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© 2013 Wiley Periodicals, Inc.
ORIGINAL ARTICLE ______________________________________________________________
Results of Coronary Artery Bypass Grafting in Myocardial Bridging of Left Anterior Descending Artery Leo A. Bockeria, M.D.,* Sergey G. Sukhanov, M.D.,y Ekaterina N. Orekhova, M.D.,y Mesrop P. Shatakhyan, M.D.,y Dmitry A. Korotayev, M.D.,y and Leonid Sternik, M.D.z *Bakoulev Scientific Center for Cardiovascular Surgery, Moscow, Russia; yBakoulev Scientific Center for Cardiovascular Surgery in Perm, Perm, Russia; and zDepartment of Cardiac Surgery, Chaim Sheba Medical Center, Tel Hashomer, Israel ABSTRACT Background: We aimed to evaluate the graft patency rate following coronary artery bypass grafting (CABG) to the left anterior descending artery (LAD) with proximal myocardial bridging (MB). While MB is generally a benign coronary abnormality, ischemia, stunning, and sudden death have been reported. In symptomatic patients with proximal LAD systolic compression of >50%, positive for ischemic noninvasive testing and noneffective optimal medical therapy, coronary intervention could be indicated. Few studies of CABG in myocardial bridging have been reported. The influence of high flow in coronaries with MB on graft patency is cause for concern. Methods: We retrospectively studied 39 patients operated on for isolated MB of proximal LAD with >50% systolic compression. All patients were severely symptomatic despite optimal medical therapy and positive noninvasive tests for myocardial ischemia. CABG was performed through the midsternotomy with cardiopulmonary bypass and cardioplegia. Patients were divided into two groups: in 20 patients, LAD was bypassed with left internal mammary artery (LIMA) (Group 1) and in 19 patients with saphenous vein graft (SVG) (Group 2). All patients underwent follow-up coronary angiography. Results: Demographics and degree of systolic compression of the LAD were similar in both groups. There was no mortality or major morbidity. Freedom from angina was 68% in Group 1 and 94% in Group 2 at 18 months postoperatively (p = 0.58). Twelve LIMA grafts and three SVGs were found occluded (p = 0.002). Conclusions: LIMA patency in myocardial bridging of the LAD can be low. SVGs should be considered in cases of CABG for myocardial bridging. doi: 10.1111/jocs.12101 (J Card Surg 2013;28:218–221)
Myocardial bridging (MB), a congenital coronary abnormality, is defined as a segment of an epicardial coronary artery, the “tunneled artery,” that goes through the myocardium beneath the muscle bridge.1,2 Myocardial bridging was first studied at autopsy by Reyman3 and first diagnosed angiographically by Portmann and Iwig.4 While angiographic studies have reported its frequency to vary from 1.5% to 16%, autopsy studies have revealed some degree of MB up to 80%.5–7 Myocardial bridging is confined to the midleft anterior descending artery (LAD) in 90% of cases.8 The main angiographic finding is systolic compression of the involved coronary artery.4 The degree of coronary
Conflict of interest: None. Address for correspondence: Leonid Sternik, M.D., Department of Cardiac Surgery, Chaim Sheba Medical Center, Tel Hashomer 52621, Israel. Fax: þ972-3-530 2410; e-mail:
[email protected]. gov.il
obstruction by the myocardial bridge depends on factors such as location, thickness and length of the muscular bridge, and degree of cardiac contractility. Generally, myocardial bridging has been considered a benign condition, but the following complications have been reported: ischemia and acute coronary syndromes,9,10 coronary spasm,11 ventricular septal rupture,12 supraventricular and ventricular tachycardia,13 stunning and transient ventricular dysfunction,14 and sudden cardiac death.15 Most cases of MB can be treated successfully with optimal medical therapy. However, some patients with proximal LAD muscular bridging, who produce >50% systolic compression of the involved coronary artery, can be symptomatic with positive noninvasive testing for ischemia and refractoriness to optimal medical therapy. In these cases, coronary stenting, surgical myotomy, and coronary artery bypass grafting (CABG) may be indicated.16 The optimal method of invasive therapy for MB remains undetermined. Few studies of coronary artery bypass in
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BOCKERIA, ET AL. RESULTS OF CORONARY ARTERY BYPASS GRAFTING
