High-resolution electrical mapping of depolarization and repolarization alternans in an ischemic dog model.

Cardiac electrical alternans have been associated with spontaneous ventricular arrhythmias during myocardial ischemia. The study aims were to use a new algorithm to measure depolarization and repolarization alternans from epicardial electrograms in an ischemia model and to evaluate which features are predictive of ventricular fibrillation (VF). The left anterior descending coronary artery was occluded in 21 dogs, of which 6 developed spontaneous VF. Four seconds of unipolar epicardial electrograms was recorded before and 5 min after occlusion from an 8 x 14-electrode plaque placed on the anterior left ventricle. Alternans amplitudes were estimated with a triangular wave-fitting algorithm and for each unipolar electrogram for various measurements of the QRS and ST-T wave amplitude. The root mean square error was computed for each fit. Receiver-operator characteristic curves were used to determine whether prevalence of alternans having estimated alternans amplitude-to-error ratio (A/E) above a given threshold could distinguish the dogs who had and did not have spontaneous VF. The prevalence of alternans after ischemia was highly predictive of VF when measured both during depolarization (sensitivity of 83% and specificity of 87%) and during repolarization (sensitivity of 100% and specificity of 73%). The optimal alternans A/E ranged from 1 to 4. There were no differences in the level of discordance or alternans amplitude between dogs who developed VF versus dogs who did not. The prevalence of alternans in the ventricles may be the key risk factor for developing VF during myocardial ischemia when short-term recordings are used.