Objectives. There is ample and well-established evidence that direct electrical stimulation of the vagus nerve can change heart rate in animals and humans. Since tachyarrhythmias cannot always be controlled through medication, we sought, in this pilot study, to elucidate whether a clinical implantable lead system that is used in cervical vagus nerve stimulation therapy (VNS therapy) also can be used for control of heart rate, and tachycardia in particular.
Materials and Methods. Experiments were carried out in three pigs (weight 21–26 kg) under general anesthesia. The right and left vagus nerves in the neck region were exposed by dissection, and bipolar, multiturn, helical, silicone leads were wrapped around the vagus nerves. Stimulation was applied by an external device with multivariable settings: frequency 10–100 Hz, pulse duration 100–700 µsec; delay 0–0.5 msec; current 0.5–14 mA. Measurements were performed under normal sinus rhythm (RR-interval 501 ± 30 msec) and during isoprenaline-induced tachycardia (RR-interval 284 ± 11 msec).
Results. VNS, under optimal pacing conditions (100 Hz; 5 mA; 0.2 msec; 70 msec delay), in an electrocardiogram-triggered (ECG-triggered) pacing mode, increased RR-intervals by approximately 40%, irrespective of the duration of the RR-interval preceding VNS. The maximum effect on heart rate was established within approximately 5 sec after the onset of stimulation and was reversible and reproducible. No differences were found between stimulation of the right or left vagus nerve.
Conclusion. VNS can be used effectively and rapidly to decrease heart rate, in acute settings, when connected to an external pacing system. Future devices that are fully implantable may be used for nonpharmacological treatment of illnesses in which tachycardia results in deterioration of cardiac function.