Acute Cardiac Autonomic Responses to High-intensity, Low-frequency, Periodic rTMS Over the Right Dorsolateral Prefrontal Cortex in Women With Recurrent Pregnancy Loss and Comorbid Anxiety Disorders: a Proof-of-concept rTMS-ECG Parameter-finding Trial (NEURO-CARD-rTMS-1)

Recurrent pregnancy loss affected approximately 2% to 5% of women of reproductive age and had been associated not only with reproductive burden, but also with substantial psychological distress, including anxiety, depression, and elevated stress. Previous studies further suggested that women with recurrent pregnancy loss could exhibit autonomic dysfunction, greater cardiovascular vulnerability, and altered interactions among emotional regulation, interoception, and autonomic control. The dorsolateral prefrontal cortex, particularly the right dorsolateral prefrontal cortex, had been implicated in anxiety-related functional laterality, threat-related processing, and regulation of stress-related physiological responses. These observations provided the conceptual basis for testing whether inhibitory low-frequency stimulation over the right dorsolateral prefrontal cortex could induce measurable acute cardiac autonomic responses in women with recurrent pregnancy loss and comorbid anxiety disorders.

The present study, NEURO-CARD-rTMS-1, will be conducted as a proof-of-concept rTMS-ECG parameter-finding clinical trial using a within-subject, single-factor repeated-measures design. Fifty-five consecutive women with recurrent pregnancy loss and comorbid anxiety disorders will be enrolled. Eligible participants will be women aged 18 to 45 years who are right-handed, meet the predefined diagnostic criteria for recurrent pregnancy loss, meet Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria for an anxiety disorder, have a Hamilton Anxiety Rating Scale score of 14 or higher, and do not have clinically significant depressive symptoms. Individuals with contraindications to transcranial magnetic stimulation, major medical conditions that may affect cardiac autonomic function or increase procedural risk, current psychotropic medication use, clinically significant suicide risk, or major psychiatric disorders other than anxiety disorders will be excluded.

Each participant will undergo a stimulation-intensity sweep protocol targeting the right dorsolateral prefrontal cortex. Resting motor threshold will first be determined over the right primary motor cortex. The scalp target for repetitive transcranial magnetic stimulation will then be localized using the mirrored adjusted BeamF3/F4 method, and the coil will be oriented at 45 degrees to the sagittal plane with the handle pointing posteriorly. After a 20-second prestimulation resting baseline, six consecutive stimulation cycles will be delivered at increasing intensities from 100% to 150% of resting motor threshold, in 10% increments. Each cycle will consist of a 40-second stimulation period delivered at 1 Hz, followed by a 20-second rest interval, thereby forming a 60-second stimulation-locked cycle. The maximum stimulation intensity will not exceed 85% of maximum stimulator output. Continuous electrocardiography will be recorded throughout the full procedure.

The primary outcome will be baseline-corrected heart-rate change across stimulation intensity conditions, defined as decreased HR. Within each stimulation cycle, the mean heart rate during the 10 seconds immediately before stimulation onset will serve as the baseline, and the mean heart-rate change during the subsequent 40-second stimulation period will be calculated relative to this baseline. More negative values will indicate greater heart-rate reduction induced by the corresponding stimulation intensity. The first secondary outcome will be mean normalized wavelet power near the frequency of the 60-second stimulation cycle, corresponding to approximately 0.0167 Hz, with the Morlet wavelet used for the primary spectral analysis. The second secondary outcome will be the rTMS-induced cardiac coupling index at each stimulation intensity, defined as the Pearson correlation across participants between decreased HR and mean normalized wavelet power near the frequency of the 60-second stimulation cycle. Safety outcomes will include non-serious adverse events and serious adverse events occurring during the procedure or during the 1-hour post-procedure observation period.

The study will test whether a high-intensity, low-frequency, periodic repetitive transcranial magnetic stimulation strategy applied over the right dorsolateral prefrontal cortex can induce a detectable acute cardiac autonomic response under a threshold-reference framework. The study will also identify the candidate stimulation intensity that optimizes detectability and physiological consistency, based on the joint characterization of heart-rate change, stimulation-cycle-frequency power, and the rTMS-induced cardiac coupling index. The outputs of this study are intended to provide a methodological and parameter basis for subsequent NEURO-CARD-rTMS studies with fixed stimulation parameters, larger samples, and longer-term follow-up.