Introduction

Battery-operated pacemakers (PMs) revolutionized the treatment of fatal electrical conduction abnormalities in 1958, just a few years after the invention of the transistor. As this science has matured, PMs have been designed to provide atrioventricular synchronization, improve the quality of life for the chronotropically incompetent patient, prevent and treat atrial fibrillation, and reduce ventricular contractile dyssynchrony in the presence of cardiomyopathy. The development of implantable cardioverter-defibrillators (ICDs), capable of antitachycardia pacing or high-energy shock, extended this science to patients who experience ventricular tachyarrhythmias. ICDs were first demonstrated in 1980 and approved by the U.S. Food and Drug Administration (FDA) in 1985. Current ICDs represent advancements of PM technology, so every ICD implanted today, in addition to high-energy therapy for ventricular arrhythmias, can provide the entire functional set of antibradycardia-pacing capabilities found in a conventional PM.

These devices are no longer confined to keeping the heart beating between a minimum rate (pacing function) and a maximum rate (ICD functions); they are now employed as therapy to improve the failing heart (biventricular [BiV] pacing, also called cardiac resynchronization therapy [CRT]). Electronic miniaturization of PMs and ICDs has permitted the design and use of sophisticated electronics in patients who need artificial pacing or automated cardioversion/defibrillation of their heart (or both).

Coupled with population aging, continued enhancements and new indications for implantation of PMs or ICDs will lead to increasing numbers of patients with these devices. Safe and efficient clinical management of these patients depends on our understanding of implantable systems, indications for their use, and the perioperative needs that they create.

However, the increasing specialization, the proprietary nature of hardware and software developments, and the complexity of cardiac generators limit generalizations that can be made about the perioperative care of these patients. Additionally, the absence of published trials, the incorrect interpretation of adverse events in published literature, and the economic and technical challenges involved in appropriately evaluating these devices preoperatively and postoperatively add to the difficulties in properly managing these patients.

These issues led the American Society of Anesthesiologists (ASA) to publish a Practice Advisory for these patients in 2005, which was updated in 2011. In addition, the Heart Rhythm Society (HRS) and ASA, in collaboration with the American Heart Association and the Society of Thoracic Surgeons, recently published an Expert Consensus Statement. Other recommendations have been published as well, although not all authors advocate routine disabling of ICD high-energy therapy in the perioperative period.

Options/Therapies

Information contained herein applies to the perioperative management of patients with PMs and ICDs. It does not address the management of patients for whom these therapies might become necessary nor instances when these devices might no longer be needed.

Evidence

Whether PM or ICD patients have increased perioperative morbidity or mortality risk remains an area ripe for investigation. Levine and colleagues reported increases in pacing thresholds (i.e., the amount of energy required to depolarize the myocardium) in some thoracic operations. In 1995, Badrinath and colleagues retrospectively reviewed ophthalmic surgery cases in one hospital in Madras, India, from 1979 through 1988 (14,787 cases) and found that the presence of a PM significantly increased the probability of a mortal event within 6 weeks postoperatively, regardless of the anesthetic technique. Pili-Floury and colleagues reported that two of 65 PM patients (3.1%) undergoing significant noncardiac surgery died postoperatively of cardiac causes over a 30-month study period. They also reported that 12% of patients required preoperative and 7.8% required postoperative modification of PM programming. In abstract form, Rozner and colleagues reported a 2-year retrospective review of 172 PM patients evaluated at a preoperative anesthesia clinic, showing that 27 of 172 (16%) needed a preoperative intervention (nine of 27 were generator replacement for battery depletion). Additionally, follow-up of the 149 patients who underwent an open surgical procedure showed five ventricular pacing threshold increases, one atrial pacing threshold increase, and one PM electrical reset, all of which took place in patients undergoing nonthoracic surgery. All of these cases involved electromagnetic interference (EMI) from a monopolar electrosurgical unit (ESU), and one large ventricular pacing threshold was observed after a significant fluid and blood resuscitation after the loss of 2500 mL of blood in a 45-year-old woman. Finally, Cheng et al prospectively evaluated 57 patients with ICDs (17% not evaluated in the past 3 months) and 35 with PMs (23% not evaluated in the past 6 months) for a variety of cases. There was no change in pacing or sensing thresholds but significantly decreased lead impedance in all chambers. One ICD reported an elective reset because of battery depletion during the case. At postoperative evaluation, several devices reported EMI but no ICDs delivered therapy.

