The diagnosis of myocardial infarction in patients with anomalous atrioventricular excitation (Wolff-Parkinson-White Syndrome)

Abstract

Anomalous atrioventricular excitation produces changes in the QRS complex which simulate myocardial infarction, and it conceals the presence of myocardial infarction by preventing the development of the QRS abnormalities which are diagnostic of this lesion. The anomalous order of ventricular excitation also produces changes in the S-T segments and T waves, which are characteristically unstable in this syndrome. Changes dependent on physiologic, or other, unknown influences, commonly occur. It is not possible to distinguish such changes from those which follow infarction of the myocardium. Moreover, similar S-T segment and T wave abnormalities occur with other types of injury and with other pathologic states, or may occur following the administration of certain drugs. These signs, then, cannot be considered reliable evidence of myocardial infarction. All these facts are important in the management of patients whose electrocardiograms display anomalous atrioventricular excitation. Error can be avoided only if great care is taken to recognize anomalous conduction, and then to refrain from making a diagnosis of infarction unless normally conducted beats ∗ occur, or can be induced. Carotid sinus stimulation, atropine, quinidine, and amyl nitrite, separately, or in combination, usually suffice to restore normal conduction. Failure with a given drug or measure on one occasion may be followed by success on another. The amount and rapidity of administration of drugs may be varied. The effect of digitalis in facilitating the appearance of, or in perpetuating the continuance of the anomalous mechanism, may explain failure to induce normal conduction in some cases. When feasible, efforts to convert the cardiac mechanism should be attempted before digitalis is administered, or, when it can be done without harm to the digitalized patient, the drug should be omitted when it seems impossible to abolish anomalous conduction otherwise.