An experimental study of acute pulmonary arterial obstruction, with special reference to the precordial electrocardiogram

Abstract

It must be concluded that in the dog the electrocardiogram, including multiple unipolar precordial leads, is of limited value in the diagnosis of minor pulmonary embolism. In major pulmonary embolism in the dog, there are usually definite electrocardiographic changes, both in the limb leads and in the unipolar precordial leads. In the limb leads, the most constant change is deviation of the RS-T segment in Leads II and III; this may be either upward or downward. In man, the upward deviation of RS-T 2 has not been reported. In the precordial leads, there was depression of the RS-T segment in the left precordial leads and elevation of the RS-T segment in the right precordial leads. In man, elevation of the RS-T segment in the right precordial leads has rarely been reported. 34 We did not attempt to evaluate the origin of these electrocardiographic changes; it has been suggested variously that they are due either to right ventricular strain or to myocardial anoxia. Previously in this paper attention has been called to the limitations of the electrocardiogram in the diagnosis of pulmonary embolism in man. But if a series of electrocardiograms are obtained in the first few days after pulmonary embolism occurs and if these are critically analyzed, valuable diagnostic aid can frequently be obtained. This study of the electrocardiograms of dogs in which pulmonary embolism has been induced experimentally would appear to support pessimism regarding the value of the electrocardiogram in the clinical diagnosis of pulmonary embolism. But it is by no means certain that these experiments in dogs duplicate the exact degree or exact mechanisms involved in pulmonary embolism in man. Furthermore, the electrocardiogram of the dog is more variable than is the electrocardiogram of man, so that electrocardiographic changes in the dog have to be of greater magnitude to have diagnostic significance. While the results of these experiments should serve to warn us that the electrocardiogram often fails to aid in the diagnosis of minor pulmonary emboli in man, it should not be concluded from this study that the procedure possesses very limited clinical value.