Effect of diltiazem on stunned myocardium evaluated with 99mTc-pyrophosphate imaging in canine heart

The effect of diltiazem on stunned myocardium was evaluated by measuring the myocardial uptake of 99mTc-PYP (pyrophosphate) in open chest experiments with dogs. Myocardial stunning was induced by a 30 min ischemic occlusion of the anterior descending coronary artery. Regional wall motion was monitored by echocardiography of the epicardium for 2 h during reperfusion. After a 30 min occlusion of the coronary artery, it was reperfused and 99mTc-PYP was injected, followed by 201Tl 2 h later. The ischemic area was defined by Evans blue dye, and the infarct area by TTC staining. No dogs showed infarcts or 201Tl defects in this study group. Five dogs of the control-1 group (C1, ischemic area = 19.1 +/- 3.2%) showed decreased regional wall motion during occlusion (15.5 +/- 3.5% of control), and a slow recovery from depressed motion after 2 h of reperfusion (20.3 +/- 9.3%) with uptake ratio (compared to the non-ischemic area uptake) of 99mTc-PYP (4.96 +/- 2.28). In contrast, both groups with diltiazem infusion (20 micrograms/kg/min), started either 30 min before ischemia (D1 = 5 dogs) or just after reperfusion (D2 = 5 dogs), showed significantly better recovery after 2 h of reperfusion (D1:115.4 +/- 36.0%, D2:109.2 +/- 44.2%) than C1 (p less than 0.05), D1 and D2 groups also showed suppressed 99mTc-PYP uptake ratio (D1:1.06 +/- 0.33, D2:2.34 +/- 2.05, p less than 0.05 vs C1) in spite of comparable ischemic area. Four dogs with small ischemic area (C2:5.3 +/- 5.0%) did not show increased 99mTc-PYP uptake (1.15 +/- 0.35), and regional wall motion after 2 h of reperfusion was 96.1 +/- 24.1% of the control value (p less than 0.05 vs C1). Thus, diltiazem was effective in enhancing the suppression of 99mTc-PYP uptake in the stunned myocardium, and similar results were obtained for small ischemic areas. The protective effect of diltiazem appears to be strongly related to the mechanism of 99mTc-PYP uptake.