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Biomedical subjects

B Pitt

Publications and source records attributed to B Pitt.

At least 307 records · Page 17Linked to original sources
PubMed1977

Thallium 201 imaging and gated cardiac blood pool scans in patients with ischemic and idiopathic congestive cardiomyopathy. A clinical and pathologic study.

In ischemic cardiomyopathy (CM) fibrosis replaces large segments of myocardium, but in idiopathic congestive CM the myocardium contains only small foci of fibrosis or is morphologically normal. As coronary disease and myocardial infarction may be clinically silent, it is not always possible to distinguish ischemic from idiopathic congestive CM during life without cardiac catheterization. To determine whether noninvasive methods, thallium 201 myocardial (Tl) imaging and technetium 99m gated cardiac blood pool scans (GCBPS), could separate the entities, we evaluated radioisotope images of the heart in 13 patients with ischemic, and eight patients with idiopathic congestive CM, and 14 patients with normal hearts. Diagnosis was setablished by cardiac catherterization and/or autopsy in each of the 35 patients. The 14 normals could be readily distinguished from CM, and ischemic could be distinguished from idiopathic dilated CM in 20 of 21 patients. All patients with myocardiopathy showed hypokinetic and dilated left ventricles, but right ventricular dilatation was evident mainly in those with idiopathic CM. Tl images in the ischemic type had defects of greater than 40% of image circumference which corresponded to segmental wall motion abnormalities on GCBPS, whereas those with the idiopathic congestive form were homogeneous or had defects of less than 20% of image circumference. Autopsy studies in 7 of 35 patients correlated Tl defects of greater than 20% of circumference with transmural myocardial fibrosis.

Adult↗
PubMed1977

Left ventricular and coronary angiographic anatomy. Relationship to ventricular irritability in the late hospital phase of acute myocardial infarction.

Late hospital phase ventricular arrhythmias in acute myocardial infarction (MI) have been associated with a high incidence of sudden death following hospital discharge. Thirty-eight patients were studied 10-24 days following onset of symptoms of MI. Each patient had a 24-hour ambulatory ECG tape recording and left ventricular and coronary angiography performed. Patients with complicated ventricular arrhythmias (multiform, coupled, R on T VPCs or ventricular tachycardia), when compared to those with uncomplicated ventricular arrhythmias (unifocal or no VPCs), had a greater number of proximally narrowed major coronary arteries (P less than 0.001), a higher coronary "score" (P less than 0.001), a greater incidence of previous myocardial infarction (P less than 0.005), a greater percentage of abnormal left ventricular segments 86% vs 69% (P less than 0.001) and lower ejection fractions. These data suggest that late hospital phase survivors of MI with complicated ventricular arrhythmias have more extensive coronary artery disease with greater left ventricular dysfunction than survivors with uncomplicated ventricular arrhythmias. This more extensive disease may result in increased areas of ischemic myocardium and may help explain the refractoriness of these arrhythmias to pharmacologic therapy.

Acute Disease↗
PubMed1977

Hypercontractile cardiac states simulating hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) or idiopathic hypertrophic subaortic stenosis (IHSS) has been defined as an autosomal dominant myocardial disease characterized by specific physical findings, echocardiographic features, asymmetric septal hypertrophy and disordered myocardial architecture. Echocardiographic and scintiphotographic studies failed to reveal evidence of asymmetric septal hypertrophy in four patients with systolic anterior movement of the mitral valve and the typical ausculatory and peripheral pulse abnormalities characteristic of HCM. Postmortem examimination in one patient demonstrated mild concentric left ventricular hypertrophy and a normal arrangement of myocardial muscle fibers. These observations in four patients demonstrate that both systolic anterior movement of the mitral valve and the physical findings characteristic of HCM are not specific for the autosomal dominant myocardial disease characterized by asymmetric septal hypertrophy and abnormal septal histology.

Adult↗
PubMed1977

The extraction of thallium-201 by the myocardium.

The concentration of thallium-201 in the myocardium immediately following injection of tracer is the result of both blood flow delivering tracer to the heart and extraction by the myocardium. In these studies, the extraction of thallium-201 by the canine myocardium was determined as a function of heart rate, coronary blood flow, hypoxia, changes in pH, and following administration of propranolol, insulin, and strophanthin. Under basal conditions, extraction fraction measured 88 +/- 2.1%, following pacing to a rate of 195 beats/min extraction fraction remained unchanged at 88.5%. Similar results were found with changes in pH, propranolol, insulin, and strophanthin. Hypoxia caused a significant decrease in extraction fraction to 77.9%. When coronary blood flow was increased in excess of demands by drugs, extraction fraction fell logarithmically.

