Avoiding tachycardia alteration or termination during attempted entrainment mapping of atrial tachycardia related to atrial fibrillation ablation Chirag R. Barbhaiya, MD, Saurabh Kumar, BSc [Med]/MBBS, PhD, Justin Ng, MD, Koichi Nagashima, MD, Eue-Keun Choi, MD, Alan Enriquez, MD, Jason Chinitz, MD, Laurence M. Epstein, MD, Usha B. Tedrow, MD, MSc, FHRS, Roy M. John, MD, PhD, FHRS, William G. Stevenson, MD, FHRS, Gregory F. Michaud, MD, FHRS From the Cardiovascular Division, Brigham and Women’s Hospital, Boston, Massachusetts. BACKGROUND Entrainment can be useful for mapping atrial tachycardias (ATs) after atrial fibrillation (AF) ablation but may result in AT alteration or termination. OBJECTIVE We aimed to determine the incidence and risk factors for AT alteration or termination. METHODS In 30 consecutive patients, 62 ATs (mean cycle length [CL] 268 ⫾ 53 ms) in which overdrive pacing for entrainment mapping was performed were retrospectively analyzed. AT was classified as altered if the CL or activation pattern remained altered 10 seconds after pacing. The variability in the PP intervals was determined over 10 beats from 2 measures: (1) the difference between the shortest and the longest CL expressed as a percentage of the CL and (2) the mean difference between sequential PP intervals expressed as a percentage of the AT CL (CLDmean). RESULTS Of 386 total pacing attempts (tachycardia CL [TCL] – pacing CL [PCL] difference 15 ⫾ 6 ms), 5 (1.3%) altered or terminated AT and 381 did not change AT (98.7%). When the TCL PCL difference was r20 ms, only 2 of 353 (0.5%) attempts altered or terminated AT. When the TCL PCL difference was 420 ms, 3 of 33 (9%) attempts altered or terminated AT. The difference between the shortest and the longest CL
expressed as a percentage of the CL was significantly greater in ATs that were altered or terminated by pacing than in those unchanged (11.0% ⫾ 9.6% vs 4.5% ⫾ 4.5%; P ¼ .007), but the mean difference between sequential PP intervals expressed as a percentage of the AT CL was not significantly different (3.8% ⫾ 2.6% vs 1.9% ⫾ 2.1%; P ¼ .06). CONCLUSION Overdrive pacing for entrainment mapping rarely alters or terminates after atrial fibrillation AT, provided that AT is stable before pacing and that the PCL is r20 ms shorter than the AT CL. KEYWORDS Atrial tachycardia; Atrial fibrillation; Mapping; Overdrive pacing; Entrainment; Catheter ablation ABBREVIATIONS AF ¼ atrial fibrillation; AT ¼ atrial tachycardia; CL ¼ cycle length; CLDmax ¼ difference between the shortest and the longest cycle length expressed as a percentage of the cycle length; CLDmean ¼ mean difference between sequential PP intervals expressed as a percentage of the atrial tachycardia cycle length; PCL ¼ paced cycle length; TCL ¼ tachycardia cycle length (Heart Rhythm 2015;12:32–35) rights reserved.
I
2015 Heart Rhythm Society. All
Introduction Dr Kumar is a recipient of the Neil Hamilton Fairley – Overseas Clinical Fellowship cofunded by the National Health and Medical Research Council and the National Heart Foundation of Australia; he is also a recipient of the Bushell Travelling Fellowship funded by the Royal Australasian College of Physicians. Dr Tedrow has received consulting fees/honoraria from Boston Scientific and St Jude Medical and research funding from Biosense Webster and St Jude Medical. Dr John has received consulting fees/honoraria from St Jude Medical. Dr Epstein has received consulting fees/honoraria from Boston Scientific, Medtronic, and Spectranetics. Dr Michaud has received consulting fees/honoraria from Boston Scientific, Medtronic, and St Jude Medical and research funding from Boston Scientific and Biosense Webster. Address reprint requests and correspondence: Dr Gregory F. Michaud, Cardiovascular Division, Brigham and Women’s Hospital, 75 Francis St, Boston, MA 02115. E-mail address: [email protected].
1547-5271/$-see front matter B 2015 Heart Rhythm Society. All rights reserved.
