence of conduction recovery and arrhythmia recurrence. However, the design of this study combined with its relatively small size does not permit further analysis to determine the independent contribution of impedance decrease and/or stability. While measurements of impedance decrease with individual RF applications are usually performed manually by the operator, we found that the sensitivity to detect ineffective ablation applications was 2.5 times greater when using an objective algorithm that measures real-time decrease in impedance and catheter stability. This allowed early termination of ablation at sites of ineffective energy delivery, potentially limiting ineffective ablation and tissue edema. Catheter stability and tissue contact were improved by repositioning of the catheter, atrial pacing, and/or apnea, and this was followed by repeat and effective ablation application. While the mean RF time for the completion of the initial anatomical PVI line was longer when guided by the automated annotation software, the total RF time as well as the procedural time trended higher in the control group
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owing to a higher rate of incomplete isolation following the initial anatomical PVI line and the additional ablation required for the treatment of conduction recovery. In addition, the reduced rate of conduction recovery following acute PVI may be related to a reduced amount of ineffective energy delivery and tissue edema, facilitating effective ablation. As contact force–sensing catheters are not routinely available in clinical practice in the United States as well as in some parts of the world, these findings may be particularly useful with currently available standard catheters.
Study limitations The results of our results are limited to a relatively small sample of patients. However, more than 8000 individual ablation lesions were analyzed systematically in 2 groups of the patients subjected to PVI by using a similar strategy. In addition, the design of our study does not allow independent correlation of catheter stability and impedance decrease with conduction recovery and clinical recurrence. The additional value of impedance decrease and catheter stability to contact force sensing catheters was not examined. A prospective study to correlate impedance decrease, catheter stability, and contact force is necessary to ensure optimal safety and efficacy.
Conclusion The automated and objective annotation of RF ablation enhances the detection of ineffective energy delivery and reduces the incidence of conduction recovery. In addition, this technology results in a lower rate of recurrent AF.
References 1. Verma A, Kilicaslan F, Pisano E, et al. Response of atrial fibrillation to pulmonary vein antrum isolation is directly related to resumption and delay of pulmonary vein conduction. Circulation 2005;112:627–635. 2. Kowal RC. PVI’s inconvenient truths: lights out for dormant reconnection? J Cardiovasc Electrophysiol 2012;23:261–263. 3. Kowalski M, Grimes MM, Perez FJ, Kenigsberg DN, Koneru J, Kasirajan V, Wood MA, Ellenbogen KA. Histopathologic characterization of chronic radiofrequency ablation lesions for pulmonary vein isolation. J Am Coll Cardiol 2012;59:930–938. 4. Cappato R, Negroni S, Pecora D, Bentivegna S, Lupo PP, Carolei A, Esposito C, Furlanello F, De Ambroggi L. Prospective assessment of late conduction recurrence across radiofrequency lesions producing electrical disconnection at the pulmonary vein ostium in patients with atrial fibrillation. Circulation 2003;108:1599–1604. 5. Ranjan R, Kholmovski EG, Blauer J, Vijayakumar S, Volland NA, Salama ME, Parker DL, MacLeod R, Marrouche NF. Identification and acute targeting of gaps in atrial ablation lesion sets using a real-time magnetic resonance imaging system. Circ Arrhythm Electrophysiol 2012;5:1130–1135. 6. Arujuna A, Karim R, Caulfield D, Knowles B, Rhode K, Schaeffter T, Kato B, Rinaldi CA, Cooklin M, Razavi R, O’Neill MD, Gill J. Acute pulmonary vein isolation is achieved by a combination of reversible and irreversible atrial injury after catheter ablation: evidence from magnetic resonance imaging. Circ Arrhythm Electrophysiol 2012;5:691–700. 7. Anter E, Contreras-Valdes FM, Shvilkin A, Tschabrunn CM, Josephson ME. Acute pulmonary vein reconnection is a predictor of atrial fibrillation recurrence following pulmonary vein isolation. J Interv Card Electrophysiol 2014. 8. Steven D, Sultan A, Reddy V, et al. Benefit of pulmonary vein isolation guided by loss of pace capture on the ablation line: results from a prospective 2-center randomized trial. J Am Coll Cardiol 2013;62:44–50. 9. Datino T, Macle L, Qi XY, Maguy A, Comtois P, Chartier D, Guerra PG, Arenal A, Fernandez-Aviles F, Nattel S. Mechanisms by which adenosine
