Sinus node function in man. Statistical analysis

The sinus function of 60 patients was studied by atrial stimulation at a fixed rate, and also at a rate linked with the preceding sinus cycle. These patients were divided into 3 groups according to the surface-recorded ECG; 10 had clear evidence of sinus dysfunction, 23 had an isolated sinus bradycardia, and 27 were considered as controls a their sinus rate was above 60/min., with a normal PR interval. Calculation of the limits of tolerance showed that at the 5% level, 95% of the values for all the controls fell between 96.8 and 568.7 ms for the corrected post-stimulatory pause, and between 114.5 and 434.3 ms for the corrected maximum return cycle. A study of the distribution zones of the graph CT/CR-AA/AA proved that an absent zone II is a pathological finding. In the group of sinus bradycardias the limits of what constitutes pathology are less clear, and the situation is not improved by noting whether atrial "echos" are present or absent. Because there is a narrow positive correlation between the values given by the two methods, the physio-pathology of sinus dysfunction can be discussed.