Ventricular fibrillation threshold and local dispersion of refractoriness in isolated rabbit hearts with left ventricular dysfunction

Abstract

Patients with congestive heart failure or left ventricular dysfunction (LVD) have a high incidence of ventricular tachyarrhythmias and sudden cardiac death. In addition to structural, metabolic and neuroendocrine changes, mechano-electrical feedback may play a role in arrhythmogenesis in heart failure. Three groups of rabbits (n = 10 for each) were studied: chronic coronary ligation with ejection fraction (EF) ≥ 0.45 or < 0.45, and sham-operated controls. Ventricular fibrillation (VF) thresholds were measured at LV pressures of 0 and 40 mmHg during modified Langendorff perfusion. Intervals between local activations during VF (VFI) were used as an index of refractoriness. Global dispersion was expressed as coefficient of variation of VFI; local dispersion by maximum difference in VFI between adjacent sites. Median VF threshold was lower at 0mmGH in the lower EF group compared to controls (30 vs. 67.5 mA, P<0.05). VF threshold in control hearts was lower at 40 mmHG than at 0 mmHg (P<0.01), but there was no further reduction in threshold in LVD hearts at 40mmHg. Global dispersion of VFI in the lower EF group was greater than in controls at 0mmHg in the infarct border zone (P<0.05). At 40 mmHg, local dispersion of VFI in zones bordering and remot from the infarct were greater in both LVD groups than in controls (P<0.05). Local inhomogeneity of refractoriness is more marked in the infarct border zone, but latent abnormalities are evident in normal myocardium of rabbits with left ventricular dysfunction and are revealed by left ventricular distension.