Failure of standard cardioplegic techniques to protect the conducting system

To determine the site of persistent electrical activity during cardioplegic arrest, microelectrodes that were also capable of recording temperature were placed along the conducting system in dogs undergoing one hour of cardioplegic arrest. Electrical activity was highest in the atrioventricular (AV) junction area (AV node and proximal bundle of His), and the temperature in this area could not be lowered to the level of the temperature in the left ventricular apex by routine cardioplegic technique. Neither changing K+ concentration (16 to 20 mEq/L) nor adding procaine hydrochloride abolished the activity of the conducting system during cardioplegia, and only 2 of 15 dogs were in sinus rhythm 30 minutes after reperfusion. When the conducting system temperatures were lowered to less than 15 degrees C by right AV lavage with iced saline solution, electrical activity was abolished during arrest and all 4 of 4 animals were in sinus rhythm 30 minutes after reperfusion. This study localizes the site of persistent conducting system activity during cardioplegic arrest, confirms it can be abolished with local cooling, and establishes the relationship between conducting system activity during cardioplegia and the incidence of conduction block and junctional rhythm following reperfusion.