Effect of B-blocker atenolol on spatial dispersion of ventricular repolarisation of sheep following acute myocardial ischemia.

AIM: To investigate the effect of beta-blockers on spatial dispersion of ventricular repolarization following acute myocardial ischemia. METHODS: Twenty sheep were randomized into control (normal saline,iv) and atenolol (1.5 mg/kg,iv) group. Acute myocardial ischemia was induced by occlusion of the obtuse marginal coronary artery. Unipolar ECG was simultaneously acquired from 64 epicardial sites in both ischemic and non-ischemic regions. Activation-recovery intervals (ARI), an index of ventricular repolarization, was determined from the epicardial ECG. The difference between the longest and shortest ARI was defined as ARI dispersion. RESULTS: Ischemic zone in atenolol group was less than that of control group (13 %+/-2 % vs 19 %+/-3 %, P=0.04). In the control group, pooled ARI dispersion was increased by (18+/-21), (27+/-21), and (16+/-10) ms at 30, 60, and 90 min of coronary artery occlusion respectively (P <0.01), whereas in the atenolol group, ARI dispersion was only increased by (6+/-4), (6+/-7), and (2+/-7) ms respectively (P >0.05). CONCLUSION: These findings indicate that atenolol suppresses ischemia-induced increase in spatial dispersion of ventricular repolarization, which may explain the antiarrhythmic effect of beta-blockers.