Effects of Procainamide on Transmural Ventricular Repolarisation

To investigate the pharmacological effect of procainamide on transmural ventricular repolarisation in normal heart, the transmural activation-recovery intervals (ARI) and their responses to procainamide (20 mg/min i.v. for 20 min) were studied in 6 open-chest, pentobarbitone-anaesthetised sheep. ARI was measured from the unipolar ECGs acquired with 4 plunge needles inserted into the basal and apical parts of the left ventricular wall. During sinus rhythm (cycle length 500-700 ms), there was no significant difference in the pooled ARI between the epicardium (266.0 ± 30.5 ms), midmyocardium (265.0 ± 28.9 ms) and endocardium (265.7 ± 28.1 ms) (p>0.05). Procainamide prolonged ARI in all myocardial layers. The pooled ARI prolongation from the epicardium, midmyocardium and endocardium of the 6 animals was 66.8 ± 18.3, 70.3 ± 14.7 and 65.3 ± 15.7 ms (p < 0.05), respectively. In conclusion, sodium channel blocker procainamide results in a similar repolarisation prolongation in the left ventricular epicardium, midmyocardium and endocardium of a healthy heart.