Quinidine Therapy and Digitalis Toxicity

In a 90-year-old man undergoing prolonged digitalis therapy, digitalis toxicity was precipitated by the administration of quinidine. The electrocardiogram revealed supraventricular bidirectional tachycardia, a rare but characteristic arrhythmia associated with digitalis toxicity. Upon withdrawal of digoxin, the clinical and ECG signs disappeared. A diagnosis of digitalis toxicity rather than quinidine intolerance led to appropriate treatment.