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Biomedical subjects

R D Okada

Publications and source records attributed to R D Okada.

At least 109 records · Page 6Linked to original sources
PubMed1984

Magnetic resonance imaging of the heart: positioning and gradient angle selection for optimal imaging planes.

Electrocardiographically gated magnetic resonance images were acquired in 20 subjects using a spin-echo pulse sequence. For optimizing the display of cardiac anatomy, a technique was developed which uses patient positioning in addition to alteration of gradient angle to select image planes. High-quality images were acquired in three basic cardiac projections: (1) the long axis of the left ventricle, through the aortic valve and apex, parallel to the interventricular septum, (2) the long axis of the left ventricle, perpendicular to the septum, and (3) the short axis of the left ventricle at multiple levels including outflow, papillary muscle, and apex. Images of the aorta included axial images at multiple levels and long-axis images oriented to display the plane of the aortic arch. Images of these planes are easily achieved and, in contrast to standard images orthogonal to the chest wall, provide a reproducible and logical display of cardiac anatomy.

Adolescent↗
PubMed1984

Evaluation in dogs of a new double-dose technique for imaging changes in myocardial perfusion.

Assessment of myocardial perfusion with thallium immediately before and after an intervention that alters blood flow has been difficult due to presence of residual activity from the first tracer dose at the time of the second imaging. In a canine model we investigated a technique using two separate thallium injections during an intervention and after its reversal. Images were obtained after each injection, and a difference image was obtained by subtracting the first from the second image to correct for tracer persisting from the first injection. Interventions on coronary blood flow included: transient occlusion, subcritical stenosis with dipyridamole infusion, and permanent occlusion. The first images showed defects corresponding to the occlusion or stenosis, while the "difference" images correlated with myocardial perfusion at the time of the second injection. This technique allows rapid evaluation of changes in perfusion in response to interventions, and may find application in several clinical procedures.

Animals↗
PubMed1983

Relation of segmental wall motion to global left ventricular function in acute myocardial infarction.

The relation of left ventricular regional wall motion to global ventricular function was evaluated by radionuclide ventriculography in 127 patients within 18 hours of acute myocardial infarction. No patient had evidence of previous myocardial infarction. The following parameters were measured: (1) wall motion index; (2) percent of abnormally contracting segment; (3) ejection fraction (EF); (4) end-diastolic volume (EDV) and end-systolic volume (ESV); and (5) peak systolic cuff pressure/end-systolic volume ratio (PSP/ESV). The measurements of global function correlated well with wall motion index (r = 0.83, p less than 0.001 for EF; r = -0.69, p less than 0.001 for ESV; and r = 0.061, p less than 0.001 for PSP/ESV), but EDV correlated less well (r = -0.35, p less than 0.001). Multiple linear regression analysis revealed that EF correlated best with wall motion index, and no other parameters of global left ventricular function added significantly to the regression. The correlation of motion in each segment with EF was determined by multiple linear regression analysis. Ejection fraction correlated best with motion in the anterobasal, then in order of correlation, in the apical-septal, inferoapical, anterolateral, and superlateral walls. The relation of EDV, ESV, and degree of percent abnormally contracting segments was as follows: EDV did not increase with a mild regional wall motion abnormality; however, ESV did increase and reduced stroke volume. As percent abnormally contracting segments worsened, enlargement of both EDV and ESV was seen and was associated with further reduction in systolic volume. These data suggest that EF is the best global left ventricular function correlate of the severity of the regional wall motion abnormality, and that abnormal motion in the territory of the left anterior descending coronary best predicts reduction in global left ventricular function. Radionuclide ventriculography is useful in characterizing global and regional left ventricular function in the early hours of acute myocardial infarction.

Aged↗
PubMed1983

Radionuclide-determined changes in pulmonary blood volume and thallium lung uptake in patients with coronary artery disease.

