Induced effects of transcranial magnetic stimulation on the autonomic nervous system and the cardiac rhythm

Abstract

Several standard protocols based on repetitive transcranial magnetic stimulation (rTMS) have been employed for treatment of a variety of neurological disorders. Despite their advantages in patients that are retractable to medication, there is a lack of knowledge about the effects of rTMS on the autonomic nervous system that controls the cardiovascular system. Current understanding suggests that the shape of the so-called QRS complex together with the size of the different segments and intervals between the PQRST deflections of the heart could predict the nature of the different arrhythmias and ailments affecting the heart. This preliminary study involving 10 normal subjects from 20 to 30 years of age demonstrated that rTMS can induce changes in the heart rhythm. The autonomic activity that controls the cardiac rhythm was indeed altered by an rTMS session targeting the motor cortex using intensity below the subject's motor threshold and lasting no more than 5 minutes. The rTMS activation resulted in a reduction of the RR intervals (cardioacceleration) in most cases. Most of these cases also showed significant changes in the Poincare plot descriptor SD2 (long-term variability), the area under the low frequency (LF) power spectrum density curve, and the low frequency to high frequency (LF/HF) ratio. The RR intervals changed significantly in specific instants of time during rTMS activation showing either heart rate acceleration or heart rate deceleration.

Figure 1

PQRST waveforms from an electrocardiography device.

Figure 2

rTMS protocol implemented for all subjects. Note that 5 stimuli were applied during intervals of 1 minute of duration.

Figure 3

12-lead ECG recording. Note: stimuli artifact (1 sec, 10 Hz) is seen at the beginning of recording in several leads.

Figure 4

Design structure of the ECG-TMS system.

Figure 5

RR interval and related histograms comparing (a) baseline to (b) active phase.

Figure 6

Poincare plot of RR intervals distribution.

Figure 7

Illustrative examples on observed changes on the RR intervals for 2 subjects: subject 1 (a); subject 2 (b).

Figure 8

Power spectrum. Note: sampling rate of the ECG was 1 Hz, so the frequency spectrum was plotted until 0.5 HZ (Nyquist frequency criteria). There is an increment of the power around 0.05 and 0.1 Hz during the stimulation using 10 Hz and 5 repetitions.

Figure 9

Power spectrum: (a) corresponds to LF and (b) to HF components.

Figure 10

Area under the curve: baseline (a) and active phase (b).