Original Cardiovascular
The Potential Impact of Functional Imaging on Decision Making and Outcome in Patients Undergoing Surgical Revascularization Andre Plass1 Robert P. Goetti2 Maximilian Y. Emmert1 Etem Caliskan1 Monika Wieser1 Olivio Donati2 Hatem Alkadhi2 Volkmar Falk1 1 Clinic for Cardiac Surgery, University Hospital Zurich, Zurich,
Switzerland 2 Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland
Paul Stolzmann2
Address for correspondence Andre Plass, MD, Clinic for Cardiovascular Surgery, Raemistr. 100, 8091 Zurich, Switzerland (e-mail: [email protected]).
Thorac Cardiovasc Surg 2015;63:270–276.
Abstract
Keywords
► coronary angiography ► magnetic resonance imaging ► computed tomography ► functional imaging ► coronary artery bypass surgery
received February 3, 2014 accepted after revision September 4, 2014 published online December 2, 2014
Objective Coronary angiography (CA) remains the standard for preoperative planning for surgical revascularization. However, besides anatomical imaging, current guidelines recommend additional functional imaging before a therapy decision is made. We assess the impact of functional imaging on the strategy of coronary artery bypass grafting (CABG) with particular regards on postoperative patency and myocardial perfusion. Methods After CA, 55 patients (47 males/8 females; age: 65.1 9.5 years) underwent perfusion cardiovascular magnetic resonance (CMR) and dual-source computed tomography (DSCT) before isolated CABG (n ¼ 31), CABG and concomitant valve surgery (valve þ CABG; n ¼ 10) and isolated valve surgery (n ¼ 14; control). DSCT was used for analysis of significant stenosis, CMR for myocardial-perfusion to discriminate between: no ischemia (normal), ischemia, or scar. The results, unknown to the surgeons, were compared with CA and related to the location and number of distal anastomoses. Nineteen CABG patients underwent follow-up CMR and DSCT (FU: 13 3 months) to compare the preop findings with the postop outcomes. Results Thirty-nine patients either received CABG alone (n ¼ 31) or a combined procedure (n ¼ 10) with a total of 116 distal anastomoses. DSCT was compared with CA regarding accuracy of coronary stenosis and showed 91% sensitivity, 88% specificity, and negative/positive predictive values of 89/90%. In total, 880 myocardial segments (n ¼ 55, 16 segments/patient) were assessed by CMR. In 17% (149/880) of segments ischemia and in 8% (74/880) scar tissue was found. Interestingly, 14% (16/116) of bypass-anastomoses were placed on non-ischemic myocardium and 3% (4/116) on scar tissue. In a subgroup of 19 patients 304 segments were evaluated. Thirty-nine percent (88/304) of all segments showed ischemia preoperatively, while 94% (83/88) of these ischemic segments did not show any ischemia postoperatively. In regard to performed anastomoses, 79% of all grafts (49/62) were optimally placed, whereas 21% (13/62) were either placed into non-ischemic myocardium or scar tissue, including 10% occluded grafts (6/62).
© 2015 Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0034-1395393. ISSN 0171-6425.
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Conclusion In the whole cohort analysis, 17% of grafts were placed in regions with either no ischemia or scar tissue. The subgroup analysis revealed that 94% of all ischemic segments were successfully revascularized after CABG. Thus, functional imaging could be a promising tool in preoperative planning of revascularization strategy. Avoidance of extensive and unnecessary grafting could further optimize outcomes after CABG.
The optimal diagnostic algorithm for coronary artery disease (CAD) remains an ongoing debate. A wide range of different diagnostic and therapeutic tools are available which can be used individually or combined. These diagnostic tools comprise coronary angiography with/without intravascular ultrasound (IVUS), computed tomography (CT) 1 (for anatomical imaging) and stress-echocardiography,2,3 single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI)4,5 (for functional imaging). Besides anatomical imaging, current guidelines increasingly recommend the use of additional functional imaging for the diagnosis and grading of CAD before interdisciplinary decision is made for the most appropriate therapy.6,7 However, in the daily clinical routine the diagnostic results considered for decision making prior to surgical revascularization are primarily based on anatomical imaging only which is also reflected in large randomized trials such as the SYNTAX trial which was only based on anatomical assessment of coronaries.8 Therefore, this study aims to demonstrate the potential impact of functional imaging on the strategy of coronary artery bypass grafting (CABG) particularly regarding postoperative patency rate and myocardial perfusion.
Materials and Methods After approval of an institutional review board and obtained informed consent, 55 patients (47 males/8 females; age 65.1 9.5 years) before isolated CABG (n ¼ 31), CABG and concomitant valve surgery (valve þ CABG; n ¼ 10), and isolated valve surgery (n ¼ 14; control) were included in this study. All patients underwent coronary angiography (CA) (anatomical) with prognostic indication and thereafter underwent perfusion cardiovascular magnetic resonance (CMR) (functional) as well as dual-source computed tomography (DSCT) before cardiac surgery. DSCT was used for further anatomical evaluation of significant stenosis, CMR for perfusion assessment of the myocardium in a 16-segment heart model detecting no ischemia (normal), ischemia, or scar. The results, unknown to the surgeons, were compared with CA and related to the location and number of distal bypass graft anastomoses. The control group with isolated valve surgery did not undergo any postoperative imaging; preoperative data obtained from DSCT and CA was used to validate the comparison methodology. Further, a subgroup of 19 patients (all CABG only) with a total of 62 bypass anastomoses (mean,
CT Data Acquisition A second-generation dual-source CT system (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany) was used for all CT scans. We have injected 70 to 80 mL of contrast material (Iopromide, Ultravist 370, 370 mg/mL, Bayer Schering Pharma, Berlin, Germany) in a right antecubital vein at a flow rate of 5 mL/second followed by 40 mL saline solution. Contrast timing was controlled by bolus tracking in the ascending aorta with an attenuation threshold 100 HU and a delay of 8 seconds. A prospectively electrocardiogram (ECG)-synchronized dual-source high-pitch acquisition mode with the following scanning parameters was used: slice collimation, 2 128 0.6 mm applying a z-flying focal spot; gantry rotation time, 280 milliseconds; pitch, 3.2; tube potential, 100 kV; and attenuation-based tube current modulation with a reference tube current–time product of 320 mA second per rotation. Images were reconstructed with a slice thickness of 0.75 mm and an increment of 0.5 mm, using a standard cardiac imaging convolution kernel (B26f).