UNLABELLED: Exercise-induced increases in radionuclide-determined pulmonary blood volume (PBV) and thallium lung uptake have been described in patients with coronary artery disease (CAD) and have been shown to correlate with transient exercise-induced left ventricular dysfunction. To compare these 2 techniques in the same patients, 74 patients (59 with and 15 without significant CAD) underwent supine bicycle exercise twice on the same day--first for thallium myocardial and lung imaging and then for technetium-99m gated blood pool imaging for the PBV ratio determination. Thallium activity of lung and myocardium was determined to calculate thallium lung/heart ratio. Relative changes in PBV from rest to exercise were expressed as a ratio of pulmonary counts (exercise/rest). Previously reported normal ranges for thallium lung/heart ratio and PBV ratio were used. The PBV ratio and thallium lung/heart ratio were abnormal in 71 and 36%, respectively, of patients with CAD (p less than 0.01). Both ratios were normal in all patients without CAD. Although the resting ejection fractions did not differ significantly in patients with normal versus those with abnormal PBV ratios or thallium lung/heart ratios, abnormal PBV ratios and thallium lung/heart ratios were associated with an exercise-induced decrease in ejection fraction. Propranolol use was significantly higher in patients with abnormal than in those with normal thallium lung/heart ratios (p less than 0.01). No significant difference in propranolol use was present in patients with abnormal or normal PBV ratios. IN CONCLUSION: (1) the prevalence of an abnormal thallium lung/heart ratio is less than that of the PBV ratio in patients with CAD; (2) both tests are normal in normal control subjects; (3) propranolol does not cause abnormal results in normal control subjects; however, propranolol may influence lung thallium uptake in patients with CAD; and (4) when both tests are abnormal, there is a high likelihood of multivessel disease.

Adult↗
PubMed1983

Spectrum of global left ventricular responses to supine exercise. Limitation in the use of ejection fraction in identifying patients with coronary artery disease.

Left ventricular function was evaluated with rest and supine bicycle exercise-multigated blood pool scans in 53 patients who had previously undergone coronary angiography for evaluation of a chest pain syndrome. There were 21 normal patients (less than 25% stenosis in any coronary artery, left ventricular end-diastolic pressure less than or equal to 12 mm Hg, and normal left ventriculography) and 32 patients with coronary artery disease (CAD) (greater than 50% narrowing in 1 or more major coronary arteries). Thirty-two (60%) were receiving propranolol at the time of the study. The normal patient group had a significant increase in mean ejection fraction (EF) during exercise (+0.08 +/- 0.09), while the CAD group had no increase (0 +/- 0.11; p less than 0.05). Mean end-systolic volume decreased significantly in the normal group (-5 +/- 8 ml/m2) but demonstrated no significant change in the CAD group (1 +/- 12 ml/m2; p less than 0.05 compared with normal patients). There was no significant change in mean end-diastolic volume in either group. Mean ejection rate, mean peak systolic pressure/end-systolic volume ratio, and mean pulmonary blood volume ratio also differed in the normal versus CAD patients. Despite mean differences, there was considerable overlap in both groups of individual EF responses: 8 of 21 (38%) of the normal group did not have an increase in EF of 0.05 with exercise, while 15 of 32 (47%) of the CAD group did have an increase in EF of 0.05 with exercise. However, the addition of peak systolic pressure/end-systolic volume ratio and pulmonary blood volume (exercise/rest) ratio improved the sensitivity for detecting CAD from 53 to 84% without adversely affecting specificity. Thus, there is a wide spectrum of left ventricular EF responses to supine exercise. In our patient population, EF alone was an insensitive and nonspecific marker of CAD. The addition of other parameters of global left ventricular function, which may be generated using radionuclide angiography, helps distinguish patients with CAD from normal subjects.

Adult↗
PubMed1983

Inability of seven-pinhole myocardial tomography to obtain accurate 201Tl kinetic data.

Seven-pinhole myocardial tomography has been reported to enhance the accuracy of thallium-201 (201Tl) studies in detecting patients with coronary artery disease. To determine if this approach can accurately assess regional 201Tl kinetics, 12 dogs with temporary occlusion (mean 15 min) of either the left anterior descending (LAD) (n = 6) or left circumflex (LCX) (n = 6) coronary artery were studied. Thallium-201 was injected and serial 7-pinhole images were acquired during occlusion and following reflow (mean duration 175 min). Time-activity analysis was obtained from normal and ischemic regions of interest in the central pinhole image and the reconstructed tomographic images (TOMO-ROI). Time-activity data from corresponding normal and ischemic regions were also obtained using a circumferential graph program (TOMO-MAX). In addition, regional myocardial 201Tl activity was recorded continuously with a cadmium telluride radiation probe sutured directly to the posterior myocardial wall. Defects in 201Tl distribution with subsequent partial or complete redistribution were present in 11 of 12 central pinhole images and tomographic studies. In the normal and ischemic anterior myocardial segments the percentage change in 201Tl activity in the central pinhole image from occlusion to the end of reflow correlated well with the percentage change in activity for both TOMO-ROI (r = 0.93) and TOMO-MAX (r = 0.85). In the normal posterior segments the percentage change in 201Tl activity in the central pinhole image correlated well with TOMO-ROI (r = 0.98) and TOMO-MAX (r = 0.87).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Serial thallium-201 imaging at rest in patients with unstable and stable angina pectoris: relationship of myocardial perfusion at rest to presenting clinical syndrome.

