High-frequency repeated transcranial magnetic stimulation (rTMS) as a treatment for major depressive disorder (MDD) has received FDA clearance for both the figure-of-8 coil (figure-8 coil) and the H1 coil. The FDA-cleared MDD protocols for both coils include high frequency (10-18 Hz) stimulation targeting the dorsolateral prefrontal cortex (dlPFC) at an intensity that is 120% of the right-hand resting motor threshold. Despite these similar parameters, the two coils generate distinct electrical fields (e-fields) which result in differences in the cortical stimulation they produce. Due to the differences in coil designs, the H1 coil induces a stimulation e-field that is broader and deeper than the one induced by the figure-8 coil. In this paper we review theoretical and clinical implications of these differences between the two coils and compare evidence of their safety and efficacy in treating MDD. We present the design principles of the coils, the challenges of identifying, finding, and stimulating the optimal brain target of each individual (both from functional and connectivity perspectives), and the possible implication of stimulating outside that target. There is only one study that performed a direct comparison between clinical effectiveness of the two coils, using the standard FDA-approved protocols in MDD patients. This study indicated clinical superiority of the H1 coil but did not measure long-term effects. Post-marketing data suggest that both coils have a similar safety profile in clinical practice, whereas effect size comparisons of the two respective FDA pivotal trials suggests that the H1 coil may have an advantage in efficacy. We conclude that further head-to-head experiments are needed, especially ones that will compare long-term effects and usage of similar temporal stimulation parameters and similar number of pulses.

中文翻译：

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经颅磁刺激治疗重度抑郁症的应用：线圈设计和神经解剖学变异性考虑

高频重复经颅磁刺激 (rTMS) 作为重度抑郁症 (MDD) 的治疗方法已获得 FDA 的 8 字形线圈（8 字形线圈）和 H1 线圈的批准。FDA 批准的两个线圈的 MDD 协议包括针对背外侧前额叶皮层 (dlPFC) 的高频 (10-18 Hz) 刺激，强度为右手静息运动阈值的 120%。尽管有这些相似的参数，但两个线圈会产生不同的电场（e 场），从而导致它们产生的皮层刺激存在差异。由于线圈设计的差异，H1 线圈感应出的刺激电场比 8 字形线圈感应的电场更宽更深。在本文中，我们回顾了两个线圈之间这些差异的理论和临床意义，并比较了它们在治疗 MDD 中的安全性和有效性的证据。我们介绍了线圈的设计原则，识别、寻找和刺激每个人最佳大脑目标的挑战（从功能和连接的角度来看），以及在该目标之外刺激的可能含义。只有一项研究在 MDD 患者中使用 FDA 批准的标准方案对两种线圈的临床有效性进行了直接比较。该研究表明 H1 线圈的临床优势，但没有测量长期效果。上市后数据表明，这两种线圈在临床实践中具有相似的安全性，而两项各自的 FDA 关键试验的效果大小比较表明 H1 线圈可能在疗效上具有优势。我们得出结论，需要进一步的头对头实验，特别是那些将比较长期影响和使用类似时间刺激参数和类似脉冲数量的实验。