Effect of diltiazem on coronary reactive hyperemia in patients with flow-limiting coronary artery stenosis

Effect of diltiazem on coronary flow reserve in patients with microvascular angina

Microvascular angina is characterized by ischemia-like symptoms in patients with normal coronary arteries and reduced coronary flow reserve. Clinical observations suggested an improvement in clinical symptomatology and exercise tolerance after treatment with calcium antagonists. The effect of diltiazem on coronary flow reserve was evaluated in controls and in patients with microvascular angina. Coronary flow reserve was measured in 16 normotensive patients (7 females, 9 males, mean age 51 +/- 10 years) with angiographically normal coronary arteries. Coronary blood flow was determined at rest, after dipyridamole (0.5 mg/kg) and following intravenous administration of diltiazem (10 mg) using coronary sinus thermodilution technique. Coronary flow reserve was calculated as coronary blood flow after dipyridamole divided by coronary blood flow at rest. Patients with normal coronary flow reserve (coronary flow reserve > 2.0) received either dipyridamole alone (group 1, controls, n = 6) or dipyridamole and diltiazem (group 2, n = 5), whereas patients with reduced coronary flow reserve (coronary flow reserve < 2.0) obtained dipyridamole and diltiazem (group 3, n = 5). Resting coronary flow was identical in the three groups, but after maximal vasodilation with dipyridamole, coronary flow increased significantly more in groups 1 and 2 than in group 3 (P < 0.05, analysis of variance (ANOVA)). Coronary flow reserve was 2.5 in group 1 and 2.3 in group 2, but was significantly reduced in group 3 (1.3; P < 0.05, ANOVA). Intravenous diltiazem failed to increase coronary blood flow in groups 2 and 3. Therefore, diltiazem does not improve reduced coronary flow reserve in patients with microvascular angina, but leaves coronary flow reserve unaffected. The failure to ameliorate impaired coronary flow reserve with diltiazem is in contrast to the reported clinical improvement after calcium channel blockade in these patients. Thus, other factors such as structural abnormalities in the microcirculation or functional abnormality in smooth muscle relaxation not responsive to calcium channel blockade are probably responsible for the occurrence of myocardial ischemia in patients with microvascular angina.

The effect of diltiazem on coronary flow reserve in humans

Calcium channel antagonists have been shown to blunt maximal coronary flow after brief coronary occlusion and during pharmacologic coronary dilation in animals. This property, if present in humans, would result in a reduction in coronary flow reserve in the absence of intrinsic abnormalities of the coronary circulation. A reduction of maximal vasodilator capacity by calcium channel antagonists could also constitute an important anti-ischemic mechanism of action of these agents. To evaluate the effect of calcium channel antagonists on coronary flow reserve in awake humans, we measured coronary flow reserve using the coronary Doppler catheter and intracoronary papaverine at baseline and after diltiazem administered by intravenous (125 or 250 micrograms/kg bolus, 5 micrograms/kg/min infusion, n = 8) or intracoronary (150-600 micrograms bolus, n = 10) routes. Intravenous diltiazem reduced heart rate from 77 +/- 18 to 72 +/- 17 beats/min (mean +/- SD, p less than 0.005) and reduced mean arterial pressure from 96 +/- 11 to 86 +/- 15 mm Hg (p less than 0.005). Intravenous diltiazem resulted in a small decrease in coronary flow reserve (peak-to-resting flow velocity ratio) from 3.9 +/- 1.2 to 3.6 +/- 1.1 (p less than 0.01). After intracoronary diltiazem, mean arterial pressure was unchanged (control 99 +/- 12 mm Hg, diltiazem 97 +/- 13 mm Hg), and heart rate was maintained constant by atrial pacing. Coronary flow reserve was unchanged at 3.8 +/- 0.9 at baseline and after intracoronary diltiazem. Thus, treatment with diltiazem does not invalidate the measurement of coronary flow reserve for diagnostic purposes. Furthermore, these results suggest that attenuation of maximal coronary dilation by diltiazem is not a mechanism responsible for its antianginal effects.