Familial aggregation of heart rate variability based on short recordings--the kibbutzim family study

The objective of this study was to assess the familial aggregation of heart rate variability (HRV), a readily measurable noninvasive reflection of cardiac autonomic function. Familial correlations were analyzed in 451 kibbutz members aged 15-97 years belonging to 80 kindreds. Five-minute duration Holter recordings made during silent supine spontaneous breathing and metronomic breathing were analyzed in the time and frequency domains. The present analysis considers the familial correlations and the heritability estimates of two time-domain indices, the standard deviation (SD) of the R-R interval (RR), reflecting total variability, and the root mean square of successive differences in RR intervals (RMSSD), reflecting vagal (parasympathetic) tone. During free breathing, age- and sex-adjusted correlations between parents and their children (r=0.24 for both indices) and between adult siblings above 30 years of age (r=0.24 and t=0.34 for SD and RMSSD, respectively) were statistically significant, whereas spouse correlations (r=-0.04, r=-0.02 for SD and RMSSD, respectively) and correlations in younger siblings (r=-0.22 and r=0.01, respectively) were not. Significant heritability estimates were demonstrated for the two indices (h2=0.41 for SD and h2=0.39 for RMSSD). These findings suggest that familial aggregation of HRV characteristics is determined mostly by genetic factors and less so by environmental factors and provide a basis for continuing the investigation into the underlying genetic influences on HRV.