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Biomedical subjects

G M Pohost

Publications and source records attributed to G M Pohost.

At least 145 records · Page 8Linked to original sources
PubMed1985

Comparison of exercise electrocardiography and quantitative thallium imaging for one-vessel coronary artery disease.

The relative value of exercise electrocardiography and computer analyzed thallium-201 imaging was compared in 124 patients with 1-vessel coronary artery disease (CAD). Of these, 78 had left anterior descending (LAD), 32 right and 14 left circumflex (LC) CAD. In patients with no previous myocardial infarction (MI), thallium imaging was more sensitive than the electrocardiogram (78% vs 64%, p less than 0.01), but in patients with previous MI, sensitivity was similar. Further, thallium imaging was more sensitive only in LAD and LC disease. Redistribution was compared with ST-segment depression as a marker of ischemia. Only in patients with prior MI (76% vs 44%, p less than 0.01) and only in LC and right CAD did redistribution occur more often than ST depression. Thallium imaging was more accurate in localizing stenoses than the electrocardiogram (p less than 0.001), but did not always correctly predict coronary anatomy. Septal thallium defects were associated with LAD disease in 84%, inferior defects with right CAD in 40% and posterolateral lesion defects with LC CAD in 22%. The results indicate the overall superiority of thallium imaging in 1-vessel CAD compared with exercise electrocardiography; however, there is a wide spectrum of extent and location of perfusion defects associated with each coronary artery. Thallium imaging complements coronary angiography by demonstrating the functional impact of CAD on myocardial perfusion.

Adult↗
PubMed1985

Increased thallium lung uptake after exercise in isolated left anterior descending coronary artery disease.

Increased thallium lung uptake during exercise correlates with an exercise-induced elevation in left ventricular filling pressure. This finding was analyzed in 48 patients with 1-vessel left anterior descending (LAD) coronary artery disease (CAD) before and after percutaneous transluminal coronary angioplasty. Patients were separated into 2 groups: 13 (27%) patients with increased (group 1) and 35 patients with normal thallium lung uptake (group 2). Compared with group 2, group 1 patients had more severe LAD luminal diameter narrowing (90 +/- 6% vs 81 +/- 11% [mean +/- standard deviation], p less than 0.003); slower clearance of thallium from the LAD territory segments (half-life 13.5 +/- 8.0 vs 6.5 +/- 5.0 hours, p less than 0.007); and more abnormal thallium segments per patient by quantitative criteria (p less than 0.02). After angioplasty, thallium lung uptake became normal in 12 of 13 patients in whom it was previously elevated. Increased thallium lung uptake after exercise occurs in 1-vessel LAD disease, and is related to the severity of ischemia by thallium scan and the severity of stenosis by angiography. Therefore, increased thallium lung uptake identifies a subset of patients with 1-vessel CAD with a greater amount of myocardium at risk.

Adult↗
PubMed1985

Value and limitations of radionuclide angiography in determining the cause of reduced left ventricular ejection fraction: comparison of idiopathic dilated cardiomyopathy and coronary artery disease.

The radionuclide angiograms of 59 patients with a left ventricular (LV) ejection fraction (EF) less than 0.40, 23 with idiopathic dilated cardiomyopathy (IDC) and 36 with coronary artery disease (CAD) were analyzed to assess the usefulness of radionuclide angiography in distinguishing these conditions. Mean right ventricular EF was lower in the IDC group than in the CAD group, 0.31 vs 0.45 (p less than 0.01). LV wall motion was scored from 3 (normal) to -1 (dyskinesia). The incidence of akinesia was similar in IDC and CAD groups, 70% and 83%, respectively. Dyskinesia was more common in the CAD group (42% vs 17%), but the difference was not statistically significant. Segmental wall motion analysis showed similar patterns of wall motion in both groups, with contraction best preserved in the anterobasal, posterobasal and superolateral segments. Patients in the CAD group had worse apical motion (p less than 0.01) and better wall motion in the anterobasal (p less than 0.05) and superolateral walls (p less than 0.01), compared with patients in the IDC group. To assess symmetry of contraction, a maximum difference score was derived for each patient. Symmetry (a score less than 1) was present in 5 IDC and no CAD patients, whereas asymmetry (a score of 2 or more) was present in 27 CAD and 7 IDC patients (p less than 0.01). Wall motion became more symmetric in both groups when LVEF was less than 0.20. Logistic regression analysis revealed that the maximum difference score was the best predictor of the diagnosis, but only because of better separation at the extremes of maximum difference score values.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Determination of cardiac risk by dipyridamole-thallium imaging before peripheral vascular surgery.

