Detection Of Intracardiac Thrombi Using Radio-Iodinated Antifibrinogen (RIAF) And Precordial Scanning

Abstract

Intracardiac thrombi were produced in 47 dogs by instillation of 5% sodium morrhuate into an empty and excluded segment of the left atrium. Twenty-four hours thereafter, 15 dogs were given 5 [mu]Ci./Kg. RIAF (131I-labelled rabbit antibody specific of canine fibrinogen) intravenously. Equivalent doses of 131I-fibrinogen (75% clottable), 131I-fibronogen (92% clottable), 131I-rabbit gamma globulin (nonspecific), 131I-human serum albumin, and 197Hg-neohydlin were given to 10, 4, 5, 7, and 5 dogs, respectively. Each animal was operated upon again at an interval appropriate to the half-life of the label employed. Fresh thrombus was invariably found within the atrium. The thrombi were removed, homogenized, and counted in a well-type scintillation detector, the radioactivity of equal volumes of atrial blood, atrial appendage, in vitro clot, and serum was also determined. In all dogs sacrificed 30-96 hr. after receiving RIAF, thrombus: blood activity ratios (At/Ab) of 3.2 to 16.1 were recorded. Antemortem precordial scans were performed in 8 of these dogs, and in each of them the thrombus was demonstrated. Of the other materials listed, only 131I-fibrinogen resulted in an At/Ab as high as 1.8, a ratio below the detection threshold for precordial scanning. Significantly, this label demonstrated a greater affinity for the inflamed atrial appendage than for the thrombus within it. In preliminary clinical trials of RIAF (human), specific labeling and At/Ab ratios above scan detection thresholds were measured in 2 left atrial thrombi recovered at operation in patients with mitral valvular disease. In a 3rd patient, a left ventricular thrombus was detected by precordial scanning, and its presence was confirmed by angiography and subsequent necropsy.