1 From the Departments of Medicine and Pharmacology, College of Physicians and Surgeons, Columbia University and The Presbyterian Hospital, New York, New York.
It is well known that atrioventricular conduction varies as a function of atrial rate. However, rate related changes in sinoatrial conduction time (SACT) have not been examined. To determine the relationship between SACT and sinoatrial cycle length (SCL) in man, atrial and His bundle electrograms were recorded during atrial premature stimulation in each of nineteen patients with sinus arrhythmia. Ten of nineteen had asymptomatic, intermittent sinus bradycardia; 3/19 had persistent sinus bradycardia with nonspecific symptoms; 6/19 were felt to represent the sick sinus syndrome. In 18/19 individuals, there was a clearcut, inverse, linear relationship between SACT and SCL, i.e., as SCL increased, SACT decreased. Although this resembles the increase in PR interval that occurs with a decrease in atrial cycle length during atrial pacing, it contrasts sharply with the unchanged or increased PR interval that accompanies spontaneous increases in SCL. Although the range of patients' SACTs at any given SCL was large, the slope of
Submitted on June 27, 1974
© 1974 American Heart Association, Inc.
The Relationship Between Sinoatrial Conduction Time and Sinus Cycle Length During Spontaneous Sinus Arrhythmia in Adults
SACT/SCL was remarkably similar in most patients and was quite steep. One patient had episodes of 2:1 S-A block. As predicted, these occurred only at her shortest SCLs. Possible explanations for this behavior are considered and the clinical relevance of these observations is discussed.
Key Words: Pacing • Sinus node functional testing • Conduction system
Accepted on July 22, 1974