Sinus node recovery time related to paced cycle length in normals and patients with sinoatrial dysfunction

Depressed conduction in the sinoatrial junction, common in the sick sinus syndrome (SSS), should decrease the maximum pacing rate at which 1:1 capture of the SA node occurs. This may result in shorter than expected sinus recovery times (SRT) and maximal prolongation of SRT at relatively slow pacing rates. To test this hypothesis we evaluated the range of pacing rates necessary to demonstrate maximal SRT in 34 patients with and 20 patients without sinus node dysfunction. Atrial pacing was performed at multiple paced cycle lengths (PCL) between 400 and greater than or equal to 1000 msec, four times at each. A mean corrected SRT (CSRT) was determined at each PCL, and the PCL of the longest CSRT was determined (PCLp). PCLp varied linearly with sinus cycle length, was dependent on sinoatrial conduction time, and was longer in patients with SSS than in normal persons. Only 2 of 20 normal persons, but 21 of 34 patients with SSS, had a PCLp greater than 600 msec. A long PCLp (greater than 600 msec) suggests the possibility of recovery times that have been limited by A-S entrance block and appears to be indicative of sinus node dysfunction.