BOLUS INTRAVENOUS NITROGLYCERIN PREDOMINANTLY REDUCES AFTERLOAD IN PATIENTS WITH EXCESSIVE ARTERIAL ELASTANCE

Objectives. We hypothesized that bolus intravenous nitroglycerin would be an afterload-reducing agent in patients with excessive initial aft erload for their level of left ventricular systolic function. Converse ly, bolus intravenous nitroglycerin should be a preload-reducing agent in patients without excessive initial afterload. Background. Although nitroglycerin has both preload- and afterload-reducing actions, metho ds to predict its predominant site of action in an individual patient have not been previously described. Methods. Left ventricular pressure -volume relations were recorded with micromanometer and conductance ca theters during bolus injection of intravenous nitroglycerin in 27 pati ents with both normal left ventricular systolic function and varying d egrees of congestive heart failure. Preload was determined by end-dias tolic volume, afterload by effective arterial elastance, left ventricu lar systolic function by end-systolic elastance and coupling of afterl oad and ventricular function by the ratio of effective arterial elasta nce to end-systolic elastance (E(a)/E(es) ratio). An E(a)/E(es) ratio > 1 was defined as excessive afterload for the level of ventricular fu nction. Results. Patients with an initial E(a)/E(es) ratio < 1 (Group 1) constituted a group of normotensive patients with intact ventricula r function who exhibited a predominant reduction in preload in respons e to intravenous nitroglycerin. Those with an initial E(a)/E(es) ratio > 1 and normal or mildly depressed ventricular function (Group 2a) co nstituted a group of patients, most of whom were hypertensive, who exh ibited a predominant afterload reduction. Finally, those with an initi al E(a)/E(es) ratio > 1 and abnormal ventricular function (Group 2b) c onstituted a group of patients with clinical congestive heart failure who exhibited both preload and afterload reduction but a predominant a fterload reduction because stroke volume increased. Conclusions. Patie nts with normal arterial elastance and ventricular function respond to nitroglycerin with a predominant preload reduction, whereas patients with either excessive arterial elastance or abnormal ventricular funct ion respond with a predominant afterload reduction.