Methods
We examined myocardial adrenergic receptor and ion channel protein levels of epileptic and age-matched sham rats (9-20 months old) using western blotting. Cardiac electrical properties were examined using optical mapping ex vivo and electrophysiology in vivo. We investigated the propensity for ventricular tachycardia (VT) and the effects of β-adrenergic blockade on ventricular electrical properties and excitability in vivo.
Objective
Sympathetic predominance and ventricular repolarization abnormalities represent epilepsy-associated cardiac alterations and may underlie seizure-induced ventricular arrhythmias. Myocardial ion channel and electrical remodeling have been described early in epilepsy development and may contribute to ventricular repolarization abnormalities and excitability. Using the pilocarpine-induced acquired epilepsy model we sought to examine whether altered myocardial ion channel levels and electrophysiological changes also occur in animals with long-standing epilepsy.
Results
In animals with long-standing epilepsy, we observed decreased myocardial voltage-gated K+ channels Kv4.2 and Kv4.3, which are known to underlie early ventricular repolarization in rodents. Decreased β1 and increased α1A adrenergic receptor protein levels occurred in the myocardium of chronically epileptic animals consistent with elevated sympathetic tone. These animals exhibited many cardiac electrophysiological abnormalities, represented by longer QRS and corrected QT (QTc) intervals in vivo, slower conduction velocity ex vivo, and stimulation-induced VT. Administration of a β-adrenergic antagonist late in epilepsy was beneficial, as the therapy shortened the QTc interval and decreased stimulation-induced VT. Significance: Our findings demonstrate that myocardial ion channel remodeling and sympathetic predominance, risk factors for increased ventricular excitability and arrhythmias, persist in chronic epilepsy. The beneficial effects of β-adrenergic antagonist treatment late in the course of epilepsy suggest that attenuating elevated sympathetic tone may represent a therapeutic target for ameliorating epilepsy-associated cardiac morbidity.
Significance
Our findings demonstrate that myocardial ion channel remodeling and sympathetic predominance, risk factors for increased ventricular excitability and arrhythmias, persist in chronic epilepsy. The beneficial effects of β-adrenergic antagonist treatment late in the course of epilepsy suggest that attenuating elevated sympathetic tone may represent a therapeutic target for ameliorating epilepsy-associated cardiac morbidity.