Improved activation time assignment of unipolar electrograms from ischemic canine epicardium.

Aims: The present study attempts to develop an objective, statistically based set of criteria for activation time determination from unipolar electrograms (U-EGMs) using a standard of activation related to biophysical theory.

Methods: A high-resolution assembly of U-EGMs obtained from the epicardial surface of the canine postinfarction heart were analyzed in order to achieve the best prediction of local versus distant activation. An activation time standard (ATS) consisted of three properties: (1) propagation of activation, evidenced by a linear temporal shift of waveforms from closely spaced U-EGMs with little or no decay in amplitude; (2) cycle length-dependent changes of those propagating waveforms; and (3) evidence of electrotonic deflections, seen as nonpropagating potentials having decaying amplitude with distance.

Mechanisms of enhanced arrhythmogenicity of regional ischemia in the hypertrophied heart.

Background: The coexistence of cardiac hypertrophy (H) and ischemia (I) can create a particularly arrhythmogenic substrate. Most studies investigate the effects of global I on H. However, global I is not a good surrogate model of the clinical situation.

Spatial dispersion of repolarization is a key factor in the arrhythmogenicity of long QT syndrome.

Introduction: The occurrence of significant spatial dispersion of repolarization in vivo as it relates to the mechanism of arrhythmia formation in the long QT syndrome (LQTS) continues to be questioned.

Methods And Results: We investigated a guinea pig model of LQT3 using anthopleurin-A (AP-A) to study the contribution of rate-dependent spatial dispersion of repolarization in the intact heart to the arrhythmogenicity of LQTS. Optical action potentials were measured using potentiometric fluorescent dye di-4ANEPPS in Langendorff-perfused hearts with induced AV block.

Mechanism of discordant T wave alternans in the in vivo heart.

Introduction: Compared to concordant T wave alternans (CA), discordant T wave alternans (DA) may be associated with an increased dispersion of repolarization (DR) and a greater propensity to develop reentrant ventricular tachyarrhythmias. The electrophysiologic mechanisms of DA in the in vivo heart are not well understood.

Methods And Results: The mechanisms of DA were investigated in the canine anthopleurin-A surrogate model of long QT3 syndrome using tridimensional analysis of activation and repolarization patterns from 256 to 384 unipolar electrograms.