To the Editor:

We thank Dr. Fayssoil for his interest in and important comments about our article. Our study was designed to investigate parameters that can predict adverse outcomes in patients with hypertrophic cardiomyopathy, including cardiac magnetic resonance parameters, and we found that left atrial (LA) volume index was independently associated with cardiovascular outcomes in patients with hypertrophic cardiomyopathy.

In our study, mitral regurgitation (MR) grade II to IV was present in 8 patients (9.8%), and 23 patients (28%) had left ventricular outflow tract (LVOT) obstructions. We agree with Dr. Fayssoil’s concern about the effects of MR and LVOT obstruction. In our study, the LA volume index was higher in patients with LVOT obstructions (45.1 ± 18.6 vs 32.3 ± 11.5 mL/m ² , P < .01) and with MR grade > II (55.6 ± 25.7 vs 33.8 ± 11.6 mL/m ² , P < .01). On univariate analysis, MR grade II to IV was associated with adverse outcomes, but LVOT obstruction showed no significant relationship with cardiovascular events. After unadjusted models were fit, we developed pruned multivariate models to assess predictors for adverse outcomes using the following procedure.

Independent variables that have been regarded as risk factors for hypertrophic cardiomyopathy in previous studies, or that were related to the outcomes in bivariate specifications ( P < .20), were chosen. Then we sequentially removed nonsignificant ( P ≥ .20) covariates whose elimination did not change the estimated coefficient on the exposure variable by >10%. Because our models may be overspecified for small numbers of patients and events, we estimated reduced-form models with covariates that showed statistical significance in the pruned adjusted models. In the final model, not including MR grade II to IV and LVOT obstruction, LA volume was proved as an independent predictor for cardiovascular events. As Dr Fayssoil suggests, we reanalyzed the data after excluding the patients with MR grade II to IV and LVOT obstructions. Even after the exclusion of patients with MR grade II to IV and LVOT obstructions, the LA volume index remained a predictor for cardiovascular events (for each 5 mL/m ² increase: hazard ratio, 1.48; 95% confidence interval, 1.08-1.75; P < .05) and cardiovascular events other than death (for each 5 mL/m ² increase: hazard ratio, 1.36; 95% confidence interval, 1.00-1.85; P < .05).

Among 81 patients, 3 patients underwent alcohol septal ablation and 2 patients underwent myectomy previously. Among the patients who underwent alcohol septal ablation and myectomy, only 1 patient experienced an adverse outcome (stroke). Because only a small number of patients had undergone septal intervention (alcohol ablation or surgical myectomy) previously, we could not confirm whether the LA volume index remain a predictor of adverse outcomes in patients with septal intervention compared to those without septal intervention. Nevertheless, in Cox regression analysis, the LA volume index remained a predictor of adverse outcomes even after adjusting for history of septal ablation or myectomy (for each 5 mL/m ² increase: hazard ratio, 1.36; 95% confidence interval, 1.20-1.54; P < .001).