Determinants and Effects of Electrical Stimulation of the Inferior Interatrial Parasympathetic Plexus During Atrial Fibrillation

Catheter stimulation of the inferior interatrial ganglionated parasympathetic plexus decreases the ventricular rate during atrial fibrillation (AF) in humans. However, the relatively high stimulation voltages might prevent implementation of neurostimulation in chronic implantable devices. From myocardial electrostimulation it is known that the required impulse energy and charge is lowest at the chronaxie time. In order to lower energy requirements for cardiac neurostimulation, the present study evaluates the impulse‐strength versus impulse‐duration relationship for a neurostimulation lead that was implanted into the inferior interatrial ganglionated plexus. Methods and Results: In nine dogs, permanent epicardial bipolar screw‐in electrodes were fixed in the inferior interatrial ganglionated plexus. AF was maintained via rapid atrial pacing. During AF, neural stimulation was performed at various frequencies (1–100 Hz), impulse durations (0.05–2 msec), and voltages (0.02–11.5 V). There was a linear correlation between R‐R interval lengthening and stimulus voltage (R = 0.99; P < 0.001) and a bell‐shaped relationship between stimulation frequency and negative dromotropic effect with maximum rate slowing at 30–50 Hz. The rheobase for a 50% R‐R interval prolongation during AF was 1.81 V and 2.72 V for high‐grade AVB yielding a chronaxie time of 0.14 msec and 0.18 msec, respectively. The impulse energy (charge) at the chronaxie time was 4–6 μJ (6–8 μC). Conclusions: Cardiac neurostimulation follows a chronaxie/rheobase behavior. Energy, charge, and voltage values needed to achieve significant negative dromotropic effects are within the limits of conventional cardiac pacemaker outputs, which may allow implementation of neurostimulation capabilities in current pacemaker technology.