The measurement of sinus node refractoriness in man.

We recently described a method for measuring sinus node refractoriness in the rabbit heart. Atrial premature beats either may result in reset return responses or may become interpolated because of encroachment on sinus node refractoriness. In previous studies with rabbits we defined the effective refractory period of the sinus node (SNERP) as the longest premature interval that is interpolated. This study presents results on the extension of this technique to the measurement of sinus node refractoriness in man. Out of 30 patients (12 with and 18 without sinus node dysfunction), SNERP could be measured in 26 at one or more basic cycle lengths. At a basic pacing cycle length of 600 msec, SNERP ranged from 250 to 380 msec (mean 325 +/- 39) in patients without sinus node dysfunction and from 500 to 550 msec (mean 522 +/- 20) in patients with sinus node dysfunction. This clear differentiation of patients with and without sinus node dysfunction by SNERP is in contrast to various results obtained by assessing sinus node function from sinus node recovery time and sinoatrial conduction time. Thus this study suggests the possible use of the measurement of SNERP in the assessment of sinus node function in man and its possible value in identifying patients with sinus node dysfunction.