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Heart Rhythm, Vol 11, No 5, May 2014 restores conduction in dormant canine pulmonary veins. Circulation 2010;121: 963–972. Yamane T, Matsuo S, Date T, et al. Repeated provocation of time- and ATPinduced early pulmonary vein reconnections after pulmonary vein isolation: eliminating paroxysmal atrial fibrillation in a single procedure. Circ Arrhythm Electrophysiol 2011;4:601–608. McLellan AJ, Kumar S, Smith C, Morton JB, Kalman JM, Kistler PM. The role of adenosine following pulmonary vein isolation in patients undergoing catheter ablation for atrial fibrillation: a systematic review. J Cardiovasc Electrophysiol 2013;24:742–751. Reddy VY, Shah D, Kautzner J, et al. The relationship between contact force and clinical outcome during radiofrequency catheter ablation of atrial fibrillation in the TOCCATA study. Heart Rhythm 2012;9:1789–1795. Kumar S, Morton JB, Lee J, Halloran K, Spence SJ, Gorelik A, Hepworth G, Kistler PM, Kalman JM. Prospective characterization of catheter-tissue contact force at different anatomic sites during antral pulmonary vein isolation. Circ Arrhythm Electrophysiol 2012;5:1124–1129. Thiagalingam A, D'Avila A, Foley L, Guerrero JL, Lambert H, Leo G, Ruskin JN, Reddy VY. Importance of catheter contact force during irrigated radiofrequency ablation: evaluation in a porcine ex vivo model using a force-sensing catheter. J Cardiovasc Electrophysiol 2010;21:806–811.
15. Yokoyama K, Nakagawa H, Shah DC, Lambert H, Leo G, Aeby N, Ikeda A, Pitha JV, Sharma T, Lazzara R, Jackman WM. Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus. Circ Arrhythm Electrophysiol 2008;1:354–362. 16. Avitall B, Mughal K, Hare J, Helms R, Krum D. The effects of electrode-tissue contact on radiofrequency lesion generation. Pacing Clin Electrophysiol 1997;20: 2899–2910. 17. Zheng X, Walcott GP, Hall JA, Rollins DL, Smith WM, Kay GN, Ideker RE. Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation. J Interv Card Electrophysiol 2000;4:645–654. 18. Dumas Iii JH, Himel Iv HD, Kiser AC, Quint SR, Knisley SB. Myocardial electrical impedance as a predictor of the quality of RF-induced linear lesions. Physiol Meas 2008;29:1195–1207. 19. Reichlin T, Knecht S, Lane C, et al. Initial impedance decrease as an indicator of good catheter contact: insights from radiofrequency ablation with force sensing catheters. Heart Rhythm 2014;11:194–201. 20. Kumar S, Haqqani HM, Chan M, et al. Predictive value of impedance changes for real-time contact force measurements during catheter ablation of atrial arrhythmias in humans. Heart Rhythm 2013;10:962–969.
Introduction Pulmonary vein isolation (PVI) is an effective therapy for patients with symptomatic atrial fibrillation (AF) and is the cornerstone of ablation. However, arrhythmia recurrence is common and often related to the resumption of conduction between the pulmonary vein (PV) and the left atrium (LA).1,2 The mechanism of recovered conduction is usually partialthickness lesion formation that causes temporary electric uncoupling but not cell death.3 Thus, lesion gaps can go undetected during the index procedure only to recover conduction after the procedure.4–6 The real-time detection of ablation gaps may be facilitated by reviewing the annotated ablation lesions on the Dr Anter has received research grants from Biosense Webster and Boston Scientific. Dr Josephson has received research grants and speaking honoraria from Medtronic. Address reprint requests and correspondence: Dr Elad Anter, Harvard-Thorndike Electrophysiology Institute, Beth Israel Deaconess Medical Center, Harvard Medical School, 185 Pilgrim Rd, Baker 4, Boston, MA 02215. E-mail address: [email protected].
