Computational and Experimental Studies of Hemodynamic Impact of Myocardial Bridging

Myocardial bridging (MB) is a congenital anomaly in which a segment of the coronary artery tunnels underneath a layer of cardiac muscle (myocardium). Severe narrowing of coronary lumen caused by either MB or obstructive atherosclerotic plaques can hinder blood flow to distal organs leading to myocardial ischemia. MBs have more severe effects in patients with coronary artery disease and hypertrophic cardiomyopathy (HCM) than MBs in patients without these conditions. However, it remains unclear how MB affects blood flow in HCM patients and how MB and atherosclerotic stenosis, possessing similar geometric characteristics, are similar or different. The aims of this study were first to determine the hemodynamic effects of MB in HCM patients and then to compare the hemodynamic significance of MB and coronary stenosis using experimental and computational approaches. Transient computational fluid dynamics (CFD) simulations were conducted in anatomically realistic models of diseased (with MB) and virtually healthy (without MB) models from fifteen patients with MB (7 HCM and 8 non-HCM controls), reconstructed from biplane angiograms. Our results showed that dynamic compression of MB led to diastolic flow disturbances and could significantly reduce the coronary flow in HCM patients as compared with non-HCM group (P < 0.01). The hemodynamic results and clinical outcomes demonstrated that HCM patients with an MB compression ratio higher than 65% required a surgical intervention. Both CFD and experimental results confirmed that the MB had a higher maximum but lower mean pressure drop in comparison with the stenosis, regardless of MB/stenosis severity. These results clarified the hemodynamic effects of MB in patients with HCM and increased our understanding of hemodynamic mechanisms of MB and provided important guidance for developing new treatment and making treatment decisions.