To evaluate the severity of coronary artery disease in patients with severe peripheral vascular disease requiring operation, we performed preoperative dipyridamole-thallium imaging in 54 stable patients with suspected coronary artery disease. Of the 54 patients, 48 had peripheral vascular surgery as scheduled without coronary angiography, of whom 8 (17 per cent) had postoperative cardiac ischemic events. The occurrence of these eight cardiac events could not have been predicted preoperatively by any clinical factors but did correlate with the presence of thallium redistribution. Eight of 16 patients with thallium redistribution had cardiac events, whereas there were no such events in 32 patients whose thallium scan either was normal or showed only persistent defects (P less than 0.0001). Six other patients also had thallium redistribution but underwent coronary angiography before vascular surgery. All had severe multivessel coronary artery disease, and four underwent coronary bypass surgery followed by uncomplicated peripheral vascular surgery. These data suggest that patients without thallium redistribution are at a low risk for postoperative ischemic events and may proceed to have vascular surgery. Patients with redistribution have a high incidence of postoperative ischemic events and should be considered for preoperative coronary angiography and myocardial revascularization in an effort to avoid postoperative myocardial ischemia and to improve survival. Dipyridamole-thallium imaging is superior to clinical assessment and is safer and less expensive than coronary angiography for the determination of cardiac risk.

Aged↗
PubMed1985

Clinical, angiographic, hemodynamic, perfusional and functional changes after one-vessel left anterior descending coronary angioplasty.

Percutaneous transluminal coronary angioplasty (PTCA) was successfully performed in 20 patients with 1-vessel left anterior descending (LAD) coronary artery disease. Exercise capacity in terms of peak workload, heart rate and systolic blood pressure all increased significantly 1 week after PTCA. All patients had some decrease in stenosis size and gradient. All patients except 1 had an improvement in functional class. Eight of 12 patients with abnormal exercise electrocardiograms before PTCA had normal electrocardiograms after the procedure. Exercise thallium-201 (TI-201) myocardial perfusion images obtained in all 20 patients before and 1 week after PTCA were analyzed using a new computer method designed to quantitate regional myocardial TI-201 distribution, redistribution and clearance rate. Significant improvement in TI-201 activity was present in the anterior and septal segments of the left ventricle 1 week after PTCA. This increase in TI-201 uptake was associated with a significant reduction in the amount of TI-201 redistribution between initial and delayed postexercise images in the same regions. TI-201 clearance rate in the segments supplied by the dilated vessel also improved significantly. Abnormal TI-201 lung uptake was seen in 17 patients before and in 4 patients after PTCA. Exercise ejection fraction response and septal wall motion also improved after PTCA of the LAD stenosis in all 17 patients who had exercise radionuclide ventriculography. Improvement in clinical, angiographic and hemodynamic factors as well as in global and regional myocardial perfusion and function occurs after PTCA for 1-vessel LAD coronary artery disease.

Adult↗
PubMed1985

Positive exercise thallium-201 test responses in patients with less than 50% maximal coronary stenosis: angiographic and clinical predictors.

The incidence and causes of abnormal thallium-201 (TI-201) myocardial perfusion studies in the absence of significant coronary artery disease were examined. The study group consisted of 100 consecutive patients undergoing exercise TI-201 testing and coronary angiography who were found to have maximal coronary artery diameter narrowing of less than 50%. Maximal coronary stenosis ranged from 0 to 40%. The independent and relative influences of patient clinical, exercise and angiographic data were assessed by logistic regression analysis. Significant predictors of a positive stress TI-201 test result were: (1) percent maximal coronary stenosis (p less than 0.0005), (2) propranolol use (p less than 0.01), (3) interaction of propranolol use and percent maximal stenosis (p less than 0.005), and (4) stress-induced chest pain (p = 0.05). No other patient variable had a significant influence. Positive TI-201 test results were more common in patients with 21 to 40% maximal stenosis (59%) than in patients with 0 to 20% maximal stenosis (27%) (p less than 0.01). Among patients with 21 to 40% stenosis, a positive test response was more common when 85% of maximal predicted heart rate was achieved (75%) than when it was not (40%) (p less than 0.05). Of 16 nonapical perfusion defects seen in patients with 21 to 40% maximal stenosis, 14 were in the territory that corresponded with such a coronary stenosis. Patients taking propranolol were more likely to have a positive TI-201 test result (45%) than patients not taking propranolol (22%) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Angiography↗
PubMed1985

The persistent defect on exercise thallium imaging and its fate after myocardial revascularization: does it represent scar or ischemia?

