Clinical safety of the Iforia implantable cardioverter-defibrillator system in patients subjected to thoracic spine and cardiac 1.5-T magnetic resonance imaging scanning conditions.

Background: Implantable cardioverter-defibrillators (ICDs) are generally considered a contraindication to magnetic resonance imaging (MRI).

Objective: The purpose of the ProMRI Phase C study, a multicenter, prospective, single-arm, nonrandomized study, was to evaluate the clinical safety of the Biotronik ProMRI Iforia ICD system during MRI.

Methods: Patients were enrolled after ICD implantation, with either a dual-chamber DR-T or single-lead VR-T DX system. Study-defined, nondiagnostic cardiac or thoracic spine MRI was performed at least 1 week after enrollment. ICDs were placed into MRI mode with ventricular fibrillation (VF) detection/therapy programmed "off" before scan and restored to non-MRI mode after scan. Interrogation was performed before, immediately after, and 1 month post-MRI. The primary end-points were (1) ventricular pacing threshold increase >0.5 V from pre-MRI to 1 month post-MRI; (2) R-wave amplitude decrease >50% from pre-MRI to 1 month post-MRI or R-wave amplitude <5 mV at 1 month post-MRI; and (3) MRI and ICD system-related serious adverse device effects.

Results: One hundred seventy patients were enrolled at 39 US centers. One hundred fifty-three patients underwent MRI (25.7% cardiac, 74.3% thoracic spine) and completed follow-up. Freedom from the primary end-points was met in all but 1 subject, in whom reduced R-wave amplitude was detected 1 month post-MRI. No serious adverse device effects occurred during the course of the study.

Conclusion: These results demonstrate the clinical safety and efficacy of the ProMRI ICD system in patients subjected to thoracic spine and cardiac MRI imaging in 1.5-T scanners.