Endocardial detection of repolarization alternans

Repolarization alternans (RPA) is prognostic of sudden cardiac death and is thought to be mechanistically linked to the initiation of ventricular tachyarrhythmias. We sought to determine whether RPA, which is inherently spatially extended, could be measured using a spatially-localized endocardial lead and, if so, whether RPA could be quantified on a beat-to-beat basis. During diagnostic electrophysiological testing, 21 patients (16M, 5F; 62±16 yr) were evaluated for surface T-wave alternans (TWA) and endocardial RPA (via a right ventricular apex unipolar recording) during 5 min of 550 ms right atrial pacing. Power spectral analysis indicated that 7/21 patients had both surface TWA and endocardial RPA, 8/21 patients had neither, and 6/21 patients had discordant results (71% concordance; p=0.04). Importantly, unlike surface TWA alternans, endocardial RPA was detectable on a beat-to-beat basis. Given the putative mechanistic link between RPA and ventricular arrhythmias, beat-to-beat endocardial RPA detection might be of diagnostic or therapeutic utility.