Prolonged Right Ventricular Ejection Delay in Brugada Syndrome Depends on the Type of SCN5A Variant　- Electromechanical Coupling Through Tissue Velocity Imaging as a Bridge Between Genotyping and Phenotyping.

Background: Patients with Brugada syndrome (BrS) and a history of syncope or sustained ventricular arrhythmia have longer right ventricular ejection delays (RVEDs) than asymptomatic BrS patients. Different types of SCN5A variants leading to different reductions in sodium current (I-Na) may have different effects on conduction delay, and consequently on electromechanical coupling (i.e., RVED). Thus, we investigated the genotype-phenotype relationship by measuring RVED to establish whether BrS patients carrying more severe SCN5A variants leading to premature protein truncation (T) and presumably 100% I-Na reduction have a longer RVED than patients carrying missense variants (M) with different degrees of I-Na reduction. Methods and Results: There were 34 BrS patients (mean [+/- SD] age 43.3 +/- 12.9 years; 52.9% male) carrying an SCN5A variant and 66 non-carriers in this cross-sectional study. Patients carrying a SCN5A variant were divided into T-carriers (n=13) and M-carriers (n=21). Using tissue velocity imaging, RVED and left ventricular ejection delay (LVED) were measured as the time from QRS onset to the onset of the systolic ejection wave at the end of the isovolumetric contraction. T-carriers had longer RVEDs than M-carriers (139.3 +/- 15.1 vs. 124.8 +/- 11.9 ms, respectively; P=0.008) and non-carriers (127.7 +/- 17.3 ms, P=0.027). There were no differences in LVED among groups. Conclusions: Using the simple, non-invasive echocardiographic parameter RVED revealed a more pronounced 'electromechanical' delay in BrS patients carrying T variants of SCN5A.