Biomedical subjects

G W Hamilton

Publications and source records attributed to G W Hamilton.

At least 55 records · Page 3Linked to original sources

PubMed1977

Thallium-201 myocardial imaging before and after coronary revascularization: assessment of regional myocardial blood flow and graft patency.

Twenty patients underwent myocardial imaging with Thallium-201 (201Tl) before and subsequent to coronary artery bypass grafting. All patients had rest and maximal treadmill exercise imaging postoperatively. Eleven of the 20 patients had rest and exercise 201Tl images preoperatively; 9/20 only had rest imaging preoperatively. Postoperative regional exercise perfusion was improved in seven of the 11 patients who had preoperative exercise images, and was associated with regional graft patency in each case. Thirteen of 20 patients showed no new defect with postoperative exercise imaging. The remaining seven patients developed or had an increased defect with exercise. The patients with no new perfusion defects during postoperative study has 26/30 grafts patent (87%). Patients developing a new perfusion defect with exercise had fewer grafts patent (7 of 13 [54%]; P less than 0.03). In these seven cases, a new exercise-induced defect was associated with regional graft closure or residual nonoperated disease. Knowledge of the preoperative coronary anatomy allowed the distinction between ungrafted areas and regional graft dysfunction. We conclude that preoperative and postoperative 201Tl imaging may noninvasively predict graft closure and/or improved regional perfusion with patent grafts.

Angina Pectoris↗

PubMed1977

The radionuclide ejection fraction: a comparison of three radionuclide techniques with contrast angiography.

Left-ventricular ejection fraction (EF) can be measured by several radionuclide methods. The EFs determined by three such methods (first-transit time-activity, equilibrium blood-pool time-activity, and equilibrium blood-pool area-length) were compared in 30 patients with EFs measured by area-length analysis of x-ray contrast angiograms. Both time-activity methods (first-transit and blood-pool) yielded EFs that correlated well with x-ray contrast EFs (r=0.86 and 0.84, respectively). Area-length analysis of blood-pool images yielded EFs that agreed less well with x-ray contrast EFs (r=0.73 in the RAO view, 0.70 in the LAO view). We conclude that first-transit and blood-pool techniques are equally accurate methods for determining EF when the time-activity method of analysis is employed.

Adult↗

PubMed1977

Myocardial imaging with thallium-201: an experimental model for analysis of the true myocardial and background image components.

The true myocardial and background components of a resting thallium-201 myocardial image were determined in an experimental dog model. True background was determined by imaging after the heart had been removed and replaced with a water-filled balloon of equal size and shape. In all studies, the background estimated from the region surrounding the heart exceeded true background activity. Furthermore, the relationship between true myocardial background and that estimated from the pericardiac region was inconsistent. Background estimates based on the activity surrounding the heart were not accurate predictors of true background activity.

Animals↗

PubMed1976

Myocardial imaging with radionuclide-labeled particles. Analysis of the normal image, abnormal image, and technical consideration.

Myocardial imaging following the direct injection of labeled particles is an effective and safe method of studying regional perfusion. Perfusion defects can conveniently be classified as apical, anterior, inferior, or posterior and related to the distribution of specific coronary arteries. The hemodynamic effects of contrast material, inadequate mixing of particles, coronary anatomy, and associated cardiac pathology are important technical considerations affecting the performance and interpretation of studies using this technique.

Albumins↗

PubMed1975

Myocardial perfusion imaging with 99m-Tc or 113m-In macroaggregated albumin: correlation of the perfusion image with clinical, angiographic, surgical, and histologic findings.

Scintillation camera myocardial perfusion images were performed in 77 patients with proved or suspected ischemic heart disease following the intracoronary injection of 1.5 mCi 99m-Tc or 113m-In macroaggregated albumin. Perfusion images were classified as normal (36) or abnormal (41), and the location of abnormality was noted. Thirty-seven out of 41 patients with abnormal images had prior myocardial infarction based on history (30), ECG Q-waves (27), local contraction pattern abnormality (23), or direct surgical (9) or histologic (4) inspection, either singly or in combination. Three out of five patients with pre-infarction angina had image defects-none had evidence of infarction by ECG, ventriculogram, or surgical inspection. Coronary artery stenosis correlated with image defects to the extent that myocardial infarction was associated; 28 out of 29 patients with total occlusions and other evidence of infarction had image defects, four patients with complete occlusions but without other evidence of infarction had normal images. We conclude that, excepting patients with pre-infarction angina, this technique is more sensitive and direct in the identification of myocardial scar than standard ECG, clinical evaluation, or biplane left ventriculography.

Autopsy↗

PubMed1975

Myocardial imaging with indium- 113m- and technetium-99m-macroaggregated albumin. New procedure for identification of stress-induced regional ischemia.

Regional coronary blood flow distribution was studied by myocardial imaging after intracoronary injection of technetium-99m- and indium-113m-macroaggregated albumin at rest and during coronary hyperemia induced by intracoronary injection of Hypaque-M, 75 percent. The four- to five-fold increase in coronary flow after injection of radiographic contrast material was similar in magnitude to that occurring with maximal exercise stress. Experimentally, resting coronary blood flow and regional distribution of radioactive particles remains normal in spite of coronary stenosis of up to 85 percent. Less severe stenosis causes flow and distribution abnormalities only during periods of increased flow, and the degree of maldistribution is directly related to the physiologic severity of the stenosis. Of 49 patients with suspected coronary artery disease, 10 had no significant lesions by coronary arteriography and all had normal images at rest and during coronary hyperemia. Thirty-seven of 39 patients with significant obstructive coronary artery disease had abnormal images at rest or during contrast agent-induced hyperemia, or both. Patients with significant coronary artery disease without previous infarction usually demonstrated abnormalities in flow distribution only during coronary hyperemia. Patients with previous infarction demonstrated resting perfusion abnormalities that often became more abnormal during hyperemia. This technique provides a new method for assessing the physiologic effects of coronary stenosis in conjuntion with coronary arteriography.

Albumins↗

PubMed1975

The effect of external pressure diastolic augmentation on regional myocardial perfusion in experimental myocardial infarction.

The effect of external pressure diastolic augmentation on the distribution of coronary blood flow following coronary occlusion was studied in 36 dogs using radionuclide tagged macroaggregated albumin and an electromagnetic flow meter. Collateral flow, approximately 30% of normal flow immediately following occlusion, increased spontaneously by approximately 50% over the first 4 h. Two and 4 h of immediate, maximal external pressure diastolic augmentation resulted in only slightly greater mean increases in collateral flow than that which occurs spontaneously during the same time period. Reduction of the level or delay in onset of diastolic augmentation resulted in even less increase in collateral flow to the ischemic area. Mean coronary flow increased only 6% with external pressure diastolic augmentation. Since neither distribution of coronary blood flow nor total coronary blood flow was significantly altered by external pressure diastolic augmentation, this technique appears to be relatively ineffective in improving oxygen delivery to acutely ischemic myocardium in the dog.

Animals↗

PubMed1974