Pacemakers

Since 1958, more than 26 companies have produced more than 2000 pacemaker models. Determining the actual number of implants and prevalence of devices is difficult. A variety of economic and market reports suggest that more than 300,000 adults and children in the United States underwent pacemaker placement (new or revision) in 2009. It is likely that more than 3 million patients have pacemakers today. Many factors lead to confusion regarding the behavior of a device and the perioperative care of a patient with a device, especially because case reports, textbooks, and literature reviews have not kept pace with technologic developments, and many of these reviews contain incorrect statements.^9,10 In addition, sometimes the preoperative consultation process leads to improper advice as well.¹¹ Most patients with a pacemaker have significant comorbid disease. The care of these patients requires attention to both their medical and psychological problems. In addition, an understanding of pulse generators and their likely idiosyncrasies in the operating or procedure room is needed. Whether the patient with a pacemaker is at increased perioperative risk remains unknown, but two reports suggest that these patients deserve extra perioperative attention. In 1995, Badrinath et al¹² retrospectively reviewed ophthalmic surgery cases in one hospital in Madras, India, from 1979 through 1988 (14,787 cases), and wrote that the presence of a pacemaker significantly increased the probability of a mortal event within 6 weeks after surgery, regardless of the anesthetic technique. In 2007, Pili-Floury et al¹³ reported a prospective study of 65 consecutive patients undergoing any anesthetic for any invasive noncardiac procedure unrelated to their device; they found seven (11%) postoperative myocardial infarctions, two (3%) patients experienced development of left ventricular failure, and two (3%) patients died of cardiac causes during their hospitalization.

No discussion of pacemakers can take place without an understanding of the generic pacemaker code (NBG; Table 25-1), which has been published by the North American Society of Pacing and Electrophysiology (HRS-NASPE) and British Pacing and Electrophysiology Group. This code, initially published in 1983, was revised in 2002.¹⁴ The code describes the basic behavior of the pacing device. Pacemakers also come with a variety of terms generally unfamiliar to the anesthesiologist, many of which are shown in the Glossary at the end of this chapter.

Pacemaker Indications

Indications for permanent pacing are shown in Box 25-1 and are reviewed in detail elsewhere.¹⁵ Devices have also been approved by the U.S. Food and Drug Administration (FDA) for three-chamber pacing (right atrium, both ventricles) to treat dilated cardiomyopathy (DCM^16,17; also called biventricular pacing [BiV] or cardiac resynchronization therapy [CRT]). Also, specially programmed devices are used to treat hypertrophic obstructive cardiomyopathy in both adults and children.^18,19 BiV and hypertrophic obstructive cardiomyopathy indications require careful attention to pacemaker programming because effective pacing in these patients often requires a pacing rate greater than native sinus or junctional escape rate (often accomplished with drugs) and an atrioventricular delay shorter than the native P-R interval so that the ventricle is paced 100% of the time.²⁰ Inhibition or loss of pacing (i.e., from native conduction, atrial irregularity, ventricular irregularity, development of junctional rhythm, or EMI) can lead to deteriorating hemodynamics in these patients. BiV can lengthen the Q-T interval in some patients, producing torsade de pointes.²¹ Multisite atrial pacing to prevent or treat atrial arrhythmias remains in clinical trial.^22,23

Pacemaker Magnets

Despite oft-repeated folklore, most pacemaker manufacturers warn that magnets were never intended to treat pacemaker emergencies or prevent EMI effects. Rather, magnet-activated switches, both electronic (Hall-effect sensor) and mechanical (reed switch), were incorporated to produce pacing behavior that demonstrates remaining battery life and, sometimes, pacing threshold safety factors. Newer pacemakers provide telephonic data “uplinks” that are routed directly to the patient’s pacemaker physician.

Placement of a magnet over a generator might produce no change in pacing because not all pacemakers switch to a continuous asynchronous mode when a magnet is placed. Also, not all models from a given company behave the same way. Although more than 90% of pacemakers have “high-rate (80 to 100 beats/min)” asynchronous pacing with magnet application, some switch to asynchronous pacing at program rate, and some respond with only a brief (60 to 100 beats) asynchronous pacing event. Possible effect(s) of magnet placement are shown in Box 25-2.^24–26 In many devices, magnet behavior can be altered via programming. Also, any pacemaker from Boston Scientific (Natick, MA)* will ignore magnet placement after any electrical reset, which is a possibility in the presence of strong EMI. Appendix 25-1 lists pacemakers by manufacturers and has a complete listing of all magnet behaviors.

For all generators, calling the manufacturer remains the most reliable method for determining magnet response and using this response to predict remaining battery life. A list of telephone numbers is shown in Appendix 25-2 at the end of this chapter.