1547-5271/$-see front matter B 2014 Heart Rhythm Society. All rights reserved.
84 ipsilateral pairs of PVs) (P ¼ .0001). Ineffective energy delivery was detected in 23% (1005 of 4362) of group A applications but only in 9% (368 of 4071) of group B applications (P ¼ .0001). The frequency of conduction recovery was lower in group A than in group B (5.9% vs 25%; P ¼ .001). Arrhythmia-free survival at 6 months trended higher in group A (38 of 42 [90%]) than in group B (32 of 42 [76%]; P ¼ .07). CONCLUSION Automated ablation lesion annotation provides real-time feedback of RF ablation that may improve effective energy delivery. KEYWORDS Atrial fibrillation; Acute reconnection; Pulmonary vein isolation; Catheter ablation; Recurrence ABBREVIATIONS AF ¼ atrial fibrillation; LA ¼ left atrium; PV ¼ pulmonary vein; PVI ¼ pulmonary vein isolation; RF ¼ radiofrequency (Heart Rhythm 2014;11:783–790) I 2014 Heart Rhythm Society. All rights reserved.
electroanatomical map. However, this method is subjected to significant limitations: (1) annotation of ablation lesions is performed subjectively in terms of the precise location and carries significant intra- and interoperator variability; (2) ablation tags are annotated in an “all or none” fashion, lacking the biophysical parameters of individual ablation lesions (ie, temperature, power, impedance change, stability, and contact force). Thus, the current annotation of ablation lesions on electroanatomical mapping systems is insufficient for the detection of sites potentially subjected to insufficient ablation. The objective of this study was to determine the utility of an automated ablation annotation algorithm for the detection of gaps during PVI and its effect on acute PV reconnection and dormant conduction.
Methods Patients We prospectively studied 84 patients with symptomatic paroxysmal AF undergoing index PVI. In 42 patients (group http://dx.doi.org/10.1016/j.hrthm.2014.02.022
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Heart Rhythm, Vol 11, No 5, May 2014 Clinical characteristics of patients
Variable
Study group A (n ¼ 42)
Control group B (n ¼ 42)
P
Age (y) Sex: male Hypertension Diabetes CAD LVEF (%) LAD (mm) OSA
56.6 ⫾ 5.1 27 (64) 9 (21) 3 (7) 5 (12) 56.6 ⫾ 5.0 46.6 ⫾ 5.8 7 (16.6)
58.6 ⫾ 8.4 27 (64) 11 (26) 4 (9) 6 (14) 59.0 ⫾ 8.2 48.4 ⫾ 10 5 (11.9)
.19 1.00 .72 .26 .18 .10 .32 .21
Values are presented as mean ⫾ SD and as n (%). CAD ¼ coronary artery disease; LAD ¼ left atrial diameter; LVEF ¼ left ventricular ejection fraction; OSA ¼ obstructive sleep apnea.
A), ablation was guided by an automated ablation annotation algorithm with predefined ablation parameters. We compared these 42 patients with the preceding 42 patients (group B) in whom ablation was performed by using the same strategy; however, the annotation of ablation tags was guided by the operator by using the conventional method. Table 1 summarizes the clinical characteristics of patients. The study protocol was approved by the Institutional Review Board of the Beth Israel Deaconess Medical Center.
