MYOCARDIAL STUNNING - A TEMPERATURE-DEPENDENT PHENOMENON

Two recently completed studies in our laboratory have evaluated the re lationship between myocardial temperature during cardioplegic preserva tion and calcium accumulation within the cell. In the large animal mod el, the pig, we investigated the influence of normothermic versus hypo thermic blood cardioplegic preservation on sarcoplasmic reticulum calc ium ATPase activity and calcium uptake following 2-hour cardioplegic a rrest and 1 hour of normothermic reperfusion. The second investigation in the small animal model, the rat, measured intracellular calcium co ncentration in hearts subjected to cardioplegic arrest by continuous a dministration of cardioplegia at temperatures from 4-degrees to 37-deg rees-C. In the pig heart, global left ventricular function and coronar y blood flow were improved, while creatine kinase release was reduced in the warm preserved heart. The rate of sarcoplasmic reticulum calciu m uptake and calcium ATPase activity were impaired only in the presenc e of hypothermic preservation, and the higher calcium ATPase activity corresponded to the higher rate of sarcoplasmic reticulum calcium upta ke observed in the warm preserved heart. Measurements of intracellular calcium concentration accomplished with a spectrofluorimeter document ed a significant increase in free calcium in the 4-degrees-C and 20-de grees-C preserved rat heart during normothermic reperfusion. At both 2 8-degrees and 37-degrees-C preservation, the free calcium level did no t increase. It is concluded that intracellular calcium accumulation is associated with hypothermic preservation. Hypothermia appears to jeop ardize the control of calcium homeostasis, which then is manifested as a more rapid increase of intracellular calcium during reperfusion. Th is would be associated with increased myocardial stunning in the hypot hermic heart. A retrospective clinical review of 58 patients undergoin g coronary revascularization with impaired left ventricular function ( left ventricular ejection fraction less-than-or-equal-to 30%) document s the superiority of warm versus cold preservation in the clinical set ting by reducing myocardial stunning.