Letter by Verheyen et al Regarding Article, “Pacemaker Malfunction Attributed to Multidetector Cardiac Computed Tomography”
To the Editor:
We read with great interest the case report by Elagha and Weissman.1 The authors reported on a pacemaker-dependent patient who underwent computed tomography (CT) coronary angiography with a 256-slice multidetector CT scanner. During direct exposure of the pacemaker to CT radiation, transient ventricular asystole was documented, and readout of device memory showed a sensed arrhythmia at a frequency similar to the CT gantry rotation speed. It is concluded that ionized radiation induced pacemaker dysfunction. The authors aim to raise awareness of this complication and recommend establishing routine safety procedures to prevent CT-induced pacemaker dysfunction, eg, asynchronous pacing.
Their elegant report raises concerns about the safety of CT procedures for patients who have pacemakers, because they may induce electromagnetic interference. Their conclusions may lead to uncertainty among patients and healthcare providers. We therefore consider it important to put their conclusions into perspective with existing literature and questions that remain unanswered in the presented case.
The authors correctly emphasize the vulnerability of pacemaker circuits to electromagnetic interference, but they make no mention of a potential involvement of the ventricular electrode. It is well known from previous magnetic resonance tomography studies, however, that pacemakers are distinctly more sensitive to magnetic flux density in unipolar than in bipolar sensing mode.2 Among 245 patients with pacemakers (38% unipolar sensing) exposed to maximum 100-µT flux density, 3 of 4 pacemakers with induced dysfunction had electrodes programmed in unipolar sensing mode. Providing intracardiac electrogram readouts of the pacemaker should help in ruling out a potential involvement of the ventricular electrode. In this case, arrhythmia sensing should be more pronounced or only occur in the ventricular intracardiac electrogram. In a study by Hirose et al,3 effects of CT radiation were tested in a series of pacemakers, and they found that pacemakers with the lowest sensing threshold were most sensitive to electromagnetic interference. We therefore kindly encourage the authors to provide intracardiac electrogram readouts, as well as data on sensing programming and minimal pacemaker sensing threshold to allow the readership a better contextualization of the described observation.
Nevertheless, we are convinced that this case should raise awareness and lead to systematical studies investigating exact mechanisms and incidence of electromagnetic interference on pacemakers during multidetector CT scans. These should be carefully performed before proposing asynchronous stimulation in this setting, with a potential risk of inducing ventricular tachyarrhythmias.4
Nicolas Verheyen, MD
Daniel Scherr, MD
Martin Manninger, MD
Circulation is available at http://circ.ahajournals.org.
- © 2016 American Heart Association, Inc.