Effects of dipyridamole and aminophylline on hemodynamics, regional myocardial blood flow and thallium-201 washout in the setting of a critical coronary stenosis

Abstract

Experiments were performed to characterize the interaction of intravenous dipyridamole and aminophylline on thallium-201 transport kinetics, regional myocardial blood flow and systemic hemodynamics in the presence of a critical coronary artery stenosis. In 12 dogs with a critical left anterior descending coronary artery stenosis, arterial pressure decreased from a mean value (+/- SEM) of 107 +/- 6 to 94 +/- 3 mm Hg (p less than 0.05) and distal left anterior descending artery pressure decreased from 70 +/- 7 to 55 +/- 4 mm Hg (p less than 0.05) after intravenous administration of dipyridamole (0.25 mg/kg body weight). In the left anterior descending perfusion zone, the endocardial/epicardial flow ratio decreased from 0.70 to 0.36 and the intrinsic thallium washout rate was significantly prolonged. Intravenous aminophylline (5 mg/kg) reversed the dipyridamole-induced systemic hypotension and transmural coronary steal and restored the thallium washout rate to baseline values. In six other dogs, aminophylline alone resulted in no alterations in systemic and coronary hemodynamics or regional myocardial blood flow. As expected, dipyridamole-induced vasodilation and coronary steal were prevented by aminophylline pretreatment. These data show that in a canine model of partial coronary stenosis, systemic hypotension, adverse regional flow effects (coronary steal) and prolonged thallium-201 washout consequent to intravenously administered dipyridamole are promptly reversed by intravenous aminophylline administration. Aminophylline alone had no significant hemodynamic and coronary flow effects. This study provides further insight into the altered thallium kinetics occurring as a consequence of dipyridamole-induced vasodilation and suggests that the prompt reversal of symptoms and signs of ischemia with aminophylline in patients receiving intravenous dipyridamole for clinical imaging studies probably reflects the reversal of transmural coronary steal.

Quantitative relation between hemodynamic changes during intravenous adenosine infusion and the magnitude of coronary hyperemia

“…There were no significant changes in systolic, diastolic, or mean arterial blood pressure during adenosine infusion. These findings are consistent with prior reports in experimental (13) and human studies (3)(4)(5)14). The increase in HR with adenosine is likely the result of sympathetic activation caused by direct stimulation of chemoreceptors in the carotid body (15) and, in some patients, by an exaggerated peripheral vasodilator response (14).…”

DETECTION OF MYOCARDIAL ISCHEMIA BY ELECTRON BEAM CT. Experimental studies

“…The steal effect of dipyridamole explains the mechanism of contrast improvement in our experiments. The mechanism is a decrease of poststenotic flow after vasodilatation, which has been observed in thallium scans (12). Dipyridamole did not significantly increase myocardial perfusion of the unobstructed flow bed in our study, which is explained by the combined effect of anesthesia and muscle relaxation.…”

Can Stress-induced Phase Change be Observed on ^99mTc Pharmacological Stress Myocardial Perfusion Imaging?

“…"True" ischemia induced by pharmacological stress is usually considered to be due to the steal phenomenon, which is not common, but can occur in cases of severe ischemia. It can occur not only in the circumferential and longitudinal directions (i.e., inter-coronary steal) (15,16), but also in the vertical direction (i. e., transmural steal), which can lead to myocardial dysfunction (17,18). In our study, patients with severest ischemia exhibited phase changes between the stress and resting conditions.…”