Initial myocardial adjustments to brief periods of ischemia and reperfusion in the conscious dog.

The changes in left ventricular (LV) dynamics induced by brief periods of ischemia (100 seconds) and subsequent reperfusion were analyzed in conscious dogs. Global LV ischemia, induced by partially occluding the left main coronary artery, reduced LV flow homogeneously and impaired LV function as reflected by decreases in LV stroke "work" (89 +/- 4% M +/- SE), systolic shortening (72 +/- 4%), velocity of shortening (56 +/- 6%), LV systolic pressure (34 +/- 5%), and dP/dt (59 +/- 6%). Regional LV ischemia, induced by occluding either the left circumflex or anterior descending coronary artery completely, reduced flow to the ischemic segment (82 +/- 3%) while decreasing segment work (96 +/- 5%), shortening (82 +/- 3%), and velocity of shortening (70 +/- 5%), with minimal depression of overall LV function. In both groups the extent of shortening was reduced more rapidly and greater (P less than 0.01) than shortening velocity. Moreover, with localized ischemia, segment work was reduced more (P less than 0.01) than shortening. With reperfusion, a transient overshoot in function above preischemic control levels was observed in both groups (global work increased by 60 +/- 12% and regional work by 28 +/- 4% above control). This overshoot was not dependent on adrenergic mechanisms, but was prevented by inhibiting reactive hyperemia. Thus myocardial ischemia induces a dissociation between extent and rate of myocardial shortening. A further dissociation between shortening and work is apparent with regional ischemia. After reperfusion there is a transient overshoot in function which appears to be dependent upon the associated reactive hyperemia.