Effects of Propranolol and Verapamil on Changes in TQ and ST Segment Potentials During Graded Coronary Flow Reduction in a Porcine Myocardial Ischemia Model.

Acute myocardial ischemia causes TQ depression and ST elevation. However, the effects of cardioprotective drugs such as β-blockers and Ca++-antagonists on the extent of TQ depression, ST elevation, and myocardial ischemic injury are not fully understood.We created a carotid-coronary shunt in 30 pigs, and extracellular K+ ([K+]e), TQ, and ST segments were recorded simultaneously with K+-selective plunge electrodes placed in the left anterior descending artery (LAD) distribution during graded LAD flow reduction before and after administration of propranolol or verapamil. Unipolar DC-coupled electrograms were recorded from the reference pole of the K+-selective plunge electrodes. The microvolt readings from the K+-selective electrodes were converted to [K+]e and then to the changes in potassium equilibrium potential (ΔEK). The shunted LAD flow was reduced in a stepwise fashion at 5-minute intervals.segment depression at the similar ΔEK was not affected by propranolol or verapamil. However, ST segment elevation was reduced by propranolol but exacerbated by verapamil at the similar ΔEK.TQ-ST changes recorded by AC coupled ECG are not a reliable index of ischemia and therefore cannot be used to evaluate the effects of drugs that might affect the electrophysiologic properties of ischemic myocardium.