Cardiac Implanted Devices and Repetitive Nerve Stimulation

Abstract & Commentary

By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.

Synopsis: Repetitive nerve stimulation studies appear to be safe in patients with modern implantable pacemakers and defibrillators.

Source: Cronin EM, et al. Safety of repetitive nerve stimulation in patients with cardiac implantable electronic devices. Muscle Nerve 2012; doi:10.1002/mus.23707.

Single-stimulation nerve conduction studies are safe in patients with cardiac implantable electronic devices (CIEDs), including pacemakers or implantable cardioverter defibrillators (ICD). However, absent any published data, the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM), in its 2009 position statement, advises against the use of repetitive nerve stimulation (RNS) in the proximal arm in patients with any such device. For the first time, we now have (limited) data addressing the safety of RNS in such patients.

To ensure maximal patient comfort, participation in this study was offered only to patients undergoing general anesthesia for implantation or revision of an ICD or pacemaker. After completion of the cardiac procedure, RNS was performed to the spinal accessory nerve posterior to the sternocleidomastoid, recording from trapezius; the axillary nerve in the supraclavicular fossa, recording from deltoid; and the median nerve at the wrist, recording from abductor pollicis brevis. Supramaximal stimulation was used, with rapid (50Hz) and slow (2 Hz) RNS applied for 3 and 4.5 seconds respectively, repeated once and twice, respectively. CIEDs were set at nominal and maximum bipolar sensitivity, and, if available, at nominal and maximum unipolar sensitivity. Real-time monitoring of the intracardiac electrogram (EGM) was continuously performed, and electromagnetic interference (EMI) on the EGM was graded as level 1, 2, or 3, depending on whether noise was visible but not detected by the CIED (Level 1); noise was detected, but not acted upon, by the CIED in the form of a significant change in pacing output or arrhythmia diagnosis (Level 2); or noise was detected by the CIED and resulted in a change in pacing output or an arrhythmia diagnosis (Level 3).

Among 14 consecutive patients studied, including 10 ICDs and four pacemakers, none demonstrated any neuromuscular disease. RNS studies were performed on the left side ipsilateral to the CIED, with only one exception due to intraoperative inaccessibility. Among the 10 ICDs, although noise was visible on EGM in two subjects, in no subject was the RNS sensed as originating from the heart. Among four pacemakers investigated (two in bipolar configuration and two in unipolar configuration), EMI was recorded in three, with one pacemaker in bipolar configuration slightly increasing the paced rate for two beats with no clinical consequence. Two pacemakers in unipolar configuration detected the RNS and transiently inhibited their ventricular pacing, for 6 seconds and a single beat, respectively. With distal, wrist RNS, nothing was sensed by the CIEDs. RNS is safe for patients with implantable cardioverter defibrillators, and in pacemaker patients during bipolar sensing. With unipolar sensing, caution is recommended.

Commentary

To avoid potential adverse reactions to the cardiac rhythm, some pacemaker companies recommend placing a magnet over their device during nerve conduction studies. This does not seem to be necessary. In a prospective study among 73 patients (29 with permanent pacemakers, 19 with ICDs, and 25 patients with both), routine nerve conduction and repetitive nerve stimulation studies were performed both with (n = 27) and without (n = 46) magnet placement. In no instance were any of the devices affected, supporting the notion that such studies are safe in patients with implanted cardiac devices. Magnet placement is unwarranted.1

Reference

1. Ohira M, et al. Nerve conduction studies in patients with implanted devices are safe regardless of magnet placement. Clinical Neurophysiology 2012;123:e67-e68.