Ablation annotation method The ablation annotation system (CARTO 3 System, VISITAG Module, Biosense Webster, Inc, Diamond Bar, CA) uses an algorithm for the automated annotation of radiofrequency (RF) ablation applications based on objective, predefined parameters. These are user-defined and include the following: (1) catheter stability range of motion r2 mm
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throughout the RF application, (2) catheter stability duration 415 seconds, and (3) impedance decrease 45% (47–8 Ω). Ablation parameters are recorded and updated 60 times/s throughout each energy application, and ablation tags are displayed accurately on the electroanatomical map on the basis of the locating coordinates of the catheter at each individual stable ablation site. In addition, the tags are color coded to provide the biophysical information of each individual ablation site. Figure 1 compares the 2 annotation methods in the same patient. In group A, ablation was guided by the automated annotation system by using the above ablation criteria. If any of these criteria were not met, ablation energy was terminated within the first 15 seconds, the catheter and supporting sheath were repositioned to improve catheter contact, and atrial pacing with or without apnea were used to further improve catheter stability. Ablation was repeated at the same location until parameters were met. Contact force criteria were not applied to the algorithm as contact force catheter technology was not commercially available in the United States during the study period. In group B, the strategy of ablation and energy settings were similar; however, the annotation of ablation tags, determination of effective vs ineffective application, and repeat energy applications were at the operator’s and technician’s discretion who use conventional modalities that included fluoroscopy, intracardiac echocardiography, and review of changes in tissue impedance and local electrogram. Ablation was defined as ineffective in the case of catheter instability visualized by using fluoroscopy or intracardiac echocardiography, lack of adequate change in local electrogram, or impedance decrease over the initial 15 seconds of energy application.
Figure 1 Radiofrequency ablation annotation techniques: standard vs automated. A:A contiguous line of ablation in a patient who underwent circumferential pulmonary vein isolation by using a standard ablation annotation method. B: The annotation of ablation tags from the same patient by using the automated algorithm with predefined criteria: annotation of ablation tag required catheter stability range of motion r2 mm for at least 15 seconds. Ablation tags are color coded according to the decrease in impedance (red represents impedance decrease 410 Ω, white represents impedance decrease o6 Ω, and pink represents an intermediate impedance decrease). In this patient, the automated annotation method revealed inadequate ablation at both the right and the left posterior line that correlated with the bilateral sites of acute reconnections.
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The energy settings were similar between the groups: ablation in the anterior and septal aspects of PVs was performed by using a power of 30–40 W for a duration of 30–40 seconds in an attempt to achieve an impedance decrease of at least 5% (47–8 Ω). Ablation at the posterior wall was performed by using a power of 15–20 W for 15–20 seconds.
Study procedure Our approach to AF ablation has been previously described.7 In brief, antiarrhythmic drugs (were discontinued for Z5 half-lives (amiodarone was discontinued for Z4 weeks) before the ablation procedure and all patients were anticoagulated for Z1 month. All procedures were performed under general anesthesia with the use of jet ventilation. PVI was performed by isolating the left and right pairs of veins en bloc by using a point-by-point ablation approach. A cavotricuspid isthmus line was created in patients with documented or induced typical atrial flutter; however, no additional LA ablation lines were made. All procedures were performed with the use of an electroanatomical mapping system (CARTO 3 System) and a dual transseptal approach by using an open-irrigated catheter (ThermoCool, Biosense Webster) and a circular mapping catheter (Lasso, Biosense Webster; adjustable circumference 15–25 mm; interelectrode spacing 1–2 mm). A long steerable sheath (Agillis, St Jude Medical, Minneapolis, MN) supported the ablation catheter and a second fixed-curve long sheath (SL1, St Jude Medical) supported the circular mapping catheter. Successful PVI was defined by the loss of PV potentials (entrance block) and failure to capture the LA during pacing from all bipoles of the circular multielectrode mapping catheter when positioned at the PV ostium (output 10 mA; pulse width 2 ms; exit block). Persistent isolation (entrance and exit block) for each PV was confirmed after a waiting period of Z30 minutes. If persistent isolation was documented, dormant conduction was then evaluated separately for each ipsilateral pairs of PVs with intravenous adenosine at a dose producing temporary atrioventricular conduction block during coronary sinus pacing. If adenosine revealed dormant conduction, further ablation was delivered at areas in which the earliest activation was transiently observed on the circular mapping catheter. In all cases of dormant conduction, challenge with adenosine was repeated until dormant conduction was no longer present.
