Junctional pacemakers in man. Response to overdrive suppression with and without parasympathetic blockade.

This study analyzes the response to overdrive suppression of junctional pacemakers (JP) and correlates it with symptoms in 21 patients. Junctional rhythm (JR) was seen in 5 patients with intact A-V conduction, and in 16 with complete heart block, the JPs were located proximal to or within the His bundle (BH). Junctional recovery time (JRT) was measured following atrial or ventricular pacing during control and after atropine (2-2.5 mg). Control cycle length of the JR ranged from 835-2100 msec (mean 1402) and the corrected JRT (CJRT) ranged from 75 to greater than or equal to 7510 msec (mean 2966). Following atropine, the cycle length ranged from 660 to 2000 msec (mean 1115) and the CJRT ranged from 90 to greater than 6000 msec (mean 2050). All symptomatic patients were treated with permanent ventricular demand pacemakers and followed clinically from 6-72 months (mean = 35). Symptomatic patients could not be differentiated from asymptomatic patients on the basis of control heart rates, chronotropic response to atropine, and/or the site of origin of the JP as determined with BH recordings. However, presence or absence of symptoms of syncope and dizziness were well correlated with a CJRT greater than or less than 200 msec, respectively, either following atropine or during control. The determination of CJRT both before and after parasympathetic blockade provides a simpler and more reliable method for the therapeutic evaluation of patients.