Diagnostic capacity of sinus node recovery time after inhibition of autonomous neural tone

Symptomatic arrhythmias often occur intermittently in patients with sinus node dysfunction. A diagnostic test with ability to reveal latent sinus disease has therefore been much sought for. Determinations of sinus node recovery time (SNRT) and corrected sinus node recovery time (CSNRT) have been attempted but limitations in their diagnostic power are well recognized. To eliminate a possible masking effect of autonomous neural tone, propranolol 0.1 mg/kg and atropine 0.02 mg/kg was administered to 30 patients with established symptomatic sinus bradydysrhythmias (SSBD) and to a control group of 18 age-matched healthy volunteers. In addition the same procedure was applied to 9 patients with symptoms suggesting SSBD in whom, however, this cause was later excluded. The upper normal limit of CSNRT defined by the control group was 545 msec before and 505 msec after drugs. In the SSBD group, CSNRT was falsely negative in 8 of the 30 patients. Repeated testing after drug inhibition reduced this number to 2 patients. Thus, the sensitivity increased from 73% to 93%. CSNRT determinations were normal in the non-SSBD patients, specificity remaining at 100%. Thus, the discriminative power of electrophysiologic testing for sinus node disease was found to be high when CSNRT determinations were performed both before and after drug inhibition of autonomous neural tone.