Overview

The high prevalence of cardiac disease in patients presenting for noncardiac operations poses a considerable challenge to the anesthesia provider. Many of these patients have pacemakers, which are being used with increasing frequency to treat conduction problems, arrhythmias, and ventricular dysfunction. More than 500,000 people in the United States have pacemakers, and nearly 115,000 new devices are implanted each year.

Early pacing systems consisted of a single-lead asynchronous pacemaker, which paced the heart at a fixed rate. Over the years, technologic advances have revolutionized pacemakers; today’s sophisticated multiprogrammable devices have dramatically increased the number of indications for the use of pacing. Care of the patient with a pacemaker during surgery, therefore, requires an understanding of the pacemaker and of the associated anesthetic and surgical implications.

Generic codes of pacemaker

Developed originally by the International Conference on Heart Disease and subsequently modified by the NASPE/BPEG (North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group) alliance, the NASPE/BPEG code consists of five letters of the alphabet that describe the five programmable functions of the pacing system (Box 151-1). The first letter of the code indicates the chamber being paced; the second, the chamber being sensed; and the third, the response to sensing (I and T indicate inhibited or triggered responses, respectively). An R in the fourth position indicates that the pacemaker incorporates a sensor to modulate the rate independently of intrinsic cardiac activity, such as with activity or respiration. A P in the fifth position, for example, indicates that the pacemaker “paces” to treat a tachyarrhythmia. However, letters in the fourth and fifth positions are uncommonly used. Table 151-1 summarizes commonly used configurations.

Preoperative evaluation

Preoperative (and postoperative, if electrocautery was used) evaluation of the patient and the pacemaker is an important aspect of the anesthetic management of a patient with a permanent pacemaker who is undergoing a noncardiac operation. The patient should be asked about the initial indication for the pacemaker and preimplantation symptoms. The location of the pulse generator should be noted. Generally, the generator for endocardial electrodes is placed subcutaneously in the left lateral subclavicular region, and the generator for epicardial electrodes is placed subcutaneously in the abdomen.

Routine biochemical and hematologic investigations should be performed as indicated on an individual basis. A 12-lead electrocardiogram, chest radiograph (for visualization of continuity of leads), and measurement of serum electrolytes (especially K⁺) should be performed.

The current standard is to have the pacemaker evaluated by a qualified technician in the preoperative period if it has not been evaluated in the past 6 weeks. The technician places an interrogator over the pacemaker, which then sends stored data to the interrogator. This information is vital to ensuring that the pacemaker is operating effectively and under the right settings. Most of the information about the pacemaker, such as type (fixed rate or demand rate), time since implantation, rate at the time of implantation, and half-life of the pacemaker battery can be found in the manufacturer’s book, which the patient should have brought to the preoperative area. A 10% decrease in the rate that was set at the time that the pacemaker was implanted indicates power-source depletion. In patients with a VVI generator in whom the intrinsic heart rate is greater than the set rate of the pacemaker, pacemaker function can be evaluated by slowing the patient’s heart rate. Slowing can be accomplished by massaging the patient’s carotid sinus while continuously monitoring the patient’s electrocardiogram, having the patient perform the Valsalva maneuver, or administering edrophonium (5-10 mg).

If the patient has an implanted cardioverter-defibrillator, it should be disabled before induction of anesthesia and before surgical procedures are performed in which electrocautery is to be used. If the risk of electromagnetic interference (EMI) is high, such as when electrocautery is used in close proximity to the generator, an alternative temporary cardiac pacing device should be available. A magnet can be used to reprogram the pacemaker to a fixed rate in patients who are pacemaker dependent and should be placed over the pacemaker in patients in whom electrocautery is to be used.

Effect of a magnet on pacemaker function

Magnets are used in the operating room to protect the pacemaker-dependent patient from the effects of EMI. A magnet placed over the pulse generator triggers the reed switch present in the pulse generator, which deactivates the demand function, deactivates the sensing function, and activates asynchronous pacing at a fixed rate. However, not all pacemakers switch to an asynchronous mode with application of a magnet. The response varies with the model and the manufacturer and may be in the form of no apparent change in rate or rhythm, brief asynchronous pacing, continuous or transient loss of pacing, or asynchronous pacing without rate response. Thus, it is advisable to have the pacemaker interrogated by a qualified technician and to consult with the manufacturer, if necessary. The routine use of a magnet during surgery is not without risk, however, and, at times, may not be justified. Switching to asynchronous pacing may trigger ventricular asynchrony in patients with myocardial ischemia, hypoxia, or electrolyte imbalance. The new generation pacemakers are relatively immune to magnet application, and placement of a magnet may not convert a pacemaker to an asynchronous mode. Constant magnet application over the pacemaker may alter its programming, leading to either inhibited or triggered pacing, or may cause continuous or transient loss of pacing. Magnets placed over programmable pacemakers, in the presence of EMI, have been known to reprogram the pulse generator. This new “surprise” program may not be evident until after the magnet is removed. A further problem with magnetic application is the variability of response between devices, as there is no universal standard. Thus, a magnet may be safe for use with nonprogrammable pacemakers; however, the newest devices should be considered programmable unless otherwise indicated.

Intraoperative management

Intraoperative monitoring should be based on the patient’s underlying disease and the type of operation to be undertaken. Depending on the pacemaker and type of operation, mechanical evidence of cardiac output should be monitored by manual palpation of the pulse, the use of pulse oximetry and a precordial stethoscope, and a blood pressure tracing from an arterial line, if indicated.

The presence of a pacemaker should not affect the choice of anesthetic agent; both intravenous (with the exception of ketamine and etomidate) and inhalation agent–based techniques can be used because they do not alter the current and voltage thresholds of the pacemaker. Skeletal myopotentials, electroconvulsive therapy, succinylcholine fasciculation, myoclonic movements, and direct muscle stimulation can inappropriately inhibit or trigger pacemaker stimulation, depending on the programmed pacing modes. Case reports have indicated that myoclonus associated with the use of etomidate and ketamine may affect pacemaker function. In patients with rate-responsive pacemakers, the rate-responsive mode should be deactivated before surgery. If this is not possible, the mode of rate response must be known so that conditions causing changes in paced heart rate can be avoided. For example, shivering and fasciculations should be avoided if the pacemaker is “activity” rate responsive, ventilation (respiratory rate and tidal volume) should be controlled in case of “minute ventilation” rate responsive, and temperature must be kept constant in “temperature” rate responsive pacemakers.

Electromagnetic interference

Among the various sources of EMI, electrocautery is the most important. Electrocautery involves the use of radiofrequency currents of 300 to 500 kHz. Fatal arrhythmias and deaths have been reported with the use of electrocautery leading to failure of pacemakers. Between 1984 and 1997, the U.S. Food and Drug Administration was notified of 456 adverse events with the use of pulse generators—255 from electrocautery—with a significant number of device failures. The following measures may decrease the possibility of adverse effects due to electrocautery:

Summary

Patients with implanted pacemakers can be managed safely for surgery and other nonsurgical procedures, but to do so requires a thorough understanding of the indication for and the programming of the pacemaker. Anesthetic management should be planned preoperatively according to patient’s medical status, and for those patients who are pacemaker dependent, intraoperative monitoring of a pulse is recommended. Precautions should be taken to minimize EMI while using electrocautery. The magnet should not be placed over the pacemaker in the operating room while electrocautery is in use. Rate-responsive pacemakers should have the rate-responsive mode disabled before the operation begins. Provision of temporary pacing should be available in the operating room to deal with pacemaker malfunction (Table 151-2).