Cardiac Tamponade

Abstract

Summary

Dogs were subjected to various procedures in an attempt to clarify several existing theories about the electrocardiographic findings in pericarditis or cardiac tamponade. In this study changes in P- and R-wave amplitude are related to decreased arterial pressure and increased central venous pressure. Problems related to volume conduction are not involved in the decreased R-wave amplitude. The presence of additional fluid in the pericardial space results in S-T segment shift and T-wave inversion. Changes in the S-T segment require the additional factor of a systemic pressure change whereas the latter is independent of pressure changes. The shift in anatomical axis of the heart in a direction which impinges on the venous return to the right atrium will cause P- and R-wave changes and may be an important factor in the etiology of the electrocardiographic changes. Coronary insufficiency, on the basis of these studies, is not thought to be contributory to early electrocardiographic changes but may be of significance in later stages of pericarditis.