Diagnostic accuracy of indium-111 platelet scintigraphy in identifying left ventricular thrombi

Monitoring the effect of anticoagulants on left atrial thrombi in patients with rheumatic heart disease: assessment with 111In-oxine-labelled platelet heart scintigraphy and transoesophageal echocardiography

111In-oxine-labelled platelet heart scintigraphy (In-plt) was used to evaluate the activity of left atrial thrombi detected by transoesophageal echocardiography (TEE) in 16 cases of rheumatic heart disease. The effect of anticoagulants on the therapeutic intervention of these patients was evaluated by In-plt and TEE. In-plt was performed in all patients in serial pre- and post-anticoagulant therapy studies with anterior, 45 degrees left anterior oblique and left lateral views taken daily from the second to sixth day after injection of labelled platelets. After discontinuing anticoagulants for at least 1 week, only nine cases of left atrial thrombi were detected among the 16 cases by initial In-plt. After anticoagulants were again used for at least 3 weeks, all nine positive cases became negative on repeat In-plt. These results suggest that the diagnostic sensitivity of In-plt is lower than that of TEE. However, In-plt is more suitable and useful for evaluating the activity of left atrial thrombi after antithrombotic agent therapy and for monitoring the effect of anticoagulant therapy on left atrial thrombi in patients with rheumatic heart disease.

Composition of human thrombus assessed by quantitative colorimetric angioscopic analysis

BACKGROUND

Angioscopy surpasses other diagnostic tools, such as angiography and intravascular ultrasound, in detecting arterial thrombus. This capability arises in part from the unique ability of angioscopy to assess true color during imaging. In practice, hardware-induced chromatic distortions and the subjectivity of human color perception substantially limit the theoretic potential of angioscopic color. We used a novel application of tristimulus colorimetry to quantify thrombus color to both aid in its detection and assess its composition.

METHODS AND RESULTS

A series of human thrombus models were constructed in vitro. Spatial homogeneity was ensured by light and electron microscopy. Quantitative colorimetric angioscopic analysis demonstrated excellent measurement reproducibility (mean difference, 0.07% to 0.17%), unaffected by illuminating light intensity (coefficient of variation, 0.21% to 3.67%). Colorimetric parameters C1 and C2 were strongly correlated (r=.99, P<.0001) with thrombus erythrocyte concentration. Principal components analysis transformed these parameters into a single value, the thrombus erythrocyte index, with little (0.06%) loss of content. Measured and predicted concentrations were similar (mean difference, 0.16 erythrocytes per 1 ng). Randomly ordered images were also subjected to visual analysis by three experienced angioscopists, with suboptimal levels of both intraobserver (mean kappa=0.63) and interobserver (mean kappa=0.48) agreement. In addition, visual ranking resulted in a Kendall rank coefficient of 0.72 to 0.76 versus a perfect 1.00 from quantitative measurement.

CONCLUSIONS

Quantitative colorimetric angioscopic analysis provides a new, objective, and reproducible analytic tool for assessing angioscopic images of human thrombus. Even under ideal circumstances, experienced angioscopists do a poor job of assessing color (and therefore composition) of human thrombi. This technique can, for the first time, provide quantitative information of thrombus composition during routine diagnostic imaging.

Selective uptake of radiolabeled annexin V on acute porcine left atrial thrombi

BACKGROUND

Annexin V is a human phospholipid binding protein that binds to activated platelets in vitro. We sought to determine the potential of this agent for imaging intracardiac thrombi in swine.

METHODS AND RESULTS

Left atrial thrombi were formed by crush injury. In initial nonimaging experiments using intravenous 125I-labeled human annexin V, the mean thrombus/whole blood ratio was 13.4 +/- 4.8 for the entire thrombus using well counting of resected specimens (n = 8). Using intravenously injected 99mTc-labeled human annexin V, the left atrial thrombus/blood ratio by well counting was similar (14.2 +/- 10.6 for the entire thrombus and 26.2 +/- 14.9 for the peak section) (n = 12). The ratio for a control protein, 125I-ovalbumin, was only 1.0 +/- 0.2. 99mTc tomographic imaging was positive (n = 10) or equivocal (n = 2) in all experiments with but negative in 10 controls without left atrial thrombi. By region-of-interest analysis of the tomographic images, the mean left atrial appendage/blood ratio at 2 hours in animals with a thrombus was 3.90 +/- 1.12 compared with 0.84 +/- 0.10 in closed chest controls and 1.01 +/- 0.23 in open chest controls (P < .001).

