Delay in right ventricular activation contributes to Brugada syndrome

Background - Although Brugada syndrome revolves around reduced net depolarizing force, the electrophysiological mechanisms of its defining features ( right precordial ST-segment elevation and ventricular tachyarrhythmias) remain unresolved. Two proposed mechanisms are ( 1) right ventricular ( RV) conduction delay and ( 2) selective and significant RV subepicardial action potential shortening. Both mechanisms must cause disparate contractile changes: delay in RV contraction and reduction of contractile force, respectively. We aimed to establish the electrophysiological mechanism of Brugada syndrome by studying the timing and force of RV contraction. Methods and Results - Using tissue Doppler echocardiography, we studied how these contractile variables change on induction of the characteristic ST-segment changes of Brugada syndrome by flecainide challenge. Accordingly, we studied patients in whom flecainide induced these changes ( inducible) and those in whom these changes were not induced ( control). We found that ( 1) the occurrence of a positive response (coved- type ST elevation) after flecainide coincides with delay in the onset of contraction between the RV and left ventricle (LV); ( 2) the extent of contraction delay between RV and LV correlates with the magnitude of ST elevation; and ( 3) RV ejection time ( duration of RV ejection phase) shortens as the Brugada ECG pattern emerges. Conclusions - These results indicate that both proposed mechanisms of Brugada syndrome may be operative.