For the patient with ventricular tachycardia or ventricular fibrillation, ICDs clearly reduce deaths, and they remain superior to antiarrhythmic drug therapy. Further, studies suggesting prophylactic placement in patients without evidence of tachyarrhythmias (Multicenter Automatic Defibrillator Implantation Trial–II [MADIT-II], which studied ischemic cardiomyopathy and patients with an ejection fraction less than 0.30, and Sudden Cardiac Death–Heart Failure Trial [SCD-HeFT], which studied any cardiomyopathy and patients with an ejection fraction less than 0.35 ) have significantly increased the number of patients for whom ICD therapy is indicated.

ICD features and advancements can present consequences particularly relevant to the perioperative practitioner. First, all ICDs have bradycardia-pacing capability, and the presence of pacing artifacts on an electrocardiogram (ECG) might lead a practitioner to mistake an ICD for a conventional PM. Second, ICD bradycardia-pacing is never converted to asynchronous mode with magnet placement; thus, for many ICDs, confirmation of appropriate magnet placement is absent. Third, ICDs respond to, and process, EMI differently than a PM.

This field is further complicated by the nature of electronics, as well as asymptomatic device malfunctions or outright device failure. Although PMs and ICDs are more reliable than almost any other technology, some devices fail prematurely. Maisel and colleagues searched the FDA database for the years 1990-2002; they found that 4.6 PMs and 20.7 ICDs per 1000 implants had been explanted for failures other than battery depletion. For the study period, 2.25 million PMs and 415,780 ICDs were implanted, and 30 PM and 31 ICD patients died as a direct result of device malfunction. Currently, alerts exist for premature ICD lead failure, which can result in inappropriate shock or failure of shock. A number of PMs and ICDs remain on “alert” for silent, premature battery failure, and one entire Guidant (now Boston Scientific) product line of ICDs has their magnet mode permanently disabled because of a switch malfunction.

Pacemaker and Implantable Cardioverter-Defibrillator Mechanics

PM and ICD implant indications are shown in Boxes 13-1A and 13-1B . These systems consist of an impulse generator and lead(s). Leads can have one (unipolar), two (bipolar), or multiple (multipolar) electrodes with connections in multiple chambers. In most defibrillations, as well as unipolar pacing, the generator case serves as an electrode, and tissue contact in a PM has been disrupted by pocket gas expanded by nitrous oxide. Pacing in a unipolar mode (not permitted in an ICD system) produces larger “spikes” on an analog-recorded ECG, and unipolar sensing is more sensitive to EMI as well as electrical muscle artifacts. ICDs can be distinguished from conventional PMs by the presence of a shock coil on the right ventricular lead. Often, bipolar PM electrodes can be identified on the chest film because they have a ring electrode 1 to 3 cm proximal to the lead tip ( Figure 13-1 ).

A Defibrillator System with Biventricular Antibradycardia Pacemaker Capability. This chest film was taken from a 50-year-old man with head and neck cancer, coronary artery disease, and ischemic cardiomyopathy with ejection fraction of 15%. The implantable cardioverter-defibrillator (ICD) generator is in the left pectoral position with three leads: a conventional, bipolar lead to the right atrium (RA), a quadripolar lead to the right ventricle (RV), and a unipolar lead to the coronary sinus (CS). This system is designed to provide “resynchronization (antibradycardia) therapy” in the setting of a dilated cardiomyopathy with a prolonged QRS (and frequently with a prolonged P-R interval as well). The bipolar lead in the RA will perform both sensing and pacing functions. The lead in this RV is a true bipolar lead with ring and tip electrodes for pacing and sensing. The presence of a “ shock” conductor (termed a shock coil ) on the RV lead in the RV distinguishes a defibrillation system from a conventional pacemaking system. The lead in the CS depolarizes the left ventricle (LV), and the typical current pathway includes the anode (ring electrode) in the RV. Because of the typically wide QRS complex in a left bundle branch pattern, failure to capture the LV can lead to ventricular oversensing (and inappropriate antitachycardia therapy) in an ICD system. Many defibrillation systems (including this one) also have a shock coil in the superior vena cava (SVC), which usually is electrically identical to the defibrillator case (called the “can”). When the defibrillation circuit includes the ICD case, it is called an “active can configuration.”

Finally, electronic devices resembling cardiac pulse generators are being implanted at increasing rates for pain control, thalamic stimulation to control Parkinson disease, phrenic nerve stimulation of the diaphragm in paralyzed patients, and vagus nerve stimulation to control epilepsy and possibly obesity. These devices may be confused with a cardiac generator.

