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Biomedical subjects

B Pitt

Publications and source records attributed to B Pitt.

At least 289 records · Page 16Linked to original sources
PubMed1978

Myocardial imaging with thallium-201: a multicenter study in patients with angina pectoris or acute myocardial infarction.

A multicenter study of rest and exercise thallium-201 myocardial imaging in 190 patients from five centers was performed. Exercise images were obtained after graded treadmill or bicycle stress with use of five different gamma camera models and were interpreted by the originating investigator without knowledge of other clinical data. Of 42 patients with less than 50 percent coronary stenosis, 4 (10 percent) had a resting image defect, 1 (2 percent) a new exercise defect and 5 (12 percent) either a resting or an exercise image defect, or both. Of 148 patients with coronary stenosis of 50 percent or greater, 64, (45 percent) had an image defect in the study at rest, 90 (61 percent) had new or increased defects after exercise, and 115 (78 percent) had resting or exercise defects, or both. New exercise image defects were more common than exercise S-T depression (90 of 148 [61 percent] versus 62 of 148[42 percent]; P less than 0.01). In a second group of 111 patients with acute myocardial infarction studied at three centers, 90 patients (81 percent) had image defects compared with 71 (64 percent) two had new electrocardiographic Q waves (P less than 0.01). Smaller infractions, as assessed with serum enzyme values, and diaphragmatic infarctions were less commonly detected than larger or anterior infarctions. These findings suggest that myocardial imaging complements the electrocardiographic identification of acute myocardial infarction of exericse-induced myocardial ischemia.

Acute Disease↗
PubMed1978

Coronary angiography and left ventriculography in survivors of transmural and nontransmural myocardial infarction.

Recent studies have suggested a similar prognosis for patients with transmural myocardial infarction and nontransmural myocardial infarction despite a smaller infarct size in the latter patients estimated by creatine phosphokinase (CPK). Thirty-one patients with transmural myocardial infarction and 17 patients with nontransmural myocardial infarction as defined by electrocardiographic criteria underwent coronary angiography and left ventriculography from 10 to 24 days after they had an acute myocardial infarction. Forty-three of these 48 patients were asymptomatic following their myocardial infarction. When compared to patients with nontransmural myocardial infarction, those with transmural myocardial infarction had greater peak CPK levels, 1,090 +/- 210 versus 290 +/- 60 IU (p less than 0.01). There was no difference in prevalence of single, double or triple vessel coronary artery disease, mean number of coronary arteries 50 per cent narrowed (2.0 +/- 0.2 versus 2.0 +/- 0.2), near total or total occlusions, coronary score (Friesinger) (7.9 +/- 0.6 versus 8.2 +/- 0.7), left ventricular ejection fraction (48 +/- 2 versus 53 +/- 4), or per cent of akinetic-dyskinetic myocardial segments (66 of 242 [27 per cent] versus 32 of 132 [24 per cent]) between two groups. The similar extent of coronary artery narrowing and degree of left ventricular dysfunction may explain the similar prognosis for patients with transmural myocardial infarction and those with nontransmural myocardial infarction despite differences in enzymatically estimated acute infarct size.

Adult↗
PubMed1978

Thallium-201 distribution in the thyroid: relationship to thyroidal trapping function.

Experiments were undertaken to determine the behavior of thallium-201 in the thyroid in relation to the iodide-trapping mechanism in rats. Iodide trapping was compared to thyroidal thallium-201 trapping 30 minutes after intravenous injection. Thallium-201 uptake followed iodide uptake in control rats. TSH- and T3-treated rats but did not decrease in the same manner as iodide concentration in perchlorate-treated rats. These studies suggest that thallium-201 distribution in the thyroid may reflect the cationic side of the iodide pump or possible thyroidal blood flow.

Animals↗
PubMed1978

The use of videotape for off-line viewing of computer-assisted radionuclide cardiology studies.

Videotape offers an inexpensive method for off-line viewing of dynamic radionuclide cardiac studies. Two approaches to videotaping have been explored and demonstrated to be feasible. In the first, a video camera in conjunction with a cassette-type recorder is used to record from the computer display scope. Alternatively, for computer systems already linked to video display units, the video signal can be routed directly to the recorder. Acceptance and use of tracer cardiology studies will be enhanced by increased availability of the studies for clinical review. Videotape offers an inexpensive flexible means of achieving this.

Computers↗
PubMed1978

Clinical comparison of cardiac blood pool visualization with technetium-99m red blood cells labeled in vivo and with technetium-99m human serum albumin.

Technetium-99m red blood cells (Tc-RBC) labeled by an in vivo technique were compared with two preparations of Tc-99m human serum albumin (HSA) for cardiac blood-pool imaging. Relative distribution of the tracers was analyzed on end-diastolic frames of gated blood-pool studies and on whole-body (head to mid-thigh) anterior pinhole images. The Tc-RBC demonstrated greater relative percentage localization in the cardiac blood pool, higher target-to-background ratios in the left ventricle, and less liver concentration. For cardiac blood-pool imaging, Tc-RBC labeled by the in vivo approach appears to be superior to the two Tc-HSA preparations studied.

