Catheter stimulation of cardiac parasympathetic nerves in humans: a novel approach to the cardiac autonomic nervous system.

BACKGROUND: Cardiac parasympathetic nerves run alongside the superior vena cava (SVC) and accumulate particularly epicardially adjacent to the orifice of the coronary sinus (CS). In animals, these nerves can be electrically stimulated inside the SVC or CS, which results in negative chronotropic/dromotropic effects and negative inotropic effects in the atria but not the ventricles. Parasympathetic nerve stimulation (PS) with 20 Hz in the CS, however, also excites the atria, thereby inducing atrial fibrillation. The present study overcomes this limitation by applying high-frequency nerve stimuli within the atrial refractory period. Using this technique, we investigated for the first time whether neurophysiological effects similar to those in animals can be obtained in humans. METHODS AND RESULTS: In 25 patients, parasympathetic nerves were stimulated via a multipolar electrode catheter placed in the SVC (stimulation with 20 Hz; n=14) or CS (pulsed 200-Hz stimuli; n=11). A significant sinus rate decrease and prolongation of the antegrade Wenckebach period was achieved during PS in the SVC. During PS in the CS, a graded-response prolongation of the antegrade Wenckebach interval was observed with increasing PS voltage until third-degree AV block occurred in 8 of 11 patients. The negative chronotropic/dromotropic effects started and terminated immediately after the onset and termination of PS, respectively. Atropine abolished these effects (n=11). CONCLUSIONS: Human parasympathetic efferent nerve stimulation induces reversible negative chronotropic and dromotropic effects. PS may serve as an adjunctive tool for the diagnosis/treatment of supraventricular tachycardias and may be beneficial for ventricular rate slowing during tachycardic atrial fibrillation in patients with congestive heart failure.

Moderate physical exercise: a simplified approach for ventricular rate control in older patients with atrial fibrillation.

AIMS: This prospective pilot-study was performed to assess whether regular moderate physical activity elevates the parasympathetic tone to the atrio-ventricular node and decreases VR during permanent AF. BACKGROUND: Adequate ventricular rate (VR) control in patients with permanent atrial fibrillation (AF) is not easy to accomplish. METHODS: 10 patients (mean age 59 +/- 10 years) with permanent AF (duration: 10 +/- 8 years) underwent moderate physical exercise adjusted to their individual physical capability (45 min walking/jogging twice a week). To analyze VR control physical exercise tests and Holter-ECG recordings were performed before and after 4 months. In addition, stepwise lactate tests and psycho-pathometric examinations were obtained. RESULTS: After 4 months of training, there was a trend toward a decrease of mean VR in 24 h Holter-ECGs by 12% from 76 +/- 20 to 67 +/- 12 bpm (P = 0.05) while there was no significant decrease of the minimal VR (38 +/- 8 vs. 36.3 +/- 4.5 bpm, P = 0.54). At a lactate threshold of 2 mmol/l there was a trend towards an increase of the running speed from 105 +/- 11 to 116 +/- 12 m/min (P = 0.05). A significant VR decrease of 8% (range 5-10%) was observed at almost all exercise levels during exercise treadmill testing. Increases of exercise capacity and decreases of VR were accompanied by subjective improvements of health perception. CONCLUSION: Regular moderate physical activity decreases VR at rest and during exercise while increasing exercise capacity. Physical training should be taken into account for ventricular rate control during AF.