Myocardial Ischemia Linked to Myocardial Bridging in Hypertrophic Cardiomyopathy

An association exists between myocardial bridging (MB) in hypertrophic cardiomyopathy (HCM) and myocardial ischemia, however MB in HCM has no significant association with cardiovascular mortality or nonfatal adverse cardiac events, according to a review and meta-analysis published in the American Journal of Cardiology.

Reviewers sought to assess clinical consequences of MB among patients with HCM, focusing on cardiovascular mortality, nonfatal adverse cardiac events, and indicators of myocardial ischemia.

This systematic review and meta-analysis screened articles in Scopus, Medline Complete, PubMed, and Web of Science and included 10 observational studies (4 prospective cohort studies, 3 retrospective cohort studies, 3 case-control studies) comparing outcomes in patients with HCM (N=1504) with MB (n=353) and without MB (n=1151). Number of participants per included studies ranged from 36 to 420.

Only pediatric populations were investigated in 2 of the studies. The other 8 studies included adult populations aged approximately 40 to 60 years. MB was identified in 2 studies using coronary computed tomography angiography and in 8 studies with conventional angiography. A single study only included patients with a rare morphologic subtype of HCM, and 2 additional studies only included patients with obstructive HCM. The other 7 studies failed to specify the form of HCM included.

Study quality was evaluated with a modified Downs and Black tool (maximum score of 23 points) with a mean score of 17.5±1.3, considered good by these reviewers. MB was defined in 4 studies as transient systolic compression of an epicardial coronary artery by 50% of its diameter. Two  studies set the diameter value lower, 1 study used 2 diameter values, 1 study defined MB as an intramural segment was surrounded by at least 1 mm of myocardium, 1 study defined MB when the intramural segment had to be fully enveloped by myocardium with no further requirements for length and depth, and 1 study simply defined MB as a segment of a coronary artery that courses through the myocardium.

The reviewers found that MB was not associated with nonfatal adverse cardiac events (odds ratio [OR], 1.80; 95% CI, 0.98-3.28; P =.06) or cardiovascular mortality (OR, 1.70; 95% CI, 0.56-5.15; P =.35) in pooled analysis (nonfatal events, 5 studies; mortality, 8 studies). MB was significantly associated with myocardial ischemia (OR, 1.89; 95% CI, 1.03-3.44; P =.04) in pooled analysis (4 studies).

Considerable review limitations include the broad range of MB parameters in the included studies. Additional significant limitations include the design nature of a review and meta-analysis, the heterogeneous nature of data reporting across studies, underpowered sample sizes in some of the included studies, heterogeneity between studies in population characteristics, outcomes evaluated, differences in imaging modalities, and modalities for measuring myocardial ischemia. Patients in 1 study (n=160) with more than 1 nonfatal adverse cardiac event may have been counted twice.

 “Overall, this review demonstrated an association between the presence of MB in HCM and myocardial ischemia but found no associations with clinical outcomes, including cardiovascular mortality and nonfatal adverse cardiac events,” the researchers wrote. “Future research should focus on identifying any specific populations that may be more vulnerable to adverse outcomes by corroborating morphologic and functional features of bridges with HCM phenotype and clinical outcomes using modern imaging techniques.”