Organized atrial tachycardia (AT) related to catheter ablation of atrial fibrillation (AF) occurs commonly during or after ablation.1–4 AT may be focal (automaticity or microreentry) or due to macroreentry,5–7 the differentiation of which is critical for effective ablation. There is not a clear consensus on whether entrainment mapping or activation mapping is the optimal approach for mapping AT related to AF ablation. Overdrive pacing for entrainment is a quick and effective means of characterizing and localizing these ATs; however, alteration or termination of AT may limit its utility. In this retrospective study, we evaluated the results of overdrive pacing of AT related to AF ablation in 30 consecutive patients to determine the risk of alteration or termination of AT. http://dx.doi.org/10.1016/j.hrthm.2014.09.002
Barbhaiya et al
Avoiding AT Alteration During Mapping
Methods Study population A total of 30 consecutive patients (11 women; mean age 64 ⫾ 10 years) who either presented with or developed a sustained left AT during radiofrequency ablation of AF at a single tertiary care medical center between July 1, 2012, and January 1, 2013, met the following entry criteria and were included: 1. One or more sustained ATs with a consistent biatrial activation pattern and consistent cycle length (CL) 4200 ms before pacing occurred. 2. More than 1 left atrial overdrive pacing attempt was made from a catheter within the coronary sinus or via transseptal approach within the left atrium. 3. During pacing, all atrial electrograms were accelerated to the pacing rate. Cavotricuspid isthmus–dependent right ATs were excluded. Overdrive pacing was performed using a paced CL (PCL) 5–40 ms below the shortest tachycardia CL (TCL). AT was classified as altered if the CL or activation pattern remained altered 10 seconds after pacing.
33
Electrophysiology study All patients provided written informed consent. All antiarrhythmic drugs except amiodarone were discontinued a minimum of 5 half-lives before the procedure. Surface and intracardiac electrocardiograms were digitally recorded and stored (Prucka CardioLab EP system, GE Healthcare, Waukesha, WI). Nonfluoroscopic 3-dimensional mapping was performed using the Carto (Biosense Webster Inc, Diamond Bar, CA) or Ensite NavX (St Jude Medical, St Paul, MN) system at the discretion of experienced operators. A 7-F multipolar (20-pole) catheter (Daig DuoDeca 2-10-2, St Jude Medical, orISMUS, Biosense Webster) was used with the distal poles (poles 1–10) placed within the coronary sinus and the proximal electrodes (poles 11–20) located along the tricuspid annulus in the lateral and inferior right atrium. For left atrial mapping and recording, a 10- or 20-pole circumferential PV mapping catheter (Optima, Irvine Biomedical, Irvine, CA, or Lasso, Biosense Webster) or a 5-spline mapping catheter with splines in the star configuration and 1-mm electrodes (PentaRay NAV, Biosense Webster) was used. Ablation was performed with a 3.5-mm open-irrigated tip ablation catheter paired with a 3-dimensional mapping system (NaviStar ThermoCool, Biosense Webster).
Statistical analysis Assessment of CL and CL stability Measurements of AT CL stability were made by an investigator blinded to the result of overdrive pacing. The 10 PP intervals preceding the first overdrive pacing attempt for each AT were measured at a sweep speed of 200 mm/s (Figure 1). The mean of these values were taken as the TCL. PP interval stability was determined by 2 measures: 1. The difference between the shortest and the longest CL expressed as a percentage of the CL (CLDmax): [CLmax – CLmin)/AT CL] 100 (Figure 1). 2. The mean difference between sequential PP intervals expressed as a percentage of the AT CL (CLDmean): (mean CL difference/CL) 100 (Figure 1).
Continuous variables are expressed as mean ⫾ SD and categorical variables as percentages. Statistical analysis was performed using Prism (version 6.0d, GraphPad Software, Inc, La Jolla, CA). Continuous variables were analyzed using the Student t test. Categorical variables were analyzed using the Fisher exact test. A 2-tailed P value of o.05 was considered statistically significant. Data collection and analysis were performed according to protocols approved by the Partners Human Subject Protection Committee.
Results Patient characteristics The mean age of the patients was 64 ⫾ 10 years; the mean left ventricular ejection fraction was 54% ⫾ 8%; and 13%
Figure 1 Representative atrial tachycardia intracardiac electrograms. Measured cycle lengths (CLs) over a 10-beat period indicated by white arrows. The mean CL is calculated as the average of measured CLs. The calculated CL differences between consecutive beats are used to calculate the mean CL difference. CLDmean is the mean CL difference as a percentage of the CL. CLDmax is the difference between the maximum CL observed (CLmax) and the minimum CL observed (CLmin) as a percentage of the CL. CS ¼ coronary sinus.
