Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T

Abstract

Background: MRI has unparalleled soft-tissue imaging capabilities. The presence of devices such as pacemakers and implantable cardioverter/defibrillators (ICDs), however, is historically considered a contraindication to MRI. These devices are now smaller, with less magnetic material and improved electromagnetic interference protection. Our aim was to determine whether these modern systems can be used in an MR environment.

Methods and results: We tested in vitro and in vivo lead heating, device function, force acting on the device, and image distortion at 1.5 T. Clinical MR protocols and in vivo measurements yielded temperature changes <0.5 degrees C. Older (manufactured before 2000) ICDs were damaged by the MR scans. Newer ICD systems and most pacemakers, however, were not. The maximal force acting on newer devices was <100 g. Modern (manufactured after 2000) ICD systems were implanted in dogs (n=18), and after 4 weeks, 3- to 4-hour MR scans were performed (n=15). No device dysfunction occurred. The images were of high quality with distortion dependent on the scan sequence and plane. Pacing threshold and intracardiac electrogram amplitude were unchanged over the 8 weeks, except in 1 animal that, after MRI, had a transient (<12 hours) capture failure. Pathological data of the scanned animals revealed very limited necrosis or fibrosis at the tip of the lead area, which was not different from controls (n=3) not subjected to MRI.

Conclusions: These data suggest that certain modern pacemaker and ICD systems may indeed be MRI safe. This may have major clinical implications for current imaging practices.

Figures

Figure 1

a, Maximal force. b, Torque.

Figure 2

EMI noise from different MR scan protocols interpreted by the device as ventricular fibrillation (VF). VT indicates ventricular tachyarrhythmia; VS, ventricular sense.

Figure 3

Gross and microscopic examination of the heart. a, The heart is opened in a parasagittal fashion, parallel to the orientation of the lead. The lead is well anchored at apex of the right ventricle (RV). The RV free wall is seen above the lead. The trabeculation of the RV side of the septum is prominent below the lead. Note the absence of scar tissue in the muscular portion of the RV. LV indicates left ventricle; IVS, interventricular septum. b, The fibrous “cuff” that covers the lead near the apex is shown after removal of the lead. c, Low-magnification view of a histo-logical section showing the lead implantation site with the fibrous tissue surrounding the lead and the anchoring screw. The myocardium is unremarkable; note the absence of inflammatory infiltrates or scarring within the muscle parenchyma. The only fibrous tissue present is at the anchoring site where the anchoring screw has been deployed. Note the 2 circular orifices left during removal of the anchoring screw of the lead (hematoxylin-eosin stain). d, Masson trichrome stain for fibrous tissue (blue staining) confirms the fibrous nature of the cuff. However, there is no evidence of interstitial or replacement fibrosis in the myocardium (red staining). e, Movat pentachrome stain shows mild elastosis within the fibrous cuff but no fibrosis or elastosis in the myocardium. f, Close-up view of the lead showing the anchoring screw delivered and some dried tissue on it. g, Composite of light microscopy of the anchoring site with a superimposed image of the lead. Note matching of the gross image and absence of myocardial fibrosis in areas surrounding the location of electrodes in the lead.

Figure 4

MRI at heart level with the use of different MR scanning sequences: FSPGR (a), tagging (b), FGRE (c), and FIESTA (d). Imaging at device level (e through h) shows different artifacts depending on scan sequence: angiography showing the level where the axial scan was done (e), FSPGR (f), FGRE (g), and FIESTA (h).