Pilot Randomized Trial of Intermittent Theta-Burst Stimulation versus H-Coil Transcranial Magnetic Stimulation for Treatment-Resistant Depression

This pilot randomized trial found that intermittent theta-burst stimulation (iTBS) and H-coil rTMS demonstrated comparable efficacy in treating treatment-resistant depression over six weeks, with no significant differences in symptom reduction, response, or remission rates, while exploratory analyses suggested a potential link between baseline executive functioning and remission.

The Gist

Imagine your brain is like a vast, complex city. In people with Treatment-Resistant Depression (TRD), certain neighborhoods in this city (specifically the parts that control mood) have gotten stuck in a traffic jam. The lights are red, the roads are clogged, and the city feels gloomy.

Doctors have two main tools to try to clear this traffic jam using magnetic waves: iTBS and H-coil rTMS.

• iTBS is like a precision sniper. It uses a small, figure-8 shaped magnet to send a very focused, high-speed burst of energy to one specific street corner (the side of the forehead). It's fast (only 3 minutes) and hits a specific target.
• H-coil is like a broad-spectrum floodlight. It uses a larger, helmet-shaped magnet to cast a wider, deeper net of energy over a bigger area of the brain (the middle of the forehead). It takes longer (about 20 minutes) and covers more ground, but the energy is less concentrated in any single spot.

For years, doctors knew both tools worked, but they didn't know which one was better at clearing the traffic jam. This study was a "pilot test"—a small practice run—to see if we could compare them head-to-head and to see if a patient's "brain fitness" (how well they think and plan) predicted who would get better.

The Experiment: A Small Race

The researchers gathered 28 adults whose depression hadn't gotten better with regular medication. They were split into two teams:

• Team iTBS: Got the "sniper" treatment 30 times over six weeks.
• Team H-coil: Got the "floodlight" treatment 30 times over six weeks.

What Happened? (The Results)

1. The Finish Line was a Tie
At the end of the six weeks, both teams improved significantly. The "traffic" cleared up in both groups.

• iTBS: 40% of people got a major improvement; 20% felt completely better.
• H-coil: 50% got a major improvement; 20% felt completely better.
• The Verdict: There was no clear winner. Both methods worked about the same. It's like two different routes to the same destination; both got the drivers there, just with slightly different scenery.

2. The "Brain Fitness" Clue
Here is the most interesting part. The researchers looked at the participants' brains before they started. They found a pattern:

• People who had sharper executive function (better at planning, focusing, and switching tasks) were more likely to get better, especially in the iTBS (sniper) group.
• The Analogy: Think of the brain as a garden. If the soil is already fertile (good executive function), a precise seed (iTBS) planted in the right spot grows beautifully. If the soil is very compacted or damaged, that precise seed might struggle to take root. The "floodlight" (H-coil) seemed to work regardless of the soil quality, perhaps because it waters the whole garden at once.

3. The Side Effects

• iTBS: Felt a bit like a gentle tap on the head. It was fast and generally well-tolerated.
• H-coil: Felt like a heavier, deeper vibration. Everyone in this group reported feeling tired (fatigue) and having headaches more often than the iTBS group. It's like the difference between a quick sprint (iTBS) and a long, heavy hike (H-coil)—both get you to the top, but the hike leaves you more exhausted.

Why Does This Matter?

This study is like a blueprint for a bigger construction project.

• Feasibility: It proved that you can run a head-to-head race between these two treatments. The patients showed up, stayed for the treatment, and the data was clean.
• No Clear Winner Yet: We still don't know which tool is "better" for everyone. We need a much larger study (with hundreds of people, not 28) to be sure.
• New Clue: The finding about "brain fitness" is a spark. It suggests that maybe doctors should test a patient's thinking skills first. If their "brain engine" is strong, the fast, precise iTBS might be the best choice. If their engine is struggling, the broader H-coil might be the safer bet.