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Heart Rhythm, Vol 12, No 1, January 2015
AT response to pacing The mean AT CL was 268 ⫾ 53 ms (range 210–440 ms). The mean TCL – PCL difference was 15 ⫾ 6 ms (range 5–40 ms). Of 386 total overdrive pacing attempts, 2 (0.5%) altered AT, 3 (0.8%) terminated AT, and 381 did not change AT (98.7%). The 5 altered ATs occurred in 4 patients (13%), and there was no significant difference in the number of overdrive pacing attempts for ATs that were unchanged vs ATs that were altered or terminated (6.1 ⫾ 6.4 vs 8.4 ⫾ 3.6; P ¼ .43). When the TCL PCL difference was r20 ms, only 2 of 353 attempts (0.5%) altered or terminated AT, whereas when the TCL PCL difference was 420 ms, 3 of 33 attempts (9%) altered or terminated AT (relative risk 0.14; P ¼ .006). Macroreentry was confirmed in 65% of unchanged ATs (27 of 57) and 20% of altered or terminated ATs (1 of 5).
CL stability analysis The mean CLDmean for all analyzed ATs was 2.0% ⫾ 2.2% (range 0%–11%); however, the CLDmean was not significantly different for altered or terminated ATs vs those unchanged (3.8% ⫾ 2.6% vs 1.9% ⫾ 2.1%; P ¼ .06). The mean CLDmax for all analyzed ATs was 5.0% ⫾ 5.5% (range 0%–22%). The CLDmax was significantly greater in ATs that were altered or terminated by pacing vs those unchanged (11.0% ⫾ 9.6% vs 4.5% ⫾ 4.5%; P ¼ .007). The CLDmax presented a significant correlation (77%) with the probability of AT alteration or termination (95% CI 56%–98%; P ¼ .04; Figure 2). The risk of AT alteration or termination was significantly lower for ATs where the CLDmax was r20% and the TCL PCL difference was r20 ms compared with where the CLDmax was 420% or the the TCL PCL difference was 420 ms (1.9% vs 44%; relative risk 0.04; P ¼ .003; Figure 3).
Sensitivity
1.0
0.5
0.0 0.0
0.5
1.0
1 - Specificity Figure 2 Receiver operating characteristic curve of the difference between the shortest and the longest cycle length expressed as a percentage of the cycle length for the alteration of atrial tachycardia with overdrive pacing.
40
TCL-PCL (ms)
(n=4) had structural heart disease. Persistent AT or AF was present in 12 patients (40%), and AT occurred during a first left atrial ablation procedure in 11 patients (37%). A total of 62 ATs were analyzed (median 2 per patient), and 386 entrainment attempts were evaluated (median 4 per AT).
AT unaltered AT altered or terminated
30 20 10 0
0
5
10
15
20
25
CLDmax (%)
Figure 3 Scatterplot of CLDmax vs TCL PCL for all analyzed ATs. Dashed lines at TCL – PCL ¼ 20 ms and at CLDmax ¼ 20% represent low risk of AT alteration or termination when AT CL is stable and TCL – PCL difference is small. AT ¼ atrial tachycardia; CL ¼ cycle length; CLDmax ¼ difference between the shortest and the longest cycle length expressed as a percentage of the cycle length; PCL ¼ paced cycle length; TCL ¼ tachycardia cycle length.