CT Data Evaluation Data were evaluated on an external workstation (MultiModality Workplace, Siemens Healthcare, Forchheim, Germany). Two radiologists, blinded to the results of CMR imaging, evaluated all bypass grafts for patency in a consensus reading using axial source images and multiplanar reformations.
CMR Data Acquisition A 1.5 T magnetic resonance imaging system (Achieva, Philips Medical Systems, Best, the Netherlands) was used for all CMR studies. Three short-axis sliced (basal, midventricular, and apical) as determined by a series of scout images were acquired. For stress imaging, 140 μg/kg of body weight of adenosine were injected intravenously during 3 minutes under ECG and blood pressure monitoring. Perfusion CMR images were acquired after the injection of 0.1 mmol/kg of body weight of gadobutrolum (Gadovist 1,0; Bayer Schering Pharma, Berlin, Germany) at a rate of 5 mL/second, followed by 40 mL saline solution. Ten minutes after stress perfusion imaging, rest perfusion images were acquired after injecting a second bolus of 0.1 mmol per kilogram of body weight of gadobutrolum. For both acquisitions, k-t sensitivity encoding (SENSE) perfusion CMR imaging was used in combination Thoracic and Cardiovascular Surgeon
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Introduction
3.1 bypass anastomoses/patient) had follow-up CT and MR exams (mean follow-up, 13 3 months), which were compared with the preoperative data to assess patency of bypass anastomoses and myocardial perfusion.
Impact of Functional Imaging on Decision Making and Outcome with a saturation recovery gradient-echo pulse sequence (repetition time/echo time, 3.1/1.1 milliseconds; flip angle, 20 degrees; saturation pre-pulse delay, 110 milliseconds; partial Fourier sampling; acquisition window, 120 milliseconds; section thickness, 8 mm; k-t factor of five with 11 k-t interleaved training profiles; effective acceleration, 3.7; three sections acquired sequentially during a single R-R interval); in-plane resolution, 2 2 mm2. Late gadolinium enhancement (LGE) images were acquired 10 minutes after rest perfusion using an inversion-recovery gradient-recalled echo sequence with the following parameters: field of view, 350 to 400 mm; repetition time/echo time, 7.4/4.3 milliseconds; inversion time, 200 to 350 milliseconds (individually optimized for myocardial signal nulling); flip angle, 20 degrees; matrix, 240 240; slice thickness, 8 mm, continuous.
Plass et al.
sensitivity, specificity, negative and positive predictive values were calculated for all patients with sufficient image quality. Two blinded readers, experienced in both cardiovascular CT and MRI from the department of radiology as well as clinic for cardiovascular surgery without any knowledge of the patient’s medical history and of the results from the specific counter examination (CT/MRI/ICA [invasive coronary angiography]) compared postoperatively the results of the preoperative imaging of each imaging technique with the finally performed CABG respectively distal anastomoses. Further, they analyzed blinded to the performed surgery the myocardium postoperatively as well as in a second step the bypass grafts regarding patency and positioning of the bypass grafts.
Results ►Tables 1 and 2 summarize the pre- and intraoperative data of the patient cohort.
CMR Data Analysis CMR data were evaluated on an external workstation (ViewForum, Philips Medical Systems) by two radiologists in a consensus reading. Perfusion CMR, as well as LGE image sets, was assessed by visual analysis of segments 1 to 16 of the 17-segment American Heart Association model. Myocardial ischemia in a segment was defined as a defect on stress perfusion CMR that was reversible at rest perfusion CMR. Myocardial scarring was defined as hyperintense myocardium with a transmurality of 50% or more in LGE images.
Table 1 Preoperative characteristics and demographics
Male (%)
47 (85.5)
Female (%)
8 (14.5)
Weight, kg
79.8 13.0
According to the standard techniques, a conventional selective CA on a Philips Integris Allura 9 Biplanesystem was performed. The contrast medium (Ultravist, Schering) consumption including the levogram averaged 140 mL. 5F diagnostic catheters (Cordis, Johnson & Johnson, Miami, Florida, United States) were used. The multiple views were stored on a CD-ROM and two cardiac surgeons blinded to the results examined the images for evaluation of the coronary arteries preoperatively. In this study, a modified classification of the guidelines of the American Heart Association was applied. The coronary arteries were segmented in 11 parts: Subdivision of the right coronary artery (RCA) and the left anterior descending artery (LAD) in a proximal, middle, and distal part; the circumflex branch (CX) in a proximal and distal segment; the left main (LM), the diagonal branch 1 (D1) of the LAD, and the first marginal branch of the CX (1st marg.) were considered as being independent segments. If the diameter reduction was >50%, the accordant vessel segment was scored as being significantly stenosed. Coronary arteries with diameter as large as 1.5 mm were analyzed, including those vessels distal to an occlusion.
