The Relative Accuracy of Echocardiography, Intravenous CO₂Studies, and Blood-Pool Scanning in Detecting Pericardial Effusions in Dogs

Abstract

This study was an attempt to determine the relative accuracy of echocardiography, intravenous carbon dioxide, and blood-pool scanning in detecting pericardial effusions. Since we usually do not know how much fluid is present in the pericardial sac of humans with effusions and the volume cannot be easily changed, dogs were used in this investigation so that the size of the effusion could be accurately controlled. Materials and Methods The 25 mongrel dogs examined were of either sex and ranged in size from 10 to 23 kg. They were anesthetized with sodium pentobarbital, and catheters were placed in the pericardial sac percutaneously by the method described by Christensen et al. (3). For acute effusions, 6 per cent isosmotic dextran was used. It stayed in the pericardial space fairly well and did not draw in any additional fluid. To test for leakage around the catheter, 75 ml of dextran was injected into the pericardial sac of smaller dogs, 100 ml with larger dogs. The fluid was then removed, and, if all of it could be recovered, we proceeded with the tests as described below. If any leakage had occurred, the study was discontinued, and the dog was re-examined at a later date. Echocardiography: An Ekoline-20 unit with a B-mode sweep and a 10 mm 2.0 megacycle transducer were used for all of the echocardiograms. All studies were done with the dogs in the left lateral decubitus position. After a preliminary echocardiogram, a series of tracings was obtained as the effusion was enlarged by 25 ml increments. Frequently, the fluid was faintly opacified at this time with Conray-60, and the fluoroscope was used to find the optimal location for echocardiography. Our early experience with echocardiography was disappointing. We employed the basic technic outlined by Feigenbaum and others in looking for fluid behind the heart (4–6, 11). Fluid, however, does not accumulate in the posterior portions of the pericardial sac in dogs until the effusions become large (7), and then in only small quantities. Others have made the same observation in humans (13, 14). With this in mind, we began looking for fluid in the anterior pericardial sac. This proved to be relatively simple, since there are few confusing echoes in the anterior mediastinum. The first pulsating echo encountered is the anterior heart wall. We considered an echocardiogram positive when a space was clearly defined between the anterior heart wall and the chest wall at all times during the cardiac cycle. If the heart wall touched the chest wall, the study was considered negative. Figure 1 shows an example of a positive echocardiogram in a dog with a 400-ml effusion. Intravenous Carbon Dioxide Studies: For the carbon dioxide studies, 30–40 ml of carbon dioxide was injected into a vein in the left foreleg with the dog in the left lateral decubitus position.