Cardiac Volume↗
PubMed1977

Sudden death in the year following myocardial infarction. Relation to ventricular premature contractions in the late hospitals phase and left ventricular ejection fraction.

Both depressed left ventricular ejection fraction and ventricular arrhythmias have been associated with a poor prognosis following acute myocardial infarction. To assess the relative role of each of these parameters in predicting mortality in the early period after hospitalization for myocardial infarction, 24 hour ambulatory electrocardiographic tape recordings and gated cardiac blood pool scans were obtained in 81 patients approximately two weeks after their admission to the hospital for myocardial infarction. Lown class 0 to II ventricular premature contractions during this period were classified as uncomplicated ventricular arrhythmias and Lown class III to V ventricular premature contractions were classified as complicated ventricular arrhythmias. Ejection fraction was calculated from biplane images of gated cardiac blood pool scans. In 35 patients the ejection fraction was greater than or equal to 0.40; only three of these had complicated ventricular arrhythmias. In 45 patients the ejection fraction was less than 0.40; 26 of these had complicated ventricular arrhythmias. Eight patients had documented ventricular fibrillation or instantaneous death during a mean 7.0 moonth (range 2 to 16 months) follow-up period outside the hospital. Although the number of patients studied was small, and there were only eight sudden deaths, life table analysis projected a one year mortality of 66 per cent in patients with complicated ventricular arrhythmias and 31 per cent in patients with an ejection fraction less than 0.40. All eight patients who died suddenly were in the subgroup of 26 patients with an ejection fraction less than 0.40 and complicated ventricular arrhymias; none was in the subgroup of 19 patients with an ejection fraction less than 0.40 and uncomplicated ventricular arrhythmias (P less than 0.02). Although a low ejection fraction may suggest a poor prognosis following myocardial infarction, the presence of complicated ventricular arrhythmias significantly increases the risk of sudden cardiac death in the early period after hospitalization in patients with low ejection fraction.

Arrhythmias, Cardiac↗
PubMed1977

Cardiovascular nuclear medicine.

Exciting developments in radiopharmaceuticals and instrumentation have established the field of cardiovascular nuclear medicine as an extremely useful clinical tool. Depending on the patient's problem, one may elect to perform myocardial perfusion images with 201Tl, infarct avid images with 99m Tc, or wall motion and other functional studies with multiple gated acquisition techniques. Often, a combination of these studies is useful in elucidating a particular problem.

Acute Disease↗
PubMed1977

Thallium-201 as a myocardial imaging agent.

The field of myocardial perfusion imaging has made many advances but still is in its infancy. The limitations in the technology at this time include limited instrument resolution of 6-9 mm, intrinsic at the energy of the mercury x-ray; significant Rayleigh scatter, which is particularly distrubing because this scatter cannot be removed by pulse-height analysis; and an effective half-life of thallium in the myocardium, which makes repeated imaging over a short period of time very difficult. Although hopes for the development of a technetium-labeled myocardial imaging tracer have burnt brightly, no new agents are presently in sight. Resolution with a technetium-labeled tracer would almost double that of thallium, and the dose that could be administered to the patient would increase by at least a factor of 4. The effective half-life of the tracer in the myocardium would permit multiple images to be obtained at least in the same day. Even with the limitations of the current techniques, however, myocardial perfusion imaging can make a real contribution to the care of the patients with heart disease. Thallium is now produced commercially and reasonably easily obtained. Extraction of thallium by the myocardium is probably somewhat, but not exactly, analogous to potassium. The tracer has major applications in defining shape and size of the heart, thickness of muscle, and especially myocardial ischemia and infarction. This review is aimed at providing a current perspective of these uses.

Alcoholism↗
PubMed1977

Time course of ventricular fibrillation threshold in infarcted and non-infacted myocardium after acute coronary ligation.

The time course of the ventricular fibrillation threshold (VFT) was studied in 10 open-chest mongrel dogs following acute occlusion of the left anterior descanding coronary artery (LAD). The VFT in the infarcted area was compared to a non-infarcted area of the left ventricle supplied by the circumflex coronary artery. Prior to coronary occlusion the mean VFT for the entire group of 10 animals was 14 ma. for the area supplied by the LAD and 17.6 ma. for the area of the left circumflex. Immediately after coronary ligation the VFT decreased in both areas. Within 90 to 120 minutes the VFT in the infarcted area was 27 ma. and after 6 hours of occlusion the VFT was 3 times the pre-ligation value. The VFT in the non-infarcted area remained near the pre-ligation values. The excitability of the infarcted area was markedly decreased after coronary occlusion and this accounted for the increase in the VFT in the infarcted area. In the non-ischemic area the excitability was unchanged during the entire six hour period following occlusion. The study stresses the importance of the location of the electrodes used for fibrillation and the natural course of the VFT in evaluating VFT's within the ischemic myocardium.

