Background-Brugada syndrome (BrS) is associated with lethal arrhythmias, which are linked to specific ST-segment changes (type-1 BrS-ECG) and the right ventricle (RV). The pathophysiological basis of the arrhythmias and type-1 BrS-ECG is unresolved. We studied the electrophysiological characteristics of the RV endocardium in BrS. Methods and Results-RV endocardial electroanatomical mapping and stimulation studies were performed in controls (nϭ12) and BrS patients with a type-1 (BrS-1, nϭ10) or type-2 BrS-ECG (BrS-2, nϭ12) during the studies. BrS-1 patients had prominent impairment of RV endocardial impulse propagation when compared with controls, as represented by: (1) prolonged activation-duration during sinus rhythm (86Ϯ4 versus 65Ϯ3 ms), (2) increased electrogram fractionation (1.36Ϯ0.04 versus 1.15Ϯ0.01 deflections per electrogram), (3) longer electrogram duration (83Ϯ3 versus 63Ϯ2 ms), (4) activation delays on premature stimulation (longitudinal: 160Ϯ26 versus 86Ϯ9 ms; transversal: 112Ϯ5 versus 58Ϯ6 ms), and (5) abnormal transversal conduction velocity restitution (42Ϯ8 versus 18Ϯ2 ms increase in delay at shortest coupling intervals). Wider and more fractionated electrograms were also found in BrS-2 patients. Repolarization was not different between groups. Conclusions-BrS-1 and BrS-2 patients are characterized by wide and fractionated electrograms at the RV endocardium.BrS-1 patients display additional conduction slowing during sinus rhythm and premature stimulation along with abnormal transversal conduction velocity restitution. These patients may thus exhibit a substrate for slow and discontinuous conduction caused by abnormal active membrane processes and electric coupling. Our findings support the emerging notion that BrS is not solely attributable to abnormal electrophysiological properties but requires the conspiring effects of conduction slowing and tissue discontinuities. (Circ Arrhythmia Electrophysiol. 2008;1:379-386.)

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