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Biomedical subjects

R D Okada

Publications and source records attributed to R D Okada.

At least 127 records · Page 7Linked to original sources
PubMed1983

Effect of glucose-insulin-potassium infusion on thallium myocardial clearance.

Factors influencing the rate of 201Tl clearance from the myocardium have not been clearly defined. This study determined the effect of an intravenous infusion of glucose-insulin-potassium (GIK) on the net 201Tl clearance rates from myocardium with and without initial 201Tl loading. Anesthetized open-chest dogs underwent 5 min of left anterior descending coronary artery occlusion and intravenous 201Tl was injected and the occlusion released 5 min later. Thirty minutes after 201Tl injection, 30 ml of either GIK (nine dogs) or saline (five dogs) was infused intravenously. The clearance rates of 201Tl from the anterior wall (without initial 201Tl loading) and from the posterior wall (with initial 201Tl loading) were monitored with miniaturized cadmium telluride detectors placed on the myocardium. Calculation of net myocardial clearance rates was performed by linear regression analysis from serial 1 min counts. Compared with saline infusion, GIK increased the net clearance of 201Tl from both myocardial regions with and without initial loading. The most marked change induced by GIK infusion was in the myocardial region without initial 201Tl loading; a net increase in 201Tl activity (72 +/- 42 cpm/30 min) was converted into a net loss (-594 +/- 228 cpm/30 min). There was no significant change in 201Tl clearance after the saline infusion. Heart rate, aortic and left atrial pressure, sonomicrometer-measured transmural myocardial wall thickness, microsphere-determined myocardial blood flow, and blood glucose and potassium concentrations did not change significantly during GIK or saline infusions. Thus, GIK infusion appears to increase net 201Tl clearance from myocardial zones with and without initial 201Tl loading.

Animals↗
PubMed1983

Serial changes in left ventricular ejection fraction in the early hours after aortocoronary bypass grafting.

To determine the course of left ventricular ejection fraction (LVEF) in the early hours after aortocoronary bypass grafting, 24 patients underwent serial gated bloodpool scanning. Twenty-two had received propranolol until the day of surgery. ECGs showed no evidence of perioperative infarction. Preoperatively, the mean (+/- SD) LVEF was 0.56 +/- 0.13; after bypass, it was 0.38 +/- 0.11 at 4 hours, 0.42 +/- 0.12 at 5 hours, 0.43 +/- 0.11 at 6 hours, 0.48 +/- 0.13 at 7 hours, 0.52 +/- 0.15 at 8 hours, and 0.54 +/- 0.15 at 10 to 14 days. The LVEFs at 4, 5, and 6 hours postoperatively were significantly lower than preoperatively (p less than 0.05). Postoperative mean heart rate was higher at all times; mean temperature was depressed at 4 and 5 hours and elevated at 7 and 8 hours; and mean arterial blood pressure was depressed at 7 hours, 8 hours, and 10 to 14 days (p less than 0.05). The degree of the early postoperative LVEF depression correlated with the daily preoperative propranolol dose (p less than 0.05) and was unrelated to bypass time, aortic cross-clamp time, or changes in temperature, heart rate, and blood pressure. The LVEF at 10 to 14 days postoperatively was not significantly different from the preoperative value. The LVEF is depressed in the early hours after aortocoronary bypass grafting and approaches the preoperative value with time. The magnitude of the early depression appears to be related to the preoperative propranolol dose, but does not significantly correlate with factors related to surgical technique.

Adult↗
PubMed1983

The acquired nonprecordial peripheral pulmonary murmur of pulmonary embolism.

Two patients had noninvasive and invasive findings consistent with massive pulmonary emboli. Both patients had an acquired nonprecordial peripheral pulmonary murmur on physical examination. One patient also demonstrated a wide, fixed-split second heart sound in addition to the acquired murmur. Both of these physical findings have rarely been reported; however, when present, both the acquired nonprecordial murmur and the widely split second heart sound seem to be associated with extensive and massive pulmonary embolism and, when occurring together, are almost pathognomonic for pulmonary embolism.

Adult↗
PubMed1982

Left ventricular systolic and diastolic function in hyperthyroidism.