In order to determine whether there are differences in myocardial perfusion at rest among patients with various unstable and stable angina syndromes, serial thallium-201 imaging was performed at rest in 19 patients presenting with rapidly worsening exertional angina (unstable angina, group A), 12 patients with rest angina alone without exertional symptoms (unstable angina, group B), and 34 patients with chronic stable angina. No patient had an episode of angina within 4 hours of study. Nineteen of 19 (100%) patients in group A demonstrated transient defects compared to only 3 of 12 (25%) patients in group B (p less than 0.0001) and 4 of 34 (12%) stable angina patients (p less than 0.0001). The majority of zones demonstrating transient defects in group A were associated with hypokinesis of the corresponding left ventriculogram segment without associated ECG evidence of previous infarction. There were no significant differences in the frequency of persistent thallium defects, severity of angiographic coronary artery disease, or frequency of regional wall motion abnormalities of myocardial segments supplied by stenotic coronary arteries among the three groups of patients. Transient defects have been shown to reflect reduction in regional coronary blood flow to viable myocardium. Therefore, we conclude that regional resting hypoperfusion of viable myocardium is far more common in patients with exertional unstable angina symptoms than in patients with rest angina alone or chronic stable angina.

Angina Pectoris↗
PubMed1983

Effect of ventricular pacing on left ventricular function assessed by radionuclide angiography.

Radionuclide angiography was used to evaluate left ventricular contraction on and off ventricular pacing in 35 patients. Twenty patients had permanent rate-adjustable ventricular demand pacemakers whose rate could be programmed to below an underlying sinus rhythm. In these patients there was no difference in left ventricular ejection fraction on and off pacing whether or not heart failure was present (n = 7) or whether or not ventriculoatrial conduction (n = 10) developed during pacing. Eight of the 20 patients also underwent supine bicycle exercise, and rest and exercise ejection fraction values were not significantly different at a similar heart rate and workload when on and off pacing were compared. During pacing, there appeared to be abnormal motion in septal, apical, and inferior walls. In addition, dysynchrony developed, consisting of early right ventricular and anterobasal and posterobasal left ventricular motion with subsequent contraction of the apex. Conversion to atrioventricular pacing produced a clinical improvement in all seven patients with heart failure and reduced ejection fraction and also in one of the remaining 13 patients without heart failure. Fifteen other patients were studied early after cardiac surgery. Temporary ventricular epicardial pacing resulted in a significant increase in right and left atrial pressure and a significant reduction in stroke volume, end-diastolic volume, and end-systolic volume with no significant change in ejection fraction. Conversion from sinus rhythm to ventricular pacing produces a deterioration in cardiac performance and severe regional left ventricular wall motion abnormalities, but no significant change in ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Nuclear magnetic resonance imaging of the heart.

Diagnostic imaging of the heart has, with the exception of echocardiography, employed techniques utilizing ionizing radiation. NMR imaging, a new technique, not only can generate images with spatial resolution closely approaching that of x-ray computed tomography without ionizing radiation, but can potentially detect the presence of intrinsic tissue damage. Although the exact role that NMR techniques will play in the assessment of cardiac disease is not currently defined, there are many instances where NMR may provide both unique and complementary information when compared with existing modalities.

Blood Circulation↗
PubMed1983

Prognostic value of exercise thallium-201 imaging in patients presenting for evaluation of chest pain.

