Noninvasive Mechanical Ventilation Reduces Cardiorespiratory Motion and Increases Heart-Stomach Distance for Stereotactic Arrhythmia Radiation Therapy: A Healthy Volunteer Study.

Abstract

Stereotactic arrhythmia radiation therapy (STAR) is an emerging noninvasive treatment for patients with therapy-refractory ventricular tachycardia. However, STAR's targeting accuracy is challenged by cardiorespiratory motion, which may necessitate compromises in dose delivery to protect nearby organs-at-risk, particularly the stomach. Noninvasive mechanical ventilation (NIMV) at 60 breaths/min with 15 cmH₂O positive end-expiratory pressure (NIMV_60P) has been shown to reduce respiratory motion and to potentially increase anatomic separation between thoracic structures. This study aimed to quantify the effect of NIMV_60P on cardiorespiratory motion of the left diaphragm and the minimal heart-stomach distance. We retrospectively analyzed magnetic resonance imaging (MRI) data from 22 healthy volunteers who underwent 2 sessions while free-breathing, breath-holding, and undergoing NIMV_60P. Diaphragm motion was quantified using coronal cine MRIs. The minimal heart-stomach distance was measured using 3-dimensional MRIs during breath-hold inhalation (BH-inhalation), exhalation (BH-exhalation), and NIMV_60P. Encompassing volumes of the heart and stomach were generated from BH-inhalation and BH-exhalation scans to evaluate overlap or separation during free-breathing. Lastly, cine frames were deformably registered to assess temporal heart-stomach distance variation. NIMV_60P significantly reduced median cranial-caudal diaphragm motion by half from 30 mm (IQR, 16 mm) during free-breathing to 15 mm (IQR, 7 mm; P < .001). The median of the minimal heart-stomach distances increased to 16.8 mm with NIMV_60P, significantly larger than during BH-inhalation (10.3 mm; P = .04) and BH-exhalation (4.6 mm; P < .01), whereas analysis emulating free-breathing showed frequent heart and stomach internal-volume overlap (27 of 41 sessions) or minimal median distance of 3.4 mm (IQR, 7 mm) between the heart and stomach, which can result in significant stomach dose during STAR. Median temporal heart-stomach distance was 19.2 mm during NIMV_60P versus 7.1 mm during free-breathing. NIMV_60P significantly reduces diaphragm motion and increases the distance between heart and stomach in healthy volunteers, supporting its integration with STAR to potentially improve targeting and reduce stomach toxicity, especially for inferior wall ventricular tachycardia targets.