Ethnic Differences in QRS prolongation
Finally, we examined the ethnicity-specific association of QRSd with a composite endpoint of HF hospitalization and all-cause mortality in a Cox regression model for HFPEF and HFREF. The association of QRSd with outcome was tested in (1) a univariable model (plus interaction analysis); (2) in a model adjusting for age and sex; and (3) in a model including covariates derived from a backward stepwise Cox regression analysis, starting with the same covariates as the linear regression analysis. Additionally, we evaluated the non-linear relation of QRSd with outcome by adding a p-spline variable for QRSd with 4 degrees of freedom to the Cox regression model. From this model, ethnicity-specific QRSd cutoffs for outcome risk could be derived. Statistical power restricted us to analyze this only in HFREF patients. All analyses were performed using Rstudio12 and R software13 for statistical computing version 3.1.2. A p-value of <0.05 was considered to be statistically significant (also for interaction terms) and all p-values were 2-sided.
Results Baseline Characteristics by ethnicity Baseline characteristics by ethnicity are presented in Table 1. Asian HF patients were younger than Whites (61.2 vs. 73.5 years, p<0.001). Height, weight and body mass index (BMI) were significantly lower in (162 vs. 171cm, 69 vs. 80kg, and 26.3 vs. 27.1, all p<0.001). Asians had more severely impaired EF (EF was <30% in 45% of Asians vs. 24% of Whites). A history of CAD was more common among Asians (53% vs. 45%, p<0.001), but valve surgery was more common among Whites (5% vs. 1%, p<0.001). AF was more frequently observed in Whites than Asians (52% vs. 21%, p<0.001). Asians with HFREF had less severe NYHA classification and lower NTproBNP levels. Overall, QRSd was longer in Asians than Whites (100 vs. 98ms, p=0.002), but the proportion of patients with prolonged QRSd (≥120ms) did not differ (16.2% vs. 15.8%, p=0.796). QRS-duration in Asians and Whites with HFPEF and HFREF The distribution of QRSd between Asians and Whites stratified by EF is depicted in figure 1 (top panels). Among HFPEF patients, QRSd was shorter in Asians than Whites (median QRSd 90 vs. 94ms, p=0.007). Accordingly, the proportion of patients with prolonged QRS (≥120ms) was lower among Asians than Whites (4.5% vs. 12.0%, p=0.001). In contrast, in HFREF patients QRSd was longer in Asians than Whites (median QRSd 102 vs. 100ms, p<0.001). The proportion of patients with prolonged QRS (≥120ms) however, did not significantly differ (19.9% vs. 17.0% in Whites, p=0.068). The relationship of QRSd with EF differed by ethnicity (figure 1, bottom panel): in Asians a reduction in EF was related to a steeper increase of QRSd compared to Whites (p for interaction <0.001).
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