CONCLUSIONS

We conclude that 99mTc-labeled human annexin V detects acute left atrial thrombi in vivo in swine. The combination of a new thrombus detection agent, annexin V, with a 99mTc label may allow in vivo imaging of thrombi in humans.

111In platelet imaging of left ventricular thrombi. Predictive value for systemic emboli

To determine whether a positive indium 111 platelet image for a left ventricular thrombus, which indicates ongoing thrombogenic activity, predicts an increased risk of systemic embolization, we compared the embolic rate in 34 patients with positive 111In platelet images with that in 69 patients with negative images during a mean follow-up of 38 +/- 31 (+/- SD) months after platelet imaging. The positive and negative image groups were similar with respect to age (59 +/- 11 vs. 62 +/- 10 years), prevalence of previous infarction (94% vs. 78%, p less than 0.05), time from last infarction (28 +/- 51 vs. 33 +/- 47 months), ejection fraction (29 +/- 14 vs. 33 +/- 14), long-term or paroxysmal atrial fibrillation (15% vs. 26%), warfarin therapy during follow-up (26% vs. 20%), platelet-inhibitory therapy during follow-up (50% vs. 33%), injected 111In dose (330 +/- 92 vs. 344 +/- 118 microCi), and latest imaging time (greater than or equal to 48 hours in all patients). During follow-up, embolic events occurred in 21% (seven of 34) of patients with positive platelet images for left ventricular thrombi as compared with 3% (two of 69) of patients with negative images (p = 0.002). By actuarial methods, at 42 months after platelet imaging, only 86% of patients with positive images were embolus free as compared with 98% of patients with negative images (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of acute experimental left ventricular thrombi with quantitative backscatter imaging

Two-dimensional echocardiography is an excellent technique for detecting left ventricular thrombi, however, acute clot is sometimes difficult to differentiate from adjacent myocardium and intracavitary signals. We hypothesized that quantitative assessment of the acoustic properties of acute left ventricular thrombi using a quantitative backscatter imaging system would permit the differentiation of thrombus from adjacent myocardium and intracavitary echoes. Acute, experimental left ventricular thrombi in seven dogs were evaluated with a quantitative backscatter imaging system that allowed the measurement of relative integrated backscatter and cyclic (i.e., diastolic minus systolic) variation in integrated backscatter. Coronary ligation abolished the cyclic variation in relative backscatter that occurred in normal myocardium. The end-diastolic relative backscatter in the thrombus (16.9 +/- 1.3 dB) was significantly higher than in apical myocardium (13.2 +/- 0.6 dB, p less than 0.05). There was no significant difference in the cyclic variation in relative backscatter among thrombus, ischemic myocardium, or intracavitary blood. Thus, the quantitative assessment of the acoustic properties of left ventricular thrombi can be useful in their detection and in the differentiation from myocardium and intracavitary signals.

Radiopharmaceuticals for thrombus detection

Most of the components of the thrombotic and fibrinolytic systems have at some time been evaluated as a means of carrying a radiolabel specifically to thrombi, although very few have been promising enough to emerge from investigational status to routine clinical use. New approaches are being explored, including improved methods of labeling platelets, chemically modified forms of previously tested plasma proteins, and new biomolecules, including monoclonal antibodies specific for fibrin and platelets. The current goal is to find one or more radiotracers that bind specifically and rapidly to thrombi, and that also have a rapid blood disappearance rate, permitting a clear diagnosis within a few hours after injection. Because this test may be needed to assess the course of therapy in an anticoagulated patient, the ideal radiopharmaceutical should be able to locate thrombi without interference by anticoagulants. Until a suitable thrombus-specific radiopharmaceutical becomes generally available, many hospitals will continue to attempt to make a diagnosis with nonspecific radiopharmaceuticals that can at best provide blood pool images to indicate filling defects. Several of the new approaches seem likely to provide the radiopharmaceutical sought, although clinical trials are at an early stage.