Discussion Main findings To our knowledge, no prior studies have investigated the relationship between the TCL PCL difference and the risk of AT alteration and termination with atrial overdrive pacing for entrainment as well as the relationship between CL stability and the risk of AT alteration and termination with overdrive pacing. Our data indicate that the overall rate of AT alteration or termination is low, and the selection of a PCL slightly shorter than the TCL may prevent alteration or termination of AT. In addition, AT with greater CL variability is more likely to be altered or terminated with overdrive pacing. Specifically, increased CLDmax, which measures the maximum range of CL oscillation, is strongly associated with AT alteration or termination with overdrive pacing. Pascale et al8 have previously reported a 3% rate of AT alteration in addition to a 3% rate of AT termination with entrainment maneuvers. These findings are consistent with our findings that 2 of 62 ATs (3%) were altered by overdrive pacing and 3 of 62 ATs (5%) were terminated by overdrive pacing the present study. The optimal selection of PCL and selection of stable AT may further reduce the already low observed rates of AT alteration or termination. Focal AT has been reported to display greater CL variability relative to macroreentrant AT9; however, CL variability, to our knowledge, has not previously been evaluated for use in determining mapping strategy. Increased CL variability is associated with increased rates of ventricular tachycardia termination with implantable defibrillator– delivered antitachycardia pacing.10 Conversely, the present study demonstrates the low rate or AT alteration or termination with overdrive pacing of stable ATs. Multiple mapping strategies incorporating overdrive pacing have been suggested to efficiently diagnose common atrial arrhythmias arising during or after catheter ablation of AF.8,11–14 Coffey et al13 reported a strategy of detailed activation mapping followed by focused entrainment mapping of AF ablation–related ATs. Rostock et al12 proposed a mapping strategy starting with entrainment
Barbhaiya et al
Avoiding AT Alteration During Mapping
mapping from TCL PCL r6 left atrial sites in order to establish the correct AT diagnosis. Pascale et al8 proposed using coronary sinus activation pattern and timing of midcoronary sinus activation relative to the surface P wave to focus entrainment mapping. Each of these strategies requires multiple overdrive pacing attempts for confirmation of arrhythmia mechanism, and thus the identification of substantial CL variability during mapping suggests a higher risk of altering or terminating AT, and so an alternative mapping strategy may be attempted first. We have recently described a novel technique to minimize the number of overdrive pacing attempts required to diagnose macroreentrant ATs using downstream overdrive pacing from multielectrode catheters,15 which may further reduce the already low risk of AT alteration or termination during mapping.
Study limitations Although 386 overdrive pacing attempts were analyzed, there were only 5 instances of AT alteration or termination in the present study. This relatively small number limits the statistical power and does not allow for multivariate analysis or subgroup analysis. The selection of AT for overdrive pacing in this retrospective study was at the discretion of experienced operators and is not representative of all ATs that arise during catheter ablation of AF. AT alteration or termination rates may be higher than those reported without careful selection of AT and PCL; however, the results emphasize the low risk of AT alteration or termination when overdrive pacing for entrainment is appropriately used.
Conclusion Overdrive pacing for entrainment mapping of ATs that occur during or after AF ablation alters or terminates after AF AT in less than 1% of overdrive pacing attempts, provided that the AT CL is stable before pacing and that the PCL is r20 ms shorter than the AT CL. These features should help select ATs for mapping with overdrive pacing.
35