In order to assess the effect of hyperthyroidism on systolic and diastolic function of the left ventricle, M-mode echocardiograms and systolic time intervals were obtained in 13 patients while they were clinically hyperthyroid and again when they were euthyroid following radioactive iodine therapy. Echocardiographic tracings of the septum and left ventricular posterior wall were digitized and analyzed to provide the maximum velocity of shortening and maximum velocity of lengthening. These velocities were normalized for left ventricular diastolic dimension. The left ventricular minor axis fractional shortening and the normalized maximum velocity of shortening were both increased during the hyperthyroid state. The normalized maximum velocity of lengthening, a measure of diastolic left ventricular function, was also increased during the hyperthyroid state when compared to the euthyroid state. The preejection period index and the preejection period/left ventricular ejection time ratio were lower when the patients were hyperthyroid than when they were euthyroid. These data confirm the increased inotropic state and demonstrated increased diastolic relaxation velocities of the hyperthyroid left ventricle.

Adult↗
PubMed1982

Initial and delayed right ventricular thallium-201 rest-imaging following dipyridamole-induced coronary vasodilation: relationship to right coronary artery pathoanatomy.

The relationship of coronary anatomy to right ventricular (RV) appearance on serial thallium-201 myocardial imaging (TI) following dipyridamole (DP)-induced coronary vasodilation was examined in 71 consecutive patients undergoing coronary angiography for the evaluation of chest pain. Transient defects of the RV were found in 18 patients. All 18 had significant (greater than or equal to 50%) stenosis of the proximal right coronary artery (RCA). Nonvisualization of RV activity occurred in 13 patients. Six of these 13 (46%) had proximal RCA disease (p less than 0.05 compared to transient defects). Normal RV appearance was seen in 40 patients, of whom only six (15%) had proximal RCA disease (p less than 0.001 compared to transient defects). RV appearance was not affected by left anterior descending or left circumflex artery disease or by the thallium-201 uptake in the left ventricle. Thus with serial (initial and delayed) TI following DP (1) transient RV defect appears to indicate significant proximal RCA disease; (2) normal RV appearance suggests the absence of proximal RCA disease; and (3) however, nonvisualization of the RV appears to be nondiagnostic.

Adult↗
PubMed1982

Serial right ventricle thallium-201 imaging after exercise: relation to anatomy of the right coronary artery.

The relation of the appearance of the right ventricle on serium thallium-201 myocardial imaging to coronary artery anatomy was examined in 88 consecutive patients undergoing exercise thallium-201 testing and coronary angiography for the evaluation of chest pain. Transient defects in the right ventricle were found in 8 patients. All had high grade (greater than or equal to 90%) stenosis of the proximal right coronary artery. Nonvisualization of right ventricular (RV) activity occurred in 10 patients. Nine of the 10 (90%) had significant (greater than or equal to 50% stenosis) disease of the proximal right coronary artery and 7 (70%) had high grade stenosis. The right ventricle appeared normal in 70 patients. Twenty-nine (41%) of these patients had significant proximal right coronary artery disease. Right ventricular appearance was not affected by the presence or absence of disease of the left anterior descending or left circumflex artery or by the appearance of the left ventricle. Thus, with serial RV thallium-201 myocardial imaging after exercise, we found that (1) RV transient defects suggest the presence of high grade proximal right coronary artery stenosis, (2) non-visualization of RV activity also predicts significant proximal right coronary disease, and (3) the right ventricle frequently appears normal despite proximal right coronary artery disease and therefore this finding does not exclude such disease.

Aged↗
PubMed1982

Hypothermic ischemic arrest versus hypothermic potassium cardioplegia in human beings.

To determine if the addition of potassium enhances the myocardial protective effect of intracoronary perfusion hypothermia during aortic cross-clamping, 50 patients undergoing aortocoronary bypass grafting were studied in a randomized, prospective, double-blind fashion. Twenty-six patients received a cold crystalloid solution infused with a handheld syringe into the root of the cross-clamped aorta every 20 minutes, and 24 patients received the same solution but with 25 mEq/L of potassium chloride added, infused in a similar manner. Both groups were analyzed by mortality, rate of perioperative myocardial infarction (electrocardiographic changes, MB-CPK enzyme release, and preoperative and postoperative gated cardiac blood pool scans), intraoperative hemodynamic changes, intraoperative lactate determinations, postoperative arrhythmias, and requirement for pressor or intraaortic balloon pump support. One patient in the potassium cardioplegia group died (massive pulmonary embolism), and none in the hypothermic perfusion group died. Possible perioperative myocardial infarction was diagnosed by more than one marker in 4 of 26 patients in the hypothermic perfusion group and 5 of 24 patients in the potassium group (p = 0.61). There were no differences between the two groups in terms of hemodynamic changes, lactate production, postoperative arrhythmias, or the need for postoperative hemodynamic support. This study in human beings could not demonstrate a specific protective effect of potassium, beyond that afforded by myocardial perfusion hypothermia and wash-out. The data suggest that myocardial hypothermia, achieved through cold intracoronary arterial perfusion, may be the most important beneficial component of so-called cardioplegia for attaining effective intraoperative myocardial preservation in human beings.