myocardial bridging have been reported.17,18 The largest study was by Huang et al.17 who reported eight cases of CABG for isolated myocardial bridging of the proximal LAD. Concerns regarding MB include competitive flow in the coronary artery and its influence on graft patency.19,20 We evaluated angiographic findings after CABG to the LAD with left internal mammary artery (LIMA) and saphenous vein graft (SVG) in myocardial bridging. PATIENTS AND METHODS From January 2004 to December 2010, we performed 230 surgical interventions in patients with MB. The procedure used was CABG with myotomy in some rare cases. All patients were operated in the Bakulev Scientific Center of Cardiovascular Surgery in Perm, Russia. All patients were symptomatic with positive noninvasive testing for ischemia and were resistant to optimal medical therapy. This retrospective study included 39 patients who were operated on between January 2009 and December 2010. The decision to study retrospectively patients operated after December 2008 was related to establishing a detailed and reliable institutional database at that time. All patients suffered from isolated myocardial bridging of the proximal LAD with >50% systolic compression. Highest degree of compression was 95%. The degree of the coronary artery narrowing and the length of MB were assessed at systole. Exclusion criteria included lesions of coronary arteries other than the LAD, or any atherosclerotic lesion with >40% narrowing of the coronary artery. Patients undergoing myotomy or coronary stenting were also excluded from the study. All patients were severely symptomatic despite optimal medical therapy. Noninvasive tests for myocardial ischemia were positive. These patients were divided into two groups: LIMA grafting to the LAD in 20 patients (Group 1), and bypassing of the LAD with SVG in the remaining 19 patients (Group 2). The decision to use either LIMA or SVG was left to the discretion of the surgeon and related to the diameter of LIMA: if LIMA was less than 2 mm diameter an SVG was used. Surgical technique All patients were operated on through the midsternotomy with cardiopulmonary bypass, aortic cross-
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clamping, and antegrade crystalloid cardioplegia. Length of cardiopulmonary bypass was 20.6 4.8 (12–28) minutes and 23.6 9.9 (14–54) minutes in Groups 1 and 2, respectively (p ¼ 0.3). Aortic crossclamping time was 11.0 3.1 (6–17) minutes and 10.5 7.9 (5–36) minutes in Groups 1 and 2, respectively (p ¼ 0.8). Postoperative follow-up and coronary angiography All patients underwent coronary angiography one year after surgery and additional angiographies if coronary problems were suspected. Criteria for normal graft function were as follows: good blood flow through the graft with good coronary artery filling, and no anastomotic narrowing. We diagnosed graft failure in cases of totally or near totally occluded coronary graft with no LAD filling from the graft. No patients were stented. Following surgery all patients were treated with b-blockers, calcium channel blockers, statins, and aspirin. Data for this study were derived from the Cardiac Surgery Department database, and received the approval of our Institutional Review Board. Each patient signed informed consent to participate in this study. Statistics Discrete variables were compared using Student’s ttest and outcome measurements were compared using x2 analysis. A p-value of 75% Length of MB (cm)
LIMA Group 1 (n = 20)
SVG Group 2 (n = 19)
p-Value
53.7 8.7 (37–72)
56 9.3 (39–71)
0.491
14 6 3.07 1.42 (1.5–6.0)
13 6 3.71 1.5 (1.5–7.0)
0.853 0.732 0.166
LAD, left anterior descending; LIMA, left internal mammary artery; MB, myocardial bridging; SVG, saphenous vein graft.
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DISCUSSION
Figure 1. Freedom from recurrent angina.
respectively (p ¼ 0.2). Group 1 patients (LIMA) were discharged from hospital in 7.9 1.5 (6–12) days, while Group 2 patients (SVG) were discharged in 7.9 2.6 (5–15) days (p ¼ 0.9). Six patients suffered from recurrent angina after surgery. It occurred in four patients with an LIMA graft and in two patients with an SVG. Angina recurred within 12 months after procedure in one patient in each group. In the period of 12–18 months after procedure angina recurred in three patients in the LIMA group and in one patient in the SVG group. Freedom from angina was 94% in SVG group and 68% in LIMA group at 18 months after surgery (p ¼ 0.58) (Fig. 1). In four patients with a LIMA graft and recurrent angina in one patient the graft was occluded and in two patients there was retrograde systolic filling of the graft from LAD showing significant competitive flow. In two patients with SVG and recurrent angina in one patient the graft was occluded. Patients with recurrent angina and occluded or nonfunctional grafts were treated medically. In one patient in each group coronary angiography was normal. Finally, all patients underwent coronary angiography. In all asymptomatic patients the coronary angiography was performed one year after surgery. On coronary angiography 12 LIMA grafts and three SVGs (15.8%) were found occluded (p ¼ 0.002). Coronary graft occlusion, competitive flow in grafts, and the degree of systolic LAD compression (50% to 75% and >75%) are presented in Table 2.