Statistics Continuous quantitative values were expressed in mean values standard deviation and categorical variables as frequencies or percentages. The diagnostic accuracy of DSCT compared with catheter CA for assessment of stenosis >70% was evaluated for vessel as well as segment. Based on these data Thoracic and Cardiovascular Surgeon
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1.71 7.3
Height, m Body mass index, kg/m
Catheter Coronary Angiography
65.1 9.5
Age, y
2
27.4 4.0
Diabetes mellitus (%)
10 (18.2)
Hypertension (%)
41 (74.6)
History of smoking (%)
30 (54.6)
Dyslipidemia (%)
38 (69.1)
Positive family history (%)
13 (23.6)
Coronary artery disease (%)
38 (69.1)
1—Vessel disease (%) 2—Vessel disease (%) 3—Vessel disease (%)
7 (12.7) 19 (34.6) 12 (21.8)
Type of surgery Isolated CABG (%) Combined procedures (%) Isolated valve (%)
31 (56.4) 10 (18.2) 14 (25.5)
Anatomical LAD (%) RCX (%) RCA (%)
31 (56.4) 25 (45.5) 32 (58.2)
Functional—Segment ischemic LAD RCX RCA
69 (in 30 patients) 41 (in 19 patients) 66 (in 27 patients)
Functional—Segment infarct/scar LAD RCX RCA
11 (in 6 patients) 34 (in 12 patients) 28 (in 15 patients)
Abbreviations: CABG, coronary artery bypass grafting; LAD, left anterior descending; LIMA, left internal mammary artery; RCA, right coronary artery; RCX, ramus circumflexus/circumflex artery; RIMA, right internal mammary artery; SVG, saphenous vein graft.
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Table 2 Intraoperative data and used grafts (in patients with CABG and combined procedures) 2.05 1.05
Total grafts
94
Arterial grafts (%) LIMA (%) RIMA (%) Radial artery (%)
50 (53.2) 33 (35.1) 9 (9.6) 8 (8.5)
SVG (%)
44 (46.8)
Distal anastomoses LAD (%) RCX (%) RCA (%)
116 58 (50.0) 27 (23.3) 31 (26.7)
Abbreviations: CABG, coronary artery bypass grafting; LAD, left anterior descending; LIMA, left internal mammary artery; RCA, right coronary artery; RCX, ramus circumflexus/circumflex artery; RIMA, right internal mammary artery; SVG, saphenous vein graft.
Whole Cohort Analysis (n ¼ 55)
In the whole cohort analysis,9 31 patients received CABG, 10 patients had additional valve surgery, and 14 isolated valve surgery. In total, 116 distal anastomoses were performed. DSCT was compared with CA regarding accuracy of coronary stenosis and showed sensitivity of 91%, specificity 88%, and negative/positive predictive value of 89/90%. In the whole cohort (n ¼ 55), a total of 880 segments (16 segments/patient) of myocardium were assessed by all imaging modalities displaying 20% of assessed segments (176/880) to be ischemic, and 8% of assessed segments (73/880) to be scar tissue (►Fig. 1). Importantly, when relating these results to the bypass anastomoses performed, it became apparent that a total of 17% of all bypass anastomoses (20/116) were sub-optimally grafted: 14% (16/116) of bypass anastomoses were placed to nonischemic myocardium and 3% (4/116) to scar tissue (►Fig. 2).
Subgroup Analysis of Patients with Postoperative CT and MR (n ¼ 19) 10
In the subgroup analysis, 19 patients underwent pre- and postoperative MR and CT assessment with a total of 304 myocardial segments (16 segments/patient) evaluated. Of these, 39% (88/304) showed ischemic myocardium under
Fig. 1 Myocardial segments assessed.
Fig. 2 Bypass anastomoses performed.
stress/rest preoperatively. In contrast, 94% (83/88) of the ischemic segments did not show any signs of ischemia in the postoperative imaging. In 6% (5/88) of segments persistent ischemia was present postoperatively (one patient with five patent bypass anastomoses and two patients with one occluded bypass anastomosis each). In regard to performed bypass anastomoses, 79% of all anastomoses (49/62) were optimally placed to supply the ischemic regions, whereas 21% (13/62) of all anastomoses were placed either into non-ischemic myocardium (nine anastomoses) or into scar tissue (four anastomoses). Postoperative imaging also revealed that 10% of all bypass anastomoses were occluded (6/62) while of these, four anastomoses were located in non-ischemic regions with potential competitive flow (three anastomoses) and in scar-tissue (one anastomosis). The remaining two occluded anastomoses were placed in ischemic regions that therefore remained ischemic postoperatively. ►Figs. 3–5 illustrate pre- and postoperative DSCT and CMR myocardial-perfusion findings in three exemplary cases.
Discussion CA and DSCT are commonly used anatomical imaging tools to diagnose and to grade CAD in clinical routine. 11,12 However, asymptomatic, elective patients carry the important aspect of prognostic indication and thus it remains an ongoing debate if the used imaging techniques are sufficient enough to determine the most efficient revascularization strategy. The latest European Society of Cardiology (ESC)/European Association for Cardio-Thoracic Surgery (EACTS) revascularization guidelines 2010 recommend functional diagnostic imaging for assessment of myocardial viability for patients with a prognostic indication and a poor left ventricular (LV)-function.6,7 However, the daily practice is contradictory and once CA has been performed, CAD diagnostics are often considered complete and the therapy already starts. Therefore, this study focused on the potential impact of additional functional imaging on the strategy of CABG with particular regards on postoperative patency rate and myocardial perfusion. Thoracic and Cardiovascular Surgeon
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Diseased vessels
Impact of Functional Imaging on Decision Making and Outcome
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Fig. 3 Case Example 1. A 60-year-old patient underwent quadruple CABG including a graft to the RCX as shown by postoperative CT (arrows in A). In the lateral wall supplied by the RCX, the preoperative delayed enhancement MRI shows a myocardial scar (arrowheads in B) with >50% transmurality, which remains unchanged postoperatively (arrowheads in C). CABG, coronary artery bypass grafting; RCX, ramus circumflexus/ circumflex artery; CT, computed tomography; MRI, magnetic resonance imaging.
Fig. 4 Case Example 2. A 71-year-old patient underwent quintuple CABG including a LIMA-LAD graft and a venous graft to the RCA. Postoperative CT shows an occluded LIMA-LAD graft (arrows in A). Whereas the preoperative ischemia demonstrated in adenosine-stress perfusion MRI in the RCA territory (arrowheads in B) is regressive postoperatively (arrowhead in C), the subtle ischemia in the LAD territory remains unchanged (arrows in B and C). CABG, coronary artery bypass grafting; LIMA-LAD, left internal mammary artery-left anterior descending; RCA, right coronary artery; CT, computed tomography; MRI, magnetic resonance imaging.