The nature of programming, which is unique to each patient and device, necessitates contact with the patient’s device physician or a preoperative device interrogation to identify programmed parameters, remaining battery longevity (voltage and impedance), lead integrity (impedance), safety margins for sensing underlying rhythm signals (signal amplitude and channel sensitivity), and safety margins for pacing in each chamber (pacing threshold and pacing output). Interrogation also allows retrieval of information about the patient’s rhythm behavior since the last reset of generator memory. For ICDs (and many PMs), rhythm abnormalities (atrial arrhythmias, supraventricular tachycardia, ventricular tachycardia, and ventricular fibrillation) are also stored.

PM and ICD programming is described with the use of pacemaker (NBG) or defibrillator (NBD) codes ( Tables 13-1A and 13-1B ). Because all ICDs perform bradycardia pacing, the most robust ICD description would include the first three characters of the NBD, followed by a dash (–), then the five character PM NBG. As an example, in Figure 13-1 , the ICD was configured as VVE-DDDRV (ventricular shock capable, ventricular antitachycardia pace capable, electrogram (rate) detection for tachyarrhythmia, plus atrioventricular pacing in a dual chamber [atrial tracking] mode, with rate responsiveness, and multisite ventricular pacing). In the United States, the two most common pacing modes are VVI (single chamber ventricular pacing in the absence of a native ventricular event) and DDD (atrioventricular pacing that forces tracking of the atrial activity, whether sensed or paced).

Conventional wisdom regarding perioperative care of PM or ICD patients somehow has become “just put a magnet on it.” This behavior seems to have originated with the incorrect beliefs that magnet application to a PM always produces asynchronous pacing and that a magnet application to an ICD always inhibits antitachycardia therapy. Thus many physicians mistakenly believe that magnet application will prevent signal oversensing from the “Bovie” ESU, which can result in no pacing; after all, any electrical signal on the ventricular lead is interpreted by the generator as ventricular activity, which then “inhibits” pacing output. For ICDs, the electrical noise (EMI) can precipitate shocks. However, many PMs and ICDs can have their magnet mode altered by programming, and for some PMs, the default magnet setting does not include sustained, asynchronous behavior. Table 13-2 shows default magnet behavior for many PMs and ICDs.

TABLE 13-2

Usual (or Default) Effects of Appropriate Magnet Placement for Most Devices

Manufacturer	Pacemaker	ICD
Biotronik	PROGRAMMABLE • Battery OK: 10 AS events at 90 beats/min, then original programmed mode without rate responsiveness • Battery not OK: 10 AS events at 80 beats/min, then 11% below LRL	NONPROGRAMMABLE NO confirmation • Disables tachy therapies
Boston Scientific (formerly Guidant) (also CPI)	PROGRAMMABLE OFF MODE • Battery OK: AS pacing at 100 (90 at the intensified follow-up interval) beats/min • ERI: AS pacing at 85 beats/min	PROGRAMMABLE OFF MODE Confirmation: short beep at 60 Hz or with each detected heartbeat, depending on model • Disables tachy therapies [CAUTION] †
Medtronic Corporation	NONPROGRAMMABLE • Battery OK: AS pacing 85 beats/min • ERI: AS single-chamber pacing at 65 beats/min	NONPROGRAMMABLE NO confirmation • Disables tachy detection
Pacesetter (owned by St. Jude Medical)	PROGRAMMABLE OFF (and VARIO * ) MODE • Battery OK: AS pacing depends on model • ERI: AS pacing below 90 beats/min	PROGRAMMABLE OFF MODE NO confirmation • Disables tachy therapy
St. Jude Medical	PROGRAMMABLE OFF MODE • Battery OK: AS pacing 98 beats/min gradually declining over life of battery • ERI: AS pacing below 87 beats/min	PROGRAMMABLE OFF MODE NO confirmation • Disables tachy therapy
Sorin Medical (was ELA)	NONPROGRAMMABLE • AS pacing at 96 beats/min gradually declining to 80 beats/min at ERI. After magnet removal, 8 additional AS pacing cycles (the final 2 cycles are at LRL with long atrioventricular delay).	NONPROGRAMMABLE Confirmation: Pacing rate (but not mode) changes to • Battery OK: 90 beats/min • ERI: 80 beats/min • Disables tachy therapy

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