Safety of rapid-rate transcranial magnetic stimulation: heart rate and blood pressure changes

Repetitive transcranial magnetic stimulation improves cardiovascular autonomic nervous system control: A meta-analysis

BACKGROUND

Cardiovascular autonomic system (ANS) may be affected by altered neural activations in the brain. This systematic review and meta-analysis investigated potential effects of repetitive transcranial magnetic stimulation (rTMS) protocols on cardiovascular ANS control.

METHODS

Through 19 qualified studies, we acquired 70 comparisons for data synthesis. Individual effect sizes were estimated by comparing changes in following cardiovascular ANS control variables between active and sham stimulation conditions: (a) blood pressure (BP), (b) heart rate (HR), and (c) heart rate variability (HRV). Moreover, two moderator variable analyses determined whether changes in cardiovascular ANS control were different based on (a) rTMS protocols (excitatory rTMS versus inhibitory rTMS) and (b) specific targeted cortical regions, respectively.

RESULTS

The random-effects model meta-analysis revealed significant improvements in cardiovascular ANS control after the rTMS protocols. Specifically, applying excitatory and inhibitory rTMS protocols significantly decreased values of BP and HR variables. For HRV variables, excitatory rTMS protocols showed significant positive effects. These improvements in cardiovascular ANS control were observed while applying either excitatory rTMS protocols to the left dorsolateral prefrontal cortex or inhibitory rTMS protocols to the right dorsolateral prefrontal cortex.

LIMITATIONS

Relatively small number of studies for inhibitory rTMS on the right dorsolateral prefrontal cortex were included in this meta-analysis.

CONCLUSION

These findings suggest that applying excitatory and inhibitory rTMS protocols on prefrontal cortical regions may be effective to improve cardiovascular ANS control.

Safety and tolerability of repeated sessions of deep transcranial magnetic stimulation in obesity

PURPOSE

Repetitive Transcranial Magnetic Stimulation (rTMS) has been demonstrated to be effective in body weight control in individuals with obesity. Most clinical trials on rTMS provided a reassuring safety profile. In the present work, we present an extensive analysis on both severe and mild Adverse Events (AEs) in obese individuals treated with rTMS.

METHODS

We examined the intensity, duration, correlation with the treatment, up to 1 year after the end of rTMS treatment.

RESULTS

Descriptive analysis included a total of 63 subjects undergoing a 5-week deep rTMS experimental treatment for obesity (age 48.3 ± 10.4 years; BMI 36.3 ± 4.4 kg/m²): 31 patients were treated with high-frequency rTMS (HF), 13 with low-frequency rTMS (LF), and 19 were sham treated (Sham). Thirty-two subjects (50.8%) reported a total of 52 AEs, including mainly moderate (51.9%) events. The most frequently reported side effects were headaches of moderate intensity (40.4%) and local pain/discomfort (19.2%) and resulted significantly more frequent in HF group compared to other groups (p < 0.05). No significant differences among groups were found for the other reported AEs: drowsiness, insomnia, paresthesia, vasovagal reactions, hypertensive crisis. No AEs potentially related to the rTMS arised up to 1 year from the end of the treatment.

CONCLUSIONS

This is the first comprehensive safety analysis in obese patients treated with rTMS. The analysis did not reveal any unexpected safety concerns. Only headaches and local pain/discomfort have been significantly more frequent in the HF group, confirming the good tolerability of rTMS even in the obese population potentially more susceptible to side effects of brain stimulation.

