B-PO03-162 MICROVOLT QRS ALTERNANS WITHOUT MICROVOLT T WAVE ALTERNANS IN HYPERTROPHIC CARDIOMYOPATHY: A NOVEL RISK MARKER OF LATE VENTRICULAR ARRHYTHMIAS

Abstract

T wave alternans (TWA) is associated with ventricular arrhythmia (VA) but QRS alternans (QRSA) has not been characterized in hypertrophic cardiomyopathy (HCM). To assess microvolt QRSA/TWA in relation to traditional risk factors (RF) and late VA outcomes in HCM. Prospectively enrolled HCM patients (n=130, age 53±14yrs) with prophylactic ICD had digital 12-lead ECGs recorded during ventricular pacing at 100-120bpm. QRSA/TWA was quantified by the spectral method. Patients were categorized as QRSA+ and/or TWA+ based on ≥2 precordial leads having an alternans signal:noise >3 in ≥3 consecutive 128-beat segments. The VA endpoint was appropriate ICD therapy. QRSA+ and TWA+ occurred together in 28% and alone in 7% and 7% of patients, respectively. QRSA and TWA magnitude (1.9±0.6 vs 6.2±2.0μV, p<0.01; 1.3±0.3 vs 3.0±0.7μV, p=0.01) increased with pacing rate. LV thickness was greater in QRSA+ than QRSA- patients (22±7 vs 20±6mm, p=0.04). At 5 years follow up, 17% of patients had VA. QRSA+ patients had more VA than QRSA-, with QRSA+/TWA- patients having the highest VA rate (Figure). In patients with <2 RF, the annual VA rate was only 0.6% in QRSA- patients. Separate multivariable Cox models revealed QRSA+ (HR[95%CI]: 2.9[1.2-7.0], p=0.02) and QRSA+/TWA- (7.9[2.9-21.7], p<0.01) as the most significant predictors of VA. TWA and traditional RF did not predict VA. In HCM, microvolt QRSA is a novel rate-dependent phenomenon that can exist without TWA and is associated with greater LV thickness. QRSA in the absence of TWA increases VA risk 8-fold in all patients, while the absence of QRSA confers low VA risk in patients with <2 RF, which may inform ICD therapy.