References 1. Chae S, Oral H, Good E, et al. Atrial tachycardia after circumferential pulmonary vein ablation of atrial fibrillation: mechanistic insights, results of catheter ablation, and risk factors for recurrence. J Am Coll Cardiol 2007;50:1781–1787. 2. Gerstenfeld EP, Callans DJ, Dixit S, Russo AM, Nayak H, Lin D, Pulliam W, Siddique S, Marchlinski FE. Mechanisms of organized left atrial tachycardias occurring after pulmonary vein isolation. Circulation 2004;110:1351–1357. 3. Gerstenfeld EP, Dixit S, Bala R, Callans DJ, Lin D, Sauer W, Garcia F, Cooper J, Russo AM, Marchlinski FE. Surface electrocardiogram characteristics of atrial tachycardias occurring after pulmonary vein isolation. Heart Rhythm 2007;4: 1136–1143. 4. Mesas CE, Pappone C, Lang CC, Gugliotta F, Tomita T, Vicedomini G, Sala S, Paglino G, Gulletta S, Ferro A, Santinelli V. Left atrial tachycardia after circumferential pulmonary vein ablation for atrial fibrillation: electroanatomic characterization and treatment. J Am Coll Cardiol 2004;44:1071–1079. 5. Chugh A, Oral H, Lemola K, Hall B, Cheung P, Good E, Tamirisa K, Han J, Bogun F, Pelosi F Jr, Morady F. Prevalence, mechanisms, and clinical significance of macroreentrant atrial tachycardia during and following left atrial ablation for atrial fibrillation. Heart Rhythm 2005;2:464–471. 6. Chugh A, Oral H, Good E, et al. Catheter ablation of atypical atrial flutter and atrial tachycardia within the coronary sinus after left atrial ablation for atrial fibrillation. J Am Coll Cardiol 2005;46:83–91. 7. Jais P, Shah DC, Haissaguerre M, Hocini M, Peng JT, Takahashi A, Garrigue S, Le Metayer J, Clementy J. Mapping and ablation of left atrial flutters. Circulation 2000;101:2928–2934. 8. Pascale P, Shah AJ, Roten L, et al. Pattern and timing of the coronary sinus activation to guide rapid diagnosis of atrial tachycardia after atrial fibrillation ablation. Circ Arrhythm Electrophysiol 2013;6:481–490. 9. Gerstenfeld EP, Callans DJ, Sauer W, Jacobson J, Marchlinski FE. Reentrant and nonreentrant focal left atrial tachycardias occur after pulmonary vein isolation. Heart Rhythm 2005;2:1195–1202. 10. Jimenez-Candil J, Hernandez J, Martin A, Morinigo J, Lopez R, Ledesma C, Martin-Luengo C. Influence of cycle length variations on antitachycardia pacing effectiveness among ICD patients. Heart Rhythm 2013;10:207–213. 11. Miyazaki H, Stevenson WG, Stephenson K, Soejima K, Epstein LM. Entrainment mapping for rapid distinction of left and right atrial tachycardias. Heart Rhythm 2006;3:516–523. 12. Rostock T, Drewitz I, Steven D, Hoffmann BA, Salukhe TV, Bock K, Servatius H, Aydin MA, Meinertz T, Willems S. Characterization, mapping, and catheter ablation of recurrent atrial tachycardias after stepwise ablation of long-lasting persistent atrial fibrillation. Circ Arrhythm Electrophysiol 2010;3:160–169. 13. Coffey JO, d’Avila A, Dukkipati S, Danik SB, Gangireddy SR, Koruth JS, Miller MA, Sager SJ, Eggert CA, Reddy VY. Catheter ablation of scar-related atypical atrial flutter. Europace 2013;15:414–419. 14. Steven D, Seiler J, Roberts-Thomson KC, Inada K, Stevenson WG. Mapping of atrial tachycardias after catheter ablation for atrial fibrillation: use of bi-atrial activation patterns to facilitate recognition of origin. Heart Rhythm 2010;7: 664–672. 15. Barbhaiya CR, Kumar S, Ng J, Tedrow U, Koplan B, John R, Epstein LM, Stevenson WG, Michaud GF. Overdrive pacing from downstream sites on multielectrode catheters to rapidly detect fusion and to diagnose macroreentrant atrial arrhythmias. Circulation 2014;129:2503–2510.
CLINICAL PERSPECTIVES Mapping atrial tachycardias (ATs) related to ablation of atrial fibrillation is often challenging. Activation sequence maps are time-consuming and can be difficult to interpret. Overdrive pacing for entrainment can quickly identify some tachycardias and determine whether the pacing site is in a macroreentry circuit, but has the risk that pacing will alter or terminate AT. This study shows that pacing for entrainment has undesirable effects on AT in fewer than 1% of pacing attempts, provided that AT has a stable cycle length and that the pacing cycle length is r20 ms shorter than the AT cycle length. These findings provide guidance in the use of entrainment mapping for mapping and ablation of these ATs.
expressed as a percentage of the CL was significantly greater in ATs that were altered or terminated by pacing than in those unchanged (11.0% ⫾ 9.6% vs 4.5% ⫾ 4.5%; P ¼ .007), but the mean difference between sequential PP intervals expressed as a percentage of the AT CL was not significantly different (3.8% ⫾ 2.6% vs 1.9% ⫾ 2.1%; P ¼ .06). CONCLUSION Overdrive pacing for entrainment mapping rarely alters or terminates after atrial fibrillation AT, provided that AT is stable before pacing and that the PCL is r20 ms shorter than the AT CL. KEYWORDS Atrial tachycardia; Atrial fibrillation; Mapping; Overdrive pacing; Entrainment; Catheter ablation ABBREVIATIONS AF ¼ atrial fibrillation; AT ¼ atrial tachycardia; CL ¼ cycle length; CLDmax ¼ difference between the shortest and the longest cycle length expressed as a percentage of the cycle length; CLDmean ¼ mean difference between sequential PP intervals expressed as a percentage of the atrial tachycardia cycle length; PCL ¼ paced cycle length; TCL ¼ tachycardia cycle length (Heart Rhythm 2015;12:32–35) rights reserved.