Few studies dealing with the surgical treatment of myocardial bridging have been reported in the literature.16–18 Some researchers have reported a few cases of coronary artery bypass as treatment for symptomatic and resistant to optimal medical therapy MB with >50% systolic narrowing of the LAD.17,18 The largest series were by Huang et al.17 who reported eight cases of CABG for isolated myocardial bridging of the proximal LAD. There are numerous studies in the literature regarding graft dysfunction and occlusion in cases of competitive flow. Barner21 reported LIMA graft dysfunction due to low-grade narrowing of the LAD, resulting in high competitive flow. The authors called this phenomenon “disused atrophy.” Ivert et al.22 postulated that the main causes of LIMA graft failure are low-grade stenosis of bypassed coronary artery and technical problems with the anastomosis. Shimizu et al.23 reported that LIMA grafts showed diffuse narrowing of the lumen on angiography (“string sign”) in all their patients with coronary stenosis of 40% to 59%. Sabik et al. showed that while LIMA graft function strongly depends on the degree of proximal stenosis of the bypassed coronary artery, SVG shows good patency in low-grade coronary lesions. The authors explain this phenomenon by the fact that the venous wall has no muscular layer and therefore cannot constrict the graft in response to competitive flow. Sabik et al. postulated that the degree of proximal coronary stenosis is an independent risk factor for LIMA graft malfunction.19,20 We feel that in cases of myocardial bridging the potential for competitive flow is very high. MB produces systolic compression of the coronary artery. Normally only 15% of coronary blood flow occurs in systole.11 During diastole there is almost normal coronary blood flow with a high probability of competition with blood flow through the graft. This situation, together with a high sensitivity of the LIMA to competitive coronary flow, could explain the very low patency of LIMA grafts in our study. We found a significant statistical difference for graft occlusion and competitive flow between LIMA and SVGs. The data favor SVG compared with LIMA grafting (Table 2). Some patients with an open LIMA graft had angina. We suspect that these patients had graft dysfunction because of retrograde
TABLE 2 Coronary Angiography Data LIMA
Occluded graft Competitive flow Patent graft with no competitive flow
SVG
Group 1 (n = 20)
No. of Patients with 50% to 75% Systolic Compression of LAD
Group 2 (n = 19)
No. of Patients with 50% to 75% Systolic Compression of LAD
p-Value
12 (60%) 6 (30%) 2 (10%)
9 5 0
3 (15.8%) 1 (5.3%) 15 (78.9%)
3 0 10
0.002 0.02 0.0001
LAD, left anterior descending; LIMA, left internal mammary artery; SVG, saphenous vein graft.
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blood flow in the graft noted on angiograms. Furthermore, freedom from recurrent angina was higher in the SVG group of patients at 18 months after surgery. However, a statistical difference between the groups was insignificant probably due to the small number of patients at 18 months of follow-up (Fig. 1). In our institution, we performed myotomy or coronary stenting in a very few patients. We feel that stenting for myocardial bridging is not satisfactory, because myocardial contraction can collapse the stent. Haager et al.18 reported that at seven weeks after coronary stenting for myocardial bridging, coronary angiography showed in-stent stenosis in five of the 11 patients. Coronary arteries themselves in MB are healthy with gentle walls so stenting can potentially cause coronary artery perforation. If a patient comes to surgery we feel more comfortable with CABG and not with myotomy. We are not sure that myotomy can relieve the pressure on coronary artery in all cases. In view of these factors, we feel that there can be a place for CABG in severely symptomatic myocardial bridging resistant to optimal medical therapy. We conclude that LIMA graft patency in myocardial bridging of the LAD can be very low, especially with systolic compression of the coronary artery