The Bottom Line

Both the "sniper" (iTBS) and the "floodlight" (H-coil) are effective tools for treating stubborn depression. They work about equally well in this small group, but they feel different to the patient. The study didn't declare a champion, but it gave doctors a new hint: How your brain works before treatment might help decide which tool is right for you.

Note: This was a small "pilot" study, meaning it's a first step. The results are promising but not yet a final rule for doctors to follow.

Technical Summary

1. Problem Statement

Major Depressive Disorder (MDD) affects approximately 300 million people globally, with up to 55% of patients failing to achieve remission with standard pharmacotherapy, leading to Treatment-Resistant Depression (TRD). While Repetitive Transcranial Magnetic Stimulation (rTMS) is an established treatment, there is a lack of head-to-head randomized evidence comparing two distinct, FDA-cleared modalities:

• Intermittent Theta-Burst Stimulation (iTBS): Delivered via a figure-8 coil targeting the left Dorsolateral Prefrontal Cortex (DLPFC). It is focal, time-efficient, and targets lateral prefrontal networks.
• H-Coil rTMS (specifically H7-coil): Delivered via an H-coil targeting the Dorsomedial Prefrontal Cortex (DMPFC). It generates a broader, deeper electromagnetic field, engaging medial prefrontal and cingulate circuits but with less focal intensity.

The core scientific question is whether the trade-off between focal, high-intensity lateral stimulation (iTBS) and broad, deep medial stimulation (H7-coil) yields superior clinical outcomes in TRD, and whether baseline cognitive functioning (specifically executive function) predicts remission.

2. Methodology

Study Design:

• Type: Pilot, randomized, single-center, two-arm, parallel-group trial.
• Setting: Centre Hospitalier de l'Université de Montréal (CHUM), Canada.
• Timeline: January 2024 – September 2025.
• Registration: ClinicalTrials.gov (NCT05902312).

Participants:

• Sample: 28 adults (21–70 years) with DSM-5 MDD and TRD (≥2 failed antidepressant trials or intolerance).
• Inclusion: Baseline 17-item Hamilton Depression Rating Scale (HRSD-17) score ≥18.
• Exclusion: Prior rTMS, bipolar/psychotic disorders, active suicidality, unstable medical conditions, or heavy benzodiazepine use.

Interventions:
Participants were randomized 1:1 to receive 30 sessions over 6 weeks (5 sessions/week):

1. iTBS Arm (n=15): Left DLPFC stimulation using a MagPro X100 with a B70 figure-8 coil.
   • Protocol: 600 pulses/session at 120% resting motor threshold (RMT).
   • Targeting: Modified Beam-F3 method.
2. H7-Coil Arm (n=13): Medial prefrontal stimulation using a BrainsWay H7 coil.
   • Protocol: 1,980 pulses/session at 120% RMT (18 Hz stimulation).
   • Targeting: Designed to engage DMPFC.

Outcomes & Measures:

• Primary Outcome: Change in HRSD-17 score from baseline to Week 6.
• Secondary Outcomes: Response (≥50% reduction), Remission (HRSD-17 ≤7), and longitudinal symptom trajectories (Weeks 7, 10, 18) using HRSD-28, MADRS, and QIDS-SR-16.
• Exploratory Outcomes: Association between baseline cognitive functioning (Executive Function composite, Verbal Fluency, Processing Speed) and remission.
• Safety: Adverse events (AEs) and tolerability.

Statistical Analysis:

• Primary analysis used ANCOVA adjusting for baseline HRSD-17 and treatment resistance level.
• Due to the pilot nature, no formal power calculation was performed; the goal was to generate preliminary estimates for a future full-scale trial.

3. Key Results

Feasibility and Retention:

• Recruitment: 29 consented; 28 randomized.
• Completion: 25 participants (89.3%) completed all 30 sessions.
  • iTBS: 100% completion (15/15).
  • H-Coil: 76.9% completion (10/13); 3 dropouts occurred in this group.
• Retention: Strong retention at follow-up (Weeks 7, 10, and 18).

