Digitalis excess mimicking the sick sinus syndrome.

Symptomatic bradycardia-tachycardia is often a feature of sick sinus syndrome. However, when alternating brady-tachycardia results from excessive use of digitalis preparations or electrolyte imbalance, it is iatrogenic and therefore not considered to be SSS per se. Sick sinus syndrome is applied to the following arrhythmias providing they are not iatrogenically induced: (1) sinus bradycardia usually unresponsive to atropine therapy or exercise, (2) sino-atrial block or arrest with long pauses, and (3) alternating bradycardia or tachycardia.