Hereditary long QT syndrome in the postoperative cardiac patient.

The purpose of the present article is to evaluate the diagnostic implications of the long QT syndrome presenting in postoperative cardiac patients. Diagnosis of long QT syndromes may be complicated by an inability to measure the QT interval correctly due to postoperative electrocardiographic changes such as right bundle-branch block. For this reason, a study of the effect of right bundle-branch block on the QT interval was undertaken. Electrocardiograms of 17 randomly selected patients undergoing a right ventriculotomy for repair of tetralogy of Fallot were evaluated for QT prolongation pre- and postoperatively. Preoperatively, no patient demonstrated QT interval prolongation. After surgery, however, right bundle-branch block created an apparent prolongation of the QT interval in 9 of the 17 patients (53%). These results suggest that in postoperative cardiac patients QT prolongation and familial long QT syndromes may be difficult to diagnose. It is, therefore, important to exclude the long QT syndrome in patients with ventricular tachycardia even if a more obvious explanation such as previous cardiac surgery is present. Usually a careful family history and preoperative electrocardiogram are all that is required.