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R M Steingart

Publications and source records attributed to R M Steingart.

34 records · Page 2Linked to original sources
PubMed1987

Lack of effect of prior training on subsequent ischaemic and infarcting myocardium and collateral development in dogs with normal hearts.

To determine whether exercise training in animals with normal coronary arteries has a salutary effect on ischaemic myocardium, 24 dogs were randomly assigned to be either trained or confined to cages for three months. All dogs then underwent left thoracotomy for placement of indwelling right and left atrial and aortic catheters and a loose snare ligature around the proximal left circumflex coronary artery. Three days after operation control scintigrams were recorded after injection of thallous chloride-201 in animals running on a treadmill to achieve exercise heart rates of 220 beats.min-1. Four days later the snares were pulled to occlude the left circumflex artery and infarct size determined by measuring venous activity of creatine phosphokinase. Three days after infarction the first post-ligation scintigram was performed after thallium-201 injection in exercising animals. Exercise scans were repeated at 10 days and 2, 4, and 6 weeks after coronary ligation. During the final exercise study collateral blood flow was measured with radioactive microspheres. There was no difference in mean creatine phosphokinase appearance time, peak creatine phosphokinase activity, or measured infarct size between the trained and sedentary dogs. The ratio of thallium-201 activity in left circumflex artery or ischaemic area to left anterior descending artery or normally perfused myocardium fell from 100% before occlusion to 86.6% in the sedentary animals and 80.6% in the trained dogs three days after coronary ligation. Although these falls were significant (p less than 0.025 and p less than 0.005 respectively), there was no difference between groups. Over the next five and a half weeks the scintigraphic defect shrank as the thallium-201 ratio gradually increased, but changes were again similar in both groups. At six weeks there was little difference in exercise collateral flow to left circumflex artery myocardium and flow to normal myocardial tissue in cage confined and trained dogs. Therefore, no beneficial effect of exercise training in dogs with normal hearts could be seen on ischaemic or infarcting myocardium or coronary collateral development after coronary ligation.

Animals↗
PubMed1987

Sex bias in considering coronary bypass surgery.

Cardiovascular nuclear medicine exercise studies may serve as a screening method to be used in making decisions to refer patients for catheterization and coronary artery bypass surgery. In a study of 390 patients consecutively referred for nuclear exercise testing, abnormal results found in 31% of the women and in 64% of the men affected physicians' decisions to recommend catheterization in men only; 4% of the women with abnormal radionuclide scans were referred for catheterization compared with 40% of the men (p less than 0.001). this 10:1 ratio was independent of age. A multiple logistic regression analysis that controlled for age, previous myocardial infarction, presence of typical and atypical angina, and abnormal test results yielded an odds ratio of 6.3 for men. The male-to-female ratio of patients with coronary artery disease given abnormal results of a cardiovascular nuclear scan is only 2:1. Thus, the sex differential in decisions to refer patients for cardiac catheterization cannot be explained entirely by differences in the sensitivity of tests or the rates of coronary artery disease; it also cannot be explained by differential benefits from surgery. These findings raise the question of whether coronary artery bypass surgery is underused in women.

Aged↗
PubMed1986

Thallium-201 scintigraphic quantitation of regional flow disparity and subsequent redistribution in dogs.

Although quantitative analysis of postexercise thallium-201 (201Tl) scintigrams has been employed clinically for the diagnosis of coronary disease, the precise relationship of the quantitated defects to microsphere determined blood flow has not been determined. Accordingly, 201Tl was injected during exercise in 12 control dogs and seven with left circumflex (LCf) artery stenosis. Gamma camera scanning was started 10 min after 201Tl injection and continued for 3 hr. In the control animals, scintigraphic 201Tl activities in left anterior descending (LAD) and LCf perfusion territories were equal 10 min after 201Tl injection and the loss of 201Tl activity over 3 hr was 54.3 +/- 3.4% and 57.0 +/- 3.6% (mean +/- s.e.e.) of initial LAD and LCf activity, respectively (p = N.S.). In the experimental group, LCf activity 10-14 min after 201Tl injection averaged 67.4 +/- 5.9% of LAD activity in the same heart (p less than 0.001). Furthermore, LCf activity in the experimental animals was significantly lower than LCf activity in the control dogs (p less than 0.005), while LAD activities were not different in the two groups. The ratio of LCf/LAD scintigraphic 201Tl activity immediately after exercise was linearly related to, but higher than, the ratio of regional blood flows at peak exercise (r = 0.88, p less than 0.001) as determined by microsphere injection. Scintigraphic redistribution was also correlated with directly measured redistribution determined by well counter analysis (r = 0.83, p less than 0.025). Thus, in this exercise model, quantitative 201Tl scintigraphy accurately assessed the initial postexercise flow disparity and subsequent redistribution.