Ablation data analysis RF ablation applications were analyzed for duration and change in impedance. Temporal and spatial catheter stability was also determined in group A. The detection of ineffective energy application lesions was determined by the automated annotation system in group A using the above-mentioned criteria and by the operator in group B. For the purpose of analysis, the isolation line around each ipsilateral pair of PVs was divided into 8 distinct segments (Figure 2A).
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6 months (⫾3 weeks) after the procedure. A 12-lead electrocardiogram was assessed at every follow-up clinic visits at 1, 3, and 6 months. Additional monitoring was performed on the basis of symptoms. Antiarrhythmic drugs, if used, were discontinued 1 month after the procedure in the absence of any atrial tachyarrhythmia. Freedom from atrial tachyarrhythmia was defined as the absence of AF, atrial flutter, or atrial tachycardia lasting more than 30 seconds and without a blanking period.
Statistical analysis Descriptive statistics are reported as mean ⫾ SD for continuous variables and as absolute frequencies and percentages for categorical variables. Continuous variables were compared by using the unpaired Student t test and categorical variables by using the Fisher exact test. Event-free survival was reported as crude event rates and estimated by using the Kaplan-Meier survival function. Pairwise comparisons of survival rates were made by using the log-rank test. Statistical analyses were performed with JMP Pro 11.0.0 (SAS Institute Inc, Cary, NC, 2007).
Results The acute procedural effectiveness was 100%, with all PVs successfully isolated in both groups. There were 4362 ablation application records in group A and 4071 ablation application records in group B. An analysis of the ablation records was divided into applications required for initial PVI and additional ablation applied for the treatment of PV reconnection including dormant conduction.
Initial PVI Following the completion of the initial anatomical line of ablation, successful PVI was achieved in 90.5% of group A patients (76 of 84 ipsilateral pairs of PVs) but only in 66.7% of group B patients (56 of 84 ipsilateral pairs of PVs) (P ¼ .0001; Figure 3A). The mean number of ablation applications per patient applied to complete the initial anatomical line of ablation was higher in group A than in group B (96 ⫾ 7 vs 78 ⫾ 8; P ¼ .0001). This increased number of ablation applications in group A was largely the result of more frequent detection and treatment of ineffective applications guided by the automated lesion annotation algorithm. In group A, 23% of all ablation applications (23.9 ⫾ 7.6 per patient) were detected as ineffective compared with only 9% (8.7 ⫾ 4.8 per patient) of group B applications (P ¼ .0001). In both study groups, incomplete PVI following the initial anatomical line was similarly distributed between the right and left ipsilateral PVs. In group A, 4 of 8 incompletely isolated ipsilateral PVs were left sided, while in group B, 16 of 28 incompletely isolated ipsilateral PVs were left sided.
Distribution of ineffective ablation applications Follow-up Patients were monitored by 14-day Holter recordings immediately after the procedure and at 3 month (⫾2 weeks) and
The topographical variability in the distribution of ineffective energy applications was analyzed and is depicted in Figure 2B. The most common anatomical sites of ineffective
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Figure 2 Anatomical subdivision of pulmonary veins (PVs). A: Anatomical subdivision of each ipsilateral pair of PVs into 8 sites for a detailed analysis of ablation data. B: Anatomical distribution of sites with ineffective energy applications. In 42 group A patients, a total of 1003 (23%) energy applications were determined as ineffective by the ablation annotation algorithm (522 in the left PVs and 481 in the right PVs). The sites that were difficult to obtain adequate ablation were the left anterior ridge (L2–L4), the right anterior superior (R8), and the right posterior carina (R3). LIPV ¼ left inferior pulmonary vein; LSPV ¼ left superior pulmonary vein; RIPV ¼ right inferior pulmonary vein; RSPV ¼ right superior pulmonary vein.
ablation applications were the left anterior ridge (L2-L4; 27.3%), followed by the right posterior carina (R3; 8.5%) and the right anterior superior (R8; 8.2%), while the most consistent site of effective ablation application was the right anterior inferior (R6). The topographical distribution of ineffective ablation applications correlated well between the groups; however, the frequency of detection and therapy was significantly higher in group A.
