During invasive electrophysiologic investigations sinus node function has been normal in the large majority of the patients. However, isolated patients have manifest sinus node disease and are pacemaker dependent. As already discussed, about 10% of patients has paroxysmal atrial fibrillation. There exist no detailed studies on the ability to induce this arrhythmia by programmed electrical stimulation.

All published studies agree on the inducibility of polymorphic ventricular tachycardia by programmed electrical stimulation in symptomatic patients. About 80% of them are inducible by giving 1 or 2 ventricular premature beats during ventricular pacing. In some patients three premature stimuli are required. The induced arrhythmia is sustained in practically all cases, results in hemodynamic collapse and has to be terminated by an external DC shock. It can be criticized that polymorphic ventricular tachycardia or ventricular fibrillation induced by programmed stimulation is a non-specific finding, because these arrhythmias can sometimes be induced in patients with a normal heart. There exist, however, major differences between the two situations: 1.- The clinical context, with symptomatic patients with Brugada syndrome having suffered from spontaneous ventricular arrhythmias, 2.- The percentage of patients inducible to a sustained polymorphic ventricular arrhythmia in Brugada syndrome (80%) as compared to individuals without the syndrome where a sustained polymorphic ventricular tachycardia or ventricular fibrillation is only exceptionally induced.

The same studies coincide in the frequent finding of conduction disturbances in patients with the disease. The H-V interval is prolonged in about the half of the patients. The prolongation is not marked, rarely exceeding the 70 ms, but being clearly abnormal in this population with an average age of 40 years. The H-V prolongation explains the slight prolongation of the P-R interval during sinus rhythm (picture 1).

Hemodynamic studies have been systematically normal.