I
2015 Heart Rhythm Society. All
Introduction Dr Kumar is a recipient of the Neil Hamilton Fairley – Overseas Clinical Fellowship cofunded by the National Health and Medical Research Council and the National Heart Foundation of Australia; he is also a recipient of the Bushell Travelling Fellowship funded by the Royal Australasian College of Physicians. Dr Tedrow has received consulting fees/honoraria from Boston Scientific and St Jude Medical and research funding from Biosense Webster and St Jude Medical. Dr John has received consulting fees/honoraria from St Jude Medical. Dr Epstein has received consulting fees/honoraria from Boston Scientific, Medtronic, and Spectranetics. Dr Michaud has received consulting fees/honoraria from Boston Scientific, Medtronic, and St Jude Medical and research funding from Boston Scientific and Biosense Webster. Address reprint requests and correspondence: Dr Gregory F. Michaud, Cardiovascular Division, Brigham and Women’s Hospital, 75 Francis St, Boston, MA 02115. E-mail address: [email protected].
1547-5271/$-see front matter B 2015 Heart Rhythm Society. All rights reserved.
Organized atrial tachycardia (AT) related to catheter ablation of atrial fibrillation (AF) occurs commonly during or after ablation.1–4 AT may be focal (automaticity or microreentry) or due to macroreentry,5–7 the differentiation of which is critical for effective ablation. There is not a clear consensus on whether entrainment mapping or activation mapping is the optimal approach for mapping AT related to AF ablation. Overdrive pacing for entrainment is a quick and effective means of characterizing and localizing these ATs; however, alteration or termination of AT may limit its utility. In this retrospective study, we evaluated the results of overdrive pacing of AT related to AF ablation in 30 consecutive patients to determine the risk of alteration or termination of AT. http://dx.doi.org/10.1016/j.hrthm.2014.09.002
Barbhaiya et al
Avoiding AT Alteration During Mapping
Methods Study population A total of 30 consecutive patients (11 women; mean age 64 ⫾ 10 years) who either presented with or developed a sustained left AT during radiofrequency ablation of AF at a single tertiary care medical center between July 1, 2012, and January 1, 2013, met the following entry criteria and were included: 1. One or more sustained ATs with a consistent biatrial activation pattern and consistent cycle length (CL) 4200 ms before pacing occurred. 2. More than 1 left atrial overdrive pacing attempt was made from a catheter within the coronary sinus or via transseptal approach within the left atrium. 3. During pacing, all atrial electrograms were accelerated to the pacing rate. Cavotricuspid isthmus–dependent right ATs were excluded. Overdrive pacing was performed using a paced CL (PCL) 5–40 ms below the shortest tachycardia CL (TCL). AT was classified as altered if the CL or activation pattern remained altered 10 seconds after pacing.
33
Electrophysiology study All patients provided written informed consent. All antiarrhythmic drugs except amiodarone were discontinued a minimum of 5 half-lives before the procedure. Surface and intracardiac electrocardiograms were digitally recorded and stored (Prucka CardioLab EP system, GE Healthcare, Waukesha, WI). Nonfluoroscopic 3-dimensional mapping was performed using the Carto (Biosense Webster Inc, Diamond Bar, CA) or Ensite NavX (St Jude Medical, St Paul, MN) system at the discretion of experienced operators. A 7-F multipolar (20-pole) catheter (Daig DuoDeca 2-10-2, St Jude Medical, orISMUS, Biosense Webster) was used with the distal poles (poles 1–10) placed within the coronary sinus and the proximal electrodes (poles 11–20) located along the tricuspid annulus in the lateral and inferior right atrium. For left atrial mapping and recording, a 10- or 20-pole circumferential PV mapping catheter (Optima, Irvine Biomedical, Irvine, CA, or Lasso, Biosense Webster) or a 5-spline mapping catheter with splines in the star configuration and 1-mm electrodes (PentaRay NAV, Biosense Webster) was used. Ablation was performed with a 3.5-mm open-irrigated tip ablation catheter paired with a 3-dimensional mapping system (NaviStar ThermoCool, Biosense Webster).
