Newer technologies for study of the action of nitrates in coronary circulation and myocardial function.

Minimally invasive evaluation of the behavior of the right and the left ventricle can be obtained in a dynamic way by using technetium-99 (99Tc) scintographic ventriculography. The "first pass" technique is particularly appropriate to the investigation of short-acting agents, such as nitroglycerin and other nitrates, but information on a 1-minute to 2-minutes steady state response can be obtained by using the "gated blood pool" method. Studies in patients with and without coronary heart disease have identified apparent improvement in regional and global left ventricular ejection fractions associated with afterload reduction caused by such interventions. However, part of the normalization of regions of previously abnormal myocardial contraction may be due to more uniform transmural distribution of coronary blood flow. Such techniques, including nitrate administration, have been used to define regional ischemia suitable for revascularization procedures. Sequential thallium studies also suggest that nitroglycerin reduces or prevents stress induced ischemia, although the mechanism (afterload versus coronary vasodilation) has not been completely elucidated. In the future subtraction angiographic techniques may lead to a more accurate estimate of regional distribution of blood flow and its pharmacologic manipulation. Digital techniques will also facilitate accurate measurement of coronary vascular narrowing in a manner that will serve to elucidate the direct actions of nitrates and similar substances on the coronary circulation.