Bertram Pitt

Effect of Ischemia and Antianginal Drugs on the Distribution of Radioactive Microspheres in the Canine Left Ventricle

Radioactive microspheres were used to estimate the changes in regional myocardial blood flow occurring during acute myocardial ischemia. Carbonized 15-μ spheres were injected into the left atrium of 28 open-chest dogs and the radioactivity of selected areas determined after sacrifice. Acute occlusion of the left circumflex coronary artery produced a significant diminution in the proportion of microspheres reaching the circumflex area. In addition, there was a disproportionate decrease in endocardial radioactivity in the ischemic area (endocardial/epicardial radioactivity ratio falling from 1.17 to 0.76, P < 0.001) but not in the nonischemic area. Both nitroglycerin (0.4 mg) and propranolol (1 mg/kg) failed to cause a significant change in the ratio of circumflex to descendens radioactivity during ischemia. They did, however, cause a significant increase in the ratio of endocardial to epicardial radioactivity in both ischemic and nonischemic areas.

A scintiphotographic method for measuring left ventricular ejection fraction in man without cardiac catheterization

A radioactive tracer method for the measurement of left ventricular ejection fraction in man without cardiac catheterization is described. The tracer (99mtechnetium-labeled albumin) is injected intravenously. Images of the heart at end-systole and end-diastole are obtained using a scintillation camera and an electronic gate triggered by the patients electrocardiogram. Each image is composed of 300,000 counts, representing a summation of 200 to 400 heartbeats at end-systole and end-diastole. An outline of the left ventricular free wall is drawn from each gated image. The position of the aortic and mitral valve planes is determined using a radionuclide angiogram obtained at the time of tracer injection. Left ventricular ejection fraction is calculated from the area and length of the long axis of the ventricular outline at end-systole and end-diastole. Determinations of ejection fraction in 20 patients using this tracer method were correlated with measurements obtained by contrast cineangiography with the following results: ejection fraction r = +0.92, P < 0.001; end-diastolic volume r = −0.76, P < 0.001; and end-systolic volume r = −0.75, P < 0.001.

The Role of Furosemide in the Treatment of Left Ventricular Dysfunction Associated with Acute Myocardial Infarction

Fifteen patients with acute myocardial infarction and an elevated pulmonary capillary wedge pressure were given 40 mg furosemide intravenously within 24 hr of diagnosis of infarction. We divided the patients into two groups on the basis of the diuretic response to furosemide: nine who responded with a diuresis of greater than 400 ml in two hours, and six with a lower diuresis. The nine patients who responded well had a 35% fall in pulmonary capillary wedge pressure, from 21 to 12 mm Hg (P < 0.01), accompanied by a small but significant decrease in arterial pressure at the end of two hours. There was no apparent increase in left ventricular function in these patients as shown by the relationship of left ventricular filling pressure and stroke work index, but all survived. The nonresponders failed to show significant hemodynamic changes, were significantly older, had a higher serum urea nitrogen (SUN) than the responders and had higher pulmonary capillary wedge pressures. Despite further therapy with much higher doses of furosemide and digitalis, five of the six nonresponders (83%) died. Furosemide is of value in relieving pulmonary congestion in patients with moderate congestive heart failure associated with myocardial infarction. It should be given cautiously, as an initial dose of 40 mg intravenously may cause a large fall in cardiac output and systemic pressure in occasional patients. Furosemide cannot, however, be recommended as the primary therapeutic agent in patients with severe left ventricular dysfunction complicating acute myocardial infarction.

