Electrophysiological studies in patients with the Wolf-Parkinson-White syndrome.

Electrophysiologic studies in patients with the Wolff-Parkinson-White (WPW) syndrome are performed for diagnostic and therapeutic reasons. Surface electrocardiographic leads plus intracardiac electrograms from different locations are stimultaneously recorded. Programmed electrical stimulation of the heart permits confirmation of pre-excitation in questionable cases and assessment of the mechanism of the arrhythmias which these patients develop as well as their therapeutic approach. The most frequent form of paroxysmal regular tachycardia observed in WPW is based on an AV-junctional re-entry mechanism utilizing the accessory pathway in the retrograde direction. The second clinically relevant arrhythmia encountered in these patients is atrial fibrillation with very rapid ventricular rates due to almost exclusive A-V conduction by way of the accessory pathway. Ventricular fibrillation may occasionally ensue as a result of these fast ventricular rates during atrial fibrillation. Determination of the antegrade effective refractory period of the accessory pathway may identify the group of patients prone to the development of this complication. The intravenous injection of Ajmaline can by a non-invasive aid in the selection of patients for further electrophysiological evaluation when this drug fails to induce complete antegrade block over the accessory pathway during sinus rhythm. Patients with tachyarrhythmias which are difficult to control with conventional drug therapy should undergo an electrophysiological investigation to select either more effective antiarrhythmic treatment or, in medically refractory patients, appropriate pacing or surgical techniques.