QRS prolongation is associated with structural remodeling in hypertrophic cardiomyopathy

Background Signal-averaged electrocardiogram (SAECG) records myocardial depolarization, and can detect inhomogeneous/slow conduction in fibrotic myocardium, which promotes reentrant ventricular arrhythmias (VAs). Hypertrophic cardiomyopathy (HCM) is associated with a high prevalence of cardiac fibrosis and VAs, but abnormal SAECG has low predictive power for VAs. We hypothesized that HCM-specific structural/electrical remodeling underlies this result. Methods We tested our hypothesis by retrospectively studying HCM patients (n=73) who underwent transthoracic echocardiography (TTE) and cardiac magnetic resonance (CMR) imaging within 12 months of SAECG and 12-lead ECG. Patients were divided into 2 groups (normal-SAECG, abnormal-SAECG) based on filtered-QRS duration ( fQRS d), root-mean-square-voltage ( RMS40 ) and low-amplitude (<40μV) signal of terminal 40ms of filtered-QRS (late potentials). Abnormal SAECG was defined as fQRS d >114ms, RMS40<20 μ V or LAS40>38ms . Results Abnormal SAECG was seen in ∼50% of HCM patients (37/73). In the abnormal-SAECG group, 78% (n=29) only had prolonged fQRS d, and 22% (n=8) had prolonged fQRS d plus late potentials ( RMS40<20 μ V or LAS40>38ms) . Mean fQRS d and LAS40 were significantly higher in the abnormal-SAECG group. The abnormal-SAECG group had significantly larger LA size, lower global-LV longitudinal systolic strain/strain rate and early-diastolic strain rate by TTE; higher LV-mass index (LVMI) and LV-scar burden by CMR; higher prevalence of repolarization abnormalities on 12-lead ECG. LVEF and adverse outcomes (VT/VF, heart failure, death) were similar in the 2 groups. Univariate analysis showed that fQRS d is positively correlated with LVMI, LV-scar mass, and negatively correlated with global-LV early diastolic strain rate. Conclusions In HCM, abnormal SAECG is associated with greater structural/electrical LV-remodeling, reflecting a severe global myopathy.