Digitalis administration: an underappreciated but common cause of short QT interval.

Common Cause of Short QT Interval To the Editor: I read with interest the recent report by Gaita et al1 of short-QT syndrome as a familial cause of sudden death. The authors enumerated other factors that shorten QT interval, such as increased heart rate, hyperthermia, hypercalcemia, hyperkalemia, acidosis, and altered autonomic tone.1 I would like to add another important and common, but underappreciated, cause of short QT interval, that is, administration of digitalis preparations. Because digitalis administration is such a common everyday occurrence in the management of patients with congestive heart failure and in those with atrial fibrillation or paroxysmal atrial tachycardia, its effect on the QT interval should be kept in mind when evaluating ECG changes. Although PR prolongation is a commonly recognized ECG manifestation of digitalis administration, QT shortening is less well known. As a matter of fact, in several case reports in which ECGs were presented,2–5 the short QT interval was not mentioned even though it was present. The property of digitalis preparations to shorten the QT interval is useful clinically in the diifferential diagnosis of ST-T changes associated with left ventricular hypertrophy, myocardial ischemia, myocardial infarction, or bundle branch block, in all of which the QT-interval is prolonged. The shortened QT interval and the characteristic sagging, “coved,” or “scooped” appearance of the asymmetric and downsloping ST depression, which resembles a reversed check mark, constitute the typical “digitalis effect” on ECG. The presence of a digitalis effect on ECG does not by itself connote digitalis intoxication. On the other hand, the same mechanism of sudden death in the familial short-QT syndrome as described by Gaita et al1 could play a role in fatal digitalis poisoning, either iatrogenic or suicidal, besides its association with hyperkalemia in patients with chronic renal insufficiency.