Acidosis↗
PubMed1977

Analysis of left ventricular function from multiple gated acquisition cardiac blood pool imaging. Comparison to contrast angiography.

Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease. The contrast ventriculograms were analyzed frame by frame to generate a volume versus time curve for each patient, while the tracer data were analyzed by two methods: 1) the standard method, in which the left ventricle is identified on the end-diastolic frame and the background corrected activity under the region of interest obtained from the entire cardiac cycle, and displayed as a time versus activity curve; and 2) by a semi-automatic method in which the computer applies a threshold detection program to define the ventricular borders, and activity in the chamber at each point in the cardiac cycle is defined after background correction. The tracer data in each patient were analyzed independently by four observers. The tracer data correlated with the contrast data on a point by point basis r = 0.87 for the standard method, and 0.93 for the semi-automatic technique. An F test of variance revealed the semi-automatic method superior to the standard approach (P less than 0.05).

Computers↗
PubMed1977

The use of 201thallium for myocardial perfusion imaging in sarcoid heart disease.

Cardiac dysfunction due to systemic sarcoidosis is most of ten due to severe restrictive pulmonary diseases. Although the diagnosis is frequently missed during life, direct granulomatous infiltration of the myocardium may occur with systemic sarcoidosis and, when present in the heart, is a major cause of death. To explore the possible use of radioactive 201thallium, a new agent for myocardial imaging, for improved clinical recognition of sarcoid heart disease, myocardial perfusion imaging with 201Tl was performed in six normal volunteers and in five patients with documented systemic sarcoidosis and clinically apparent cardiac dysfunction. Two of the patients with sarcoidosis had severe restrictive pulmonary disease. Their myocardial perfusion scans revealed relatively uniform uptake of 201Tl by the left ventricle, similar to that found in the normal volunteers; however, the right ventricular uptake of 201Tl and right ventricular thickness in these two patients with sarcoidosis was greater than normal. The other three patients with sarcoidosis had unexplained congestive heart failure, mitral regurgitation, or arrhythmias. Myocardial perfusion imaging in these patients revealed normal right ventricular uptake of radioactivity but segmental defects in the left ventricle compatible with an infiltrative disease of the myocardium. Segmental myocardial infiltration by sarcoid was confirmed by autopsy in one of these patients and at operation in another. Thus, myocardial imaging with 201Tl may provide a noninvasive technique for the improved clinical recognition of primary myocardial sarcoid and for distinguishing it from cardiac dysfunction secondary to pulmonary disease.

Adult↗
PubMed1977

Thallium-201: non-invasive determination of the regional distribution of cardiac output.

Sapirstein (1) employed cationic radiopotassium to determine the fractional distribution of cardiac output to several organs. Thallium-201 can substitute for radiopotassium in myocardial imaging, and was evaluated in the present studies to determine the distribution of cardiac output in the anesthetized dog in comparison with tracer microspheres, both under control circumstances and following the infusion of norepinephrine in a dose sufficient to raise the blood pressure 20 mm Hg above control levels. The concentrations of thallium-201 and microspheres were similar in the heart, kidney, thyroid, and skeletal muscle in both control and norepinephrine-treated animals (r=0.93). Thallium concentration in the liver and lung exceeded that of microspheres, however, and probably is not related solely to the regional distribution of arterial perfusion. These data suggest that in the heart, kidney, thyroid, and skeletal muscle, thallium-201 distribution reflects the fractional distribution of cardiac output.

Animals↗
PubMed1977

Determination of extraction fraction by a double-tracer method.

A relatively simple dual-tracer method for measuring renal extraction fraction was compared with the direct method. In the dual-tracer method an extracted and nonextracted tracer are mixed together and administered into the arterial circuit and samples of venous blood are obtained. The ratio of recovered to injected tracer then determines the extraction fraction. In the direct method tracer is administered directly into the renal artery and the total venous effluent is collected. Extraction fraction is then calculated as arteriovenous difference divided by the quantity injected. In our experiments the extraction for 201Tl and 203Hg-chlormerodrin were determined. The extraction fraction for 201Tl averaged 81 +/- 5% by the direct method and 81 +/- 6% by the dual-tracer technique (r = 0.94). The extraction fraction for 203Hg-chlormerodrin was found to change as a function of the renal blood flow. At normal flow the extraction fraction averaged 48% by the direct method and 45% by the dual-tracer technique. At reduced flow, in contrast, it averaged 78% by the direct method and 71% by the dual-tracer technique.

