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Biomedical subjects

J L Ritchie

Publications and source records attributed to J L Ritchie.

At least 109 records · Page 6Linked to original sources
PubMed1982

Streptokinase in acute myocardial infarction: western Washington randomized trial--protocol and progress report.

A randomized trial of intracoronary thrombolysis in a multicenter, geographically limited community has been undertaken. There have been no deaths or important morbidity because of heart catheterization. Preliminary data analysis has shown that patient entry within 3 hours of the onset of infarction has been the exception rather than the rule. It is anticipated that this trial will be completed by mid 1983. It is hoped that the data obtained from this study will help clarify the role of thrombolysis in acute myocardial infarction.

Adult↗
PubMed1982

111In-oxine platelet imaging in hemodialysis patients: detection of platelet deposition at vascular access sites.

The value of 111In-oxine platelet imaging to assess abnormal platelet deposition at different vascular access sites was studied in 19 hemodialysis patients. Platelets were labelled immediately following dialysis and imaging was performed 2 and 48 h later; abnormal platelet deposition was defined as a localized increase in activity over time when compared to the opposite, control extremity. 10 patients had bovine grafts, 4 had arteriovenous fistulae, and 5 had Gore-Tex grafts. 111In-oxine platelet imaging demonstrated abnormal platelet deposition in 13 out of 19 patients. Positive images were obtained in some patients with each type of vascular access. Preliminary evaluation showed no clear relationship between image positivity and the history of prior graft occlusion. The imaging method provided in vivo evidence of the efficacy of treatment with the antiplatelet agent sulfinpyrazone in half of the treated patients. Following 1 week of sulfinpyrazone, 200 mg t.i.d., in 6 patients, 3 showed a definite decrease in platelet deposition, 2 showed a probable decrease, and 1 showed no change following therapy. We conclude that platelet imaging may provide organ-specific, in vivo evidence for abnormal platelet deposition in several types of vascular access sites, and may be useful in assessing the thrombogenicity of prosthetic materials and the efficacy of antithrombotic drugs.

Adult↗
PubMed1982

Detection of left ventricular thrombus by two-dimensional echocardiography: sensitivity, specificity, and causes of uncertainty.

To define the sensitivity, specificity and predictive accuracy of two-dimensional echocardiographic detection of left ventricular thrombus, the echocardiograms of 78 patients who had independent proof of the presence or absence of a left ventricular thrombus were interpreted without knowledge of any clinical data. The presence of thrombus was established by autopsy in four patients, by aneurysmectomy in three, and by indium-111 platelet imaging in 15; the absence of thrombus was proved by autopsy in 55 patients and by aneurysmectomy in one patient. The characteristics of true-positive and false-positive echocardiograms, interobserver variability, and clinical features associated with proved thrombus were also defined. The echocardiogram was positive for thrombus in 22 patients, equivocal in seven and negative in 49. For detection of thrombus, a positive or equivocal echocardiogram had a sensitivity of 95% (21 of 22), a specificity of 86% (48 of 56), and a predictive value of 72% (21 of 29); the predictive value of a negative study was 98% (48 of 49). Considering positive and equivocal studies separately, the predictive value of a positive study was 86% (19 of 22), while that of an equivocal study was only 29% (two of seven). Compared with patients who had no thrombus, patients with proved thrombus had a higher prevalence of electrocardiographic transmural anterior infarction (86% vs 13%), left ventricular aneurysm (73% vs 5%), and clinical systemic emboli (36% vs 7%) (all p less than 0.05). These clinical features help to identify a subset of patients most likely to have left ventricular thrombi who may benefit from echocardiography. Two-dimensional echocardiography is highly sensitive in detecting left ventricular thrombus, but false-positive studies are relatively common. Several echocardiographic criteria derived from analysis of the true and false positives in this study may help minimize diagnostic errors.

Diagnosis, Differential↗
PubMed1982

Regional distribution of myocardial blood flow measured by single-photon emission tomography: comparison with in vitro counting.

An emission computed tomography system (SPECT), which uses a single large-field-of-view gamma camera, was evaluated for its ability to measure the relative distribution of myocardial blood flow and to assess the effect of attenuation, scatter, and cardiac motion on the tomographic images. Normalized regional myocardial counts from the SPECT images of the living dogs correlated closely with those from the anatomic slices and the samples counted at necropsy except for an over-estimate of tracer in the perfusion defect (SPECT) 57.7 compared to tissue count 32.1; p less than 0.05. The differences were less for the other imaging conditions. Heart and thorax motion, attenuation, and scatter contributed less than 25% to the over-estimate of defect counts. We conclude that the SPECT system accurately reflects regional distribution of myocardial blood flow except for overestimation of flow in regions of perfusion defects. Small perfusion defects might therefore be missed, but no artifactual defects are created.

Animals↗
PubMed1981

Detection of left ventricular thrombi with radionuclide angiography.

