Absence of respiratory sinus arrhythmia: a manifestation of the sick sinus syndrome.

The failure of changes in autonomic drive to affect heart rate is a common finding in patients with the sick sinus syndrome (SSS). The normal respiratory sinus arrhythmia is vagally mediated and should therefore be attenuated in SSS. This hypothesis was tested in a series of 32 symptomatic patients with SSS, mean age 68 years, and an age-matched control group of 75 normal subjects. The degree of sinus arrhythmia present in routine 12-lead electrocardiograms was quantitated as (1) the coefficient of variation (CV) of the R-R interval, and (2) the maximal R-R interval difference (delta R-Rmax). Mean CV was 2.7% in SSS compared to 3.8% in the control group (p less than 0.01). Mean delta R-Rmax was 72 ms in SSS and 140 ms in controls (p less than 0.01). Sixteen of 32 patients (50%) compared to only 4/75 (5%) control subjects had delta R-Rmax of less than 80 ms (p less than 0.01). Thus, SSS is frequently associated with a significant attenuation of sinus arrhythmia and the simple measurement of delta R-Rmax in standard ECG recordings provides useful diagnostic information.