Animals↗
PubMed1976

Common procedures for the noninvasive determination of regional myocardial perfusion, evaluation of regional wall motion and detection of acute infarction.

A brief description is given of imaging techniques to record and analyze the myocardial perfusion scan, study changes in segmental wall motion, measure ejection fraction and ventricular volumes and detect acute myocardial infarction. Attention to the details of collimation, pulse height analyzer settings, intrinsic resolution of the imaging device and quality of the tracers utilized for these studies will permit information of high quality to be obtained from subjects with use of these noninvasive techniques.

Cardiac Output↗
PubMed1976

Myocardial perfusion imaging and gated cardiac blood pool scanning: clinical application.

Myocardial perfusion imaging with thallium-201 and gated cardiac blood pool scanning are finding increasing use in clinical cardiology. These noninvasive techniques have been found useful in detecting myocardial infarction independent of the electrocardiogram and determining the site and extent of the infarct as well as its effect on left ventricular function. These studies provide important prognostic data and are proving to be of value in evaluating patients with cardiogenic shock. Neither the thallium-201 myocardial perfusion image nor the gated cardiac blood pool scan can distinguish between acute and chronic myocardial damage. In clinical situations where this is important, infarct avid imaging with technetium-99m pyrophosphate allows determination of whether a given perfusion defect or wall motion abnormality is acute. Myocardial perfusion imaging with thallium-201 at rest and after exercise is also proving to be of value in evaluating patients with suspected ischemic heart disease. Initial studies suggest that the technique may be more sensitive than exercise electrocardiography and is of special value in minimizing the occurrence of false positive exercise tests for the diagnosis of ischemic heart disease. The combined tracers technique is also of value in the evaluation of patients undergoing coronary bypass graft surgery and those with cardiomyopathy.

Angina Pectoris↗
PubMed1976

Effect of nitroglycerin on ventricular fibrillation threshold of nonischemic myocardium.

The threshold for ventricular fibrillation induced by a 200 msec train of pulses was measured during a control period and during an intravenous infusion of nitroglycerin in 14 nonischemic open chest dogs. Infusion of nitroglycerin in doses sufficient to reduce mean arterial blood pressure an average of 17 mm Hg was associated with a rise in ventricular fibrillation threshold from a control value of 24 +/- 3 (mean +/- 1 standard error of the mean) to 41 +/- 6 milliamperes (P less than 0.001). In a subgroup of six animals simultaneous infusions of nitroglycerin and phenylephrine abolished the hypotensive effect of nitroglycerin but did not significantly alter the rise in ventricular fibrillation threshold observed with nitroglycerin infusion alone. In five other animals mean arterial blood pressure was similarly reduced an average of 17 mm Hg by venous hemorrhage, but was associated with a lowering than a rise in ventricular fibrillation threshold from a prehemorrhage value of 28 +/- 6 to 15 +/- 2 milliamperes, (P less than 0.005). Thus, intravenously administered nitroglycerin raises ventricular fibrillation threshold in nonischemic canine myocardium independent of its hypotensive effects.

Action Potentials↗
PubMed1976

Myocardial imaging in the noninvasive evaluation of patients with suspected ischemic heart disease.

Three noninvasive radioactive tracer techniques for evaluating patients with ischemic heart disease are described: (1) myocaridal perfusion imaging, (2) acute infarct imaging, and (3) the gated blood pool scan. Myocardial perfusion imaging with tracers that distribute in the myocardium in relation to regional blood flow allows detection of patients with transmural and nontransmural infarction by the finding of decreased tracer concentration in the affected region of the myocardium. If these tracers are injected at the time of maximal stress to patients with significant coronary arterial stenosis but without infarction, areas of transient ischemia can be identified as zones of decreased tracer concentration not found when an examination is performed at rest. Acute infarct imaging with tracers that localize in acutely damaged tissue permits separation of patients with acute myocardial necrosis from those without infarction and those with more chronic damage. The gated blood pool scan permits assessment of left ventricular function and regional wall motion. The measurement of ventricular volumes, ejection fraction and regional wall motion adds significantly to the determination of hemodynamic variables in assessing patients with acute infarction. The technique also permits detection of right ventricular dysfunction. Performance of a combination of these radioactive tracer techniques is often advantageous, particularly in patients with suspected infarction. The techniques can establish whether infarction is present, whether it is acute, where the damage is located and how extensive it is; they can also provide a measure of the effect of this damage on left ventricular function.

