Abstract 8208: Scar Border and Transmural Core Defined by Magentic Resonance Imaging Contribute to T wave Alternans in Patients with Cardiomyopathy: Implications for Identifying Arrhythmogenic Substrate

Abstract

BACKGROUND Structural barriers can lead to discordant action potential (AP) alternans in animal studies by slowing conduction and increasing AP gradients. We hypothesized that border zone and midwall scar will promote T wave alternans (TWA) in patients with cardiomyopathy by potentially slowing conduction and uncoupling transmural APs, respectively. METHODS AND RESULTS We prospectively studied 40 patients (53±14 yrs, LVEF 40±17%) with ischemic (n=12), dilated (n=12), or hypertrophic cardiomyopathy (n=16). Scar core and border zone were quantified as a percent of LV mass by applying signal-intensity thresholding to late gadolinium enhanced cardiac magnetic resonance images. The transmural distribution of core was determined from the short-axis LV slices and classified as endocardial, epicardial, midwall and full thickness core. TWA was evaluated during incremental atrioventricular pacing at 100, 110 and 120 bpm. TWA was quantified from ECG recordings using the spectral method and classified as positive if Valt >1.9 µV and k >3. +TWA was detected in 27 (68%) patients. The percentages of border zone, epicardial core and midwall core were greater in +TWA vs. - TWA. Maximum TWA magnitude correlated with the relative size of border zone (r=0.52, P<0.001), epicardial core (r=0.54, P<0.001) and midwall core (r=0.40, P=0.01). The heart rate onset for TWA (Valt >0 µV, k >3) was significantly lower in those patients with greater border zone and epicardial core. Multivariate analysis revealed border zone to be the only independent predictor of +TWA (Odds Ratio 1.22/10%, P=0.003). CONCLUSIONS In cardiomyopathy patients, scar border zone, epicardial core and midwall core contribute to +TWA. These structural barriers in the presence of +TWA may together provide a potent substrate for lethal ventricular arrhythmias.