Animals↗
PubMed1985

Exercise thallium-201 scintigraphy in dogs: effects of long-term coronary occlusion and collateral development on early and late scintigraphic images.

To examine the effects of coronary collateral development on thallium-201 (201Tl) distribution the left circumflex coronary artery was ligated in eight dogs. Three days later these animals ran on a treadmill, and 201-thallous chloride was injected into the right atrium at peak exercise. Scintigraphic scanning was begun within 10 min and continued for 3 hr. Scanning was repeated weekly for 6 weeks. In the last week radioactive microspheres were injected into the left atrium at peak exercise to measure regional myocardial blood flow. The scintigraphically determined disparity between perfusion of the ischemic and normal myocardium was most marked at 3 days after ligation. This difference gradually lessened over the first 4 weeks until there was no difference in 201Tl distribution to normally perfused myocardium and tissue distal to the ligation. Concomitant with the improvement in the scintigrams, exercise hemodynamics also improved over this 4 week period with significant increases in cardiac output and decreases in left atrial pressure. Serial coronary angiographic studies in two animals demonstrated the appearance of collaterals in the initial weeks after coronary occlusion, and by 4 weeks the left circumflex artery distal to the obstruction was completely opacified by collateral flow. The ratio of directly measured exercise blood flow to the left circumflex and normally perfused tissues was 0.89 +/- 0.08 at 6 weeks after ligation. Scintigraphic 201Tl redistribution after 3 hr also changed over the weeks after ligation. Three days after ligation washout from the ischemic area was significantly slower than that from the normal myocardium. By 6 weeks loss of 201Tl from the two regions occurred at nearly equal rates. Thus myocardial perfusion and function during exercise after coronary occlusion are dynamic events that change with time. It is likely that coronary collateral development is responsible for these phenomena. Therefore coronary collaterals do have salutary effects in the dog.

Animals↗
PubMed1985

Maintenance of exercise stroke volume during ventricular versus atrial synchronous pacing: role of contractility.

Although atrial synchronous and rate-responsive ventricular pacing have been compared, the importance of maintaining synchronized atrial systole in addition to rate responsiveness has been incompletely defined. That is, the effects of these two pacing modes on cardiac volumes and contractility have not been studied. Accordingly, 16 patients with normal ventricular function were studied while in the upright position and at rest with gated radionuclide ventriculography during both atrial synchronous and ventricular pacing. Twelve of these patients were also studied during low-level upright exercise (300 kilopond-meters). Rest and exercise ventricular pacing heart rates were matched to those recorded with synchronous pacing. Ventricular volumes were determined with a counts-based method. The ejection fraction and peak systolic pressure/end-systolic volumes or contractility between the two pacing modes. However, during exercise to identical heart rates, blood pressures, and workloads, although stroke volume was the same during exercise with atrial synchronous and ventricular pacing (78 +/- 13 vs 75 +/- 12 ml), end-diastolic and end-systolic volumes were lower with ventricular pacing than with atrial synchronous pacing (end-diastolic volume 101 +/- 13 vs 113 +/- 16 ml, p less than .001; end-systolic volume 26 +/- 4 vs 35 +/- 7 ml, p less than .001). Stroke volume during ventricular paced exercise was maintained at atrial synchronous pacing levels by means of increased contractility (ejection fraction of 74 +/- 4% during ventricular pacing vs 69 +/- 5% during atrial synchronous pacing, p = .002; peak systolic pressure/end-systolic volume ratio of 6.51 +/- 1 during ventricular pacing vs 4.85 +/- 1 during atrial synchronous pacing, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Radionuclide ventriculographic responses to graded supine and upright exercise: critical role of the Frank-Starling mechanism at submaximal exercise.

To assess the influence of work load and posture on the response to exercise, 25 patients with coronary artery disease (CAD) and 17 normal subjects underwent graded supine and upright exercise radionuclide ventriculography. In both groups, end-diastolic counts increased with supine exercise (p less than 0.001). The ejection fraction and peak systolic pressure-end-systolic volume relation increased in normal subjects (p less than 0.02), but not in patients with CAD. At upright rest, end-diastolic counts decreased in both groups (p less than 0.001) and then increased with exercise (p less than 0.001). The increase in end-diastolic counts was most pronounced on the transition from upright rest to the 150-kpm work load and resulted in a significant increase in stroke counts (p less than 0.05) for both patients with CAD and normal subjects, without a measurable change in the ejection fraction or the peak systolic pressure-end-systolic volume relation. Later in exercise, end-diastolic counts plateaued, and the ejection fraction and the peak systolic pressure, end-systolic volume relation increased only among normal subjects. Thus, low-level upright exercise is highly dependent on the Starling mechanism in both normal subjects and patients with CAD, with enhanced contractility apparent only during more vigorous exercise in normal subjects.

Blood Pressure↗
PubMed1984

Use of electrocardiographic-thallium exercise testing in clinical practice.