Accurate prognostic information is important in determining optimal management of patients presenting for evaluation of chest pain. In this study, the ability of exercise thallium-201 myocardial imaging to predict future cardiac events (cardiovascular death or nonfatal myocardial infarction) was correlated with clinical, coronary and left ventricular angiographic and exercise electrocardiographic data in 139 consecutive, nonsurgically managed patients followed-up over a 3 to 5 year period (mean follow-up, 3.7 +/- 0.9), using a logistic regression analysis. Among patients without prior myocardial infarction (100 of 139), the number of myocardial segments with transient thallium-201 defects was the only statistically significant predictor of future cardiac events when all patient variables were evaluated. Among patients with myocardial infarction before evaluation (39 of 139), angiographic ejection fraction was the only significant predictor of future cardiac events when all variables were considered. This study suggests an approach to evaluate the risk of future cardiac events in patients with possible ischemic heart disease.

Adult↗
PubMed1983

A noninvasive radiographic technique for evaluation of exercise-induced changes in cardiac function.

An electrocardiographic-triggered radiographic technique for obtaining a single image of the heart at both end-systole and end-diastole was used in conjunction with upright bicycle exercise to detect stress-induced changes in 1) systolic and diastolic cardiac transverse diameter, and 2) regional motion of the free left ventricular wall. Twenty-one patients were studied; 10 had normal coronary arteries and 11 had significant coronary artery disease. Twenty patients (10 with normal coronary arteries and 10 with coronary artery disease) also had multigated radionuclide blood pool scans at rest and with exercise. All patients without coronary disease showed a decrease in systolic cardiac transverse diameter with exercise and a slight increase in amplitude of motion of the left ventricular free wall. Eight (73%) of the 11 patients with coronary artery disease showed an increase in systolic transverse cardiac diameter with exercise (p less than 0.001), and 5 developed either new regional left ventricular asynergy or deterioration of segments with rest asynergy. Eight of the 10 patients with coronary artery disease who had rest and exercise radionuclide scans had an abnormal ejection fraction response to exercise. However, only 4 of the 10 control patients who had multigated scans had a normal ejection fraction response, although all showed normal regional wall motion with exercise. This new approach is inexpensive and easily performed. These preliminary data suggest that it may be a useful adjunct to cardiac stress testing and is worthy of further study.

Adult↗
PubMed1983

Exercise testing in asymptomatic or minimally symptomatic aortic regurgitation: relationship of left ventricular ejection fraction to left ventricular filling pressure during exercise.

Exercise radionuclide angiography is being used to evaluate left ventricular function in patients with aortic regurgitation. Ejection fraction is the most common variable analyzed. To better understand the rest and exercise ejection fraction in this setting, 20 patients with asymptomatic or minimally symptomatic severe aortic regurgitation were studied. All underwent simultaneous supine exercise radionuclide angiography and pulmonary gas exchange measurement and underwent rest and exercise measurement of pulmonary artery wedge pressure (PAWP) during cardiac catheterization. Eight patients had a peak exercise PAWP less than 15 mm Hg (group 1) and 12 had a peak exercise PAWP greater than or equal to 15 mm Hg (group 2). Group 1 patients were younger and more were in New York Heart Association class I. Group 1 patients also had a higher mean rest ejection fraction (0.64 +/- 0.08 vs 0.49 +/- 0.13, p less than 0.01, higher exercise ejection fraction (0.63 +/- 0.10 vs 0.40 +/- 0.18, p less than 0.01), lower end-systolic volume (38 +/- 13 vs 79 +/- 36 ml/m2, p less than 0.01) and higher peak oxygen uptake (24.9 +/- 5.1 vs 16.6 +/- 4.9 ml/kg/min, p less than 0.01) than group 2 patients. However, the two groups had similar cardiothoracic ratios, changes in ejection fractions with exercise, and rest and exercise regurgitant indexes. Using multiple regression analysis, the best correlate of the exercise PAWP was peak oxygen uptake (r = -0.78, p less than 0.01). No other measurement added significantly to the regression. When peak oxygen uptake was excluded, rest and exercise ejection fraction also correlated significantly (r = -0.62 and r = -0.60, respectively, p less than 0.01). Patients with asymptomatic or minimally symptomatic severe aortic regurgitation have a wide spectrum of cardiac performance in terms of the PAWP during exercise. The absolute rest and exercise ejection fraction and the level of exercise achieved are noninvasive variables that correlate with exercise PAWP in aortic regurgitation, but the change in ejection fraction with exercise by itself is not.

Adolescent↗