The heart side of brain neuromodulation

Neuromodulation refers to invasive, minimally invasive or non-invasive techniques to stimulate discrete cortical or subcortical brain regions with therapeutic purposes in otherwise intractable patients: for example, thousands of advanced Parkinsonian patients, as well as patients with tremor or dystonia, benefited by deep brain stimulation (DBS) procedures (neural targets: basal ganglia nuclei). A new era for DBS is currently opening for patients with drug-resistant depression, obsessive-compulsive disorders, severe epilepsy, migraine and chronic pain (neural targets: basal ganglia and other subcortical nuclei or associative fibres). Vagal nerve stimulation (VNS) has shown clinical benefits in patients with pharmacoresistant epilepsy and depression. Non-invasive brain stimulation neuromodulatory techniques such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are also being increasingly investigated for their therapeutic potential in several neurological and psychiatric disorders. In this review, we first address the most common neural targets of each of the mentioned brain stimulation techniques, and the known mechanisms of their neuromodulatory action on stimulated brain networks. Then, we discuss how DBS, VNS, rTMS and tDCS could impact on the function of brainstem centres controlling vital functions, critically reviewing their acute and long-term effects on brain sympathetic outflow controlling heart function and blood pressure. Finally, as there is clear experimental evidence in animals that brain stimulation can affect autonomic and heart functions, we will try to give a critical perspective on how it may enhance our understanding of the cortical/subcortical mechanisms of autonomic cardiovascular regulation, and also if it might find a place among therapeutic opportunities in patients with otherwise intractable autonomic dysfunctions.

[French guidelines on the use of repetitive transcranial magnetic stimulation (rTMS): safety and therapeutic indications]

During the past decade, a large amount of work on transcranial magnetic stimulation (TMS) has been performed, including the development of new paradigms of stimulation, the integration of imaging data, and the coupling of TMS techniques with electroencephalography or neuroimaging. These accumulating data being difficult to synthesize, several French scientific societies commissioned a group of experts to conduct a comprehensive review of the literature on TMS. This text contains all the consensual findings of the expert group on the mechanisms of action, safety rules and indications of TMS, including repetitive TMS (rTMS). TMS sessions have been conducted in thousands of healthy subjects or patients with various neurological or psychiatric diseases, allowing a better assessment of risks associated with this technique. The number of reported side effects is extremely low, the most serious complication being the occurrence of seizures. In most reported seizures, the stimulation parameters did not follow the previously published recommendations (Wassermann, 1998) [430] and rTMS was associated to medication that could lower the seizure threshold. Recommendations on the safe use of TMS / rTMS were recently updated (Rossi et al., 2009) [348], establishing new limits for stimulation parameters and fixing the contraindications. The recommendations we propose regarding safety are largely based on this previous report with some modifications. By contrast, the issue of therapeutic indications of rTMS has never been addressed before, the present work being the first attempt of a synthesis and expert consensus on this topic. The use of TMS/rTMS is discussed in the context of chronic pain, movement disorders, stroke, epilepsy, tinnitus and psychiatric disorders. There is already a sufficient level of evidence of published data to retain a therapeutic indication of rTMS in clinical practice (grade A) in chronic neuropathic pain, major depressive episodes, and auditory hallucinations. The number of therapeutic indications of rTMS is expected to increase in coming years, in parallel with the optimisation of stimulation parameters.

Magnetic-stimulation-related physiological artifacts in hemodynamic near-infrared spectroscopy signals

Hemodynamic responses evoked by transcranial magnetic stimulation (TMS) can be measured with near-infrared spectroscopy (NIRS). This study demonstrates that cerebral neuronal activity is not their sole contributor. We compared bilateral NIRS responses following brain stimulation to those from the shoulders evoked by shoulder stimulation and contrasted them with changes in circulatory parameters. The left primary motor cortex of ten subjects was stimulated with 8-s repetitive TMS trains at 0.5, 1, and 2 Hz at an intensity of 75% of the resting motor threshold. Hemoglobin concentration changes were measured with NIRS on the stimulated and contralateral hemispheres. The photoplethysmograph (PPG) amplitude and heart rate were recorded as well. The left shoulder of ten other subjects was stimulated with the same protocol while the hemoglobin concentration changes in both shoulders were measured. In addition to PPG amplitude and heart rate, the pulse transit time was recorded. The brain stimulation reduced the total hemoglobin concentration (HbT) on the stimulated and contralateral hemispheres. The shoulder stimulation reduced HbT on the stimulated shoulder but increased it contralaterally. The waveforms of the HbT responses on the stimulated hemisphere and shoulder correlated strongly with each other (r = 0.65–0.87). All circulatory parameters were also affected. The results suggest that the TMS-evoked NIRS signal includes components that do not result directly from cerebral neuronal activity. These components arise from local effects of TMS on the vasculature. Also global circulatory effects due to arousal may affect the responses. Thus, studies involving TMS-evoked NIRS responses should be carefully controlled for physiological artifacts and effective artifact removal methods are needed to draw inferences about TMS-evoked brain activity.

Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research

This article is based on a consensus conference, which took place in Certosa di Pontignano, Siena (Italy) on March 7-9, 2008, intended to update the previous safety guidelines for the application of transcranial magnetic stimulation (TMS) in research and clinical settings. Over the past decade the scientific and medical community has had the opportunity to evaluate the safety record of research studies and clinical applications of TMS and repetitive TMS (rTMS). In these years the number of applications of conventional TMS has grown impressively, new paradigms of stimulation have been developed (e.g., patterned repetitive TMS) and technical advances have led to new device designs and to the real-time integration of TMS with electroencephalography (EEG), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Thousands of healthy subjects and patients with various neurological and psychiatric diseases have undergone TMS allowing a better assessment of relative risks. The occurrence of seizures (i.e., the most serious TMS-related acute adverse effect) has been extremely rare, with most of the few new cases receiving rTMS exceeding previous guidelines, often in patients under treatment with drugs which potentially lower the seizure threshold. The present updated guidelines review issues of risk and safety of conventional TMS protocols, address the undesired effects and risks of emerging TMS interventions, the applications of TMS in patients with implanted electrodes in the central nervous system, and safety aspects of TMS in neuroimaging environments. We cover recommended limits of stimulation parameters and other important precautions, monitoring of subjects, expertise of the rTMS team, and ethical issues. While all the recommendations here are expert based, they utilize published data to the extent possible.

Antidepressive Stimulationsverfahren

Affective disorders, especially major depression, are the most common psychiatric disorders. Although well treatable, a number of patients do not or do not sufficiently respond to antidepressant pharmacotherapy. Therefore there is a need for safe and efficient alternative therapeutic strategies. Neurostimulatory therapies such as electroconvulsive therapy, repetitive transcranial magnetic stimulation, and vagus nerve stimulation belong to these alternatives. In this article we review their mechanisms of action and summarize efficacy and adverse effects.

Changes in blood pressure and heart rate by repetitive transcranial magnetic stimulation in rats

We examined whether repetitive transcranial magnetic stimulation (rTMS) could influence blood pressure (BP) and heart rate (HR) in rats and the possible mechanisms involved. In urethane anesthetized Wistar-Kyoto rats, BP and HR were recorded from the femoral artery around the point of rTMS at a frequency of 10 Hz and an intensity of 1.88-2.44 Tesla. rTMS but not sham stimulation reduced BP and HR by approximately 20 mmHg and approximately 30 beats/min, respectively (n = 22). Pretreatment with an alpha-adrenoceptor antagonist, prazosin, or a beta-adrenoceptor antagonist, atenolol, significantly attenuated the response, whereas the muscarinic acetylcholine antagonist, atropine, had little effect. An inhibitory effect of prazosin on BP reduction by rTMS was also observed when basal BP was preserved by a combination of prazosin and a nitric oxide synthase inhibitor, N-monomethyl-L-arginine. These results suggest that rTMS reduces BP through the inhibition of the sympathetic nervous system but not through activation of the parasympathetic nervous system.

Transcranial magnetic stimulation and epilepsy

Transcranial magnetic stimulation has been used to study generalized and focal epilepsies for more than a decade. The technique appears safe and has yielded important information about the mechanisms underlying epilepsy. Transcranial magnetic stimulation findings differ depending on the epilepsy syndrome, lending support to the concept that there are distinct pathophysiologies underlying each condition. In most studies of generalized epilepsies, transcranial magnetic stimulation has indicated a state of relative hyperexcitability of excitatory cortical interneurons and possibly inhibitory interneurons as well, which can be reversed through the actions of anticonvulsant medications. Transcranial magnetic stimulation studies in patients with a seizure focus in the motor cortex indicate increased cortical excitability and reduced inhibition, but in patients with seizure foci located elsewhere the findings are similar to those in generalized epilepsies. Transcranial magnetic stimulation has also been used to study the mode of action of anticonvulsants and may prove to be a useful means of testing the potential for new drugs to act as anticonvulsants. Repetitive transcranial magnetic stimulation may prove to have a therapeutic role by producing long-lasting cortical inhibition after a train of impulses.

