Search PubMed⌕ Search

Biomedical subjects

R D Okada

Publications and source records attributed to R D Okada.

At least 73 records · Page 4Linked to original sources
PubMed1986

Influence of peak exercise heart rate on normal thallium-201 myocardial clearance.

Measurement of myocardial clearance rates between initial and delayed images is a major justification for adding computer quantification to the interpretation of exercise 201TI images. To clarify the range of normal thallium clearance and its relationship to the level of exercise achieved, exercise thallium images in 89 normal subjects were analyzed: 45 asymptomatic subjects with less than 1% probability of coronary artery disease (CAD) (Group I), and 44 patients with chest pain found to have no significant CAD on angiography (Group II). Mean initial regional thallium uptake was similar in the two groups, but myocardial thallium clearance (mean +/- 1 s.d.) was slower in Group II, expressed as a longer half-life in the myocardium (8.2 +/- 7.6 hr compared with 3.4 +/- 0.7 hr p less than 0.001). Analysis of variance using ten clinical and exercise variables as covariates showed that the slower clearance in Group II was related to a lower peak exercise heart rate (HR) (154 +/- 27 compared with 183 +/- 11, respectively, p less than 0.001). By linear regression analysis, a decrease in peak HR of 1 beat/min was associated with a slower thallium clearance (longer half-life) of 0.05 hr. Using this formula, the clearance value in each patient was then corrected for peak exercise heart rate by decreasing measured clearance by 0.05 hr multiplied by the amount peak exercise heart rate which was below 183 (the mean value in Group I). There were no differences in the "corrected" clearance between the two groups. We conclude that thallium myocardial clearance after exercise is related in part to factors other than the presence of CAD, being slower when peak exercise HR is lower. Therefore, thallium clearance rates alone uncorrected for peak exercise heart rate should be used with caution when diagnosing CAD.

Adult↗
PubMed1985

Myocardial kinetics of thallium-201 after stress in normal and perfusion-reduced canine myocardium.

Despite the emerging use of quantitative computer programs for assessing myocardial thallium uptake and clearance after exercise, little is known about the kinetics of thallium after exercise stress. Accordingly, 11 mongrel dogs with experimental left anterior descending coronary stenoses were given thallium during norepinephrine infusion to simulate exercise. The infusion was discontinued and thallium activity was monitored regionally using miniature radiation detectors for 3 hours. Heart rate, arterial pressure and double product all increased significantly during norepinephrine infusion. The mean fractional myocardial thallium clearance was lower (0.47 +/- 0.03 [+/- standard error of the mean]) for the stenosis zone than for the no-stenosis zone (0.57 +/- 0.03) (p less than 0.0001). The stress blood flow ratio (stenosis/no-stenosis zone = 0.27 +/- 0.06) was significantly lower than the final thallium activity ratio (0.68 +/- 0.07) (p less than 0.001), consistent with thallium redistribution occurring over the 3-hour period. Myocardial thallium activity in the stenosis zone peaked in a mean of 2.2 minutes, then washed out biexponentially with a final decay constant of 0.0035 +/- 0.0005 min-1. Myocardial thallium activity in the no-stenosis zone peaked within 1 minute in all dogs, then washed out biexponentially, with a final decay constant of 0.0043 +/- 0.0003 (p less than 0.001 compared with stenosis zone). In conclusion, fractional clearance of thallium can differentiate myocardium distal to a coronary artery stenosis from that supplied by a normal coronary vessel.

Animals↗
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

Magnetic resonance imaging: present and future applications.

Magnetic resonance (MR) imaging has created considerable excitement in the medical community, largely because of its great potential to diagnose and characterize many different disease processes. However, it is becoming increasingly evident that, because MR imaging is similar to computed tomography (CT) scanning in identifying structural disorders and because it is more costly and difficult to use, this highly useful technique must be judged against CT before it can become an accepted investigative tool. At present MR imaging has demonstrated diagnostic superiority over CT in a limited number of important, mostly neurologic, disorders and is complementary to CT in the diagnosis of certain other disorders. For most of the remaining organ systems its usefulness is not clear, but the lack of ionizing radiation and MR's ability to produce images in any tomographic plane may eventually prove to be advantageous. The potential of MR imaging to display in-vivo spectra, multinuclear images and blood-flow data makes it an exciting investigative technique. At present, however, MR imaging units should be installed only in medical centres equipped with the clinical and basic research facilities that are essential to evaluate the ultimate role of this technique in the care of patients.

