The use of coronary vasodilators in myocardial imaging with ⁴³K

Abstract

As an alternative procedure to the exercise stress test used in myocardial scanning, vasoactive drugs were employed to elicit deficits in blood flow to myocardial regions supplied by stenotic arteries which maintain normal resting flow or collateral circulation. The data were collected from 35 dogs, some of which had partial stenosis (70–75%) on either major branch of the left coronary artery, and others which had Ameroid constrictor implants. The effects of lidoflazine, dipyridamole, and nitroglycerin on coronary hemodynamics and myocardial dispersion of potassium 43(⁴³K) in animals with partial stenosis were evaluated in ten acute experiments. In the pilot studies, four rapid serial rectilinear control scans from ⁴³K (750 μCi) were reported; dipyridamole (Persantin), lidoflazine, or nitroglycerin were then administered intravenously. When the selected drug reached a peak vasodilatative effect, a second equal bolus of ⁴³K was given and four additional scans recorded. The last scan from the first set was subtracted from the corresponding regional count rates of all serial scans from the second set, and the resulting images were interpreted to be myocardial perfusion patterns induced by the drug intervention. The later studies were performed by giving only a single isotope injection after administering the drug.

The control scans from dogs with partial stenosis or an Ameroid constrictor showed homogeneous distribution of the myocardial ⁴³K. When drugs were used, the region supplied by compromised circulation became apparent because of lower counts when compared to the normally perfused ones. Coronary vasodilators, as opposed to postexercise in myocardial imaging, have a lesser effect on cardiac dynamics, peripheral hemodynamics, and also double the ⁴³K uptake in normally perfused myocardium.