The impact of repetitive transcranial magnetic stimulation on pituitary hormone levels and cortisol in healthy subjects

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a new therapeutic tool in the treatment of affective disorders but only few studies on its safety exist. We aimed to determine the impact of rTMS on (neuro)endocrinological serum levels by a placebo-controlled cross-over study.

METHODS

23 healthy subjects were stimulated by rTMS in a typical paradigm used in the treatment of depression (coil placed over left dorsolateral prefrontal cortex, 10 and 20 Hz stimulation). Placebo, infrathreshold, and suprathreshold stimulation were applied in random order. The serum levels of cortisol, prolactin, FSH, and TSH were measured before and after stimulation.

RESULTS

After infrathreshold stimulation, cortisol and TSH serum levels decreased mildly but significantly. All other stimulations had no significant impact on hormone levels. In female, but not in male, subjects placebo stimulation yielded a significant increase of prolactin.

CONCLUSIONS

rTMS as applied for the treatment of depression leads to only very mild and safe changes of hormones. These changes, in particular the decrease of cortisol levels, might explain in part the efficacy of rTMS.

Influence of transcranial magnetic stimulation on pupil size

In 22 healthy subjects, painless repetitive transcranial magnetic stimulation (rTMS) was used to investigate the role of the cortex in the regulation of pupil size and the influence of TMS on the central autonomic nervous system. RTMS was performed over three brain regions of each hemisphere (frontal, central, parieto-occipital), over cervical nerve roots and in front of the ear (sham stimulation) while the size of the pupil was measured by infrared oculography. rTMS always elicited a dilatation of both pupils, with its maximum after approximately 1.5 s and without significant R-L difference in latency or amplitude of pupillary response. No differential effects were observed for stimulation over different cortex regions of one hemisphere, but stimulation over the right central region evoked a larger dilatation of the pupil than stimulation over the left. Pupillary dilatation was larger for cervical nerve root stimulation (+13.2+/-8.3% (S.D.) of baseline) than for suprathreshold cortex stimulation (+8.4+/-4.5%, five 10-Hz stimuli). Pupillary dilatation in response to magnetic cortex stimulation appears to reflect a mainly unspecific activation of the sympathetic system rather than an activation of a cortical pupillomotor centre. Sympathetic activation following rTMS of the cortex does not limit its experimental and therapeutic application.

Are autonomic signals influencing cortico-spinal motor excitability? A study with transcranial magnetic stimulation

In order to investigate the role of visceral afferent inputs flowing along autonomic fibers on corticospinal tract excitability, the variability of Motor Evoked Potentials (MEPs), elicited by Transcranial Magnetic Stimulation (TMS), was analysed during simultaneous monitoring of electrocardiogram (EKG) phases, breathing phases and sudomotor skin responses (SSRs) in a group of 10 healthy subjects. A cascade of at least 60 consecutive magnetic stimuli, with an interstimulus interval randomly varying between 20 and 40 s, was acquired. At the end of the recording session, the subject was asked to make at random five not consecutive self-paced forced inspirations. TMS was carried out at an intensity 10% above motor threshold excitability via a circular coil placed over the motor area of the right hemisphere. MEPs were recorded from the contralateral abductor digiti minimi muscle (ADM). Sudomotor Skin Responses (SSRs) were recorded on both hand palms. MEPs latency and amplitude did not show significant correlation with any of the EKG and respiratory phases. During forced inspiration, a significant latency shortening was found. TMS elicited SSRs, whose amplitudes were not correlated with MEP parameters. During forced inspiration a significant SSR amplitude increment, not correlated with MEP latency shortening, was also observed. These results assign a minor if any role to the considered autonomic parameters in modulating corticospinal motor excitability.

Coil design for real and sham transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) can be used to excite the human cortex noninvasively. TMS also activates scalp muscles and sensory receptors; additionally, the loud sound from the stimulating coil activates auditory pathways. These side effects complicate the interpretation of the results of TMS studies. For control experiments, we have designed a coil that can produce both real and sham stimulation without moving the coil. The sham TMS is similar to the real TMS, except for the different relative direction of the currents in the two loops of the figure-of-eight coil. While the real TMS elicited activation of hand muscles, sham TMS had no such effect; however, the auditory-evoked potentials were similar.