Acute Disease↗
PubMed1976

Measurement of regional myocardial blood flow in dogs using a catheter semiconductor radiation detector.

Simultaneous total left coronary and regional myocardial blood flow were measured by injecting 85Kr into the left coronary artery and recording its clearance using a precordial gamma detector and a catheter tip beta detector (CASRAD) placed directly on selected regions of the myocardium. There were no significant differences between total left coronary (175 ml-100 g-1/min) measured by the precordial gamma detection and regional myocardial blood flow (183 ml-100 g-1/min) determined in the area of the left anterior descending coronary artery (LAD) by the beta detector in five open chest dogs. After ligation of the LAD regional clearance of 85Kr ceased in the area of myocardium distal to the ligation while total coronary blood flow decreased only slightly from 152 to 126 ml-100 g-1/min. Measurement of regional myocardial blood flow by CASRAD may be of value in determining the extent of myocardial ischaemia in experimental animals and assessing the effect of therapeutic interventions.

Animals↗
PubMed1976

Effects of intravenous nitroglycerin on left ventricular function and ST segment changes in acute myocardial infarction.

It has been shown previously that 30-minute infusions of intravenous nitroglycerin in patients with acute myocardial infarction are able to lower left ventricular filling pressure and improve left ventricular function while lowering mean arterial pressure by only 7 mmHg (0.9 kPa). A decrease in sigmaST in praecordial ST segment mapping studies during nitroglycerin infusion in patients with anterior infarction suggested a decrease in the extent of myocardial ischaemia. In the present study, 30 patients with acute myocardial infarction received 1- to 3-hour infusions of intravenous nitroglycerin at infusion rates sufficient to lower mean arterial pressure by an average of 22 mmHg (2.9 kPa). An improvement in ventricular function was noted in that subgroup of patients with the msot severe left ventricular dysfunction. All patients with anterior myocardial infarction underwent serial ST segment mapping and, irrespective of the presence or absence of left ventricular failure, showed a decrease in sigmaST during nitroglycerin infusion (P less than 0.005). These findings suggest that infusion of nitroglycerin improves left ventricular function and/or alters left ventricular compliance in patients with left ventricular failure complicating myocardial infarction and furthermore decreases sigmaST in all patients, irrespective of the presence or absence of left ventricular failure, suggesting that the extent of myocardial ischaemia is decreased.

Acute Disease↗
PubMed1976

Gallium-67 myocardial imaging for the detection of bacterial endocarditis.

Eleven patients with a clinical diagnosis of bacterial endocarditis underwent scintillation scanning of the precordial region 2-7 days after the intravenous administration of 3 mCi of gallium-67 citrate. Seven had positive scans, 3 of which were confirmed by postmortem imaging at autopsy. Serial images revealed the scans to be frequently negative at 48 hours and positive from 3 to 8 days following injection. Uptake was not seen in the region of the myocardium 48 hours or longer after the injection of 15 patients without endocarditis used as controls.

Adult↗
PubMed1976

Effect of ethyl adenosine on myocardial flow after coronary artery occlusion.

The effect of ethyl adenosine-5'-carboxylate hydrochloride (EA) was determined in 17 dogs by the radioactive microsphere technique. In both experimental and control animals, microspheres were injected 5 min before (preocclusion period), 60 min after (occlusion period), and 75 min after (saline or vasodilation period) ligation of the left anterior descending coronary artery (LAD). Ten seconds prior to the third microsphere injection, saline was administered to five control animals, and saline with 0.5 mg/kg of EA was given to 12 experimental animals. There was no significant change in myocardial blood flow after saline injection. After EA, mean arterial pressure fell 10% (P less than .001); myocardial blood flow increased 275% (P less than .001) in the nonischemic left circumflex artery (CIRC) area and increased 82% (P less than .01) in the occluded LAD area. In addition, those animals with extensive collateral development showed a significantly greater increase in collateral blood flow than those with minimal collateral development (P less than .05). Thus, EA may increase flow to ischemic areas of myocardium dependent upon the extent of preexistent collateral supply.

Adenosine↗