Apparent filling defects compatible with left ventricular thrombus are occasionally noted in equilibrium radionuclide angiocardiograms. To define the usefulness of the radionuclide angiogram in detecting left ventricular thrombus, the anterior and left anterior oblique radionuclide angiograms of 39 patients with proved presence or absence of thrombus were blindly interpreted. The presence of thrombus was proved at autopsy in 5 patients, at cardiac operation in 2, or on indium-111 platelet imaging in 6; the absence of thrombus was proved at autopsy in 24 or at cardiac operation in 2. Overall, 13 radionuclide angiograms were interpreted as positive (n = 10) or equivocally positive (n = 3) for thrombus, and 26 studies were judged negative. The sensitivity of a positive or equivocally positive radionuclide angiogram for detection of thrombus was 77 percent (10 of 13 patients), the specificity 88 percent (23 of 26 patients), the positive predictive value 77 percent the negative predictive value 88 percent. If the three equivocal studies are instead considered negative for thrombus, the sensitivity was 62 percent, the specificity 92 percent, the positive predictive value 80 percent and the negative predictive value 93 percent. All thrombi were visualized in the anterior view in an area of akinetic or dyskinetic wall motion. A small group of 13 patients (8 with thrombus, 5 without) underwent two dimensional echocardiography, which was 100 percent sensitive and specific. The finding of a discrete filling defect or squared or cutoff ventricular apex in an area of abnormal wall motion in the anterior view of the radionuclide angiogram should suggest the diagnosis of ventricular thrombus, which may be confirmed by other noninvasive studies.

Autopsy↗
PubMed1981

Left ventricular thrombi: in vivo detection by indium-111 platelet imaging and two dimensional echocardiography.

Indium-111 platelet imaging, which can identify sites of active intravascular platelet deposition, and two dimensional echocardiography, which can identify intracardiac masses, can both be used to detect left ventricular thrombi noninvasively. We compared these techniques in 44 men at risk for thrombi from remote transmural myocardial infarction (31 patients) or cardiomyopathy (13 patients). All 44 patients underwent platelet imaging; 35 underwent echocardiography. On platelet imaging nine patients had thrombi and one had a possible thrombus. Of these 10 studies, none were positive at 2 hours, 5 were positive at 24 hours and all were positive 48 or 72 hours after platelet labeling. Nine of these patients underwent echocardiography, and all had an intraventricular mass. The findings on platelet scanning were negative in six patients who had positive (four patients) or equivocally positive (two patients) findings on echocardiography. All patients with thrombi detected by either noninvasive method had transmural anterior myocardial infarction with ventricular aneurysm. Of the seven patients who underwent cardiac surgery or autopsy, three had thrombi. Platelet imaging failed to identify one thrombus in a patient in whom imaging was performed only at 24 hours after labeling. There were no false positive platelet images in this group. Five of these seven patients (two with thrombi, three without) underwent echocardiography; in all cases the echocardiographic findings agreed with the pathologic findings. Both platelet imaging and echocardiography detect ventricular thrombi. Platelet imaging may detect only the most hematologically active thrombi. Both techniques may help define patients at risk of embolization and may be useful for in vivo assessment of antithrombotic drugs.

Aged↗
PubMed1981

Indium-111 platelet imaging for detection of platelet deposition in abdominal aneurysms and prosthetic arterial grafts.

Thirty-four platelet imaging studies were performed in 23 patients to determine whether platelet deposition could be detected in patients with vascular aneurysms (18 patients) or in patients in whom Dacron prosthetic grafts had been place (5 patients). In patients in whom abnormal platelet deposition was detected, the effect of administration of platelet-active drugs on platelet deposition was examined. Of the 18 patients with an aneurysm, 12 had positive studies on initial imaging and 2 had equivocally positive images. Of five patients with Dacron arterial grafts in place, four had diffuse platelet deposition in the grafts; the fifth patient had platelet deposition only in a pseudoaneurysm. Eight patients with an abdominal aneurysm and positive or equivocally positive baseline images were restudied during platelet-active drug therapy either with aspirin plus dipyridamole (seven patients) or with sulfinpyrazone (four patients). No patient studied during treatment with aspirin plus dipyridamole had detectably decreased platelet deposition compared with baseline determinations. In contrast, two of four patients studied while receiving sulfinpyrazone showed decreased platelet deposition. Thus, platelet imaging may be of value for studying platelet physiology in vivo and for assessing platelet-active drugs and the thrombogenicity of prosthetic graft materials in human beings.

Abdomen↗
PubMed1981

Seven-pinhole emission tomography with thallium-201 in patients with prior myocardial infarction.

