Periprocedural management of cardiac implanted electronic devices

Cardiac implanted electronic devices (CIED) include implantable cardioverter defibrillators (ICD) and permanent pacemakers. These devices act by sensing the intrinsic cardiac rhythm as well as delivering pacing or defibrillation. Pacemaker ‘dependency’ means that there is no underlying cardiac rhythm, and the pacemaker paces all the time.

Surgical diathermy causes electrical interference, which can affect electrocardiogram (ECG) monitoring, making it difficult for the clinician to determine the cardiac rhythm. The electrical interference can also be misinterpreted by a CIED as a cardiac signal, causing the CIED to inappropriately inhibit pacing or deliver a shock. To minimise the effect of electrical interference, CIEDs have automatic protective mechanisms, including a ‘noise mode’ during which pacing continues despite electrical interference; however, an inappropriate response to electrical interference can still occur. Rarely, interference from surgical diathermy can cause more serious adverse outcomes.

Interference is more likely during head, neck or chest surgery because the diathermy circuit intersects the pacemaker-sensing circuit. Diathermy applied below the iliac crest is unlikely to cause interference with a pacemaker and preprocedural reprogramming is not necessary. Electroconvulsive therapy (ECT) rarely causes interference.

To prevent an inappropriate response to electrical interference, the CIED can be reprogrammed in the periprocedural period. This usually involves switching off ICD therapy (ie switching off the ability to deliver defibrillation shocks), and, for a patient who is pacemaker dependent, switching on asynchronous pacing (ie pacing without sensing intrinsic rhythm or electrical interference).

Rather than reprogramming the CIED, a magnet is often used to temporarily stop the effect of interference. A magnet can be placed over:

• a permanent pacemaker to turn off the sensing of intrinsic rhythm, causing the pacemaker to pace every beat while the magnet is in place even if there is interference (which could otherwise be misinterpreted as intrinsic rhythm)
• an ICD to turn off the sensing of tachycardia so ventricular fibrillation is not detected and interference from diathermy is not mistaken for ventricular fibrillation. This prevents the ICD from delivering an inappropriate shock.

The effect of the magnet on pacing by the ICD depends on the model of the ICD. A magnet will usually have no effect on ICD pacing. This is a particular concern for a patient who is pacemaker dependent; if interference is misinterpreted by the ICD as intrinsic rhythm, pacing can be inappropriately inhibited.

The magnet must be taped in place for its effect to continue.

Despite efforts to standardise the CIED responses to a magnet, there are still significant differences between devices made by different manufacturers, so always seek expert advice.

The mnemonic ICD-PM-PM can be used to guide management of a patient with a CIED who requires a procedure—see Management of patients with a cardiac implanted electronic device who require a procedure.

The presence of a CIED is not a specific indication for surgical antibiotic prophylaxis. See Cardiac implantable electronic device infections for further information.