Direct mechanical stimulation of brainstem modulates cardiac rhythm and repolarization in humans

Natural mechanical stimulation of the brainstem area by the blood pressure waves propagating in the adjacent arteries plays an important role in the homeostasis of the brainstem centers of cardiovascular control. However, effects of direct mechanical stimulation of this area on the cardiac elecrophysiology have never been studied in humans. In 12 patients (age: 54 +/- 13 years, 5 females) undergoing microvascular decompression, the left (9 patients) or the right (3 patients) side of the ventro-lateral surface of the medulla oblongata was exposed during the surgery, and a mechanical stimulation (duration: 1 min, frequency: 1-2 Hz) of the roots of the cranial nerves and the surface of the brainstem was performed at 3-7 sites using a 2-mm metallic ball. Spatial changes in cardiac repolarization were examined using the 32-lead/192 site electrocardiographic body surface potential maps. Blood pressure was monitored using intra-arterial line. The intervals between the onset of the Q-wave and the offset of the T-wave (QTe) and between the onset of the Q-wave and the peak of the T-wave (QTp), the activation-recovery intervals (ARi), the peak T-wave amplitude, and the QRS and STT integrals were measured using custom software. During the stimulation between the caudal rootlets of the 10th nerve, the peak T-wave amplitude decreased 22% (range: 6-50%) and RR-intervals decreased from 923 +/- 190 to 794 +/- 111 ms compared to the recordings obtained before the stimulation (P =.025 and.063, respectively), whereas QTe, QTp, Ari, and the QRS- and the STT-integrals did not change. Decreased T-wave amplitudes and unchanged QT-intervals suggest that brainstem stimulation might evoke spatially inhomogenious repolarization changes. Stimulation of a localized region surrounding the caudal rootlets of the 10th nerve elicits pronounced effects on cardiac rhythm and repolarization.