Statistical analysis Assessment of CL and CL stability Measurements of AT CL stability were made by an investigator blinded to the result of overdrive pacing. The 10 PP intervals preceding the first overdrive pacing attempt for each AT were measured at a sweep speed of 200 mm/s (Figure 1). The mean of these values were taken as the TCL. PP interval stability was determined by 2 measures: 1. The difference between the shortest and the longest CL expressed as a percentage of the CL (CLDmax): [CLmax – CLmin)/AT CL] 100 (Figure 1). 2. The mean difference between sequential PP intervals expressed as a percentage of the AT CL (CLDmean): (mean CL difference/CL) 100 (Figure 1).
Continuous variables are expressed as mean ⫾ SD and categorical variables as percentages. Statistical analysis was performed using Prism (version 6.0d, GraphPad Software, Inc, La Jolla, CA). Continuous variables were analyzed using the Student t test. Categorical variables were analyzed using the Fisher exact test. A 2-tailed P value of o.05 was considered statistically significant. Data collection and analysis were performed according to protocols approved by the Partners Human Subject Protection Committee.
Results Patient characteristics The mean age of the patients was 64 ⫾ 10 years; the mean left ventricular ejection fraction was 54% ⫾ 8%; and 13%
Figure 1 Representative atrial tachycardia intracardiac electrograms. Measured cycle lengths (CLs) over a 10-beat period indicated by white arrows. The mean CL is calculated as the average of measured CLs. The calculated CL differences between consecutive beats are used to calculate the mean CL difference. CLDmean is the mean CL difference as a percentage of the CL. CLDmax is the difference between the maximum CL observed (CLmax) and the minimum CL observed (CLmin) as a percentage of the CL. CS ¼ coronary sinus.
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Heart Rhythm, Vol 12, No 1, January 2015
AT response to pacing The mean AT CL was 268 ⫾ 53 ms (range 210–440 ms). The mean TCL – PCL difference was 15 ⫾ 6 ms (range 5–40 ms). Of 386 total overdrive pacing attempts, 2 (0.5%) altered AT, 3 (0.8%) terminated AT, and 381 did not change AT (98.7%). The 5 altered ATs occurred in 4 patients (13%), and there was no significant difference in the number of overdrive pacing attempts for ATs that were unchanged vs ATs that were altered or terminated (6.1 ⫾ 6.4 vs 8.4 ⫾ 3.6; P ¼ .43). When the TCL PCL difference was r20 ms, only 2 of 353 attempts (0.5%) altered or terminated AT, whereas when the TCL PCL difference was 420 ms, 3 of 33 attempts (9%) altered or terminated AT (relative risk 0.14; P ¼ .006). Macroreentry was confirmed in 65% of unchanged ATs (27 of 57) and 20% of altered or terminated ATs (1 of 5).
CL stability analysis The mean CLDmean for all analyzed ATs was 2.0% ⫾ 2.2% (range 0%–11%); however, the CLDmean was not significantly different for altered or terminated ATs vs those unchanged (3.8% ⫾ 2.6% vs 1.9% ⫾ 2.1%; P ¼ .06). The mean CLDmax for all analyzed ATs was 5.0% ⫾ 5.5% (range 0%–22%). The CLDmax was significantly greater in ATs that were altered or terminated by pacing vs those unchanged (11.0% ⫾ 9.6% vs 4.5% ⫾ 4.5%; P ¼ .007). The CLDmax presented a significant correlation (77%) with the probability of AT alteration or termination (95% CI 56%–98%; P ¼ .04; Figure 2). The risk of AT alteration or termination was significantly lower for ATs where the CLDmax was r20% and the TCL PCL difference was r20 ms compared with where the CLDmax was 420% or the the TCL PCL difference was 420 ms (1.9% vs 44%; relative risk 0.04; P ¼ .003; Figure 3).
Sensitivity
1.0
0.5
0.0 0.0
0.5
1.0
1 - Specificity Figure 2 Receiver operating characteristic curve of the difference between the shortest and the longest cycle length expressed as a percentage of the cycle length for the alteration of atrial tachycardia with overdrive pacing.
40
TCL-PCL (ms)
(n=4) had structural heart disease. Persistent AT or AF was present in 12 patients (40%), and AT occurred during a first left atrial ablation procedure in 11 patients (37%). A total of 62 ATs were analyzed (median 2 per patient), and 386 entrainment attempts were evaluated (median 4 per AT).
