Experimental evaluation of myocardial preservation techniques: IV. Potassium cardioplegia

To investigate whether potassium per se plays a significant role in cold potassium cardioplegia, isolated blood-perfused rabbit papillary muscle preparations were used to determine the recovery of myocardial contractility after normothermic anoxia. Cardioplegia was induced by infusing an isotonic electrolyte solution containing either 5 or 40 mEq/liter of potassium chloride. Anoxic periods of 30 minutes (9 experiments each) 45 minutes (10 experiments each), and 60 minutes (1 experiment each) were compared. Hearts stopped contracting in 45 seconds with infusion of a 40mEq/liter of potassium chloride solution compared to 5 minutes with a 5 mEq/liter solution. After 30 minutes of anoxia, myocardial recovery was 65.39 +/- 24.48 per cent with 5 mEq/liter of potassium chloride and 90.05 +/- 6.40 per cent with 40mEq/liter of potassium chloride. The difference was highly significant (p less than 0.01). After 45 minutes of anoxia the same trend as just described was noted, but the difference was statistically insignificant. After 60 minutes of anoxia, recovery was extremely poor regardless of the potassium concentration of the cardioplegic solution. Our conclusion was that a high potassium solution will arrest the heart rapidly and provide protection against anoxic injury of the myocardium. Its protective effect becomes less significant, however, as the anoxic time is prolonged.