The pharmacodynamics of nitroglycerin have been studied in dogs and man. In dogs, intravenous nitroglycerin (TNG) caused a decrease in left ventricular work, myocardial blood flow (MFB), and myocardial oxygen consumption, and no significant change in coronary vascular resistance. Intracoronary artery TNG in dogs caused an immediate increase in MBF and a decrease in coronary vascular resistance that persisted until arterial pressure fell. In man, sublingual TNG (0.4 mg.) caused a decrease in left ventricular work, MBF, and myocardial oxygen consumption, and no significant decrease in coronary vascular resistance in patients with and without arteriographically proven coronary artery disease. The injection of doses of 0.1 to 0.2 mg. of TNG directly into the coronary artery in man caused an immediate increase in MBF and a decrease in coronary vascular resistance in patients with and without arteriographically proven coronary artery disease. The hypothesis proposed for the mechanism of action of TNG in the relief of angina pectoris is first, a decrease in coronary vascular resistance due to its effect on the coronary circulation, and, secondly, a decrease in cardiac work due to its effect on the systemic circulation.

SUMMARYThe phases of systole were measured in 51 patients with acute myocardial infarction and three control groups: (1) a group of 40 patients without heart disease, (2)

SUMMARYLeft bundle-branch block (LBBB) was found to be associated with an unusually short left main coronary artery in 11 T HE frequent association of left bundlebranch block (LBBB) with cardiovascular disease,1-particularly coronary artery disease and hypertensive heart disease,3 often results in the implication that for all patients with this conduction disturbance the prognosis is poor. However, isolated LBBB in asymptomatic, apparently healthy persons has been shown to be associated with a relatively good prognosis,3' 8 suggesting that there may be two distinct populations of subjects with this electrocardiographic abnormality The clinical and laboratory features with special attention to the coronary arteriographic findings in 12 patients with left bundle-branch block are reported here.

ANGIOCARDIOGRAPHY and cineangiocardiography are employed with increasing frequency for the diagnosis of cardiovascular diseases. These commonplace technics of cardiovascular radiology depend upon the rapid injection of radiopaque materials into the heart or central circulation. A wide variety of substances are in use, but all are hypertonic and some are considerably more viscous than blood. A variety of studies are available to indicate that the hemodynamic effects can be related to chemical structure, -3 but as newer and safer agents have become available it seems clear that the pharmacodynamic effects are related most importantly to the hypertonicity of these compounds. The effects of the injection of oontrast media can therefore be considered to be the effects of hypertonicity on the circulation, and the study of these effects assumes considerable practical importance.Numerous reports are available that deal with the effects of hypertonic (and radiopaque) materials injected into the right heart and pulmonary circulation in animals,4-10 but comparable systematic studies in man are not available. The hemodynamic consequences associated with the injection of radiopaque ma-From the

Current methods of measuring myocardial blood flow using 133xenon have failed to separate normals from patients with ischemic heart disease at rest. In the present study such a separation was attempted by utilizing pacing-induced tachycardia (PIT) to stress the myocardium. 133Xenon was injected into the left coronary artery to measure blood flow in 27 patients at rest and during pacing-induced tachycardia. Oxygen content was simultaneously measured in the aorta and coronary sinus of 13 of these patients. Pacing rates of 150 beats/min or greater were obtained in 21 patients. In 10

A total of 58 observations of simultaneous left ventricular pressure and apex-cardiograms (ACG) was made on 18 patients. An a wave percentage amplitude (aWPA) of greater than 15% of the total deflection of the ACG indicated an increase in left ventricular end-diastolic pressure (LVEDP). In 12 observations on six patients, an aWPA of less than 15% was associated with a high LVEDP. Patients with high LVEDP and aWPA of less than 15% had a high early left ventricular diastolic pressure with further rise in pressure prior to atrial contraction. These patients had small LV a waves ("atrial kick"). The aWPA of the ACG correlated better with the magnitude of the LV a wave than the absolute level of LVEDP in all patients. Correlation was good between changes in aWPA and changes in LVEDP in individual patients; but the ACG as an indirect means of evaluating left ventricular function is limited by the fact that elevations in LVEDP can exist in the presence of a normal aWPA. The ACG is a complex tracing reflecting not only intracardiac pressures, but changes in left ventricular volume, compliance, position, and perhaps left atrial function as well.

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