Regional sensitivity to verapamil in ventricular myocardium

Area of Science:

• Cardiovascular Physiology
• Pharmacology

Background:

• Verapamil is a calcium channel blocker used to treat heart conditions.
• Understanding its effects on different cardiac tissues is crucial for optimizing its therapeutic use.

Purpose of the Study:

• To investigate the regional effects of verapamil on the transmembrane action potential configuration in the cat left ventricular endocardium.
• To explore the relationship between regional endocardial activation patterns and verapamil's efficacy.

Main Methods:

• Electrophysiological recordings of transmembrane action potentials in various regions of the cat left ventricular endocardium.
• Administration of verapamil at concentrations ranging from 0.1 to 4.0 micrograms/ml.
• Analysis of surface electrograms to determine the sequence of fiber activation.

Main Results:

• Verapamil demonstrated regional variations in its effects on action potential duration and repolarization.
• Basal muscle fibers showed minimal changes, while cells at the papillary muscle tip exhibited increased phase 2 slope and accelerated early repolarization.
• Disparate patterns of endocardial activation were observed between muscle and Purkinje fibers.

Conclusions:

• Regional differences in verapamil's effects on the left ventricular endocardium are influenced by distinct activation sequences.
• These findings suggest that the effectiveness of verapamil in managing ventricular arrhythmias may be region-dependent.