Although there is a great deal of data on the accuracy of combined electrocardiographic-thallium exercise testing, little is known about the use of these tests in clinical practice. A quantitative likelihood system was employed to characterize referral patterns for such testing, and the impact of test results on the likelihood of coronary artery disease was examined. Two hundred thirteen subjects consecutively referred for the purpose of establishing or excluding the presence of coronary artery disease were studied. No subject had a history of a prior myocardial infarction. By historical evaluation, 96 had a low likelihood of coronary disease (less than or equal to 0.20), 88 an intermediate likelihood (0.21 to 0.80) and 29 a high likelihood (greater than 0.80). As anticipated from theoretical analyses, testing produced the greatest shifts in disease likelihood in subjects with an intermediate pretest disease likelihood, and confirmed the historical evaluation in patients at the extremes of pretest disease likelihood. Therefore, although electrocardiographic-thallium stress testing is best suited for subjects with intermediate pretest disease likelihood, the majority of referrals had either a high or low likelihood. Clinicians appear to value confirmatory results in patients at the extremes of pretest disease likelihood. Electrocardiographic exercise testing would serve a similar purpose.

Coronary Disease↗
PubMed1983

Radionuclide ventriculographic study of adaptations to exercise in aortic regurgitation.

Exercise-gated radionuclide ventriculography has been proposed as a method to evaluate cardiac reserve in patients with aortic regurgitation (AR). Characterization of ventricular function, however, in AR is complicated by the dynamic nature of the leak in individual patients and by variations in severity among patients. Twenty patients with isolated AR were studied to assess the effects of exercise on the regurgitant index. The regurgitant index (left ventricular divided by right ventricular stroke counts) estimates the severity of the leak. The regurgitant index at rest was significantly higher in patients with AR than in patients without AR (3.46 +/- 1.25 versus 1.08 +/- 0.16, p less than 0.001). In patients with AR, the regurgitant index decreased during exercise to 2.6 +/- 0.8 (p less than 0.001), whereas it did not change in the control group (1.16 +/- 0.21, difference not significant). Further, in patients with AR, the greater the regurgitant index at rest, the greater the decrease during exercise (y = 0.56x -- 1.08, r = 0.78, p less than 0.001). End-diastolic counts and stroke count responses from rest to exercise were highly variable, but were explained in part by the decreasing regurgitant index. These data support previous catheterization studies and confirm gated radionuclide ventriculography as a useful tool for monitoring adaptations to exercise in AR.

Adolescent↗
PubMed1982

Gamma camera quantitation of thallium-210 redistribution at rest in a dog model.

Defects seen at rest on thallium-201 (201TI) scintigraphy can disappear over time. We obtained sequential 5-minute scans over 127 +/- 9.4 minutes in seven open-chest dogs with fixed, stable regional flow reductions (normal zone flow 0.76 +/- 0.09 ml g-1/min, ischemic zone flow 0.49 +/- 0.04 ml g-1 min [mean +/- SEM], p less than 0.05) as determined by microsphere injection. Sequential 5-minute scans were obtained after i.v. injection of 1.5 mCi of 201TI. Data were stored in a 64 x 64 pixel computer matrix. Qualitatively, defects that showed redistribution were seen in all dogs. Quantitatively, greater count loss from peak activity distinguished the normal zone, but overlap was great. Alternate quantitative methods using background subtraction altered the characteristics of the time-activity curves, but did not enhance the separation of ischemic from normal zones. Patterns of 201TI redistribution from gamma camera imaging are profoundly influenced by the method of quantitation. No single method of quantitative analysis separated ischemic from normal zones in all dogs. The clinical significance of patterns at rest requires redefinition.

Animals↗
PubMed1981

Physiologic Intervention in Cardiovascular Nuclear Medicine.

Homeostasis of cardiac output is maintained by a complex intergration of many physiologic responses, both central and peripheral, including pulse,the contractile state of the ventricle, and pre-and after load. In the abnormal ventricle at rest, any or all of the measurable parameters that define left ventricular function may be normal. However, in disease states, exercise can provoke abnormalities in these parameters indicating a reduction in myocardial reserve. Regional asynergy occurs in patients with significant ischemic heart disease during exercise reflecting a local supply-demand mismatch. Recently, radionuclide ventriculography has been combined with exercise techniques in attempts to elucidate details of the normal and abnormal ventricular response to stress noninvasively. The majority of data describe the response of the ventricle during graded supine bicycle exercise. The normal response is to increase myocardial contractility, reducing end-systolic volume, while end-diastolic volume remains constant. This results in an increase in ejection fraction. In ischemic ventricles, regional asynergy develops and ejection fractions may either fall or fail to rise. This appears to be accomplished by an increase or no change in the end-diastolic volume, with an increase in end-systolic volume, particularly in patients with angina during exercise. Radionuclide methods can be applied to large mumbers of patients providing informaton that is unobtainable by more invasive procedures. This review traces the development of knowledge of the ventricular response to exercise, emphasizing the role of radionuclide ventriculography. Although radionuclide angiography has the capacity for advancing the understanding of the ventricular response to exercise, the technical limitations of this technique in specific diagnostic conditions has yet to be defined adequately.

