Scintillation scanning to detect atrial thrombi after intravenous administration of 131I labeled antibodies to human fibrinogen was performed on 30 patients who had mitral valve surgery under cardiopulmonary bypass. Twenty-six patients had negative scans and at operation no thrombus was found in 25. Of the 4 patients with positive scans, 3 had left atrial thrombi at surgery and 1 had a highly calcified valve. 131I determinations of blood, surgically removed cardiac tissue, and thrombi demonstrated that the thrombi could have as much as 25 times more 131I than that in an equivalent amount of blood. Little 131I accumulation was found in organized, avascular portions of the thrombus or atrial appendage, mitral valve, and tricuspid valve. Because of the high concentration of 131I in the thrombus compared to that in the cardiac tissue and blood, this procedure seems promising as a means of detecting atrial thrombi with little discomfort to the patient. It is suggested that the use of an antiserum to rabbit gamma globulin to remove immunologically the major portion of the blood-borne 131I rabbit antiserum to human fibrinogen may appreciably increase the ratio of thrombus to blood and this would decrease the possibility of falsenegative scans and increase the resolution of positive scans. © 1969.
