Myocardial Bridge and Acute Plaque Rupture

Abstract

A myocardial bridge (MB) is a common anatomic variant, most frequently located in the left anterior descending coronary artery, where a portion of the coronary artery is covered by myocardium. Importantly, MBs are known to result in a proximal atherosclerotic lesion. It has recently been postulated that these lesions predispose patients to acute coronary events, even in cases of otherwise low-risk patients. One such mechanism may involve acute plaque rupture. In this article, we report 2 cases of patients with MBs who presented with acute coronary syndromes despite having low cardiovascular risk. Their presentation was life-risking and both were treated urgently and studied with coronary angiographies and intravascular ultrasound. This latter modality confirmed a rupture of an atherosclerotic plaque proximal to the MB as a likely cause of the acute events. These cases, of unexplained acute coronary syndrome in low-risk patients, raise the question of alternative processes leading to the event and the role MB play as an underlying cause of ruptured plaques. In some cases, an active investigation for this entity may be warranted, due to the prognostic implications of the different therapeutic modalities, should an MB be discovered.

Keywords: acute coronary syndrome; intravascular ultrasound; myocardial bridge.

Figure 1.

Coronary angiogram (1) showing a hazy lesion in the proximal LAD (single blue arrow). Following thrombectomy (2) and predilatation with balloon angioplasty (3), IVUS demonstrated a thrombus (turquoise arrow heads) in the culprit lesion (4). LAD, left anterior descending artery; IVUS, intravascular ultrasound.

Figure 2.

The final angiogram showing a good result of stenting of the proximal LAD, before the take-off of the first diagonal branch. LAD, left anterior descending artery; LCX, left circumflex artery; D1, first diagonal branch; S1, first septal perforator artery; S2, second septal perforator artery; MB, myocardial bridge.

Figure 3.

Top panel: IVUS still frames demonstrating cross-sectional images of vessel area (VA) from within the MB segment from end-diastole and end-systole resulting in an arterial compression of 14.3 %. Bottom panel: The maximum plaque burden (PB), the difference in cross-sectional area between the red circle (the external elastic membrane) and yellow circle (lumen intima border) was 86%. The MB thickness (halo) was 0.41 mm. MB, myocardial bridge; IVUS, intravascular ultrasound.

Figure 4.

Coronary angiogram showing a hazy lesion in the proximal LAD, consistent with an acute thrombus formation. The green area shows the MB segment. The large blue arrow points to the total occlusion of the mid to distal LAD from distal embolization. On the left: a magnification of the hazy area in the LAD, consistent with a thrombus. Bottom images: the left picture shows an IVUS image of the ruptured plaque (red arrow) and to the right the thrombus on top of the plaque (blue arrow). MB, myocardial bridge; LAD, left anterior descending artery; IVUS, intravascular ultrasound.

Figure 5.

Top panel: IVUS still frames demonstrating cross-sectional images of vessel area from within the MB resulting in an arterial compression of 24.2%. Bottom panel: The maximum plaque burden (PB) was 48%. The halo (MB thickness), blue arrows, was 0.4 mm. MB, myocardial bridge; VA, vessel area; IVUS, intravascular ultrasound.