Anatomic Properties of Myocardial Bridge Predisposing to Myocardial Infarction

Abstract

Background-A myocardial bridge (MB) that partially covers the course of the left anterior descending coronary artery (LAD) sometimes causes myocardial ischemia, primarily because of hemodynamic deterioration, but without atherosclerosis. However, the mechanism of occurrence of myocardial infarction (MI) as a result of an MB in patients with spontaneously developing atherosclerosis is unclear. Methods and Results-One hundred consecutive autopsied MI hearts either with MBs [MI(ϩ)MB(ϩ) group; nϭ46] orwithout MBs (nϭ54) were obtained, as were 200 normal hearts, 100 with MBs [MI(Ϫ)MB(ϩ) group] and 100 without MBs. By microscopy on LADs that were consecutively cross-sectioned at 5-mm intervals, the extent and distribution of LAD atherosclerosis were investigated histomorphometrically in conjunction with the anatomic properties of the MB, such as its thickness, length, and location and the MB muscle index (MB thickness multiplied by MB length), according to MI and MB status. In the MI(ϩ)MB(ϩ) group, the MB showed a significantly greater thickness and greater MB muscle index (PϽ0.05) than in the MI(Ϫ)MB(ϩ) group. The intima-media ratio (intimal area/medial area) within 1.0 cm of the left coronary ostium was also greater (PϽ0.05) in the MI(ϩ)MB(ϩ) group than in the other groups. In addition, in the MI(ϩ)MB(ϩ) group, the location of the segment that exhibited the greatest intima-media ratio in the LAD proximal to the MB correlated significantly (PϽ0.001) with the location of the MB entrance, and furthermore, atherosclerosis progression in the LAD proximal to the MB was largest at 2.0 cm from the MB entrance. Conclusions-In the proximal LAD with an MB, MB muscle index is associated with a shift of coronary disease more proximally, an effect that may increase the risk of MI. (Circulation. 2009;120:376-383.)Key Words: myocardium Ⅲ myocardial infarction Ⅲ anatomy Ⅲ atherosclerosis T he coronary artery that runs through epicardial adipose tissue is often covered in part with myocardial tissue. This structure is known as a myocardial bridge (MB) 1 ; it exists almost exclusively in the left anterior descending coronary artery (LAD), 2 and it is regarded as a common anatomic variant rather than a congenital anomaly. 3 The frequency of an MB in the LAD is high, sometimes Ͼ50% by autopsy, 2 but it is Ͻ5% by angiography. 4 Because MBs have been identified angiographically indirectly through a "milking effect" phenomenon induced by systolic compression of the MB, a thin or short MB is often missed. 4 The use of other invasive imaging, such as intracoronary ultrasound and Doppler, has improved MB detection. 5,6 More recently, multidetector computed tomography (CT) has been used noninvasively to detect the MB itself directly, 7 and surprisingly, the use of multidetector CT for myocardial ischemia increases Editorial see p 357 Clinical Perspective on p 383The clinical outcome of patients with MBs has been considered benign 4 ; however, the significance of an MB to myocardial ischemia remains controversial. By multidetector CT imaging,...

Myocardial bridging: what have we learned in the past and will new diagnostic modalities provide new insights?

“…Several studies using CAG, CTCA and IVUS have demonstrated that myocardial bridging of the LAD is often associated with atherosclerotic lesions proximal to the bridge whereas the tunnelled segment and the distal portion are conspicuously free from atherosclerosis [9,15,31,33,34] (Fig. 3).…”

“…3). Factors that may play a role in causing the atherosclerotic lesions include flow disturbances (such as retrograde flow during systole), pressure disturbances that may cause endothelial injury, high wall stress proximal to the bridge and tensile stress; conversely development of atherosclerosis may be prevented in the tunnelled and distal segments by inhibition of coronary artery wall motion of the tunnelled segment and lower pressures [5,19,31,34,35].…”

Ausência de arteriosclerose na porção intramiocárdica das artérias coronárias

“…Inflammatory mediators such asadiponectin and adrenomedullin seem to play a protective effect, while the pro-inflammatory mediator such as interleukins1and 6 (IL-1, IL-6) and tumor necrosis factor alpha (TNF-á) supposedly exert detrimental effect [12] (Figure 3). variations of the myocardial bridges with a predisposition to the risk of cardiac ischemia is still a detail to be clarified [10,11].…”

Angiographic prevalence of myocardial bridging İn our department

“…MB, genellikle asemptomatik bir anomali olmasına rağmen miyokardiyal iskemi ve infarktüs, ileti anomalileri, ventriküler aritmi ve ani ölüm görülebilmektedir (10,(21)(22)(23)(24)(25)(26)(27). İntravasküler ultrasonografi ve intrakoroner doppler gibi tekniklerin gelişmesi, iskemi mekanizmasının daha iyi anlaşılmasına katkıda bulunmaktadır (28). MB'de kan akımının engellenmesi sistol sırasında oluştuğu saptanmıştır (10).…”

“…Yapılan çalışmalarda sistolik koroner kan akımındaki bozulmaya ilaveten diyastolik koroner kan akımının da bozulduğu tespit edilmiştir (10,29). MB olan segmentin uzunluğu, kalınlığı, lokalizasyonu, taşikardi, hipotansiyon ve artmış platelet agregasyonu MB'li hastalarda semptom oluşmasına etkili olan anatomik ve fizyolojik mekanizmalardır (28). MB içinde kalan segmentin uzunluğu iskemi oluşturmada oldukça önemlidir (30).…”