The Duration of the Sinus Node Depolarization on Transvenous Sinus Node Electrograms Can Identify Sinus Node Dysfunction and Can Suggest Its Severity

Abstract

Catheter recorded sinus node electrograms (SNE) allow visualization of sinus node depolarization (SND). The SND on a bipolar SNE is probably a composite reflecting both P cell action potentials and intranodal conduction. Reduced rate of rise, prolonged action potential duration and/or delayed intranodal conduction might each prolong the SND duration. Thus, SND duration might reflect several clinically important sinus node abnormalities and aid in the recognition of sick sinus syndrome. Moreover, the SND duration might be expected to be the most prolonged in patients with the most severe sinus node dysfunction. To test this hypothesis, we determined SND duration in 32 patients and correlated it with the presence or absence of evidence of sinus node dysfunction by ECG and/or electrophysiological (EP) studies. Seven patients had no sinus node dysfunction (group 1); 10 patients had mild sinus node dysfunction (a single abnormality of corrected sinus recovery time, sinoatrial conduction time, PCLp, or ECG) (group 2); and 15 patients had two or more abnormalities electrocardiographically and/or by EP testing (group 3). The SND duration (mean/range) was 129/95-190 msec in group 1, 151/95-225 msec in group 2, and 196/140-260 msec in group 3. In group 3, three patients who had ECG evidence of sick sinus syndrome and abnormalities on all three EP parameters, the SND duration was 230/200-260 msec. Carotid sinus massage (CSM) was found to prolong the SND duration in 5/7 patients in groups 2 and 3 where the SND could be measured both before and during CSM. CSM was necessary to allow visualization of the SND in 3/7 group 1 patients; thus their recorded values may be falsely long. The normal with a SND duration greater than 150 (190 msec) had it measured during CSM. None of the group three patients with SND duration less than msec had a prolonged CSRT or ECG evidence of sick sinus syndrome. Literature review revealed SNE recordings on 18 patients with sick sinus syndrome on which the SND duration could be measured; it was greater than or equal to 200 msec in all. Thus, the SND duration appears to reflect the presence and degree of sinus node dysfunction. Sinus node dysfunction appears unlikely if the SND duration is less than 150 msec and is likely to be severe if the SND duration is greater than 200 msec.