Arrhythmias, Cardiac↗
PubMed1982

Regional myocardial radiotracer kinetics in dogs using miniature radiation detectors.

An implantable device for continuous measurement of regional myocardial radioisotope activity was designed and validated. The probe consists of a 2-mm3 cadmium telluride crystal surrounded by lead foil housed in a 4.5-mm outer diameter steel cylinder. Activity in serial dilutions of thallium-201 measured by this miniature gamma detector correlated well with activity measured in the well counter (r = 0.99). In vivo probe measurements of regional myocardial thallium-201 activity in a canine model were compared with activity in punch biopsies, again with excellent correlation (r = 0.90). The crystal was mounted on a modified arterial clamp, which was inserted into the left ventricle through, the apex and situated on the endocardial surface of the anterior or posterior wall. It was thus possible to measure regional isotope activity without excessive background from the blood pool and opposite heart wall. The probe was found best suited for monitoring activities of isotopes with energies between 60 and 250 keV. With a pair of these devices, dynamic studies of the myocardial kinetics of radioisotopes such as thallium-201 in normal and ischemic myocardium are now possible.

Animals↗
PubMed1982

Serial thallium-201 myocardial imaging after dipyridamole infusion: diagnostic utility in detecting coronary stenoses and relationship to regional wall motion.

After a 4-minute i.v. dipyridamole infusion, 0.14 mg/kg/min, serial thallium-201 scans were obtained in 60 patients undergoing cardiac catheterization. Forty patients had significant (greater than or equal to 50% stenosis) coronary artery disease (CAD), and 20 patients had normal coronary arteries or trivial lesions. The images were graded qualitatively for thallium activity by three observers. Sensitivity was 93% (37 of 40) and specificity was 80% (16 of 20). The sensitivity and specificity of the thallium-201 study were not affected by the extent of CAD, the presence of Q waves, or propranolol therapy. Twenty-seven of 37 patients who had initial defects (73%) had complete thallium redistribution of one or more defects. Patient-by-patient analysis using a regression model of all patients showed that the fate of a segmental thallium defect predicted abnormal wall motion by angiography better than ECG Q waves. The presence of propranolol therapy or collaterals did not significantly affect the thallium redistribution results. We conclude that qualitative interpretation by multiple observers of thallium images after dipyridamole infusion is a highly sensitive and specific test for CAD. After dipyridamole, as with exercise stress, the extent of thallium redistribution is related to the degree of myocardial wall motion abnormality.

Adult↗
PubMed1982

Myocardial kinetics of thallium-201 after dipyridamole infusion in normal canine myocardium and in myocardium distal to a stenosis.

The purpose of the present study was to define myocardial and blood thallium-201 (Tl-201) kinetics after infusion of dipyridamole in normal canine myocardium and in myocardium distal to a coronary artery stenosis. Miniature radiation detector probes were implanted in the left ventricle in 39 open-chest dogs. A balloon constrictor was placed around the proximal left circumflex coronary artery. Electromagnetic flow probes were positioned proximally around both the left circumflex and left anterior descending coronary arteries. In five control dogs (group 1) the balloon occluder was not inflated; in 12 dogs (group 2) a mild stenosis was created such that resting flow was not reduced, yet the hyperemic response after 10 s of total occlusion was partially attenuated; in nine dogs (group 3) a moderate stenosis was created such that resting flow was not reduced, yet the hyperemic response was completely eliminated; and in 13 dogs (group 4) a severe stenosis was created such that resting flow was reduced. After intravenous dipyridamole (0.08 mg/kg . min-1 x 4 min), 1.5 mCi Tl-201 was injected intravenously and probe counts were collected continuously for 4 h. The mean 4-h fractional myocardial Tl-201 clearance for nonstenotic zones was 0.35, 0.27 for group 2 stenotic zones, 0.19 for group 3 stenotic zones, and 0.05 for group 4 stenotic zones (P less than 0.0001). After reaching peak activity, myocardial Tl-201 activity cleared biexponentially with a final decay constant lambda 2 = 0.0017 +/- 0.0001 min-1 (SE) for nonstenotic zones, 0.0011 +/- 0.0001 min-1 for group 2 stenotic zones, and 0.0006 +/- 0.0001 min-1 for group 3 stenotic zones (P less than 0.01). Group 4 stenotic zone Tl-201 clearances were negligible (decay constant essentially zero). Blood Tl-201 activity decayed triexponentially with a final blood lambda 3 = 0.0018 +/- 0.0001 min-1, which was almost identical to the final myocardial lambda 2 decay constant. Thus, the rate of myocardial Tl-201 clearance can distinguish between coronary stenoses of graded hemodynamic severity. These results may be applicable to quantitative techniques for determining myocardial Tl-201 clearance rates on serial clinical images after dipyridamole administration.

