Effects of hypokalemia on transmural dispersion of ventricular repolarization in left ventricular myocardium

Objective: To observe effects of hypokalemia on transmural heterogeneity of ventricular repolarization in left ventricular myocardium of rabbit, and explore the role of hypokalemia in malignant ventricular arrhythmia (MVA). Methods: A total of 20 rabbits were randomly divided into control group and hypokalemic group. Isolated hearts in the control group were simply perfused with modified Tyrode's solution, and were perfused with hypokalemic Tyrode's solution in hypokalemic group. Ventricular fibrillation threshold (VFT), 90% monophasic action potential repolarization duration (APD(90)) of subepicardial, midmyocardial and subendocardial myocardium, transmural dispersion of repolarization (TDR) and Cx43 protein expression in three layers of myocardium were measured in both groups. Results: VFT in the control group and the hypokalemic group were (13.40 +/- 2.95) V, and (7.00 +/- 1.49) V, respectively. There was a significant difference between two groups (P<0.01). APD(90) of three myocardial layers in the hypokalemic group were significantly prolonged than those in the control group (P<0.01). Delta APD(90) in the hypokalemic group and the control group were (38.10 +/- 10.29) ms and (23.70 +/- 5.68) ms, and TDR were (52.90 +/- 14.55) ms and (36.10 +/- 12.44) ms, respectively. Delta APD(90) and TDR in the hypokalemic group were significantly higher than those in the control group (P<0.05), and the increase in APD(90) of midinyocardium was more significant in the hypokalemic group. Cx43 protein expression of all three myocardial layers were decreased significantly in the hypohdemic group (P<0.01), and Delta Cx43 was significantly increased (P<0.05). Reduction of Cx43 protein expression was more significant in the midmyocardium. Conclusions: Hypokalemic can increase transmural heterogeneity of Cx43 expression and repolarization in left ventricular myocardium of rabbit, and decrease VFT and can induce MVA more easily.