Surgical intervention of myocardial bridge combined coronary artery disease: could a combination of supra-arterial myotomy and CABG be a better option?

Myocardial bridge (MB) is a congenital coronary artery variant in which a portion of the epicardial coronary arterial segment runs in the myocardium and mainly in the left anterior descending coronary artery (LAD) [1]. It has been characterized by systolic compression of part of an epicardial vessel by a segment of the overlying myocardium. It is one of the most common coronary artery malformations, with a prevalence between 1.5% and 16% assessed by coronary computed tomographic angiography (CCTA) and up to 80% at autopsy [1‐3]. Although coronary artery myocardial bridge is usually considered a benign condition, some studies have reported that myocardial bridges are associated with acute coronary syndromes and angina pectoris, fatal arrhythmias, left ventricular dysfunction, and even cardiac sudden death [1]. Our previous studies demonstrated that supera-arterial myotomy is a safe and effective procedure for patients with medication refractory isolated LAD-MB [4‐6].

Pathological studies have clearly shown that atherosclerotic changes are present in the intima proximal to the MB [7]. Although the incidence of coronary artery disease combined with atherosclerotic stenosis proximal to the LAD-MB is not reported in the literature, such patients are still found in clinical practice. Unfortunately, there are many contradictions in the choice of the treatment strategy for patients with myocardial bridge and coronary artery disease. In this study, we describe a group of patients who underwent supra-arterial myotomy and coronary artery bypass grafting for severe stenosis proximal to the LAD-MB and summarize the outcomes of their treatment.

The baseline clinical, echocardiographic and angiographic characteristics are presented in Table 1. Twelve of 16 patients were male, the age ranged from 42 to 75 years (median 60 years). The echocardiography examination confirmed the left ventricular end-diastolic dimension: 49.6 ± 4.7 mm, and the left ventricular ejection fraction: 59.4 ± 6.3%. The compression and the length of LAD-MB were 63 ± 17.9% and 25.9 ± 16.3 mm, respectively. Of the 16 patients, one patient with LAD-MB and proximal coronary stenosis, and 15 patients with LAD-MBs and multivessel lesions.Preoperative coronary angiography showed compression of the LAD-MB during systole (Fig. 1A) and recovery during diastole (Fig. 1B). Atherosclerotic stenosis of the proximal left anterior descending branch artery (Fig. 1C).

Table 2 lists the operative characteristics and postoperative results. Fifteen patients underwent myotomy and CABG with cardiopulmonary bypass, and one patient received off-pump myotomy and graft surgery. All patients recovered uneventfully without the complications of right ventricular rupture or coronary artery injury during the surgery. The median transfusion amount of red blood cells in the operation was 2 units, and no patients required unplanned reoperation for bleeding. The average length of intensive care unit stay was 2.74 days.

Table 3 represents preoperative and final follow-up visit Seattle angina questionnaire (SAQ) score and median change in the score for each category. All five categories (physical limitation due to angina, stability of angina, frequency of angina, satisfaction with treatment, and quality of life) were improved significantly after supra-arterial myotomy and CABG (p < 0.01, Table 3). The follow-up periods ranged from 6 to 146.1 months (mean 45.3 ± 42.9 months), and one patient was lost to follow-up. Of the 15 patients followed up, one patient in this group had a recurrence of angina 1 year after surgery and was found restenosis of the LIMA graft by coronary angiography. The patient's symptoms were reduced by increasing the dose of beta-blockers and calcium antagonists. Fourteen patients had no symptoms of myocardial ischemia, nor major cardiac adverse events during the follow-up periods. Some patients underwent coronary computed tomographic angiography (CCTA) at postoperative review showing complete release of the left anterior descending myocardial bridge and patency of the graft (Fig. 1D).

Our study demonstrated that in patients with coronary artery disease combined with proximal stenosis to the LAD-MB, supra-arterial myotomy and simultaneous CABG could completely relieve the compression of the myocardial bridge on the tunnel artery and increase blood flow through the graft to the distal branches with satisfactory long-term results.

