CALCIUM RESPONSIVENESS IN REGIONAL MYOCARDIAL SHORT-TERM HIBERNATION AND STUNNING IN THE IN-SITU PORCINE HEART - INOTROPIC RESPONSES TO POSTEXTRASYSTOLIC POTENTIATION AND INTRACORONARY CALCIUM

Background We tested the hypothesis that decreased calcium responsiven ess is responsible for the reduction in contractile function in region al hibernating and stunned myocardium in situ. Methods and Results In 19 anesthetized swine, the left anterior descending coronary artery fl ow was reduced to decrease anterior myocardial work index (sonomicrome try) by approximate to 60%. During 90 minutes of hypoperfusion, creati ne phosphate recovered (as determined by biopsy specimens and biolumin escence) and no necrosis developed (as determined by staining with tri phenyl tetrazolium chloride). In 10 swine, changes in the intracellula r calcium concentration were induced by systematic variation of the po stextrasystolic time interval at a constant prematurity. In 9 addition al swine, a graded IC calcium infusion was performed. Under control co nditions, anterior myocardial work increased with a fully compensated postextrasystolic time interval from 380+/-93 (mean+/-SD) to 523+/-98 mm Hg . mm. IC calcium infusion increased anterior myocardial work und er control conditions from 356+/-85 to a maximum of 428+/-93 mm Hg . m m. Although the maximal responses were decreased during postextrasysto lic potentiation (222+/-68 versus 523+/-98 mm Hg . mm) and calcium inf usion (176+/-32 versus 428+/-93 mm Hg . mm) after 90 minutes of ischem ia, the relationships between increases in anterior myocardial work an d, respectively, postextrasystolic time interval and IC calcium were n ot different. The same was true after 30 minutes of reperfusion. Concl usions Both regional hibernating myocardium and stunned myocardium in situ are characterized by a decrease in overall myocardial calcium res ponsiveness; however, there appears to be no significant myocardial de sensitization to calcium.