MRI conditional pacemakers

MRI conditional pacemakers

Conventionally MRI (magnetic resonance imaging) is contraindicated in those with implanted pacemakers due to possibility of electromagnetic interference (EMI) with pacemaker function. MRI-conditional means that there are no known hazards when MRI is performed with pre specified device programming, patient monitoring and imaging protocols. They were first introduced in 2008 [1]. These pacemakers have less ferromagnetic material and lead design changes reduce the chance for heating. Reduction of ferromagnetic material also reduces the potential for artifacts induced by the pacemaker system in the MR images. The winding pattern of the filament of inner lead coil and geometric design of the leads have been changed to avoid resonance at the MR signal frequency to avoid heating [1]. It may be noted that MRI conditional devices should be connected to MRI conditional leads only. Otherwise the system will not be MRI conditional.

Reed switch is replaced by a solid state Hall effect sensor which perform better within the MR console, by avoiding unpredictable reed switch behaviour. Reed switch behaviour will vary with the strength of the magnetic field and the orientation of the reed switch in the field.

Easily programmable MRI mode is available in these devices. This will prevent inappropriate pacemaker inhibition and competing rhythms [1]. These devices have special circuitry to prevent damage to internal power supply when exposed to MRI signals.

Wilkoff BL et al in a prospective randomized controlled worldwide clinical trial evaluated the safety and effectiveness of MRI conditional pacemakers in 464 patients [2]. Patients were randomized to undergo an MRI scan between 9 and 12 weeks after implantation of specially designed dual chamber pacemaker and leads. MRI was done at 1.5 Tesla and patients were monitored for arrhythmias, symptoms and pacemaker function. Brain and lumbar MRI sequences were obtained. No complications related to MRI occurred during or after the scan.

ProMRI Phase B Study was a multicenter prospective non randomized study to evaluate the clinical safety of the Biotronik ProMRI pacemaker system in patients undergoing thoracic spine and cardiac MRI [3]. The study enrolled 245 patients with stable baseline pacing. 216 patients completed the MRI scan and 1 month follow up. One adverse event possibly related to the implanted system and MRI procedure occurred and the serious adverse device effect-free rate was 99.6%.

Real world data of 4 year prospective follow up in 2,629 patients with MRI conditional pacemaker system has been published by Williamson BD et al [4]. 526 patients underwent 872 clinically indicated MRI scans including 58 thoracic scans. No MRI-related complications occurred during or after MRI. Six MRI related observations were reported, which included atrial fibrillation, increase in pacing capture threshold and chest symptoms. 171 patients underwent 2 or more scans, with no cumulative increase in pacing capture threshold.

MRI using 3 Tesla devices has been reported by Ning X et al [5]. Twenty patients with MRI-conditional pacemakers underwent 23 MRI scans of different regions of the body including brain, lumbar spine, cervical spine and heart (4 patients). Standardized protocol was developed by cardiologists, pacemaker engineers, and radiologists. No adverse events were detected and image quality was grade 1 in 16 patients. Artifacts of pulse generators and leads in cardiac MRI scan caused grade 2 quality in 4 patients, without any impact on diagnostic value.

References

1. António M Ferreira, Francisco Costa, António Tralhão, Hugo Marques, Nuno Cardim, Pedro Adragão. MRI-conditional Pacemakers: Current Perspectives. Med Devices (Auckl). 2014 May 7;7:115-24.
2. Wilkoff BL, Bello D, Taborsky M, Vymazal J, Kanal E, Heuer H, Hecking K, Johnson WB, Young W, Ramza B, Akhtar N, Kuepper B, Hunold P, Luechinger R, Puererfellner H, Duru F, Gotte MJ, Sutton R, Sommer T; EnRhythm MRI SureScan Pacing System Study Investigators. Magnetic resonance imaging in patients with a pacemaker system designed for the magnetic resonance environment. Heart Rhythm. 2011 Jan;8(1):65-73.
3. Bailey WM, Mazur A, McCotter C, Woodard PK, Rosenthal L, Johnson W, Mela T; ProMRI Study Investigators. Clinical safety of the ProMRI pacemaker system in patients subjected to thoracic spine and cardiac 1.5-T magnetic resonance imaging scanning conditions. Heart Rhythm. 2016 Feb;13(2):464-71.
4. Williamson BD, Gohn DC, Ramza BM, Singh B, Zhong Y, Li S, Shanahan L; SureScan Post-Approval Study Investigators. Real-World Evaluation of Magnetic Resonance Imaging in Patients With a Magnetic Resonance Imaging Conditional Pacemaker System: Results of 4-Year Prospective Follow-Up in 2,629 Patients. JACC Clin Electrophysiol. 2017 Nov;3(11):1231-1239.
5. Ning X, Li X, Fan X, Chen K, Hua W, Liu Z, Dai Y, Chen X, Lu M, Zhao S, Zhang S. 3.0 T magnetic resonance imaging scanning on different body regions in patients with pacemakers. J Interv Card Electrophysiol. 2020 Aug 17. doi: 10.1007/s10840-020-00854-3. Epub ahead of print. PMID: 32808082.