Persistent defects on serial thallium scans are commonly thought to represent fibrosis or scar. However, such a pattern may also represent severe ischemia. To better understand persistent defects, exercise thallium and resting gated blood pool scans were reviewed in 52 patients pre and post coronary angioplasty for single-vessel left anterior descending (LAD) coronary artery disease, and the fate of persistent defects after successful revascularization was determined. Persistent and transient defects were defined from the average scores of three observers. Ten patients with 16 myocardial segments with persistent defects were compared to another 11 patients with 20 myocardial segments with transient defects. After angioplasty (PTCA), 75% of the regions that had persistent defects and 85% of the regions that had transient defects were normal by visual assessment. In the persistent defect group, only regional wall motion on the resting gated blood pool scan pre PTCA helped to distinguish those segments that would or would not revert to normal. We conclude that regions of persistent defect on thallium scan often revert to normal after PTCA (75%), suggesting that persistent defects may represent hypoperfusion of viable myocardium, and should not preclude consideration of an intervention.

Adult↗
PubMed1985

Decrease in the ability to detect elevated lung thallium due to delay in commencing imaging after exercise.

Post-exercise elevation of the lung/myocardial thallium ratio and a high lung clearance rate between initial and delayed images have been reported to be markers for exercise-induced left ventricular (LV) dysfunction associated with coronary artery disease (CAD). We performed thallium exercise tests on 60 patients, 42 with CAD, in order to determine the effect of delaying initial imaging on detection of elevated lung thallium. In addition to images obtained at 2 minutes and at 2 hours after exercise, 18-minute images were also obtained to simulate such a delay. Because of rapid isotope clearance in those with initially elevated lung activity, there was decreased sensitivity of both the initial lung/myocardial ratio and lung thallium clearance for detecting CAD, using the 18-minute image as the initial post exercise study. We conclude that initial imaging should be done in the anterior view early after exercise to optimize detection of elevated lung thallium.

Adult↗
PubMed1985

Quantitative split dose thallium-201 imaging with exercise: a technique for obtaining rest and exercise perfusion images in one setting and markedly reducing the study time.

In the current study, a technique for performing serial thallium imaging after two separate tracer injections was applied to exercise thallium imaging, thus allowing the acquisition of rest and exercise images within 1 hour. Twenty-four patients with and 10 patients without significant coronary artery disease were studied. One mCi of thallium-201 was injected intravenously and imaging was performed at rest in three projections. The patient was then stressed and an additional 1 mCi of thallium injected during exercise. Images in the same three projections were collected. After computer realignment, the rest image was subtracted from the exercise image to produce an image representing perfusion during exercise. All 24 patients with coronary artery disease had a positive study, while 9 of 10 without disease had a negative study. The images were then interpreted using a computer method designed to quantitate regional myocardial thallium distribution and redistribution. With quantitative interpretation, 23 of 24 patients with coronary disease had a positive study, while only 1 without disease had a positive study. With qualitative interpretation, 39 (89%) of 44 stenosed coronary arteries demonstrated thallium defects in corresponding myocardial segments, while 54 (93%) of 58 nonstenosed coronary arteries did not. With quantitative interpretation, 38 (86%) of 44 stenosed coronary arteries demonstrated thallium defects in corresponding myocardial segments, while 53 (91%) of 58 nonstenosed coronary arteries did not. A split dose thallium imaging technique that allows imaging before and immediately after exercise, thus markedly reducing the study time, has been validated.

Adult↗
PubMed1985

Effect of hyperaemia on thallium-201 redistribution in normal canine myocardium.

The specific effect of hyperaemia on thallium redistribution is not known. Therefore we evaluated the effect of initial (group A) and delayed (group B) hyperaemia on thallium kinetics in normal canine myocardium. In group A dogs (n = 14) adenosine was infused into the left circumflex artery (LCx) prior to thallium injection and was continued for either 5, 30 or 120 min after thallium administration. In group B dogs (n = 10) LCx adenosine was begun 10 min post thallium injection and continued for 2 h. Radioactive microspheres were injected simultaneously with thallium and just prior to death in all but the 5 min experiments. The region of the left anterior descending artery (LAD) served as a normal control for each heart. The mean LCx/LAD flow ratio in all group A hearts was 3.81 +/- 1.24 (SD) and the final thallium LCx/LAD ratios averaged 2.29 +/- 0.26, 1.52 +/- 0.27 and 0.93 +/- 0.16 at 5, 30 and 120 min respectively, which represents a significant redistribution of thallium (p less than 0.05). In group B hearts, the mean LCx/LAD flow ratio was 1.06 +/- 0.07 during thallium injection and after LCx adenosine infusion the flow ratio rose to 2.91 +/- 0.75 (p less than 0.001). This resulted in a final thallium LCx/LAD ratio of 0.96 +/- 0.07 which was significantly less than the initial microsphere determined flow ratio (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1985

Assessment of myocardial ischemia with proton magnetic resonance: effects of a three hour coronary occlusion with and without reperfusion.

