Influence of Nitroglycerin on Myocardial Metabolism and Hemodynamics during Angina Induced by Atrial Pacing

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Abstract
Myocardial lactate extraction, arterial-coronary sinus difference (A-CS) of potassium (K + ), hemodynamics, and S-T segments were studied in 15 patients with coronary artery disease who developed angina during atrial pacing. The study consisted of the following periods: control (C 1 ), pacing (P 1 ), recovery (C 2 ), control after nitroglycerin (C GTN ), second pacing (P 2 ), and recovery. During C 1 , mean lactate extraction, S-T segments, and left ventricular end-diastolic pressure (LVEDP) were normal, and there was no myocardial K + loss. During P 1 the mean lactate production was –12.0%, mean K + loss –0.26 mEq/liter, and mean S-T segment depression 1.97 mm, while the average LVEDP remained unchanged, increasing when pacing was discontinued to a mean value of 23.3 mm Hg. These values returned to control levels by the time GTN was administered. After GTN there were significant decreases in mean cardiac index, LVEDP, brachial artery pressure, and left ventricular stroke work. During P 2 , eight subjects had no pain, five experienced less severe angina, mean lactate production and K + loss were abolished, S-T segments became less depressed (0.8 mm), and mean LVEDP decreased during pacing, rising only to 11.4 mm Hg when pacing was discontinued. Myocardial lactate production reverted to extraction in two patients and decreased in another two, whereas seven patients showed a decreased K + loss or uptake. It is concluded that GTN may prevent or reduce pacing-induced angina, as well as improve the electrocardiogram and hemodynamics, and in some patients decrease myocardial anaerobiosis.