Electrocardiographic QRS Fragmentation as a Marker for Myocardial Fibrosis in Hypertrophic Cardiomyopathy

INTRODUCTION: Myocardial fibrosis in patients with hypertrophic cardiomyopathy (HCM) usually shows a patchy distribution, which may not be detected by pathological Q waves on 12-lead ECGs. Fragmented QRS complexes (fQRS) reflect intraventricular conduction delay and can be a marker of myocardial fibrosis. We assessed whether fQRS show better correlation with myocardial fibrosis than pathological Q waves in HCM. METHODS AND RESULTS: This cross-sectional study included 108 patients with HCM who underwent 12-lead ECG and cardiac magnetic resonance imaging with late gadolinium enhancement (LGE-CMR). The number of leads with pathological Q waves was not correlated with the extent of LGE measured at any different standard deviations (SDs) (2, 4, 6, 8, and 10 SD), whereas the number of leads with fQRS showed the best correlation with LGE at 6 SD (r = 0.32, P = 0.0008). Further, the number of leads with fQRS was an independent predictor for the extent of LGE at 6 SD. fQRS showed higher accuracy for detecting myocardial fibrosis defined by LGE at 6 SD than pathological Q waves; the overall sensitivity, specificity, and accuracy of fQRS were 40%, 80%, and 64%, respectively, whereas those of pathological Q waves were 7%, 97%, and 60%, respectively. fQRS in lateral leads showed the highest accuracy (75%), followed by inferior leads (59%) and anterior leads (57%), for detecting LGE at 6 SD in the corresponding left ventricular segment. CONCLUSIONS: These findings suggest that fQRS may have a substantially higher sensitivity and diagnostic accuracy compared with pathological Q waves for detecting myocardial fibrosis in HCM.