111In-labeled platelet scintigraphy and two-dimensional echocardiography for detection of left atrial appendage thrombi. Studies in a new canine model

111In-labeled platelet scintigraphy and two-dimensional echocardiography were performed in 40 dogs to determine the ability of the two techniques to detect left atrial appendage thrombi. Thrombi were induced in 33 dogs that were classified into two groups, "acute" or "chronic," according to the time of labeled-platelet injection after thrombus induction. In the acute group (17 dogs), platelets were injected 24 hours after thrombus induction. In the chronic group (16 dogs), platelets were injected 4-8 days after thrombus induction. "Sham" thoracotomies were performed on seven additional control dogs who did not receive thrombin injections. Analog and blood pool-corrected 111In-labeled platelet scintigraphy images were obtained 4-72 hours later. Closed-chest two-dimensional echocardiography was performed before thoracotomy and repeated at the time of scintigraphy. The location and size of each thrombus were verified at autopsy. Two-dimensional echocardiography detected three of 17 acute (mean volume, 1.2 +/- 1.0 cc) and three of 10 chronic (mean volume, 0.4 +/- 0.3 cc; p less than 0.025) left atrial appendage thrombi. 111In-labeled platelet scintigraphy detected all 17 acute thrombi but only two of 10 chronic thrombi. The measured radioactivity levels of the excised thrombi were 1,949 +/- 1,665 cpm/clot/dose in group 1 and 228 +/- 213 cpm/clot/dose in group 2 (p less than 0.005). In this model, 111In-labeled platelet scintigraphy was able to detect acute left atrial appendage thrombi that could not be identified by two-dimensional echocardiography. Both techniques showed poor sensitivity for detection of chronic thrombi. The decline in sensitivity of 111In-labeled platelet scintigraphy for detection of older thrombi is probably due to diminished labeled-platelet incorporation.

Digital ischaemia and palpable pedal pulses

Digital ischaemia in the presence of an otherwise well-perfused foot in the non-diabetic patient presents diagnostic problems especially as the manifestations are frequently evanescent. Eighty such patients (sixty men and twenty women aged 55-84 years) who presented to St. Laurence's Hospital from 1982 to 1985 inclusive were evaluated. Micro-embolization was inferred from the demonstration of a cardiac (20) or an arterial source (42) in 62 of 80 patients. In 14 of the remaining 18 patients a malignancy was diagnosed, which was found to be visceral cancer in 11 cases. Indium platelet scanning revealed platelet aggregation in 14 of 26 patients examined. Laboratory evidence of abnormalities of platelet aggregation or blood coagulation was found in only 6 patients. There have been no further symptoms in 37 patients who have been treated surgically or in 17 of 21 patients who have been treated with either anticoagulation or antiplatelet therapy.

Indium-111 platelet scintigraphy and two-dimensional echocardiography for detection of left ventricular thrombus: influence of clot size and age

Two-dimensional echocardiography and indium-111 platelet scintigraphy were performed on 50 dogs to determine the influence of clot age and size on the detection of experimentally induced left ventricular mural thrombus. Thrombus was induced by apical infarction and injection of a sclerosing agent and thrombin. The animals were classified into four groups according to the time of indium-111 platelet injection after thrombus induction: Group I (17 dogs, 1/2 hour after induction; 3 dogs, before induction), Group II (12 dogs, 24 hours after induction) and Group III (12 dogs, 1 week after induction). In Group IV (six control dogs) apical infarction was produced, but thrombin was not injected; indium-111 platelets were injected 1/2 to 1 hour after infarction. The dogs were studied by indium-111 platelet scintigraphy and by two-dimensional echocardiography 1/2 to 5 hours (Group I) and 1 to 5 and up to 72 hours (Groups II to IV) after platelet administration and before death was induced. Two-dimensional echocardiography showed the best overall sensitivity for detection of acute thrombus (97%; 29 of 30). The sensitivity of indium-111 platelet scintigraphy was 86% (18 of 21) for clots greater than or equal to 0.08 ml in size, and 67% (20 of 30) for detection of all clots. Thrombus did not form in 14 dogs of Groups I to III and in 6 of 6 control dogs. The specificity of scintigraphy was 100% (20 of 20) compared with 80% (16 of 20) for echocardiography. Echocardiography was more sensitive than scintigraphy for detecting very small clots in this experimental model.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of intracardiac thrombi in stroke patients with indium-111 platelet scintigraphy