Fig. 5 Case Example 3. A 64-year-old patient underwent quintuple CABG including a LIMA-LAD graft and a venous graft to the intermediate artery and two diagonal branches as shown by postoperative CT (A). The extensive ischemia of the LAD territory demonstrated in preoperative adenosine-stress perfusion MRI (arrowheads in [B]) can no longer be found postoperatively (C). CABG, coronary artery bypass grafting; LIMA-LAD, left internal mammary artery-left anterior descending; CT, computed tomography; MRI, magnetic resonance imaging.
Several techniques such as MRI, PET, SPECT, stress-echocardiography, and fractional flow reserve are available to perform specific additional functional diagnostics.2–4,13 However, in this study, CMR and DSCT were used demonstrating a high image quality along with high sensitivities and specificities for CAD evaluation, to date, no algorithms are established regarding the ideal type of additional functional imaging for the respective clinical setting. As all imaging Thoracic and Cardiovascular Surgeon
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modalities carry specific advantages, and also disadvantages, clear consensus remains to be established.14,15 In this regard, the recent ESC guidelines6,7,14,15 further recommend to establish the concept of the interdisciplinary Heart Team to determine the optimal diagnostic and therapeutic algorithm for each CAD patient. While this concept represents a significant step towards a more objective decision making,16,17 establishing a standardized functional
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Impact of Functional Imaging on Decision Making and Outcome References
1 Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-
2
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Conclusion In the whole cohort analysis, 17% of grafts were placed in regions with either no ischemia or scar tissue. The subgroup analysis revealed that 94% of all ischemic segments were successfully revascularized after CABG. This study shows that functional imaging could be a promising tool in the preoperative planning of an optimized surgical revascularization strategy. Avoidance of extensive and unnecessary grafting could further optimize outcomes after CABG. Note Parts of this article were presented at the annual meetings of the International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS), 2011 and 2012.
11
12
13
14
15
Conflict of Interest None
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multidetector row coronary computed tomographic angiography for evaluation of coronary artery stenosis in individuals without known coronary artery disease: results from the prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial. J Am Coll Cardiol 2008;52(21):1724–1732 Sicari R, Nihoyannopoulos P, Evangelista A, et al; European Association of Echocardiography. Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registered branch of the ESC). Eur J Echocardiogr 2008; 9(4):415–437 Sicari R, Nihoyannopoulos P, Evangelista A, et al; European Association of Echocardiography. Stress echocardiography expert consensus statement–executive summary: European Association of Echocardiography (EAE) (a registered branch of the ESC). Eur Heart J 2009;30(3):278–289 Chung SY, Lee KY, Chun EJ, et al. Comparison of stress perfusion MRI and SPECT for detection of myocardial ischemia in patients with angiographically proven three-vessel coronary artery disease. AJR Am J Roentgenol 2010;195(2):356–362 Ishida M, Kato S, Sakuma H. Cardiac MRI in ischemic heart disease. Circ J 2009;73(9):1577–1588 Kolh P, Wijns W, Danchin N, et al; Task Force on Myocardial Revascularization of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS); European Association for Percutaneous Cardiovascular Interventions (EAPCI). Guidelines on myocardial revascularization. Eur J Cardiothorac Surg 2010;38(Suppl):S1–S52 Wijns W, Kolh P, Danchin N, et al; Task Force on Myocardial Revascularization of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS); European Association for Percutaneous Cardiovascular Interventions (EAPCI). Guidelines on myocardial revascularization. Eur Heart J 2010;31(20):2501–2555 Serruys PW, Morice MC, Kappetein AP, et al; SYNTAX Investigators. Percutaneous coronary intervention versus coronary-artery bypass grafting for severe coronary artery disease. N Engl J Med 2009;360(10):961–972 Plass A, Emmert MY, Azemaj N, et al. Importance of advanced imaging in coronary bypass surgery. Innovations 2011; Annual Meeting, International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS), Conference Abstract:6 Plass A, Emmert MY, Goetti R. Dual-source computed tomography and magnetic resonance perfusion imaging: How good do we revascularize? Innovations 2012; Annual Meeting, International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS), Conference Abstract:7 Dikkers R, Willems TP, Piers LH, et al. Coronary revascularization treatment based on dual-source computed tomography. Eur Radiol 2008;18(9):1800–1808 Favaloro RG. Critical analysis of coronary artery bypass graft surgery: a 30-year journey. J Am Coll Cardiol 1998;31 (4, Suppl B):1B–63B Hachamovitch R, Berman DS, Shaw LJ, et al. Incremental prognostic value of myocardial perfusion single photon emission computed tomography for the prediction of cardiac death: differential stratification for risk of cardiac death and myocardial infarction. Circulation 1998;97(6):535–543 Greenwood JP, Maredia N, Younger JF, et al. Cardiovascular magnetic resonance and single-photon emission computed tomography for diagnosis of coronary heart disease (CE-MARC): a prospective trial. Lancet 2012;379(9814):453–460 Schwitter J, Wacker CM, Wilke N, et al; MR-IMPACT investigators. Superior diagnostic performance of perfusion-cardiovascular magnetic resonance versus SPECT to detect coronary artery
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imaging protocol into the clinical routine may be challenged mainly by logistical issues as costs and time consumption. Limited access and availability as well as non-elective appointments can make the planning and course very difficult. In line with that, in our study also a major problem was the logistics that resulted in a difficult patient acquisition for this study. Although appointments and scans could be done after the official hours and patients were very cooperative, still it was difficult to organize it efficiently. Therefore, it remains questionable how this concept needs to be organized to fit into clinical routine for a larger number of patients. In our subgroup of patients that underwent pre- and postoperative functional imaging we could demonstrate an overall high success rate of 94% for revascularization of ischemic segments based only on anatomical imaging. However, 17% (20/116) of the distal anastomosis in the whole cohort analysis were suboptimally placed, either to non-ischemic or scared myocardium. In line with that, also in the subgroup cohort who underwent additional postoperative imaging our data showed that even 21% (13/62) of all bypass anastomoses were not perfectly positioned. Retrospectively these bypass grafts were not necessary and the coronaries should have been left untouched. This is important, as even certain damage may occur to the vessel wall when an incision is done to perform an anastomosis. While it remains unclear what deleterious effects can result if a bypass-graft is placed into healthy, non-ischemic myocardium, early graft occlusion is well known to occur in these circumstances. Finally, it is necessary to establish a more patient tailored imaging route for diagnostic of CAD in the clinical routine. While the present guidelines primarily recommend myocardial perfusion diagnostic in patients with poor LV function, our data indicate that the patient spectrum for additional functional imaging may be expanded to other patient populations such as chronic CAD patients to determine whether such patients may benefit more from a MIDCAB (minimally invasive direct coronary artery bypass) or HYBRID (MIDCAB plus percutaneous coronary intervention) procedure instead of a standard CABG.