Relationship between ineffective ablation applications and gaps We examined the relationship between sites of ineffective ablation applications and linear gaps. In order to do so, we analyzed the data from all veins that were not isolated following the initial anatomical line (presumably due to remaining gaps) and correlated these sites with the efficacy of ablation as determined by the automated ablation algorithm. In group A, 8 of 84 PVs were not isolated following
the initial anatomical line. In 2 of 8 (25%) PVs, the gap was mapped and successfully ablated at the circumferential line (L3 and R3); however, 6 of 8 (75%) PVs had no detectable gaps over the line and were mapped and successfully ablated at the carina between the veins, presumably owing to epicardial connections. In group B, 28 of 84 PVs were not isolated following the initial circumferential PVI. In 20 (71.4%) PVs, the gap was mapped and ablated at the circumferential line. Of these 20 gaps in the circumferential line, 17 (85%) were mapped and ablated at the sites of low ablation efficacy as detected in group A: 9 gaps were mapped to L2-L4, 5 gaps were mapped to R8, and 3 gaps were mapped to R3.
Acute PV reconnection The frequency of conduction recovery between the LA and the PV in response to 30-minute waiting period and intravenous adenosine was examined in each ipsilateral pair of
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Figure 3 Success rate of acute pulmonary vein isolation (PVI). A: Comparison of the success rate of PVI following the completion of the initial anatomical line in the 2 groups. In group A, the annotation of ablation lesions was performed by using the automated algorithm, while in group B, the annotation of ablation was performed manually by the operator. B: Comparison of the incidence of acute pulmonary vein (PV) reconnection and dormant conduction between the groups.
PVs. The rate of reconnection was lower in group A patients with 5 of 84 (5.9%) ipsilateral PVs that recovered conduction than in group B patients with 21 of 84 (25%) ipsilateral PVs (P ¼ .001; Figure 3B). The conduction recovery was in response to waiting time alone in 4 of 5 group A PVs and in 13 of 21 group B PVs. Dormant PV conduction in response to adenosine was detected in 1 of 5 group A veins and in 8 of 21 group B veins. Figure 4 demonstrates acute reconnection in a site of linear gap as depicted by the automated annotation algorithm but missed by the conventional annotation method.
(P ¼ .07; Figure 5). The recurrent arrhythmia was AF in 3 of 4 patients in group A and in 8 of 10 patients in group B.
RF ablation time
Discussion
Although the mean RF time for the completion of the initial anatomical line of ablation was higher in group A (2873 ⫾ 264 seconds vs 2513 ⫾ 211 seconds; P ¼ .0001), the mean total RF time trended higher in group B owing to a higher rate of incomplete isolation following the initial circumferential line and the additional ablation required for the treatment of reconnection and dormant conduction (2992 ⫾ 271 seconds vs 3013 ⫾ 287 seconds; P ¼ 0.76). Similarly, the procedure time to complete the initial circumferential PVI line of ablation was longer in group A; however, the total procedural time (defined from the initial to the last ablation application) trended higher in group B owing to a higher rate of incomplete isolation and addition ablation required for the treatment of reconnection and dormant conduction (97 ⫾ 17 minutes vs 113 ⫾ 22 minutes; P ¼ NS).
