Cardiac loading conditions modify the ventricular repolarization in conscious dogs with heart failure

Changes in myocardial loading conditions influence the ventricular action p otential via mechanoelectric feedback, a mechanism impaired in pathology. I n vivo the QT interval of the electrocardiogram which reflects the action p otential duration allows appropriate determination of its modifications. Th e effects of changes in cardiac loading conditions (load reduction with tri nitrin volume loading with Plasmion) On regional function and ventricular l ocal electrogram were investigated in conscious dogs before (control) and a fter 4 weeks of rapid pacing (dilated cardiomyopathy, DCM). In controls bot h interventions increased heart rate. Trinitrin in creased end-diastolic wa ll thickness (EDWth, P<0.001) and reduced absolute QT interval duration (P< 0.05). Plasmion decreased EDWth (P<0.001) and increased left ventricular en d diastolic pressure (LVEDP, P<0.001) without QT interval alteration. Howev er, the corrected QT interval was unchanged in both interventions. In DCM, trinitrin did not change the QT interval. Plasmion increased LVEDP (P<0.01) and prolonged QT and corrected QT intervals (P<0.01) despite the tachycard ia. In controls the changes in cardiac loading conditions did not modify th e QT interval, suggesting intact endogenous regulation of repolarization. T he impaired adaptation observed in DCM contributed to an increase in QT int erval following volume loading. In this model, a prolonged repolarization a fter abrupt volume loading may result from enhanced or disclosed mechanoele ctric feedback.