Cardioversion and the digitalized patient

Transthoracic synchronized direct current discharge or cardioversion was introduced nearly 25 years ago to restore sinus rhythm in patients with diverse tachyarrhythmias (I). This simple, expeditious and nearly complication-freemethod has withstood the test of time. The likelihood of serious adverse reactions is related more to the underlying mechanism being treated than to the electrical discharge itself. Systemic and pulmonary embolism are among the more serious complications and are encountered in about I% of those who undergo cardioversion of atrial fibrillation without anticoagulant drug prophylaxis. In rare instances, cardioversion induces or aggravates preexisting pulmonary congestion. Immediately after the procedure, arrhythmias are common, usually consisting of atrial, junctional or ventricular ectopic beats that disappear within several minutes. Malignant arrhythmias are the result of improper synchronization or excessive electrical energy, generally in patients with severe degrees of myocardial dysfunction. Shortly after the introduction of cardioversion, the report of two deaths (2,3) raised the concern that the digitalized patient may be susceptible to electrical shock-induced arrhythmias. Both patients were overdigitalized and the electrical discharge provoked irreversible ventricular fibrillation. Animal experiments (4) have confirmed that digitalization enhances the arrhythmogenic effect of transthoracic shock. In normal dogs digitalized to near toxicity, the median energy for inducing ventricular tachycardia is lowered from 400 to 0.2 J, a 2,OOO-fold reduction. The arrhythmia provoked by electrical discharge in the digitalized heart is identical in configuration and rate to that resulting from excess