Major findings
Clinical recurrence of arrhythmia The recurrence of atrial arrhythmia during a follow-up period of 6 months was higher in 10 of 42 (23.8%) group B patients compared with only 4 of 42 (9.5%) patients group A patients
Procedural complications One patient from group A developed atrioventricular fistula that resolved spontaneously after a month. A single patient from group B developed venous pseudoaneurysm that required thrombin injection. There were no pericardial effusions, strokes, phrenic nerve paralysis, atrioesophageal fistulas, or other complications.
This study examined the utility of an automated RF ablation annotation algorithm for the detection and treatment of ablation gaps during PVI. We report the following findings: (1) the automated assessment of RF ablation increased the success rate of acute circumferential PVI, (2) its application led to a dramatic reduction in acute PV reconnection and dormant conduction, (3) the topographic distribution of inadequate ablation applications correlated well with the anatomical distribution of ablation gaps detected in the control arm. Acute PVI can be achieved after the partial circumferential line of ablation, irrespective of intervening ablation gaps. This is thought to result from a combination of irreversible and reversible atrial injury.5 Reversible tissue injury stems from the incomplete lesion formation, resulting in temporarily electric uncoupling without cell death.3 Thus, ablation gaps often go unrecognized only to resume conduction after the procedure. Permanent conduction block across linear lesions requires transmural linear lesions. The real-time assessment of lesion
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Figure 4 Correlation between linear gap and conduction recovery. A: A contiguous line of ablation in a patient who underwent circumferential pulmonary vein isolation as annotated by the standard method. B and C: A linear gap in the right posterior carina (R3, yellow star) as noted by the lack of catheter stability and inadequate impedance decrease, respectively. D: Following the initial successful isolation, acute pulmonary vein reconnection occurred at this site. A single ablation lesion (pink tag) resulted in the re-isolation of the vein.
formation with the confirmation of electrical contiguity and transmural tissue injury is desirable, but is clinically unavailable. Emerging technologies that hold promise include lesion thermography, intraprocedural high-resolution magnetic resonance imaging, and near-field ultrasound.
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Figure 5 Arrhythmia-free survival. Kaplan-Meier survival curve showing freedom from any atrial tachyarrhythmia after pulmonary vein isolation in each group at a follow-up of 6 months.
In clinical practice, mapping of ablation gaps is usually performed by the detection of residual electrical signals or pacing along the circumferential PVI line.8 Although these methods are effective, certain limitations exist, as ablation gaps are often electrically silent owing to edema and can therefore be missed while the additional ablation required to achieve loss of tissue excitability is often substantial and may be associated with significant procedural prolongation. Another method to detect incomplete lesion formation is the presence of dormant conduction in response to adenosine that hyperpolarizes atrial cell membranes, permitting transient conduction at sites with incomplete cell destruction.9 Although further ablation at these sites may reduce arrhythmia recurrence, it also identifies patients with a greater likelihood of arrhythmia recurrence despite additional ablation.7,10,11 A possible explanation might be the presence of tissue edema at sites with incomplete cell death, potentially limiting additional effective ablation. In this regard, the use of reliable and easily reproducible methods for the real-time assessment of ablation energy delivery may improve effective tissue injury and lesion completeness. A recent technology aimed to improve
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effective ablation is contact force–sensing catheters. The use of this technology, although not presently available in the United States, has been shown to improve lesion efficacy and reduce recovery of conduction and recurrence of arrhythmia.12 The use of contact force was of particular added value in ablation at difficult anatomical sites of low contact force.12,13 Low contact force was prevalent in 35%–40% of all ablation sites and appeared to have a particular topographical distribution. Interestingly, in the present study, we observed a prevalence of 23% ineffective ablation applications at a similar topographical distribution seen with contact force–sensing catheters. The most common anatomical sites of ineffective ablation applications were the left anterior ridge (L2-L4), the right anterior superior (R8), and the right posterior carina (R3). We also found that effective ablation application was most