Sinus node potential during cold cardioplegia

Epicardial potentials of the sinus node, the right atrium, and the right ventricle were recorded in dogs during cold potassium-induced cardioplegia. We found that the sinus node fibers were more resistant to the cardioplegia than were the other myocardial fibers. When the cardioplegia rendered the atrial muscle inexcitable, the high frequency atrial potential was delayed and then abolished in the sinus node electrogram, and a smooth tracing similar to the action potential of the sinus node cell appeared. These findings should be pertinent for the cardiac surgeon attempting to avoid surgically-induced sinoatrial arrhythmias.