AT unaltered AT altered or terminated
30 20 10 0
0
5
10
15
20
25
CLDmax (%)
Figure 3 Scatterplot of CLDmax vs TCL PCL for all analyzed ATs. Dashed lines at TCL – PCL ¼ 20 ms and at CLDmax ¼ 20% represent low risk of AT alteration or termination when AT CL is stable and TCL – PCL difference is small. AT ¼ atrial tachycardia; CL ¼ cycle length; CLDmax ¼ difference between the shortest and the longest cycle length expressed as a percentage of the cycle length; PCL ¼ paced cycle length; TCL ¼ tachycardia cycle length.
Discussion Main findings To our knowledge, no prior studies have investigated the relationship between the TCL PCL difference and the risk of AT alteration and termination with atrial overdrive pacing for entrainment as well as the relationship between CL stability and the risk of AT alteration and termination with overdrive pacing. Our data indicate that the overall rate of AT alteration or termination is low, and the selection of a PCL slightly shorter than the TCL may prevent alteration or termination of AT. In addition, AT with greater CL variability is more likely to be altered or terminated with overdrive pacing. Specifically, increased CLDmax, which measures the maximum range of CL oscillation, is strongly associated with AT alteration or termination with overdrive pacing. Pascale et al8 have previously reported a 3% rate of AT alteration in addition to a 3% rate of AT termination with entrainment maneuvers. These findings are consistent with our findings that 2 of 62 ATs (3%) were altered by overdrive pacing and 3 of 62 ATs (5%) were terminated by overdrive pacing the present study. The optimal selection of PCL and selection of stable AT may further reduce the already low observed rates of AT alteration or termination. Focal AT has been reported to display greater CL variability relative to macroreentrant AT9; however, CL variability, to our knowledge, has not previously been evaluated for use in determining mapping strategy. Increased CL variability is associated with increased rates of ventricular tachycardia termination with implantable defibrillator– delivered antitachycardia pacing.10 Conversely, the present study demonstrates the low rate or AT alteration or termination with overdrive pacing of stable ATs. Multiple mapping strategies incorporating overdrive pacing have been suggested to efficiently diagnose common atrial arrhythmias arising during or after catheter ablation of AF.8,11–14 Coffey et al13 reported a strategy of detailed activation mapping followed by focused entrainment mapping of AF ablation–related ATs. Rostock et al12 proposed a mapping strategy starting with entrainment
Barbhaiya et al
Avoiding AT Alteration During Mapping
mapping from TCL PCL r6 left atrial sites in order to establish the correct AT diagnosis. Pascale et al8 proposed using coronary sinus activation pattern and timing of midcoronary sinus activation relative to the surface P wave to focus entrainment mapping. Each of these strategies requires multiple overdrive pacing attempts for confirmation of arrhythmia mechanism, and thus the identification of substantial CL variability during mapping suggests a higher risk of altering or terminating AT, and so an alternative mapping strategy may be attempted first. We have recently described a novel technique to minimize the number of overdrive pacing attempts required to diagnose macroreentrant ATs using downstream overdrive pacing from multielectrode catheters,15 which may further reduce the already low risk of AT alteration or termination during mapping.
Study limitations Although 386 overdrive pacing attempts were analyzed, there were only 5 instances of AT alteration or termination in the present study. This relatively small number limits the statistical power and does not allow for multivariate analysis or subgroup analysis. The selection of AT for overdrive pacing in this retrospective study was at the discretion of experienced operators and is not representative of all ATs that arise during catheter ablation of AF. AT alteration or termination rates may be higher than those reported without careful selection of AT and PCL; however, the results emphasize the low risk of AT alteration or termination when overdrive pacing for entrainment is appropriately used.
Conclusion Overdrive pacing for entrainment mapping of ATs that occur during or after AF ablation alters or terminates after AF AT in less than 1% of overdrive pacing attempts, provided that the AT CL is stable before pacing and that the PCL is r20 ms shorter than the AT CL. These features should help select ATs for mapping with overdrive pacing.
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CLINICAL PERSPECTIVES Mapping atrial tachycardias (ATs) related to ablation of atrial fibrillation is often challenging. Activation sequence maps are time-consuming and can be difficult to interpret. Overdrive pacing for entrainment can quickly identify some tachycardias and determine whether the pacing site is in a macroreentry circuit, but has the risk that pacing will alter or terminate AT. This study shows that pacing for entrainment has undesirable effects on AT in fewer than 1% of pacing attempts, provided that AT has a stable cycle length and that the pacing cycle length is r20 ms shorter than the AT cycle length. These findings provide guidance in the use of entrainment mapping for mapping and ablation of these ATs.