Myocardial Blood Flow in Pacing-Induced Angina

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 patients (group I), who developed ischemia, manifested either by typical angina or ischemic electrocardiographic changes during PIT, myocardial blood flow increased 32 ml/min/100 g of tissue (P < 0.001). In 17 patients (group II), who did not develop ischemia, myocardial blood flow increased 12 ml/min/100 g of tissue (P < 0.02). The increase in group I patients was significantly greater than in group II (P < 0.02). Myocardial oxygen consumption increased 4.63 ml/min/100 g of tissue (P < 0.01) in ischemic responders (group I) and 2.62 ml/min/100 g of tissue in nonischemic responders (group II). It is concluded that patients with an ischemic response to pacing-induced tachycardia had a greater increase in myocardial blood flow and myocardial oxygen consumption than patients who did not develop an ischemic response. This unexpected finding is best explained by an increased myocardial blood flow in the nonischemic areas of the myocardium which may result from a vasodilator response to ischemia.

Myxoma of the Left Atrium Hemodynamic and Phonocardiographic Consequences of Sudden Tumor Movement

Two patients with myxoma of the left atrium were studied by left heart catheterization and cineangiography, and the diagnosis was confirmed at operation in both cases. An electrocardiographic timing signal on the cineradiographs permitted correlation of heart sounds and pressure waves with movement of the tumor between the left atrium and the left ventricle. In early systole, the tumor suddenly moved from the left ventricle to the left atrium, and a notch in the rising left ventricular pressure, a prominent c wave, and loud, late elements of the first sound were noted. In early diastole, the tumor moved rapidly through the mitral valve, causing an abrupt diminution in the left atrial volume, thus causing a rapid y descent despite severe obstruction of the mitral valve. An early diastolic sound, thought to be an opening snap, appeared to be related to the checking of the tumor in the left ventricle (“tumor plop”).The unusual left atrial pressure pulse seen in these two cases resembles data from other cases of myxoma reported in the literature, and recognition of these unusual pressures may permit accurate preoperative diagnosis in other patients. Diagnostic changes may be present on apexcardiograms.

Exercise tolerance in patients with angina pectoris: Daily variation and effects of erythrityl tetranitrate, propranolol and alprenolol☆

Abstract One hundred exercise tolerance tests were performed in 10 hospitalized male patients with typical angina pectoris during 5 consecutive days to (1) evaluate the test to test variation, (2) quantitate the training effect of repeated testing, and (3) compare the immediate effects of placebos, propranolol, alprenolol, erythrityl tetranitrate and the additive actions of erythrityl tetranitrate with propranolol, and with alprenolol. The intraindividual standard deviation from one exercise to another was ± 10.8 percent of the work performed. There was no evidence that repeated testing resulted in improved exercise tolerance attributable to training or conditioning. Propranolol, alprenolol and erythrityl tetranitrate improved exercise tolerance significantly. Synergistic effect of erythrityl tetranitrate and propranolol, and erythrityl tetranitrate and alprenolol were evident in only 2 of the 10 patients.

Activation of the Plasma Kallikrein System During Myocardial Ischemia

Sicuteri (1) and a number of other investigators have postulated that the kallikrein system may play a role in the hemodynamic response to myocardial ischemia and may be responsible for the associated anginal pain. This hypothesis is based upon the observation that bradykinin has been shown to be a potent coronary vasodilator (2) and in addition is known to cause pain (3).

The Effect of Cardiopulmonary Bypass Perfusion Pressure on Myocardial Gas Tensions in the Presence of Coronary Stenosis

Mass spectrometry was utilized to determine myocardial gas tensions in dogs subjected to cardiopulmonary bypass. Myocardial ischemia occurred in animals with normal coronary arteries when cardiopulmonary bypass perfusion pressure fell 40 to 60 mm Hg below the mean aortic pressure measured prior to bypass. Myocardial ischemia did not occur, or could be eliminated when present, if cardiopulmonary bypass perfusion pressure was maintained near prebypass mean aortic pressure. In animals with constricted circumflex coronary arteries, the adverse effect of low perfusion pressure on myocardial metabolism during cardiopulmonary bypass was found to be more severe in areas of myocardium supplied by the stenotic coronary artery. It is concluded that maintenance of cardiopulmonary bypass perfusion pressure near the level of preoperative mean aortic pressure will help prevent myocardial ischemia during operation; particularly in patients with coronary artery disease.

