[Sinus arrhythmia: quantitative evaluation and possible use in the diagnosis of sick sinus syndrome (author's...

This research was done in order to quantify the sinus arrhythmia and to determine any possible quantitative difference between normal subjects and patients with Sick Sinus Syndrome (SSS). The ECG of 200 normal subjects and 30 patients with SSS diagnosed with electrophysiologic evaluation have been studied. 50 consecutive PP intervals have been measured in each ECG, and the average and standard deviation (SD) were calculated. The variableness of the sinus cycle was expressed by the Sinus Arrhythmia Index (SAI), obtained by the ratio between the SD and the average length of the cycle. It was observed that in normal subjects the SAI decreases with aging, and its value is not related to the heart rate. The SAI was significantly higher in the patients with SSS than in the normal ones. Since a sinus arrhythmia of high degree may be observed in the SSS, the quantitative evaluation of this arrhythmia, obtained by the index we proposed, may be useful to the detection of this syndrome.