Angiography↗
PubMed1981

Pharmacologic intervention in cardiovascular nuclear medicine procedures.

Relevant questions in ischemic heart disease are (1) what is the ischemic threat? (2) What is the extent of ventricular dysfunction? (3) Is the observed dysfunction reversible? Exercise testing can help to identify the ischemic threat. Catheterization studies have shown that resting ventricular dysfunction can be reversed in some patients through pharmacologic or surgical intervention. However, improved ventricular performance in ischemic heart disease may be achieved through a variety of mechanisms. Insight into all components of cardiac performance (regional and global contractillity, preload, afterload, and heart rate) and myocardial perfusion may be required to adequately describe the influence of intervention. Exercise radionuclide ventriculographic studies have demonstrated that stress-induced ventricular dysfunction can be reversed through surgical and pharmacologic intervention. Studies at rest have demonstrated that radionuclide techniques can detect drug-induced changes in ventricular performance in groups of patients. The challenge to cardiovascular nuclear medicine is the prospective identification of patients who would benefit most from aggressive intervention aimed at preventing or reversing ischemic ventricular dysfunction.

Arteries↗
PubMed1980

Pulsed doppler echocardiographic measurement of beat-to-beat changes in stroke volume in dogs.

Measurement of stroke volume by pulsed Doppler echocardiography has not been validated against a reference method in vivo. We compared Doppler systolic frequency shift integrals with electromagnetic flowmeter stroke volume in seven open-chest dogs. A pulsed Doppler echocardiographic transducer was held on the aortic arch with the sample volume in the ascending aorta. Stroke volume was varied by epinephrine or pentobarbital infusions, fluid administration or inferior vena caval construction. Linear regression analysis of stroke volume vs Doppler systolic frequency shift integrals revealed strong correlations and intercepts close to zero (tau = 0.74-0.096, rho less than 0.001). Minor changes in transducer position did not influence Doppler frequency shift integrals substantially. Therefore, pulsed Doppler echocardiography served as an excellent measurement of stroke volume changes in model. However, serious limitations are presented that may limit its clinical application.

Animals↗
PubMed1980

Myocardial visualization on a perfusion lung scan.

Myocardial activity was noted on a lung scan performed following the i.v. administration of Tc-99m macroaggregated albumin. The patient had primary pulmonary hypertension with a right-to-left shunt through a functionally patent foramen ovale.

Adult↗
PubMedDate not supplied

TNK-tissue plasminogen activator compared with front-loaded alteplase in acute myocardial infarction: results of the TIMI 10B trial. Thrombolysis in Myocardial Infarction (TIMI) 10B Investigators.

BACKGROUND: Bolus thrombolytic therapy is a simplified means of administering thrombolysis that facilitates rapid time to treatment. TNK-tissue plasminogen activator (TNK-tPA) is a highly fibrin-specific single-bolus thrombolytic agent. METHODS AND RESULTS: In TIMI 10B, 886 patients with acute ST-elevation myocardial infarction presenting within 12 hours were randomized to receive either a single bolus of 30 or 50 mg TNK-tPA or front-loaded tPA and underwent immediate coronary angiography. The 50-mg dose was discontinued early because of increased intracranial hemorrhage and was replaced by a 40-mg dose, and heparin doses were decreased. TNK-tPA 40 mg and tPA produced similar rates of TIMI grade 3 flow at 90 minutes (62.8% versus 62.7%, respectively, P=NS); the rate for the 30-mg dose was significantly lower (54.3%, P=0.035) and was 65. 8% for the 50-mg dose (P=NS). A prespecified analysis of weight-based TNK-tPA dosing using median TIMI frame count demonstrated a dose response (P=0.001). Similar dose responses were observed for serious bleeding and intracranial hemorrhage, but significantly lower rates were observed for both TNK-tPA and tPA after the heparin doses were lowered and titration of the heparin was started at 6 hours. CONCLUSIONS: TNK-tPA, given as a single 40-mg bolus, achieved rates of TIMI grade 3 flow similar to those of the 90-minute bolus and infusion of tPA. Weight-adjusting TNK-tPA appears to be important in achieving optimal reperfusion; reduced heparin dosing appears to improve safety for both agents. Together with the safety results from the parallel Assessment of the Safety of a New Thrombolytic: TNK-tPA (ASSENT I) trial, an appropriate dose of this single-bolus thrombolytic agent has been identified for phase III testing.

Aged↗