Myocardial blood flow as a determinant factor in the electrical stability of the myocardium

Abstract The role of regional myocardial blood flow on the electrical stability as determined by ventricular fibrillation threshold (VFT) was evaluated in 12 dogs during subendocardial and transmural ischemia. With selective subendocardial ischemia produced by partial stenosis of left anterior descending coronary artery (LAD), both VFT and myocardial blood flow (MBF) decreased 66.6 per cent (p After ligation of LAD, VFT in the subepicardium and subendocardium of LAD fell 74.6 per cent (p 1. 1. During selective subendocardial ischemia produced by partial stenosis of the LAD, VFT and MBF showed a parallel decline in the LAD subendocardial zone, suggesting a direct relationship between these parameters. 2. 2. Following LAD ligation with production of transmural ischemia, the entire left ventricle became electrically unstable, as measured by VFT, independent of regional myocardial blood flow. This suggests that factors other than MBF significantly influence electrical instability during transmural ischemia.

Determination of the Site, Extent, and Significance of Regional Ventricular Dysfunction during Acute Myocardial Infarction

Infarct site, extent, and the degree of associated asynergy are major determinants of the hemodynamic consequences of myocardial infarction. Although conventional electrocardiography and vectorcardiography are routinely employed in assessing the location and size of infarction, they are relatively nonspecific. The newer techniques of high-frequency electrocardiography and isopotential mapping offer promise but have yet to undergo systematic evaluation. A rough measure of the extent of infarction is obtained from serum enzyme measurements. However, they furnish no information with regard to localization.The region of infarction may be detected by precordial scanning following the intravenous or intracoronary injection of a radioisotope. The infarct may be revealed as an area of decreased perfusion (cold spot) or as an area to which a specific radioactive label is bound (hot spot). With the availability of newer radionuclides such as 43potassium and the use of computer techniques, a more precise means of localizing and quantifying myocardial infarction may become available.Optimal definition of asynergy is obtained with contrast angiography. However, the risk of this procedure has limited its use, to date, in acute myocardial infarction. Apex- and kinetocardiography, chest X-ray, and fluoroscopy often suggest regional ventricular dysfunction, but these techniques are not sufficiently specific. Newer noninvasive methods for objectively evaluating regional ventricular dysfunction are ECG-gated cardiac scintiphotography and radarkymography. With ECG-gated scintiphotography, end-diastolic and end-systolic cardiac isotope images are obtained following intravenous injection of 99mtechnetium-albumin. From these images, assessment of asynergy and extent and location of infarct can be made. With radarkymography, heart-wall motion is assessed and quantitated by tracking segments of the cardiac silhouette visualized on a cinefluorogram. These techniques are ideally suited to the acutely ill patient. Echocardiography is another noninvasive technique with potential application to the study of asynergy. However, at present, only posterior-wall motion can be measured.At the time of surgery regions of infarction may be localized by means of chemical indicators (fluoroscein), isotope techniques, or epicardial electrocardiographic mapping. Recently much has been learned about the hemodynamics of myocardial infarction. Through the use of the techniques described, further insight into regional ventricular abnormality and extent and localization of myocardial infarction could be obtained. With this information better approaches to therapy and prognosis could be developed.Many students of the coronary circulation must have noted that the ventricular zone affected by ligating a large coronary branch not only appears cyanotic and dilated, but that it seems to alter in its mode of contraction. The detailed and sequential changes in contraction are not easily followed by the unaided eye and so far have not been recorded myographically. The reasons for this were the lack of an adequate and suitable myograph and a technique for the application of one to a limited ventricular surface so that records obtained represent, at least reasonably well, changes in muscle length and not predominantly artifacts due to position changes, thrusts and vibrations of the vigorously beating ventricle.1