Suppression of calcium-induced repolarization heterogeneity as a mechanism of nitroglycerin's antiarrhythmic action.

Abstract

This study examined whether the antifibrillatory action of nitroglycerin (NTG) is attributable to reduction in calcium-induced heterogeneity of repolarization independent of autonomic and coronary vasodilatory influences. The effects of intrapericardial (IPC) NTG on coronary blood flow, contractility, repolarization, and arrhythmia susceptibility were measured in anesthetized pigs (N = 43). Autonomic influences were minimized by vagotomy and beta-adrenergic blockade (metoprolol, 1.25 mg/kg, intravenous). Electrophysiological parameters were tested at 30 min, a time when coronary hemodynamics had returned to baseline. Intracoronary calcium chloride (CaCl2, 50-mg bolus) injection augmented contractility (dP/dt(max), 1760 +/- 144 to 2769 +/- 274 mmHg/s, and following NTG, 1531 +/- 384 to 2138 +/- 242 mmHg/s, P < 0.0002), reflecting increased myocardial intracellular calcium. Calcium increased repolarization heterogeneity (interlead precordial T-wave heterogeneity, 95 +/- 15 to 264 +/- 33 microV, P < 0.006; T(peak)-T(end), an index of transmural dispersion of repolarization, 37 +/- 3 to 76 +/- 6 ms, P < 0.05) and lowered repetitive extrasystole threshold (RET; 24 +/- 2 to 13 +/- 1 mA, and following NTG, 32 +/- 4 to 18 +/- 1 mA, P < 0.0001). IPC NTG raised the RET from baseline by 33% and blunted calcium-induced contractility (dP/dt(max) by 23%, P < 0.05), repolarization changes (T-wave heterogeneity by 24%, P < 0.006; T(peak)-T(end) by 18%, P = 0.04), and arrhythmia vulnerability (RET by 39%, P < 0.003). Thus, the capacity of NTG to suppress calcium-induced repolarization heterogeneity is an important mechanism of its antiarrhythmic action, which is independent of autonomic and vasodilatory actions.

• Authors: Susan Xiuqing Zhao, Lani Mei Lee, Bruce D Nearing, Veronica O Busso, Kevin F Kwaku, Richard L Verrier
• Journal: Journal of cardiovascular pharmacology (J Cardiovasc Pharmacol) Vol. 48 Issue 2 Pg. 22-9 (Aug 2006) ISSN: 0160-2446 [Print] United States
• PMID: 16954817 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Anti-Arrhythmia Agents
• Nitroglycerin
• Calcium

Topics

• Animals
• Anti-Arrhythmia Agents (pharmacology)
• Blood Pressure (drug effects)
• Calcium (antagonists & inhibitors)
• Coronary Circulation (drug effects)
• Electrocardiography (drug effects)
• Female
• Heart Rate (drug effects)
• Male
• Myocardial Contraction (drug effects)
• Nitroglycerin (pharmacology)
• Swine