Abdomen↗
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

Tellurium-labeled fatty-acid analogs: relationship of heteroatom position to myocardial kinetics.

To determine the effects of tellurium-heteroatom position on myocardial fatty-acid kinetics, a series of tellurium Te 123m-labeled heptadecanoic-acid analogs (123mTe-THDA) were evaluated in dogs. The left-anterior descending coronary artery was partially occluded, and 123mTe-THDA labeled at either the 5, 6, 9, 10, 11, 12, or 13 position from the carboxyl group was administered intravenously. In 24 dogs, the 123mTe activity in the ischemic and normal zones was monitored continuously for 3 h using miniature radiation detectors. There were no significant differences between the ischemic- and normal-wall 123mTe clearance rates for any of the compounds. There was minimal fractional 3-h myocardial clearance for the 123mTe-THDA labeled at the 5, 6, and 9 position (range of means, 0.02-0.05). There was significant clearance of 123mTe-THDA labeled at the 11, 12, and 13 position (range of means, 0.37-0.44). The myocardial clearance of the 123mTe-THDA labeled at the 10 position was intermediate between the two extremes. Thus, as the 123mTe heteroatom is placed further from the carboxyl portion of the molecule, there is a progressive increase in the myocardial clearance. Selection of the heteroatom position should depend on whether initial fatty-acid distribution or subsequent clearance rates are being studied.

Animals↗
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

The effect of glucose-insulin-potassium on thallium-201 myocardial redistribution.

Intravenous infusion of glucose-insulin-potassium (GIK) has been shown to alter the net rate of clearance of 201Tl from transiently ischemic and normally perfused canine myocardium. This study was performed to determine if GIK would also decrease the extent of thallium redistribution after transient myocardial ischemia. Six anesthetized, open-chest dogs underwent two studies, one with GIK and another with saline infusion. The left anterior descending coronary artery was occluded, 201Tl injected, and the occlusion released 5-min later. An i.v. infusion of either GIK (4 dogs) or saline (2 dogs) was then begun and continued for the 120-min duration of serial myocardial imaging using a standard scintillation camera. The experiment was then repeated with an infusion of saline (4 dogs) or GIK (2 dogs). The dose of 201Tl for the second study was at least 5 times more than was used for the first study. The serial 2-min images were then displayed on computer and regions of interest were drawn over the areas of transient ischemia (TI) and normal perfusion (NP). The ratio of average counts per picture element for the area of TI compared to NP was calculated. One hundred and twenty minutes after 201Tl administration, the change in the TI/NP ratio (% fill-in) was significantly less for the GIK infusion compared to saline infusion (control) 15.4 +/- 4.0% vs 26.2 +/- 6.0% (mean +/- SE) (P less than 0.01), respectively. Therefore, GIK infusion appeared to decrease the extent of thallium redistribution compared to saline control.

Animals↗
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

Selection of patients for preoperative coronary angiography: use of dipyridamole-stress--thallium myocardial imaging.

To identify patients likely to benefit from preoperative coronary angiography, a method utilizing pharmacologically induced coronary vasodilatation in conjunction with serial thallium 201 myocardial perfusion imaging was investigated. Fifty-four patients admitted for elective aortic or femoropopliteal procedures were studied. There were no cardiac ischemic complications in 32 patients with normal scans or persistent defects (scar). In contrast, 7 of 15 patients with thallium redistribution (ischemia) on pre-operative scanning had perioperative ischemic events, including one death and two acute infarcts. An additional seven patients with positive scans (redistribution) underwent coronary angiography prior to vascular surgery; surgically important two- or three-vessel disease was confirmed in all. Dipyridamole-thallium imaging facilitates selection of the subset of truly high-risk patients in whom preoperative coronary angiography may be warranted.

Aged↗
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↗