Platelet scintigraphy (PSC) with indium-111 labelled platelets has been confirmed as an adequate method for the detection of intracardiac thrombi in patients with heart disease. We performed PSC of the heart and the neck vessels in 27 stroke patients with suspected cardiac embolism and as control on 10 patients with atherosclerotic lesions of the carotid arteries without evidence of heart disease. The carotid PSC was positive in 6 of 10 patients with carotid disease, and twice in the 27 with suspected cardiac embolism. In these 27 the PSC of the heart indicated pathological conditions 13 times. Pathological platelet accumulations could be visualized in 3 cases in the atrial space, in 9 cases in the region of the left ventricle, and once at the aortic valve. Scintigraphy was negative in all 10 patients with atherosclerosis of the neck vessels. The two-dimensional echocardiography revealed pathological findings in 8 of the 13 patients with positive heart PSC (3 with intraventricular thrombi, 3 with valvular disease, 2 with decreased ventricular contractility) and was normal in the 10 control patients. Open-heart surgery was performed in 2 patients with pathological PSC and revealed an intracardiac thrombus. Three of 4 patients with positive atrial PSC showed mitral or aortic valve disease. These results suggest that PSC can provide a valuable method for detecting cardiac thrombi in stroke patients.

Thrombosis and embolism from cardiac chambers and infected valves

In a number of cardiac conditions (acute myocardial infarction, chronic left ventricular aneurysm, dilated cardiomyopathy, infective endocarditis and atrial fibrillation in the absence of valvular disease), the risk of embolism gives cause for concern. Although anticoagulation with warfarin (Coumadin)-derivatives has been shown to be effective in some of these situations, there is no evidence regarding the role of antiplatelet agents. The common factor in the thromboembolic potential of acute myocardial infarction, chronic left ventricular aneurysm and dilated cardiomyopathy is mural thrombus. This can be detected by two-dimensional echocardiography and indium-111 platelet scintigraphy. Although of value in elucidating the natural history of mural thrombus, in most cases, management is not substantially aided by these investigations. In patients with extensive myocardial infarction, particularly anterior infarction, moderate intensity anticoagulation started soon after hospital admission reduces the rate of embolism. After 8 to 12 weeks, embolic risk is low so that anticoagulants can usually be discontinued. Patients with chronic left ventricular aneurysm have a low incidence of embolism; anticoagulation is, therefore, inappropriate. Dilated cardiomyopathy is associated with a high risk of embolism; moderate intensity anticoagulation may be advisable in many such cases. Little information is available regarding the incidence of thromboembolism or the role of antithrombotic therapy in the patient with a diffusely dilated left ventricle due to ischemic heart disease. In native valve infective endocarditis, the risk of hemorrhage is high, and the efficacy of conventional anticoagulants unclear; thus, anticoagulation should not be instituted for the cardiac condition as such. However, in prosthetic valve endocarditis, the risk of embolism seems to be very high, and anticoagulant therapy should be continued, but with great care because there is a substantial risk of cerebral hemorrhage. Atrial fibrillation in patients with valvular heart disease is dealt with in a previous review. Patients with nonvalvular atrial fibrillation are at varying risk of embolism, depending on the etiology of the arrhythmia; trials of antithrombotic therapy are needed for the various subsets of patients. In most elderly patients, the etiology is not known, and their stroke risk is high. The risk of embolism in younger patients with idiopathic atrial fibrillation is so low as to make any antithrombotic therapy unnecessary.(ABSTRACT TRUNCATED AT 400 WORDS)

Detection of ventricular thrombosis in acute myocardial infarction: value of indium-111 platelet scintigraphy in relation to two-dimensional echocardiography and clinical course

In order to detect left ventricular (LV) thrombosis, 111In-platelet scintigraphy and two-dimensional echocardiography were performed in 40 patients 15 days +/- 6 days after acute myocardial infarction. A dual isotope subtraction method, using 111In-platelet scintigraphy and 99mTc-blood pool scintigraphy, was used to assess LV platelet deposition expressed as LV counts per pixel. Seven patients (group A) had a positive 111In-platelet scintigram and 33 patients (group B) had a negative 111In-platelet scintigram (LV counts per pixel: 0.56 +/- 0.23 and 0.28 +/- 0.19, respectively, P less than 0.05). Three group A patients but no group B patients had a positive echocardiogram. Arterial embolism was noted in four patients, of whom two showed both positive echocardiogram and platelet scintigram. LV counts per pixel were 0.57 +/- 0.13 and 0.31 +/- 0.21, respectively (P less than 0.02) in patients with and without arterial embolism. Thus, both 111In-platelet scintigraphy and two-dimensional echocardiography can detect LV thrombosis. 111In-platelet scintigraphy may help to define patients at risk for embolization and may be used in conjunction with echocardiography to study the effect of antithrombotic therapy.

