Myocardial bridging: contemporary understanding of pathophysiology with implications for diagnostic and therapeutic strategies

Abstract

Patients with myocardial bridging are often asymptomatic, but this anomaly may be associated with exertional angina, acute coronary syndromes, cardiac arrhythmias, syncope, or even sudden cardiac death. This review presents our understanding of the pathophysiology of myocardial bridging and describes prevailing diagnostic modalities and therapeutic options for this challenging clinical entity.

Keywords: coronary wall shear stress; intracoronary Doppler velocity and pressure; intravascular imaging; myocardial bridge; myotomy; percutaneous coronary intervention.

Figure 1. Relative Wall Shear Stress Profile of the Left Anterior Descending Artery in the Context of Myocardial Bridging

Relative WSS profile of a 3-dimensional angiographically reconstructed left anterior descending coronary artery during systole from a patient with myocardial bridging. Coronary segments proximal and distal to myocardial bridge show relative low WSS as compared to the bridged segment. S1: First septal branch; WSS: Wall shear stress.

Figure 2. Schematic Diagram of the Effects of Aging on the Myocardial Bridge

A: Heart with myocardial bridging, early stage. B: Longitudinal view of the bridged vessel. C: Cross-sectional view of the vessel in the middle of the myocardial bridge. A’: Heart with myocardial bridging, late stage, with ventricular hypertrophy and diastolic dysfunction. B’: Longitudinal view of the bridged vessel, with hypertrophied muscle and plaque progression proximal to the bridge. C’: Cross-sectional view of the vessel in the middle of the myocardial bridge showing hypertrophied muscle and the negative remodeling of the vessel with decreased lumen diameter. Images were drawn by Clare Wang.

Figure 3. “Milking Effect” in Coronary Angiography

A: Systolic compression of myocardial bridges, the “milking effect” B: Subsequent increase in vessel lumen diameter during diastole. White arrows represent areas of myocardial bridging.

Figure 4. Systolic Narrowing at the Myocardial Bridge Accentuated By Intracoronary Nitroglycerin

A: Systolic compression of myocardial bridge at baseline. B: Systolic narrowing at the myocardial bridge accentuated by intracoronary injection of nitroglycerin. White arrows point to area of myocardial bridging.

Figure 5. Intravascular Ultrasound “Half-moon” Sign

In this example of the “half-moon” sign, the echolucent area is present only between the bridged coronary segment and the epicardial tissue.

Figure 6. Finger Tip Phenomenon During Intracoronary Doppler Measurements

A: Example of normal flow pattern. B: Example of the “finger tip” phenomenon, a characteristic velocity profile demonstrating abrupt early diastolic acceleration, rapid mid-diastolic deceleration, and mid-to-late diastolic plateau.

Figure 7. Intracoronary Hemodynamic Measurements Distal to a Myocardial Bridge

Coronary blood velocity (blue tracing), proximal pressure (Pa, red tracing) and distal pressure (Pd, yellow tracing) measurements distal to a myocardial bridge. Electrocardiogram (white tracing). Blue circles indicate the tracings’ portions magnified above each circle. A: adenosine (140 mcg/Kg/min), FFR=0.83, APV=28 cm/s; HR=96 bpm. B: dobutamine (60 mcg/Kg/min), FFR=0.82, APV=38 cm/s, HR=122 bpm. APV: Average peak blood velocity; BPM: Beats per minute; FFR: Fractional flow reserve; HR: Heart rate.

Figure 8. Myotomy Procedure

A: View before incision showing intramyocardial LAD. B: Fat incised, showing LAD (yellow arrows) and the bridging muscle (blue arrows). C: Unroofed LAD with cut ends of bridging muscle (blue arrows). LAD: Left anterior descending artery.

Figure 8. Myotomy Procedure

A: View before incision showing intramyocardial LAD. B: Fat incised, showing LAD (yellow arrows) and the bridging muscle (blue arrows). C: Unroofed LAD with cut ends of bridging muscle (blue arrows). LAD: Left anterior descending artery.

Figure 8. Myotomy Procedure

A: View before incision showing intramyocardial LAD. B: Fat incised, showing LAD (yellow arrows) and the bridging muscle (blue arrows). C: Unroofed LAD with cut ends of bridging muscle (blue arrows). LAD: Left anterior descending artery.