Aims: 

Recently, we showed that an increase in the 'absolute' beat-to-beat variability and instability parameters of the EKG intervals predicted the occurrence of phase-1 ischaemic ventricular fibrillation (VF) in isolated rat hearts. We sought to investigate whether 'absolute' beat-to-beat variability and instability parameters decrease when we reduce VF incidence with Class-I antiarrhyhtmic drugs. If yes, then it shows good correlation between electric instability and VF occurrence.

Methods: 

Isolated, Langendorff perfused rat hearts were treated with one lower and one higher concentration of quinidine, lidocaine, and flecainide, representing the peak unbound plasma and total blood concentrations, respectively, at "therapeutic" dosage in man. The hearts were subjected to local ischaemia for 30 min. Arrhythmia incidences were calculated. The 'absolute' beat-to-beat variability and instability of the ECG intervals were measured at preset times, irrespective of whether or not hearts were in stable sinus rhythm ('absolute' variability and instability).

Results: 

Only flecainide reduced VF incidence significantly at low concentration. The high concentrations of all three drugs were effective against VF. Significantly reduced VF incidence coincided with significantly reduced frequency of 'R on T' ventricular premature beats and significantly reduced instability of repolarisation quantified by the 'absolute' beat-to-beat variability and instability parameters of the RT interval.

Conclusions: 

According to our results, there is a strong correlation between instability of repolarization and VF occurrence in isolated rat hearts. The frequency of 'R on T' ventricular premature beats and the instability of repolarization measured by the 'absolute' beat-to-beat variability and instability parameters of the RT interval predict phase-1 ischaemic VF in isolated rat hearts.