Comparative recognition of left ventricular thrombi by echocardiography and cineangiography

Studies performed in 47 patients, 11 of whom underwent surgery for aneurysmectomy and 36 of whom underwent cardiac transplantation, were reviewed to assess the diagnostic accuracies of cross sectional echocardiography and cineangiography in detecting left ventricular mural thrombi and the effect of anticoagulation treatment on the incidence of such thrombi. Cross sectional echocardiography in 37 patients and cineangiography in 26 (16 patients were examined by both methods) were analysed independently by sets of two observers experienced in the respective methods. All four observers were blinded to the pathological or surgical findings regarding mural thrombus. Mural thrombus was confirmed by pathological investigation in 14 of 47 (30%) cases; 11 of these 14 patients had intra-aneurysmal thrombi. The negative predictive value was quite good for both methods, but cross sectional echocardiography had a superior positive predictive value. This was due both to detailed soft tissue resolution by cross sectional echocardiography and to overdetection of mural thrombi by cineangiography in cases of aneurysms without mural thrombi. Mural thrombi were present in three of 20 patients with preceding anticoagulation and in 10 of 19 patients without anticoagulation. The results emphasise that cross sectional echocardiography is more reliable than cineangiography in recognising thrombi.

Left ventricular platelet deposition after acute myocardial infarction. An attempt at quantification using blood pool subtracted indium-111 platelet scintigraphy

Since indium-111 platelet scintigraphy for the detection of left ventricular thrombosis often shows considerable non-specific blood pool activity a subtraction method using simultaneous technetium-99m blood pool scintigraphy was undertaken in 11 subjects with well documented remote myocardial infarction, who served as positive or negative controls, and in 18 consecutive patients with acute myocardial infarction. The results were compared with those of cross sectional echocardiography. Thirteen patients had transmural myocardial infarction and the calculated count per pixel in the left ventricle of the subtracted indium-111 platelet scintigram was (mean (SD)) 0.28(0.35), but five patients with subendocardial myocardial infarction had a mean count of 0.04(0.06). In seven patients with transmural myocardial infarction (two anterior and five inferior) left ventricular thrombosis was detected by indium-111 platelet scintigraphy but in only one of these by cross sectional echocardiography. None of the patients with subendocardial myocardial infarction had left ventricular thrombosis. Subtracted left ventricular counts correlated well with the visual results. It is concluded that left ventricular platelet sequestration after acute myocardial infarction may be quantified and precisely located and that quantitative longitudinal studies of the natural history and drug intervention are now possible.

Detection of left atrial thrombi in man using indium-111 labelled autologous platelets

A scintigraphic technique using indium-111 labelled platelets to detect left atrial thrombi was used in 28 patients, 14 of whom had mitral valve disease and 14 combined valve disease. Imaging was performed in the anterior, right anterior oblique (45 degrees), and left lateral views on the day of injection and thereafter at one or two day intervals for a maximum of four days. When scintiphotos obtained in two or three views 72 or 96 hours after the platelet injection showed "hot spot areas" within the left atrial pool and indium-111 activity in these areas did not decrease with time they were interpreted as positive for thrombi. Of 28 patients, seven had positive platelet images by this criterion; of these, three underwent surgery and were found to have left atrial thrombi. One patient died, and a thrombus was found at necropsy. The remaining 21 patients had normal scintiphotos; of these, seven had no thrombi at operation and one had false negative images. The diagnostic accuracy of platelet scintigraphy by this criterion of positivity in the 12 patients in whom surgical or postmortem confirmation of thrombi could be obtained was 92%. These results indicate that this technique is a promising method for detecting active left atrial thrombi.