Increased QT dispersion does not reflect the increased regional variation of cardiac sympathetic nervous activity in hypertrophic cardiomyopathy

Background QT dispersion (QTD) reflects regional variation of ventricular r epolarization. However, the relationship between QTD and the regional varia tion of cardiac sympathetic nerve activity in hypertrophic cardiomyopathy ( HCM) is not yet elucidated. Methods Cardiac sympathetic nerve activity was evaluated in 25 patients wit h HCM by iodine 123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy. With planar MIBG imaging, heart and mediastinum ratios (H/M) at early (20 minutes) and delayed (3 hours) acquisition and the washout rate (WR) were c alculated, Polar maps of left ventricular myocardium were divided into 20 s egments. The SD of early uptake (EU-SD), delayed uptake (DU-SD), and WR (WR -SD) in 20 segments as indices of regional variation were calculated. QT in tervals were corrected by use of the Bazett formula. Results Maximum QTc correlated positively with H/M early, WR, and left vent ricular wall thickness (LVWT). Minimum QTc correlated positively with WR an d LVWT. Corrected QTD (QTDc) correlated negatively with EU-SD, DU-SD, and W R-SD and positively with the interventricular septal thickness/posterior wa ll thickness ratio. Stepwise regression analysis revealed that the most pow erful determinants for maximum QTc, minimum QTc, and QTDc were WR, LVWT, an d EU-SD, respectively, Conclusions QTD correlated negatively rather than positively with the regio nal variability index of cardiac sympathetic nerve activity. These results suggest that increased QTD in patients with HCM may not reflect increased h eterogeneity of cardiac sympathetic nerve activity.