In their recent report “Relation of High Heart Rate Variability to Healthy Longevity,” Zulfiqar et al calculated 4 standard 24-hour time-domain measures of heart rate variability by decade in 344 healthy subjects aged 10 to 99 years. In this cross-sectional study, the investigators observed a sharp increase in the root mean square of the successive normal sinus RR interval difference (rMSSD) and the percentage of successive normal sinus RR intervals >50 ms (pNN50) in the 20 subjects aged >80 years. They concluded that this association was an explanation for the longevity of this group. This interpretation is based on the idea that higher values of rMSSD and pNN50, which quantify beat-to-beat changes in heart rate variability, reflect increased parasympathetic control of heart rate.

This interpretation is completely without basis. As my group has already shown, in older adults, there is an increasing prevalence of sinus arrhythmia that is not of respiratory origin. We have called this “erratic rhythm.” The prevalence of erratic rhythm increases with increasing age. Thus, increased values of beat-to-beat heart rate variability measures are completely confounded in the elderly and cannot be taken as measures of parasympathetic control of heart rate without first verifying that this is truly due to respiratory sinus arrhythmia rather than erratic rhythm. The more likely interpretation of the findings of this study is that pNN50 and rMSSD were increased because the subjects were elderly, rather than the current interpretation that these subjects lived to be elderly because they had higher values of pNN50 and rMSSD.