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Impact of Functional Imaging on Decision Making and Outcome disease: The secondary endpoints of the multicenter multivendor MR-IMPACT II (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease Trial). J Cardiovasc Magn Reson 2012;14:61 16 Holmes DR Jr, Rich JB, Zoghbi WA, Mack MJ. The heart team of cardiovascular care. J Am Coll Cardiol 2013;61(9):903–907
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17 Long J, Luckraz H, Thekkudan J, Maher A, Norell M. Heart team
discussion in managing patients with coronary artery disease: outcome and reproducibility. Interact Cardiovasc Thorac Surg 2012;14(5):594–598
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The Potential Impact of Functional Imaging on Decision Making and Outcome in Patients Undergoing Surgical Revascularization Andre Plass1 Robert P. Goetti2 Maximilian Y. Emmert1 Etem Caliskan1 Monika Wieser1 Olivio Donati2 Hatem Alkadhi2 Volkmar Falk1 1 Clinic for Cardiac Surgery, University Hospital Zurich, Zurich,
Switzerland 2 Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland
Paul Stolzmann2
Address for correspondence Andre Plass, MD, Clinic for Cardiovascular Surgery, Raemistr. 100, 8091 Zurich, Switzerland (e-mail: [email protected]).
Thorac Cardiovasc Surg 2015;63:270–276.
Abstract
Keywords
► coronary angiography ► magnetic resonance imaging ► computed tomography ► functional imaging ► coronary artery bypass surgery
received February 3, 2014 accepted after revision September 4, 2014 published online December 2, 2014
Objective Coronary angiography (CA) remains the standard for preoperative planning for surgical revascularization. However, besides anatomical imaging, current guidelines recommend additional functional imaging before a therapy decision is made. We assess the impact of functional imaging on the strategy of coronary artery bypass grafting (CABG) with particular regards on postoperative patency and myocardial perfusion. Methods After CA, 55 patients (47 males/8 females; age: 65.1 9.5 years) underwent perfusion cardiovascular magnetic resonance (CMR) and dual-source computed tomography (DSCT) before isolated CABG (n ¼ 31), CABG and concomitant valve surgery (valve þ CABG; n ¼ 10) and isolated valve surgery (n ¼ 14; control). DSCT was used for analysis of significant stenosis, CMR for myocardial-perfusion to discriminate between: no ischemia (normal), ischemia, or scar. The results, unknown to the surgeons, were compared with CA and related to the location and number of distal anastomoses. Nineteen CABG patients underwent follow-up CMR and DSCT (FU: 13 3 months) to compare the preop findings with the postop outcomes. Results Thirty-nine patients either received CABG alone (n ¼ 31) or a combined procedure (n ¼ 10) with a total of 116 distal anastomoses. DSCT was compared with CA regarding accuracy of coronary stenosis and showed 91% sensitivity, 88% specificity, and negative/positive predictive values of 89/90%. In total, 880 myocardial segments (n ¼ 55, 16 segments/patient) were assessed by CMR. In 17% (149/880) of segments ischemia and in 8% (74/880) scar tissue was found. Interestingly, 14% (16/116) of bypass-anastomoses were placed on non-ischemic myocardium and 3% (4/116) on scar tissue. In a subgroup of 19 patients 304 segments were evaluated. Thirty-nine percent (88/304) of all segments showed ischemia preoperatively, while 94% (83/88) of these ischemic segments did not show any ischemia postoperatively. In regard to performed anastomoses, 79% of all grafts (49/62) were optimally placed, whereas 21% (13/62) were either placed into non-ischemic myocardium or scar tissue, including 10% occluded grafts (6/62).
© 2015 Georg Thieme Verlag KG Stuttgart · New York
DOI http://dx.doi.org/ 10.1055/s-0034-1395393. ISSN 0171-6425.
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Conclusion In the whole cohort analysis, 17% of grafts were placed in regions with either no ischemia or scar tissue. The subgroup analysis revealed that 94% of all ischemic segments were successfully revascularized after CABG. Thus, functional imaging could be a promising tool in preoperative planning of revascularization strategy. Avoidance of extensive and unnecessary grafting could further optimize outcomes after CABG.
The optimal diagnostic algorithm for coronary artery disease (CAD) remains an ongoing debate. A wide range of different diagnostic and therapeutic tools are available which can be used individually or combined. These diagnostic tools comprise coronary angiography with/without intravascular ultrasound (IVUS), computed tomography (CT) 1 (for anatomical imaging) and stress-echocardiography,2,3 single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI)4,5 (for functional imaging). Besides anatomical imaging, current guidelines increasingly recommend the use of additional functional imaging for the diagnosis and grading of CAD before interdisciplinary decision is made for the most appropriate therapy.6,7 However, in the daily clinical routine the diagnostic results considered for decision making prior to surgical revascularization are primarily based on anatomical imaging only which is also reflected in large randomized trials such as the SYNTAX trial which was only based on anatomical assessment of coronaries.8 Therefore, this study aims to demonstrate the potential impact of functional imaging on the strategy of coronary artery bypass grafting (CABG) particularly regarding postoperative patency rate and myocardial perfusion.
