Detection of coronary artery disease by vasodilator thallium imaging of the heart with amyl nitrite inhalation: a pilot study.

Thallium imaging of the heart using dipyridamole-induced coronary arteriolar vasodilation has proven to be an effective means of detecting significant coronary stenosis. However, intravenous dipyridamole has not yet been made available for general use. We therefore examined the feasibility of substituting amyl nitrite inhalation as an arteriolar vasodilator prior to thallium imaging. Seventeen patients, all of whom had catheterization-proven coronary stenosis, inhaled amyl nitrite for 2-5 min. Thallium was injected after 45-60 s of inhalation. Completion of inhalation was followed immediately by planar imaging. Of 6 patients who inhaled amyl nitrite for at least 4 min, 5 had moderate or severe image defects on immediate scans which completely resolved on delayed scans. Only 3 of 11 who inhaled amyl nitrite for 2 min or less prior to scanning had similarly positive tests. Overall sensitivity for significant stenosis was 8 of 17 (47%). Inhalation was well tolerated with only one episode of angina and hypotension. We conclude that amyl nitrite inhalation for at least 4 min may offer an effective and readily available alternative to intravenous dipyridamole for vasodilator imaging of the heart.