Proton (hydrogen-1) magnetic resonance imaging techniques have potential for the detection and characterization of changes associated with myocardial ischemia. Since image contrast is dependent on T1 and T2 relaxation times, we examined these parameters in a canine preparation of occlusion of the left anterior descending coronary artery. Of 16 dogs studied, seven underwent 3 hr of coronary artery occlusion and nine underwent 3 hr of occlusion followed by 1 hr of reperfusion. After the dogs were killed, the hearts of four from each group were imaged in a small bore, 1.4 tesla magnet. From all hearts myocardial segments were obtained from the normal zone and the central ischemic zone (CZ). These segments were divided into epicardial and endocardial sections and studied in a spectrometer (20 MHz). After 3 hr of occlusion, CZ endocardial T1 and T2 increased significantly (p less than .01 and p less than .05, respectively). Changes in CZ epicardial relaxation times were not as marked. Although T1 and T2 tended to be higher in the reperfused group compared with the nonreperfused group, the differences did not reach statistical significance. In keeping with the spectrometric findings, T1-dependent inversion recovery images and T2-dependent spin-echo images of the excised hearts demonstrated excellent contrast between normal and ischemic myocardium. Modest correlations were noted for both groups between blood flows during occlusion measured by the microsphere technique and T1 and T2 relaxation times. In summary, relaxation times T1 and T2 increase regionally after 3 hr of coronary artery occlusion and tend to be accentuated by reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

The relationship between proton nuclear magnetic resonance relaxation parameters and myocardial perfusion with acute coronary arterial occlusion and reperfusion.

Previous investigators have demonstrated that acute myocardial ischemia, whether followed by reperfusion or not, is associated with prolongation of the proton nuclear magnetic resonance (NMR) relaxation times T1 and T2. Heretofore, the relationship between the severity of ischemia and alterations of these relaxation times has not been assessed. In our studies, changes in T1 and T2 were compared with myocardial perfusion in dogs both before and during 30 and 60 min of coronary arterial occlusion. In addition, studies were performed to assess the impact of reperfusion on relaxation times after 30 and 60 min of coronary occlusion. In the reperfusion studies the relationship between myocardial relaxation times and flow during the preocclusion, occlusion, and the 15 min reperfusion periods were studied. In the occlusion-only preparations, there was a significant inverse relationship between the relaxation times and flow during occlusion. In the reperfusion preparations there was a significant direct relationship between T1 and T2 and flow during the period of reperfusion. There was no significant relationship between the relaxation times and flow during occlusion in groups that subsequently underwent reperfusion, and no relationship between T1 and T2 and preocclusion flow in either the occlusion-only or reperfusion groups. These data suggest that the proton relaxation times provide an indication of the severity of an ischemic insult. Since NMR images can be generated that are sensitive to differences in these relaxation parameters, NMR imaging may provide a means to assess noninvasively the severity of the myocardial ischemic insult.

Acute Disease↗
PubMed1985

Evaluation of the cardiovascular system using NMR.

The current status and suggestions of the future potential for nuclear magnetic resonance imaging of the cardiovascular system are described. With many of the potential applications, there is overlap with existing methods. For example, imaging of the left ventricle can be accomplished with either echocardiography or radionuclide techniques with adequate evaluation of the left ventricular function. At current costs these conventional techniques may provide a more cost-effective approach for morphologic and functional assessment of the cardiovascular system. For this type of imaging, the advantages of NMR include its excellent resolution, the inherent tissue contrast, the sensitivity to blood motion, the 3-dimensional measure, and the lack of ionizing radiation. Because of these, NMR could provide an important adjunct for evaluation of the cardiovascular system. However for NMR to achieve its full promise as a cardiovascular imaging technique, some of its unique potentials need to be developed. These include: the ability to reliably image at least the proximal coronary arteries, the ability to delineate regional myocardial blood flow distribution, the ability to evaluate regional metabolic activity such as high-energy phosphate metabolites, and the ability to characterize myocardial disease using proton T1 and T2 alterations.

Angiography↗
PubMed1985

Effect of a delay in commencing imaging on the ability to detect transient thallium defects.

Sixty patients, 42 with coronary disease and 18 normals, were studied to assess the impact of a delay following exercise in commencing thallium imaging on the sensitivity for detecting ischemic transient defects. Three sets of images were obtained beginning 2 min, 18 min, and 2 hr after exercise. Each patient's images were separated into two pairs of studies for analysis: 2 min-2 hr and 18 min-2 hr. Of the 42 patients with coronary disease, a greater number had transient defects detected on the 2 min-2 hr compared with the 18 min-2 hr study (22 compared with 14, p less than 0.05). False positives were not increased by earlier imaging. We conclude that a modest (18 min) delay obtaining the first set of images causes a significant reduction in the ability to detect transient thallium defects, and that imaging should begin several minutes after exercise.

Adult↗