Animals↗
PubMed1977

Noninvasive detection of subcritical coronary arterial narrowings with a coronary vasodilator and myocardial perfusion imaging.

Myocardial perfusion imaging after administration of the potent coronary vasodilator ethyl adenosine-5'-carboxylate, which increases flow to normal areas in excess of that to areas supplied by subcritically stenosed vessels, was investigated as a nonischemia-producing stimulus for detecting subcritical coronary stenosis. Preliminary studies in 10 dogs with reactive hyperemia were performed with thallium-201 and potassium-43 to determine which tracer was a better indicator of increased flow. Neither agent was a linear indicator of increased flow caused by reactive hyperemia but thallium-201, because of its imaging characteristics, was selected as a flow indicator after administration of ethyl adenosine. Five dogs were studied after placement of a subcritical stenosis on the left circumflex coronary artery. Strontium-85 microspheres were injected into the left atrium after placement of the stenosis to verify that changes in resting blood flow were only minimal. Thereafter, intravenous administration of ethyl adenosine was followed by injection of chromium-51-labeled microspheres into the left atrium and intravenous administration of thallium-201. The mean ratio of left circumflex to left anterior descending coronary arterial flow was 0.96 +/- 0.16 for the control experiment after subcritical stenosis; after administration of the vasodilator the ratio of activity levels in the two arteries was 0.43 +/- 0.09 with the chromium-51 microspheres and 0.56 +/- 0.07 with thallium-201. Imaging performed in three additional dogs after injection of microspheres in the presence of subcritical stenosis revealed a normal pattern, whereas imaging after administration of the vasodilator and thallium-201 revealed a perfusion deficit. In two additional dogs without subcritical stenosis, thallium was administered after injection of ethyl adenosine to determine that the drug alone did not cause perfusion deficits. The perfusion scans in these two dogs were normal. These studies suggest that a coronary vasodilator and thallium-201 myocardial imaging can be used to detect subcritical coronary stenosis.

Adenosine↗
PubMed1977

Effects of atrial pacing on regional myocardial gas tensions with critical coronary stenosis.

Changes in myocardial carbon dioxide (PmCO2) and oxygen tension (PmO2) measured by mass spectrometry have been shown to reflect quantitatively progressive degrees of regional myocardial ischemia associated with stepwise reduction in coronary blood flow. The present study utilized mass spectrometry to assess the severity of regional myocardial ischemia developing during atrial pacing in the presence of a flow-limiting proximal critical coronary artend subendocardial layers was measured by the radioactive microsphere technique. Application of a "critical stenosis" resulted in a 6-mmHg decrease in PmO2 and a 17-mmHg increase in PmCO2 in the region of the myocardium supplied by the stenosed vessel. The addition of atrial pacing resulted in a 3-mmHg further decrease in Pmo2 and a 40-mmHg further increase in PmCO2. In the region of myocardium supplied by the critically stenosed vessel MBF increased in the subepicardial layer, but decreased or remained unchanged in the subendocardial layer. The failure of myocardial blood flow to increase in deeper myocardial layers in response to the increased myocardial oxygen demand of atrial pacing would provide a mechanism for the development of subendocardial ischemia in the presence of a critical coronary stenosis.

Animals↗
PubMed1977

Thallium-201 myocardial perfusion imaging at rest and during exercise. Comparative sensitivity to electrocardiography in coronary artery disease.

The sensitivity of myocardial perfusion imaging (MPI) using thallium-201 injected both at rest and during peak exercise was compared to simultaneously recorded 12 lead electrocardiography (ECG) for the detection of transient ischemia in 20 normal subjects and 63 patients with coronary artery disease (CAD). No significant perfusion defects or ECG changes were seen on either the rest or exercise studies in any of the normal subjects. Fifty-six percent of patients with CAD developed new perfusion defects with exercise compared to 38% who developed ischemic ST-segment depression (P less than 0.02). However, when chest pain and/or ST depression were considered indices of ischemia, the sensitivity of exercise testing and thallium-201 MPI was similar. The increased sensitivity of MPI compared to ST-segment depression on the ECG was due to patients with baseline ECG abnormalities and those who failed to achieve 85% of predicted maximum heart rate with exercise. Analysis of the exercise results according to the extent of coronary artery disease revealed a progressive increase in both positive ECGs and MPI with the number of vessels involved. In patients with single vessel disease the MPI was more sensitive than the ECG (P less than 0.02). The combination of the rest and exercise ECG, MPI and chest pain during exercise failed to identify 11% of patients with CAD. Exercise thallium-201 MPI is a useful adjunct to conventional exercise testing particularly when evaluating patients with abnormal resting ECGs, those who develop ventricular conduction defects of arrhythmias during exercise, and those who fail to achieve their predicted heart rate because of fatigue or breathlessness.

Adult↗