Intraoperative Electromagnetic Interference

Intraoperative Electromagnetic Interference

With Implanted Pacemakers and ICDs

It is important to be aware of the potential for adverse

interactions between electrical/magnetic activity and pacemaker or ICD function that may occur during the operative period. These interactions result from electrical current generated by electrocautery or cardioversion, as well as the impact of metabolic derangements, antiarrhythmic agents, and anesthetic agents on pacing and sensing thresholds. The probability of these adverse interactions can be minimized if certain precautions are taken. Although this topic has been analyzed in a number of review articles and book chapters, no formal guidelines have been developed by the ACC, the AHA, or the Heart Rhythm Society. Of note, however, is a practice advisory that has been published by the American Society of Anesthesiology.434

Electrocautery involves the use of radiofrequency current

to cut or coagulate tissues. It is usually applied in a unipolar fashion between the cautery device and an indifferent plate attached to the patient’s skin. The indifferent plate is often placed on the patient’s thigh. Although bipolar cautery systems are available, they are not widely used. The potential for electromagnetic interference with an implanted device is related to the amount of current generated in the vicinity of the pacemaker or ICD device. In general, high current is generated if the cautery device is close to the pacemaker, particularly if the current path of the cautery lies along the axis of the pacemaker or ICD lead. The electrical current generated by electrocautery can cause a variety of responses by the implanted device, including the following: 1) temporary or permanent resetting to a backup, reset, or noisereversion pacing mode (eg, a dual-chamber pacemaker may be reset to VVI pacing at a fixed rate); 2) temporary or permanent inhibition of pacemaker output; 3) an increase in pacing rate due to activation of the rate-responsive sensor; 4) ICD firing due to activation by electrical noise; or 5) myocardial injury at the lead tip that may cause failure to sense and/or capture. Cardioversion can have similar effects on pacemaker or ICD function. Although the probability of

any of these adverse interactions occurring has fallen dramatically owing to the almost universal use of bipolar leads (which greatly reduces the probability of electromagnetic interference) and improved pacemaker and ICD design, they still may occur.

The likelihood and potential clinical impact of adverse

interactions occurring in patients with ICDs and pacemaker devices will be influenced by a number of factors, including whether the patient is pacemaker dependent, whether the pacemaker has unipolar or bipolar leads, whether the electrocautery is bipolar or unipolar, and the relative distance from and orientation of the electrocautery relative to the pacemaker and pacemaker lead. These factors, combined with the urgency and type of surgery (interactions are far more likely to occur with surgical procedures that involve the chest or abdomen) and the availability of expertise in pacing and/or ICDs, will ultimately determine the type and extent of evaluation that is performed in a particular institution. Patients with pacemakers must be assessed as to whether they are pacer dependent. This may be determined by a chart review and examination of the ECG, as opposed to requiring the interrogation of the device. When the patient is not pacer dependent and/or the cautery is remote and will be administered in brief bursts, and the operative team can monitor the ECG and pulse oximeter (which allows pulse determination even when electrical interference by cautery interferes with the ECG), it may be unnecessary to interrogate the pacer at all.

Several general recommendations can be made concerning the preoperative and operative management of patients with implanted devices who are undergoing surgical procedures.

 Patients with implanted ICDs or pacemakers need to be identified before surgery so that appropriate records from

the device clinic that is monitoring the patient’s device can be obtained. In addition, the original indication for device placement should be identified before surgery. Patients with permanent pacemakers, who are pacemaker dependent, should have their device evaluated within 3 to 6 months before significant surgical procedures, and also after surgery.

Significant surgical procedures include major abdominal or thoracic surgery, particularly when the surgery involves large amounts of electrocautery. This evaluation should include 1) determining the type of device, 2) determining whether the patient is pacemaker dependent for antibradycardia pacing, and 3) determining device programmed settings and battery status. If a patient is pacemaker dependent, the device should be reprogrammed to an asynchronous mode during surgery (VOO or DOO), or a magnet should be placed over the device during surgery. Implantable cardioverter defibrillator devices should have their tachyarrhythmia treatment algorithms programmed off before surgery and turned on after surgery to prevent unwanted shocks due to spurious signals that the device might interpret as ventricular tachycardia or fibrillation.

During the period of time when device therapy has been

inactivated, the patient should be monitored continuously for a life-threatening arrhythmia. All patients with implanted devices should have both continuous ECG monitoring and continuous pulse monitoring during surgery. This reflects the fact that electrocautery may interfere with ECG monitoring and make it difficult or impossible to determine the patient’s rhythm. Efforts should be made to minimize the chance for interactions by careful management of potential sources of electromagnetic interference. These include 1) the use of a bipolar electrocautery system if possible, 2) the use of short and intermittent bursts of electrocautery at the lowest possible energy levels, 3) maximization of the distance between the electrocautery and the device, and 4) if a unipolar cautery is to be used, placement of the ground patch in a position so as to minimize current flow through the pacemaker or ICD device. Finally, if emergency cardioversion is required, the paddles should be placed as far from the implanted device as possible and in an orientation likely to be perpendicular to the

orientation of the device leads (anterior-posterior paddle

position is preferred). After the surgery, the function of the implanted device should be assessed and in some cases formally evaluated. If the pacemaker or ICD was reprogrammed before surgery, it should be programmed back to its original settings after surgery. In the case of an ICD, an interrogated programmer printout should be produced to verify that its antitachycardia function has been restored to its active status.

Placement of a magnet over an implanted device has

variable effects depending on the type of device, its manufacturer, and its model. Most bradycardia pacemakers will respond to magnet application with asynchronous pacing at a pre-prescribed rate. However, this magnet function can, in a minority of pacemaker models, be programmed off, and therefore, a magnet may not elicit a response from those models. If a magnet will be used during surgery in a patient with a pacemaker who is pacemaker dependent, it should be applied before surgery to be certain that appropriate asynchronous pacing is triggered by the magnet. Unlike bradycardia pacemakers, a magnet will not change the pacing function of an ICD. Magnet application will affect only the antitachycardia function of an ICD. With some models of ICDs, the magnet will first suspend the antitachycardia (shocking) function and then actually turn the therapy off. With other ICD models, the magnet will only temporarily disable the shock function (while the magnet is in place), and the therapy will then become active again on its removal (either intentional or unintentional). Programming the shock function off with an ICD programmer (and turning it back on after the surgery) is the preferred method of addressing these issues. Because some patients with ICDs are also pacemaker dependent, the pacing function of the ICD may need to be programmed to an asynchronous mode (eg, VOO or DOO) during surgery to prevent electromagnetic interference–induced inhibition. Communication of the status of the pacemaker or ICD to the anesthesiologist, surgeon, and intensivist is imperative.