Materials and Methods After approval of an institutional review board and obtained informed consent, 55 patients (47 males/8 females; age 65.1 9.5 years) before isolated CABG (n ¼ 31), CABG and concomitant valve surgery (valve þ CABG; n ¼ 10), and isolated valve surgery (n ¼ 14; control) were included in this study. All patients underwent coronary angiography (CA) (anatomical) with prognostic indication and thereafter underwent perfusion cardiovascular magnetic resonance (CMR) (functional) as well as dual-source computed tomography (DSCT) before cardiac surgery. DSCT was used for further anatomical evaluation of significant stenosis, CMR for perfusion assessment of the myocardium in a 16-segment heart model detecting no ischemia (normal), ischemia, or scar. The results, unknown to the surgeons, were compared with CA and related to the location and number of distal bypass graft anastomoses. The control group with isolated valve surgery did not undergo any postoperative imaging; preoperative data obtained from DSCT and CA was used to validate the comparison methodology. Further, a subgroup of 19 patients (all CABG only) with a total of 62 bypass anastomoses (mean,
CT Data Acquisition A second-generation dual-source CT system (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany) was used for all CT scans. We have injected 70 to 80 mL of contrast material (Iopromide, Ultravist 370, 370 mg/mL, Bayer Schering Pharma, Berlin, Germany) in a right antecubital vein at a flow rate of 5 mL/second followed by 40 mL saline solution. Contrast timing was controlled by bolus tracking in the ascending aorta with an attenuation threshold 100 HU and a delay of 8 seconds. A prospectively electrocardiogram (ECG)-synchronized dual-source high-pitch acquisition mode with the following scanning parameters was used: slice collimation, 2 128 0.6 mm applying a z-flying focal spot; gantry rotation time, 280 milliseconds; pitch, 3.2; tube potential, 100 kV; and attenuation-based tube current modulation with a reference tube current–time product of 320 mA second per rotation. Images were reconstructed with a slice thickness of 0.75 mm and an increment of 0.5 mm, using a standard cardiac imaging convolution kernel (B26f).
CT Data Evaluation Data were evaluated on an external workstation (MultiModality Workplace, Siemens Healthcare, Forchheim, Germany). Two radiologists, blinded to the results of CMR imaging, evaluated all bypass grafts for patency in a consensus reading using axial source images and multiplanar reformations.
CMR Data Acquisition A 1.5 T magnetic resonance imaging system (Achieva, Philips Medical Systems, Best, the Netherlands) was used for all CMR studies. Three short-axis sliced (basal, midventricular, and apical) as determined by a series of scout images were acquired. For stress imaging, 140 μg/kg of body weight of adenosine were injected intravenously during 3 minutes under ECG and blood pressure monitoring. Perfusion CMR images were acquired after the injection of 0.1 mmol/kg of body weight of gadobutrolum (Gadovist 1,0; Bayer Schering Pharma, Berlin, Germany) at a rate of 5 mL/second, followed by 40 mL saline solution. Ten minutes after stress perfusion imaging, rest perfusion images were acquired after injecting a second bolus of 0.1 mmol per kilogram of body weight of gadobutrolum. For both acquisitions, k-t sensitivity encoding (SENSE) perfusion CMR imaging was used in combination Thoracic and Cardiovascular Surgeon
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Introduction
3.1 bypass anastomoses/patient) had follow-up CT and MR exams (mean follow-up, 13 3 months), which were compared with the preoperative data to assess patency of bypass anastomoses and myocardial perfusion.
Impact of Functional Imaging on Decision Making and Outcome with a saturation recovery gradient-echo pulse sequence (repetition time/echo time, 3.1/1.1 milliseconds; flip angle, 20 degrees; saturation pre-pulse delay, 110 milliseconds; partial Fourier sampling; acquisition window, 120 milliseconds; section thickness, 8 mm; k-t factor of five with 11 k-t interleaved training profiles; effective acceleration, 3.7; three sections acquired sequentially during a single R-R interval); in-plane resolution, 2 2 mm2. Late gadolinium enhancement (LGE) images were acquired 10 minutes after rest perfusion using an inversion-recovery gradient-recalled echo sequence with the following parameters: field of view, 350 to 400 mm; repetition time/echo time, 7.4/4.3 milliseconds; inversion time, 200 to 350 milliseconds (individually optimized for myocardial signal nulling); flip angle, 20 degrees; matrix, 240 240; slice thickness, 8 mm, continuous.
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sensitivity, specificity, negative and positive predictive values were calculated for all patients with sufficient image quality. Two blinded readers, experienced in both cardiovascular CT and MRI from the department of radiology as well as clinic for cardiovascular surgery without any knowledge of the patient’s medical history and of the results from the specific counter examination (CT/MRI/ICA [invasive coronary angiography]) compared postoperatively the results of the preoperative imaging of each imaging technique with the finally performed CABG respectively distal anastomoses. Further, they analyzed blinded to the performed surgery the myocardium postoperatively as well as in a second step the bypass grafts regarding patency and positioning of the bypass grafts.
Results ►Tables 1 and 2 summarize the pre- and intraoperative data of the patient cohort.
CMR Data Analysis CMR data were evaluated on an external workstation (ViewForum, Philips Medical Systems) by two radiologists in a consensus reading. Perfusion CMR, as well as LGE image sets, was assessed by visual analysis of segments 1 to 16 of the 17-segment American Heart Association model. Myocardial ischemia in a segment was defined as a defect on stress perfusion CMR that was reversible at rest perfusion CMR. Myocardial scarring was defined as hyperintense myocardium with a transmurality of 50% or more in LGE images.