Animals↗
PubMed1981

Relationship of thallium-201 myocardial perfusion pattern to regional and global left ventricular function with exercise.

Thallium-201 redistribution pattern after exercise was related to rest and exercise left ventricular regional and global function, measured by radionuclide ventriculography, in 61 patients, 50 with coronary artery disease (CAD). Sixteen patients had exclusively transient thallium defects, suggesting ischemia: in this group, mean left ventricular ejection fraction (LVEF) was 65% at rest, falling to 58% during exercise (p less than 0.01). Eight patients had exclusively persistent thallium defects, suggesting scar: LVEF was unchanged during exercise, 58% to 59%. LVEF increased during exercise in the 17 patients without exercise thallium defects, seven with CAD: 66% to 73% (p less than 0.05). Individual LV wall segments which exhibited transient or persistent thallium defects contracted abnormally both at rest and during exercise; (2) both transient and persistent thallium defects can be associated with resting dyssynergy; and (3) in some CAD patients, apparent hypoperfusion does not necessarily predict left ventricular dysfunction during exercise.

Adult↗
PubMed1981

Mitral valve replacement for isolated mitral regurgitation: analysis of clinical course and late postoperative left ventricular ejection fraction.

One hundred five patients underwent mitral valve replacement for relief of isolated mitral regurgitation between 1974 and 1979. There were 4 in-hospital deaths (4 percent) and 12 late deaths giving an 82 percent predicted 5 year survival rate. An age of 60 years or more at the time of surgery and a preoperative left ventricular ejection fraction of less than 0.40 were the only variables that correlated with decreased survival at 3 to 5 years after operation (p less than 0.05). Postoperatively, 87 (98 percent) of 89 long-term survivors were in New York Heart Association functional class I or II (68 in class I and 19 in class II). Survival did not differ between patients with porcine versus mechanical valve replacement, but patients with a mechanical valve had a greater incidence of postoperative cerebrovascular accident (8.6/100 patient years) than did patients with a porcine valve (2.8/100 patient years) (p less than 0.002). Ejection fraction at rest was determined with multigated cardiac imaging 12 to 75 months postoperatively in 34 of 89 long-term survivors. The mean preoperative ejection fraction was 0.62 +/- 0.09 (mean +/- 1 standard deviation) and the mean postoperative ejection fraction was 0.50 +/- 0.15 (p less than 0.001). When the preoperative value was compared with the postoperative value at rest the ejection fraction increased by 0.10 or more in 1 patient (3 percent), remained within +/- 0.09 of the preoperative value in 12 patients (35 percent) and decreased by 0.10 or greater in 21 patients (62 percent). Sixteen (94 percent) of 17 patients whose postoperative ejection fraction was greater than 0.50 were in functional class I postoperatively compared with 11 (65 percent) of 17 patients whose postoperative ejection fraction was 0.50 or less (p less than 0.05). No preoperative factor, including preoperative ejection fraction or cardiothoracic ratio, predicted the postoperative ejection fraction. A postoperative exercise ejection fraction was obtained in 29 patients, and an abnormal ejection fraction change with exercise (increase less than 0.05) was observed in 20 patients (69 percent). Patient age at the time of study correlated inversely with the change in ejection fraction from rest to exercise; no other variables were predictive. It is concluded that, in addition to age, only preoperative left ventricular function as measured by ejection fraction predicts survival in patients undergoing mitral valve replacement for isolated mitral regurgitation. Clinical recovery is good even though the majority of long-term survivors have a postoperative decrease in ejection fraction.

Aged↗