Morphological changes associated with hemodynamically significant myocardial bridges in sudden cardiac death

Although myocardial bridging (MB) is a common coronary anomaly, its cardiovascular consequences are still disputed. A positive link between sudden cardiac death (SCD) and myocardial bridging has not yet been definitively proved, even though many case reports and small scale studies support this association. For myocardial bridging to be associated with sudden cardiac death it must exhibit certain specific characteristics involving coronary or myocardial changes sufficient to explain a terminal cardiac event. In this study we aimed to analyze the morphological changes (both myocardial and coronary) associated with hemodynamically significant myocardial bridging and the morphological differences between hemodynamically significant MB and MB considered to be non-hemodynamically significant.

We analyzed 53 cases of sudden cardiac death, of which 21 cases had hemodynamically significant myocardial bridging, 14 had non-hemodynamically significant myocardial bridging and 20 cases suffered sudden cardiac death without myocardial bridging, using a morphological score with seven histological parameters.

Myocardial fibrosis and interstitial edema were found to be highly correlated with hemodynamically significant myocardial bridging (HSMB), as were interstitial edema and interstitial fibrosis.

Hemodynamically significant myocardial bridging can be discovered during heart dissection by analyzing a series of morphological markers (width, distribution of atherosclerosis, distal hypoplasia). Our study showed that MB was associated with increased myocardial fibrosis and edema, both of which have an increased risk of electrical instability. Compared to non-hemodynamically significant myocardial bridging, HSMB shows a distinct histological pattern, with increased myocardial fibrosis and edema. The main cause of SCD in association with HSMB seems to be electrical due to increased electrical myocardial heterogeneity, but large scale studies are needed to test this.