Table 1 Preoperative characteristics and demographics
Male (%)
47 (85.5)
Female (%)
8 (14.5)
Weight, kg
79.8 13.0
According to the standard techniques, a conventional selective CA on a Philips Integris Allura 9 Biplanesystem was performed. The contrast medium (Ultravist, Schering) consumption including the levogram averaged 140 mL. 5F diagnostic catheters (Cordis, Johnson & Johnson, Miami, Florida, United States) were used. The multiple views were stored on a CD-ROM and two cardiac surgeons blinded to the results examined the images for evaluation of the coronary arteries preoperatively. In this study, a modified classification of the guidelines of the American Heart Association was applied. The coronary arteries were segmented in 11 parts: Subdivision of the right coronary artery (RCA) and the left anterior descending artery (LAD) in a proximal, middle, and distal part; the circumflex branch (CX) in a proximal and distal segment; the left main (LM), the diagonal branch 1 (D1) of the LAD, and the first marginal branch of the CX (1st marg.) were considered as being independent segments. If the diameter reduction was >50%, the accordant vessel segment was scored as being significantly stenosed. Coronary arteries with diameter as large as 1.5 mm were analyzed, including those vessels distal to an occlusion.
Statistics Continuous quantitative values were expressed in mean values standard deviation and categorical variables as frequencies or percentages. The diagnostic accuracy of DSCT compared with catheter CA for assessment of stenosis >70% was evaluated for vessel as well as segment. Based on these data Thoracic and Cardiovascular Surgeon
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1.71 7.3
Height, m Body mass index, kg/m
Catheter Coronary Angiography
65.1 9.5
Age, y
2
27.4 4.0
Diabetes mellitus (%)
10 (18.2)
Hypertension (%)
41 (74.6)
History of smoking (%)
30 (54.6)
Dyslipidemia (%)
38 (69.1)
Positive family history (%)
13 (23.6)
Coronary artery disease (%)
38 (69.1)
1—Vessel disease (%) 2—Vessel disease (%) 3—Vessel disease (%)
7 (12.7) 19 (34.6) 12 (21.8)
Type of surgery Isolated CABG (%) Combined procedures (%) Isolated valve (%)
31 (56.4) 10 (18.2) 14 (25.5)
Anatomical LAD (%) RCX (%) RCA (%)
31 (56.4) 25 (45.5) 32 (58.2)
Functional—Segment ischemic LAD RCX RCA
69 (in 30 patients) 41 (in 19 patients) 66 (in 27 patients)
Functional—Segment infarct/scar LAD RCX RCA
11 (in 6 patients) 34 (in 12 patients) 28 (in 15 patients)
Abbreviations: CABG, coronary artery bypass grafting; LAD, left anterior descending; LIMA, left internal mammary artery; RCA, right coronary artery; RCX, ramus circumflexus/circumflex artery; RIMA, right internal mammary artery; SVG, saphenous vein graft.
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Table 2 Intraoperative data and used grafts (in patients with CABG and combined procedures) 2.05 1.05
Total grafts
94
Arterial grafts (%) LIMA (%) RIMA (%) Radial artery (%)
50 (53.2) 33 (35.1) 9 (9.6) 8 (8.5)
SVG (%)
44 (46.8)
Distal anastomoses LAD (%) RCX (%) RCA (%)
116 58 (50.0) 27 (23.3) 31 (26.7)
Abbreviations: CABG, coronary artery bypass grafting; LAD, left anterior descending; LIMA, left internal mammary artery; RCA, right coronary artery; RCX, ramus circumflexus/circumflex artery; RIMA, right internal mammary artery; SVG, saphenous vein graft.
Whole Cohort Analysis (n ¼ 55)
In the whole cohort analysis,9 31 patients received CABG, 10 patients had additional valve surgery, and 14 isolated valve surgery. In total, 116 distal anastomoses were performed. DSCT was compared with CA regarding accuracy of coronary stenosis and showed sensitivity of 91%, specificity 88%, and negative/positive predictive value of 89/90%. In the whole cohort (n ¼ 55), a total of 880 segments (16 segments/patient) of myocardium were assessed by all imaging modalities displaying 20% of assessed segments (176/880) to be ischemic, and 8% of assessed segments (73/880) to be scar tissue (►Fig. 1). Importantly, when relating these results to the bypass anastomoses performed, it became apparent that a total of 17% of all bypass anastomoses (20/116) were sub-optimally grafted: 14% (16/116) of bypass anastomoses were placed to nonischemic myocardium and 3% (4/116) to scar tissue (►Fig. 2).
Subgroup Analysis of Patients with Postoperative CT and MR (n ¼ 19) 10
In the subgroup analysis, 19 patients underwent pre- and postoperative MR and CT assessment with a total of 304 myocardial segments (16 segments/patient) evaluated. Of these, 39% (88/304) showed ischemic myocardium under
Fig. 1 Myocardial segments assessed.
Fig. 2 Bypass anastomoses performed.
stress/rest preoperatively. In contrast, 94% (83/88) of the ischemic segments did not show any signs of ischemia in the postoperative imaging. In 6% (5/88) of segments persistent ischemia was present postoperatively (one patient with five patent bypass anastomoses and two patients with one occluded bypass anastomosis each). In regard to performed bypass anastomoses, 79% of all anastomoses (49/62) were optimally placed to supply the ischemic regions, whereas 21% (13/62) of all anastomoses were placed either into non-ischemic myocardium (nine anastomoses) or into scar tissue (four anastomoses). Postoperative imaging also revealed that 10% of all bypass anastomoses were occluded (6/62) while of these, four anastomoses were located in non-ischemic regions with potential competitive flow (three anastomoses) and in scar-tissue (one anastomosis). The remaining two occluded anastomoses were placed in ischemic regions that therefore remained ischemic postoperatively. ►Figs. 3–5 illustrate pre- and postoperative DSCT and CMR myocardial-perfusion findings in three exemplary cases.
