Clinical and Pathological Impact of Tissue Fibrosis on Lethal Arrhythmic Events in Hypertrophic Cardiomyopathy Patients With Impaired Systolic Function

BACKGROUND: The natural history of hypertrophic cardiomyopathy (HCM) varies from an asymptomatic benign course to a poor prognosis. Myocardial fibrosis may play a critical role in ventricular tachyarrhythmias (VT/VF); however, the clinical significance of tissue fibrosis by right ventricular (RV) biopsy in the long-term prognosis of HCM patients remains unclear. METHODS AND RESULTS: We enrolled 185 HCM patients (mean age, 57±14 years). The amount of fibrosis (%area) was quantified using a digital microscope. Hemodynamic, echocardiographic, and electrophysiologic parameters were also evaluated. Patients with severe fibrosis had longer QRS duration and positive late potential (LP) on signal-averaged ECG, resulting in a higher incidence of VT/VF. At the 5±4 year follow-up, VT/VF occurred in 31 (17%) patients. Multivariate Cox regression analysis revealed that tissue fibrosis (hazard ratio (HR): 1.65; P=0.003 per 10% increase), lower left ventricular ejection fraction (HR: 0.64; P=0.001 per 10% increase), and positive SAECG (HR: 3.14; P=0.04) led to a greater risk of VT/VF. The combination of tissue fibrosis severity and lower left ventricular ejection fraction could be used to stratify the risk of lethal arrhythmic events in HCM patients. CONCLUSIONS: Myocardial fibrosis in RV biopsy samples may contribute to abnormal conduction delay and spontaneous VT/VF, leading to a poor prognosis in HCM patients.