consistently achieved at the right anterior inferior (R6). The association between impedance decrease during RF ablation and tissue contact force has been assessed in both animals and humans.14–18 While animal studies have found a direct correlation between impedance decrease and contact force, with the magnitude of impedance decrease strongly correlating with the imparted contact force, lesion depth, diameter, and volume, human data have shown conflicting results.19,20 Reichlin et al19 found that a median impedance decrease of 6%–8% (8–10 Ω) was a surrogate for good catheter contact in a group of 49 patients undergoing PVI, while Kumar et al20 found only a modest correlation, with significant overlap between contact force and impedance decrease during RF ablation. While discrepancy between these studies could potentially be attributed to variability in procedural strategy, impedance decrease alone may be a simple, but insufficient, marker for lesion formation. In our study, we found that the combination of impedance decrease 45% (47–8 Ω) coupled with catheter stability range of motion r2 mm correlated with a reduced incidence of conduction recovery and arrhythmia recurrence. However, the design of this study combined with its relatively small size does not permit further analysis to determine the independent contribution of impedance decrease and/or stability. While measurements of impedance decrease with individual RF applications are usually performed manually by the operator, we found that the sensitivity to detect ineffective ablation applications was 2.5 times greater when using an objective algorithm that measures real-time decrease in impedance and catheter stability. This allowed early termination of ablation at sites of ineffective energy delivery, potentially limiting ineffective ablation and tissue edema. Catheter stability and tissue contact were improved by repositioning of the catheter, atrial pacing, and/or apnea, and this was followed by repeat and effective ablation application. While the mean RF time for the completion of the initial anatomical PVI line was longer when guided by the automated annotation software, the total RF time as well as the procedural time trended higher in the control group
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owing to a higher rate of incomplete isolation following the initial anatomical PVI line and the additional ablation required for the treatment of conduction recovery. In addition, the reduced rate of conduction recovery following acute PVI may be related to a reduced amount of ineffective energy delivery and tissue edema, facilitating effective ablation. As contact force–sensing catheters are not routinely available in clinical practice in the United States as well as in some parts of the world, these findings may be particularly useful with currently available standard catheters.
Study limitations The results of our results are limited to a relatively small sample of patients. However, more than 8000 individual ablation lesions were analyzed systematically in 2 groups of the patients subjected to PVI by using a similar strategy. In addition, the design of our study does not allow independent correlation of catheter stability and impedance decrease with conduction recovery and clinical recurrence. The additional value of impedance decrease and catheter stability to contact force sensing catheters was not examined. A prospective study to correlate impedance decrease, catheter stability, and contact force is necessary to ensure optimal safety and efficacy.
Conclusion The automated and objective annotation of RF ablation enhances the detection of ineffective energy delivery and reduces the incidence of conduction recovery. In addition, this technology results in a lower rate of recurrent AF.
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15. Yokoyama K, Nakagawa H, Shah DC, Lambert H, Leo G, Aeby N, Ikeda A, Pitha JV, Sharma T, Lazzara R, Jackman WM. Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus. Circ Arrhythm Electrophysiol 2008;1:354–362. 16. Avitall B, Mughal K, Hare J, Helms R, Krum D. The effects of electrode-tissue contact on radiofrequency lesion generation. Pacing Clin Electrophysiol 1997;20: 2899–2910. 17. Zheng X, Walcott GP, Hall JA, Rollins DL, Smith WM, Kay GN, Ideker RE. Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation. J Interv Card Electrophysiol 2000;4:645–654. 18. Dumas Iii JH, Himel Iv HD, Kiser AC, Quint SR, Knisley SB. Myocardial electrical impedance as a predictor of the quality of RF-induced linear lesions. Physiol Meas 2008;29:1195–1207. 19. Reichlin T, Knecht S, Lane C, et al. Initial impedance decrease as an indicator of good catheter contact: insights from radiofrequency ablation with force sensing catheters. Heart Rhythm 2014;11:194–201. 20. Kumar S, Haqqani HM, Chan M, et al. Predictive value of impedance changes for real-time contact force measurements during catheter ablation of atrial arrhythmias in humans. Heart Rhythm 2013;10:962–969.
