Cardiac effects of repeated focal seizures in rats induced by intrahippocampal tetanus toxin:bradyarrhythmias, tachycardias and prolonged interictal QT interval

Abstract

Objective: To determine electrical changes in the heart in a chronic, non-status model of epilepsy.Methods: Electrocorticogram (ECoG) and electrocardiogram (ECG) of 9 animals (5 made epileptic by intrahippocampal injection of tetanus neurotoxin (TeNT) and 4 control), are monitored continuously by radiotelemetry for up to 7 weeks.Results: Epileptic animals develop a median of 168 seizures, with postictal tachycardias reaching a mean of 487 beats/min and lasting a mean of 661 seconds. Ictal changes in heartrate include tachycardia and in the case of convulsive seizures, bradyarrhythmias resembling Mobitz type 1 second degree atrioventricular block; notably the P-R interval increased before block. Postictally the amplitude of T wave increases. Interictally, QT dependence on RR is modest and conventional QT corrections prove ineffective. Interictal QT intervals, measured at a heartrate of 400 bpm, increased from 65 ms to 75 ms, an increasedependent on seizure incidence over the preceding 10-14 days.Significance: Repeated seizures induce a sustained tachycardia and increase in QT interval of the ECG and evoke arrhythmias including periods of atrioventricular block during Racine Type 4 and 5 seizures. These changes in cardiac function may predispose to development in fatal arrhythmias and sudden death in humans with epilepsy