Sinus Node Function
In order to ascertain baseline sinus function, we identified 86 patients
who had a 24-hour Holter monitor performed when they were not using any
chronotropic medications (beta blockers, calcium channel blockers, Class
I-IV antiarrhythmics). Average, minimum and peak heart rate recorded as
well as metrics of heart rate variability including SDNN (standard
deviation of NN intervals in ms) and RMSDD (Root mean square of
successive RR interval differences in ms) were
documented10. We used SDNN as the index of heart rate
variability over a 24 h period and RMSSD as the primary time-domain
measure for estimation of the vagally mediated changes reflected in
HRV11.