The coronary myocardial bridge, as a congenital coronary artery malformation, was first described anatomically by Reyman in 1737 [10]. Pathological studies have clearly shown that atherosclerotic changes are present in the intima proximal to the MB [7]. Since the majority of coronary perfusion occurs during the diastolic phase of the cardiac cycle, the effect of systolic compression of the artery on the total effective perfusion of the myocardium should be mild. However, studies have shown that systolic compression of MB results in delayed relaxation of a vessel and leads to impaired diastolic myocardial perfusion [1]. The severity of systolic compression of MB and hemodynamic perturbations in the proximal segment was associated with decreased shear stress and increased blood residence time [11]. A recently study demonstrated that MB located in the middle distal segment of the LAD is independently associated with coronary stenosis proximal to the MB, but the prevalence of coronary artery disease combined with LAD-MB are unclear [12]. For the dynamic bridge compression averaging 55% diameter stenosis, the main artery downstream has adequate coronary flow reserve and fractional flow reserve (FFR) but the isolated septal artery may be ischemic due to septal “branch steal” [13]. In clinical cases, there is a large number of patients with atherosclerotic stenosis proximal to LAD-MB combined with multiple coronary artery lesions. For these patients, whether complete supra-arterial myotomy is performed in conjunction with CABG has not been reported in the literature. In this study, although postoperative coronary angiography or CCTA was not performed in all patients, no serious adverse cardiac events such as myocardial infarction, arrhythmia, or sudden cardiac death occurred in the patients during long-term follow-up. We suggest that it may be useful in relieving severe myocardial bridge compression caused by the tunnel artery and branches steal, thereby increasing diastolic blood supply and reducing myocardial ischemia.

Coronary artery bypass grafting can increase blood flow through the graft to the distal branches for patients with severe atherosclerotic lesions proximal to MBs. However, for the patients with vessel diameter of less than 1.5 mm distal to the myocardial bridge, it is difficult to select a suitable anastomosis site for patients with an extensive MB without performing an MB myotomy [14, 15]. In particular, for diffuse myocardial bridges located in the middle and distal segments of the anterior descending branches with a distal caliber of less than 1.5 mm, a myotomy is necessary. The key point for this procedure is to find the exact location of MB by angiographic findings and dissect the cardiac muscle carefully and completely. Concerning the choice of treatment strategy, there is no literature on whether to completely or partially release the myocardial bridge in patients with atherosclerotic stenosis proximal to the LAD-MB. Although postoperative intravascular ultrasound (IVUS) was not performed in this study, based on the prior literature [13], we believe that complete release of the compression caused by the myocardial bridge increases anterior wall and septal perfusion and reduces myocardial ischemia. In the case of diffuse myocardial bridges, we usually use a retrograde approach to select the target vessel site. It is of concern that avoiding right ventricular rupture and coronary artery injury is a key technique for myotomy. Our experience is that surgery under cardiac arrest with extracorporeal circulation is a safe and effective method for the patients with diffuse myocardial bridges.

In this small cohort of patients, we used the Seattle Angina Questionnaire (SAQ) score to compare quality of life before and after CABG and myotomy. We observed a significant less physical limitation, lower angina frequency and a significant symptomatic improvement in across all five dimensions of the SAQ after surgery. Bianco F and colleagues analyzed the echocardiographic changes and quality of life after surgical unroofing of myocardial bridges and demonstrated that MB unroofing surgery could provide benefits in terms of quality of life and left ventricular global longitudinal strain improvement compared with one year of optimal medical therapy [16]. Maeda analyzed 13 pediatric myocardial bridge patients who underwent surgical unroofing of MB and all patients had significant improvement in symptoms and quality of life using the SAQ score at postoperative follow-up [17]. Overall, surgical unroofing of myocardial bridges can relieve the compression of the tunnel artery, relieve myocardial ischemia, and improve the patients' quality of life after surgery.

Limitations of this study: first, it is a single-institute retrospective, observational study with a small sample size, which would affect the generalizability of the findings. Multiple centers, large sample, randomized controlled studies are needed for final study conclusions. Second, only some patients in this study underwent postoperative coronary angiography or CCTA, and most patients were followed up with symptom questionnaires, making evaluation difficult to achieve accuracy.

For patients with coronary artery disease combined with extensive LAD-MB and proximal stenosis, performing a myotomy is necessary to make a landing site for the distal anastomosis and provide better coronary perfusion to areas distal to the coronary artery. Supra-arterial myotomy concomitant bypass surgery may be a better option for the treatment of LAD-MB combined with severe proximal stenosis.