Thirty-six patients with prior myocardial infarction, and 14 patients without, had myocardial imaging at rest using both seven-pinhole emission tomography and planar imaging with thallium-201. The sensitivity and specificity of the two approaches for the detection of prior myocardial infarction were compared. Qualitatively, planar imaging yielded sensitivities of 69% (25 of 36) and 80% (29 of 36) with Polaroid and video display formats, respectively. A semiquantitative analysis gave a sensitivity of 75% (27 of 36). Specificities for these three planar approaches were, respectively, 100% (14 of 14), 93% (13 of 14), and 71% (10 of 14) for the Polaroid, video, and semiquantitative analyses. Seven-pinhole tomography had a sensitivity of 83% (30 of 36) by qualitative or visual inspection and 86% (31 of 36) by semiquantitative analysis. Specificities by these two techniques were 71% (10 of 14) and 57% (8 of 14). There were no statistically significant differences in either sensitivity or specificity between the planar and tomographic approaches. Repeat seven-pinhole images were identical in 95% (46 of 48) of patients, showing that reproducibility was satisfactory. We conclude that the seven-pinhole tomographic approach has no advantage over standard planar imaging in the detection of prior myocardial infarction.

Adult↗
PubMed1980

Anthracycline cardiotoxicity: clinical and pathologic outcomes assessed by radionuclide ejection fraction.

A clinical syndrome of severe cardiomyopathy often accompanies administration of high doses of anthracycline agents. We studied 36 patients serially with radionuclide angiography. At three weeks following drug administration, 8 of 36 patients showed depression of ejection fraction (EF). All had received at least 280 mg/m2 of the drug and 7 had received more than 380 mg/M2. Definite clinical syndromes of congestive cardiomyopathy developed only in patients showing EF depression and in some patients, EF depression developed without signs of congestive heart failure. Ejection fraction studies at 5 minutes, 1 hour, 4 hours, 24 hours, 72 hours, and one week following drug administration showed no changes when compared to immediate preg-drug EF. Seven patients who died during the study underwent histologic examination. Only the single patient with a depressed EF showed histologic evidence of athracycline cardiotoxicity, although all but 1 of these patients had received at least 400 mg/M2. We conclude that serial radionuclide EF just prior to anthracycline administration is a potentially useful predictor of cardiac toxicity, and that EF depression and/or preservation of a normal EF should be weighed in the decision for administering a drug of this type at high dosage levels.

Antibiotics, Antineoplastic↗
PubMed1980

In vivo simulation of thallium-201 myocardial scintigraphy by seven-pinhole emission tomography.

Seven-pinhole emission tomography has been studied under conditions that simulate clinical myocardial imaging with thallium-201, and is compared with planar imaging with a heart phantom. The seven-pinhole technique produces reconstructed images that offer a tomographic presentation of the object but do not quantitatively represent true cross sections of the object's activity distribution. Tomography produces significantly greater image contrast than planar imaging, even when maximal background subtraction is used to enhance the planar images. Two quantitative limitations of seven-pinhole tomography are noted for a simulated 24-g, 1.5-cm-thick complete transmural infarct: (a) the defect's activity concentration is not accurately reconstructed, and (b) it propagates longitudinally into some reconstructed planes that do not contain it. The imaging limitations of seven-pinhole tomography under the conditions studied are shown to be consistent on several camera/computer/software configurations.

Heart↗
PubMed1980

The role of platelets in acute vascular events.

Platelets are postulated to have an important role in acute and chronic cardiovascular events. Clinical events may result during the sequence of platelet activation reactions of adhesion, aggregate formation, release of granular constituents, thromboxane A2 formation, microembolization and platelet vascular occlusion. For example, sudden death may occur in patients with increased platelet sensitivity to catecholamine stimulation, platelet aggregate formation and thromboxane A2 generation resulting in ischemic ventricular arrhythmia induced by small-vessel platelet microembolization and local thromboxane A2 vasoconstriction. Whereas angina might be manifest if the microemboli disaggregated and vasospasm were transient, myocardial infarction would follow extensive permanent occlusion of small vessels or localized narrowing by vasospasm and extension of platelet thrombus formation at the site of intimal thickening. Platelets may also have an important role in atherogenesis through the mediation of the platelet-derived growth factor in the proliferative smooth muscle cell intimal lesion. Direct experimental and indirect clinical studies support the concept that platelets are important in cardiovascular events, but the relationship to spasm and to other possibly even more important mechanisms is not clear. Acute myocardial infarction and mural thrombogenesis appear to have the greatest evidence of being platelet-related.

Acute Disease↗
PubMed1980

Performance characteristics of a commercial ECG gate.

A commercial ECG gate was tested to evaluate its ability to predict accurately the time of end-systole. The predicted times followed the manufacturer's specifications quite well. These times were compared with the actual times of end-systole as determined by computer-derived left-ventricular time-activity curves using Tc-99m-labeled red blood cells. Although there was moderate scatter, the predicted times of end-systole correlated well with the actual times (n = 59, r = 0.829). If the left-ventricular ejection fraction was calculated using the predicted time of end-systole, the error would be 0.03, or less, for 95% of the subjects.

Cardiac Output↗