Clinical Efficacy (Week 6):

• Primary Outcome: No significant difference in adjusted Week 6 HRSD-17 scores between groups (Mean Difference: –0.40; 95% CI –5.23 to 4.43; p = .865).
• Response Rates: iTBS (40.0%) vs. H-Coil (50.0%); p > .60.
• Remission Rates: Identical at 20.0% for both groups.
• Longitudinal Trajectory: Significant symptom improvement over time (p = .024), but no significant group-by-time interaction. Both groups followed parallel improvement trajectories.

Exploratory Cognitive Findings:

• Remitters vs. Non-Remitters: Remitters (MADRS ≤10 at Week 7) showed significantly higher baseline executive functioning scores compared to non-remitters (p = .045, d = 0.69).
• Group Specificity: This association was primarily driven by the iTBS group. In the H-Coil group, no significant difference in baseline executive function was observed between remitters and non-remitters.
• Regression Models: Logistic regression suggested a positive (though non-significant in adjusted models) association between baseline executive function and remission likelihood (OR = 4.95).

Safety and Tolerability:

• Adverse Events (AEs): 100% of participants reported at least one AE.
• Stimulation Site Discomfort: Reported by 100% in both groups (Mean pain scores: iTBS 3.91 vs. H-Coil 3.57).
• Systemic AEs: The H-Coil group reported significantly higher rates of systemic side effects:
  • Fatigue: 100% (H-Coil) vs. 46.7% (iTBS).
  • Headache/Migraine: 100% (H-Coil) vs. 46.7% (iTBS).
• Serious AEs: None occurred. No discontinuations due to AEs.

4. Key Contributions

1. First Head-to-Head Pilot: This is the first randomized trial directly comparing left-DLPFC iTBS (figure-8) with H7-coil rTMS (DMPFC) in TRD.
2. Feasibility Validation: Demonstrated that a comparative trial of these distinct modalities is feasible, with high recruitment and retention rates, providing a blueprint for a larger Phase III trial.
3. Cognitive Biomarker Signal: Identified a preliminary signal suggesting that baseline executive function may predict remission specifically for focal DLPFC stimulation (iTBS), but not necessarily for broad medial stimulation (H-Coil). This supports the hypothesis that iTBS relies on the integrity of frontoparietal cognitive control networks.
4. Tolerability Profile: Highlighted that while focal pain is comparable, the H-Coil induces a higher burden of systemic side effects (fatigue, headache) compared to iTBS.

5. Significance and Implications

• Clinical Equivalence (Preliminary): The study suggests that both modalities are effective for TRD, with similar response and remission rates in this small sample. Neither modality demonstrated clear superiority in symptom reduction.
• Mechanistic Insights: The differential cognitive predictors suggest distinct mechanisms of action. iTBS may require intact executive networks to facilitate plasticity, whereas H-Coil stimulation of medial networks might bypass these specific cognitive deficits or operate via different pathways (e.g., direct engagement of affective/self-referential networks).
• Trial Design Guidance: The results provide critical variance estimates and effect size data necessary to power a definitive, large-scale randomized controlled trial (RCT) to determine if one modality is clinically superior for specific patient subgroups.
• Safety Considerations: The higher systemic side effect profile of the H-Coil (despite similar local pain) is a crucial factor for clinical decision-making and patient selection in future studies.

Limitations:

• Small sample size (N=28) limits statistical power to detect modest differences.
• Open-label design (due to device differences) introduces potential bias, though assessors were blinded.
• Single-center design limits generalizability.
• Cognitive findings are exploratory and require replication.

Conclusion:
This pilot trial confirms the feasibility of comparing iTBS and H7-coil rTMS. While no significant clinical differences were found, the exploratory link between executive function and iTBS response offers a promising avenue for personalized medicine in depression treatment. Larger, adequately powered trials are required to validate these findings and optimize stimulation targets for specific patient phenotypes.