1

Case report

A 75-year old patient presented with persistent angina in our department. The electrocardiogram (ECG) was consistent with a STEMI of the anterior wall with significant ST-elevations in leads V1–V4 ( Fig. 1 ). Coronary angiography revealed subtotal occlusion of the LAD segment 7 and a significant MB with more than 75% compression of the lumen during systole in segment 8. After implantation of the proximal stent (Integrity resolute 3.0/15, Medtronic, Minneapolis, USA), implantation of the distal stent (Integrity resolute 2,75/28, Medtronic, Minneapolis, USA) caused coronary artery perforation with flow of the contrast medium into the right ventricle (RV), with concomitant malperfusion of the distal left anterior descending coronary artery (LAD), resulting in progressive ST-elevations. Implantation of a PTFE-covered stent (Jostent Graftmaster 3.0/26, Abbott Vascular, Illinois, USA) initially stopped flow of the contrast medium, and the ECG showed a decrease of ST-elevations. A follow-up coronary angiography one week later, due to persistent clinical symptoms (right ventricular cardiac decompensation, dyspnoea), showed shunting once again of the contrast medium into the RV. Intravascular ultrasound (IVUS) was used to identify the exact site of extravasation, which was underneath the initially implanted PTFE-covered stent. Percutaneous transluminal coronary angioplasty (PTCA) was performed using a high-pressure balloon (Quantum maverick 2.75/8, Boston Scientific, Natick, USA) both at the proximal and distal ends of the stent, which stopped flow of the contrast medium into the RV ( Fig. 2 ). The patient was discharged from the hospital two days later.

The ECG showed an acute STEMI of the anterior wall, which corresponded to subtotal occlusion of the LAD.

Primary coronary angiography revealed subtotal occlusion of segment 7 and stenosis in segment 8 due to an MB (A). Implantation of a stent (B) caused vessel rupture with flow of contrast medium into the RV (C). A PTFE-covered stent was implanted (D) and showed initially no further shunting (E). Persistent shunting discovered in the follow-up angiography was treated by inflation of a high-pressure balloon at the distal and proximal ends of the stent. IVUS showed correct implantation of the stent (F).

2

Characteristics of myocardial bridges

A myocardial bridge is a common anatomic variation of a coronary artery. The vessel is running intramurally and thus is being bridged by muscle fibers. Myocardial bridging predominantly involves the LAD . A superficial and a deep type of MB may be distinguished. The superficial type is described as the LAD running on the interventricular groove, being crossed by muscle fibers at a perpendicular or acute angle. The deep type is characterized as the LAD deviating towards the right ventricle, being deeply situated on the interventricular septum and being encircled by deep muscle fibers . In a retrospective study analyzing data from 1275 dual-source CT-scans (DSCT), superficial MB were found in 66% of cases, while 34% were of the deep type. The mean length of the superficial type was 16.4 mm with a depth less than 1 mm. The deep type had a mean length of 27.6 mm and a mean depth of 3 mm .

Diagnostic tools for MB include coronary angiography (CAG) and multi-detector computed tomography (MDCT). Sensitivity differs significantly between the two commodities. An MB is identified in 0.4% to 15.8% of CAGs and in 3.5% to 58% of MDCTs. Autopsy studies yield an even higher rate of MB in up to 50% of individuals . CAG is seen as the gold standard in detecting MBs. Characteristic findings on the coronary angiogram include the “milking effect” and “step-down step-up sign”, both describing caliber changes of the vessel during systole. Additionally, IVUS may be used to characterize an MB (“half moon sign”) . Interestingly, the incidence of MB is much higher if being sought after by the examiner . It increases from 1.7% to 9.7% if being actively looked after. This indicates that a high percentage of MBs may be missed in “every day” coronary angiography.

While usually associated with a good prognosis, some individuals with an MB exhibit symptoms. Sudden death (2.3%), arrhythmias (2.8%), HCM-related diseases (9.3%), cardiac failure (0.9%) and other cardiac anomalies (3.7%) are rare events . In contrast, coronary heart disease is diagnosed in 79.6% of symptomatic patients with an MB. It usually affects the segments proximal to the MB while the bridged vessel itself is spared from atherosclerotic alterations. The mechanism behind this seems to be high shear stress underneath the tunneled segment induced by systolic compression. High shear stress leads to alignment of endothelial cells in the direction of blood flow, therefore being more resilient to the diffusion of pro-atherogenic factors. Atherosclerosis is induced in the segments proximal to an MB however, caused by turbulent and complex blood flow due to systolic flow reversal and increased intra luminal pressure in the proximal segment .

2

Characteristics of myocardial bridges

A myocardial bridge is a common anatomic variation of a coronary artery. The vessel is running intramurally and thus is being bridged by muscle fibers. Myocardial bridging predominantly involves the LAD . A superficial and a deep type of MB may be distinguished. The superficial type is described as the LAD running on the interventricular groove, being crossed by muscle fibers at a perpendicular or acute angle. The deep type is characterized as the LAD deviating towards the right ventricle, being deeply situated on the interventricular septum and being encircled by deep muscle fibers . In a retrospective study analyzing data from 1275 dual-source CT-scans (DSCT), superficial MB were found in 66% of cases, while 34% were of the deep type. The mean length of the superficial type was 16.4 mm with a depth less than 1 mm. The deep type had a mean length of 27.6 mm and a mean depth of 3 mm .

Diagnostic tools for MB include coronary angiography (CAG) and multi-detector computed tomography (MDCT). Sensitivity differs significantly between the two commodities. An MB is identified in 0.4% to 15.8% of CAGs and in 3.5% to 58% of MDCTs. Autopsy studies yield an even higher rate of MB in up to 50% of individuals . CAG is seen as the gold standard in detecting MBs. Characteristic findings on the coronary angiogram include the “milking effect” and “step-down step-up sign”, both describing caliber changes of the vessel during systole. Additionally, IVUS may be used to characterize an MB (“half moon sign”) . Interestingly, the incidence of MB is much higher if being sought after by the examiner . It increases from 1.7% to 9.7% if being actively looked after. This indicates that a high percentage of MBs may be missed in “every day” coronary angiography.

While usually associated with a good prognosis, some individuals with an MB exhibit symptoms. Sudden death (2.3%), arrhythmias (2.8%), HCM-related diseases (9.3%), cardiac failure (0.9%) and other cardiac anomalies (3.7%) are rare events . In contrast, coronary heart disease is diagnosed in 79.6% of symptomatic patients with an MB. It usually affects the segments proximal to the MB while the bridged vessel itself is spared from atherosclerotic alterations. The mechanism behind this seems to be high shear stress underneath the tunneled segment induced by systolic compression. High shear stress leads to alignment of endothelial cells in the direction of blood flow, therefore being more resilient to the diffusion of pro-atherogenic factors. Atherosclerosis is induced in the segments proximal to an MB however, caused by turbulent and complex blood flow due to systolic flow reversal and increased intra luminal pressure in the proximal segment .