Discussion CA and DSCT are commonly used anatomical imaging tools to diagnose and to grade CAD in clinical routine. 11,12 However, asymptomatic, elective patients carry the important aspect of prognostic indication and thus it remains an ongoing debate if the used imaging techniques are sufficient enough to determine the most efficient revascularization strategy. The latest European Society of Cardiology (ESC)/European Association for Cardio-Thoracic Surgery (EACTS) revascularization guidelines 2010 recommend functional diagnostic imaging for assessment of myocardial viability for patients with a prognostic indication and a poor left ventricular (LV)-function.6,7 However, the daily practice is contradictory and once CA has been performed, CAD diagnostics are often considered complete and the therapy already starts. Therefore, this study focused on the potential impact of additional functional imaging on the strategy of CABG with particular regards on postoperative patency rate and myocardial perfusion. Thoracic and Cardiovascular Surgeon
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Diseased vessels
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Fig. 3 Case Example 1. A 60-year-old patient underwent quadruple CABG including a graft to the RCX as shown by postoperative CT (arrows in A). In the lateral wall supplied by the RCX, the preoperative delayed enhancement MRI shows a myocardial scar (arrowheads in B) with >50% transmurality, which remains unchanged postoperatively (arrowheads in C). CABG, coronary artery bypass grafting; RCX, ramus circumflexus/ circumflex artery; CT, computed tomography; MRI, magnetic resonance imaging.
Fig. 4 Case Example 2. A 71-year-old patient underwent quintuple CABG including a LIMA-LAD graft and a venous graft to the RCA. Postoperative CT shows an occluded LIMA-LAD graft (arrows in A). Whereas the preoperative ischemia demonstrated in adenosine-stress perfusion MRI in the RCA territory (arrowheads in B) is regressive postoperatively (arrowhead in C), the subtle ischemia in the LAD territory remains unchanged (arrows in B and C). CABG, coronary artery bypass grafting; LIMA-LAD, left internal mammary artery-left anterior descending; RCA, right coronary artery; CT, computed tomography; MRI, magnetic resonance imaging.
Fig. 5 Case Example 3. A 64-year-old patient underwent quintuple CABG including a LIMA-LAD graft and a venous graft to the intermediate artery and two diagonal branches as shown by postoperative CT (A). The extensive ischemia of the LAD territory demonstrated in preoperative adenosine-stress perfusion MRI (arrowheads in [B]) can no longer be found postoperatively (C). CABG, coronary artery bypass grafting; LIMA-LAD, left internal mammary artery-left anterior descending; CT, computed tomography; MRI, magnetic resonance imaging.
Several techniques such as MRI, PET, SPECT, stress-echocardiography, and fractional flow reserve are available to perform specific additional functional diagnostics.2–4,13 However, in this study, CMR and DSCT were used demonstrating a high image quality along with high sensitivities and specificities for CAD evaluation, to date, no algorithms are established regarding the ideal type of additional functional imaging for the respective clinical setting. As all imaging Thoracic and Cardiovascular Surgeon
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modalities carry specific advantages, and also disadvantages, clear consensus remains to be established.14,15 In this regard, the recent ESC guidelines6,7,14,15 further recommend to establish the concept of the interdisciplinary Heart Team to determine the optimal diagnostic and therapeutic algorithm for each CAD patient. While this concept represents a significant step towards a more objective decision making,16,17 establishing a standardized functional
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Impact of Functional Imaging on Decision Making and Outcome References
1 Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-
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Conclusion In the whole cohort analysis, 17% of grafts were placed in regions with either no ischemia or scar tissue. The subgroup analysis revealed that 94% of all ischemic segments were successfully revascularized after CABG. This study shows that functional imaging could be a promising tool in the preoperative planning of an optimized surgical revascularization strategy. Avoidance of extensive and unnecessary grafting could further optimize outcomes after CABG. Note Parts of this article were presented at the annual meetings of the International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS), 2011 and 2012.
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14
15
Conflict of Interest None
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imaging protocol into the clinical routine may be challenged mainly by logistical issues as costs and time consumption. Limited access and availability as well as non-elective appointments can make the planning and course very difficult. In line with that, in our study also a major problem was the logistics that resulted in a difficult patient acquisition for this study. Although appointments and scans could be done after the official hours and patients were very cooperative, still it was difficult to organize it efficiently. Therefore, it remains questionable how this concept needs to be organized to fit into clinical routine for a larger number of patients. In our subgroup of patients that underwent pre- and postoperative functional imaging we could demonstrate an overall high success rate of 94% for revascularization of ischemic segments based only on anatomical imaging. However, 17% (20/116) of the distal anastomosis in the whole cohort analysis were suboptimally placed, either to non-ischemic or scared myocardium. In line with that, also in the subgroup cohort who underwent additional postoperative imaging our data showed that even 21% (13/62) of all bypass anastomoses were not perfectly positioned. Retrospectively these bypass grafts were not necessary and the coronaries should have been left untouched. This is important, as even certain damage may occur to the vessel wall when an incision is done to perform an anastomosis. While it remains unclear what deleterious effects can result if a bypass-graft is placed into healthy, non-ischemic myocardium, early graft occlusion is well known to occur in these circumstances. Finally, it is necessary to establish a more patient tailored imaging route for diagnostic of CAD in the clinical routine. While the present guidelines primarily recommend myocardial perfusion diagnostic in patients with poor LV function, our data indicate that the patient spectrum for additional functional imaging may be expanded to other patient populations such as chronic CAD patients to determine whether such patients may benefit more from a MIDCAB (minimally invasive direct coronary artery bypass) or HYBRID (MIDCAB plus percutaneous coronary intervention) procedure instead of a standard CABG.
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Impact of Functional Imaging on Decision Making and Outcome disease: The secondary endpoints of the multicenter multivendor MR-IMPACT II (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease Trial). J Cardiovasc Magn Reson 2012;14:61 16 Holmes DR Jr, Rich JB, Zoghbi WA, Mack MJ. The heart team of cardiovascular care. J Am Coll Cardiol 2013;61(9):903–907
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17 Long J, Luckraz H, Thekkudan J, Maher A, Norell M. Heart team
discussion in managing patients with coronary artery disease: outcome and reproducibility. Interact Cardiovasc Thorac Surg 2012;14(5):594–598
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