Effect of diltiazem on myocardial blood flow.

We examined the effects of diltiazem on transmural myocardial blood in the presence of a flow-limiting stenosis and during acute total coronary artery occlusion in awake, chronically instrumented dogs. Regional myocardial perfusion was estimated with left atrial injections of 15-mu-diameter radionuclide labeled microspheres. An electromagnetic flowmeter probe and hydraulic occluder were used to monitor blood flow and produce total and subtotal occlusions of the left circumflex coronary artery. A 10-second total arterial occlusion produced intense coronary vasodilation and a pronounced reactive hyperemic response. When a proximal coronary stenosis prevented reactive hyperemia, ischemic coronary vasodilation after a 10-second arterial occlusion caused transmural redistribution of blood flow toward the subepicardium. resulting in subendocardial underperfusion despite a normal net volume of arterial flow. Although diltiazem did not increase coronary collateral flow during acute arterial occlusion, it did blunt the vasodilation that occurred in response to a 10-second total coronary occlusion, and partially corrected the subendocardial underperfusion that occurred with a proximal flow-limiting coronary stenosis.