For generators with programmable magnet behavior (Biotronik [Berlin, Germany; US Headquarters: Lake Oswego, OR], Boston Scientific, and St. Jude Medical [Syl Mar, CA]), only an interrogation with a programmer can reveal current settings. Most manufacturers publish a reference guide, although not all of these guides list all magnet idiosyncrasies.

Preanesthetic Evaluation and Pacemaker Reprogramming

Preoperative management of the patient with a pacemaker includes evaluation and optimization of coexisting disease(s). No special laboratory tests or radiographs (chest films are remarkably insensitive for determination of lead problems) are needed for the patient with a pacemaker. Such testing should be dictated by the patient’s underlying disease(s), medication(s), and planned intervention. For programmable devices, interrogation with a programmer remains the only reliable method for evaluating lead performance and obtaining current program information. A chest film might be useful to document the position of the coronary sinus lead in a patient with a BiV pacemaker or defibrillator, especially if central venous catheter placement is planned, because spontaneous coronary sinus lead dislodgement was found in more than 11% of patients in early studies.^27,28 A chest radiograph is certainly indicated for the patient with a device problem discovered during his or her pacemaker evaluation.

The prudent anesthesiologist will review the patient’s pacemaker history and follow-up schedule. Under the name NASPE, the HRS has published a consensus statement suggesting that pacemakers should be evaluated routinely with telephone checks for battery condition at least every 3 months. NASPE also recommends a comprehensive evaluation (interrogation) at least once per year. There are additional checks for devices implanted fewer than 6 or greater than 48 (dual chamber) or 72 (single chamber) months.²⁹ In abstract form, Rozner et al³⁰ reported a two-year retrospective review of follow-up intervals in patients who presented for an anesthetic, finding that more than 32% of 172 patients presenting for an anesthetic at their hospital did not meet the HRS-NASPE guideline for comprehensive evaluation. They also reported that 5% of the patients presented for their anesthetic with a pacemaker in need of replacement for battery depletion, and nearly 10% of patients had less than optimal pacing settings.³⁰ Note that a recent preoperative interrogation remains a part of the American College of Cardiology guidelines.²

Important features of the preanesthetic device evaluation are shown in Box 25-3. Determining pacing dependency might require temporary reprogramming to a VVI mode with a low rate. In patients from countries where pacemakers might be reused,^31,32 battery performance might not be related to length of implantation in the current patient. Clinicians also should note that in a registry of 345 pacemaker generator failures, 7% of failures were not related to battery depletion.³³

Appropriate reprogramming (Box 25-4) might be the safest way to avoid intraoperative problems, especially if monopolar “Bovie” electrocautery will be used. For lithotripsy, consideration should be given to programming the pacing function from an atrial-paced mode, as some lithotriptors are designed to fire on the R wave, and the atrial pacing stimulus could be misinterpreted as the contraction of the ventricle.³⁴

Most cardiac rhythm management device manufacturers stand ready to assist with this task (see Appendix 25-2 for company telephone numbers). Reprogramming a pacemaker to asynchronous pacing at a rate greater than the patient’s underlying rate usually ensures that no oversensing or undersensing during EMI will take place, thus protecting the patient. Reprogramming a device will not protect it from internal damage or reset caused by EMI.

Experts do not agree on the appropriate reprogramming for the pacing-dependent patient. Setting a device to asynchronous mode to prevent inappropriate oversensing and ventricular output suppression can cause the pacemaker to ignore premature atrial or ventricular systoles, which could have the potential to create a malignant rhythm in the patient with significant structural compromise of the myocardium.³⁵ Reviews by Stone and McPherson,⁷ as well as Rozner,³⁶ and several case reports^37,38 demonstrate inappropriate R-on-T pacing with the development of a malignant ventricular rhythm. Hayes and Strathmore³⁹ suggest the VVT mode for the pacing-dependent patient because EMI will generally increase the pacing rate rather than inhibit the pacing output. However, they do not consider the upper pacing rate for this mode. Although some pacemakers limit VVT pacing rates to the maximum tracking rate (i.e., Boston Scientific), others will pace to the lower of the runaway pacing rate (typically around 200 beats/min) or the minimum V-V interval defined by the ventricular refractory period (i.e., Medtronic Corporation, Minneapolis, MN), which is typically 200 milliseconds (representing 300 beats/min). There are two other caveats for this mode: for the patient with a dual-chamber device and in need of atrioventricular synchrony to sustain cardiac output, hemodynamics might be compromised during VVT operation because ventricular pacing will take place without regard to atrial activity. In addition, in the VVT mode without rate-smoothing enabled, considerable increases and decreases in paced rate could result during EMI. If VVT reprogramming is to be considered, the manufacturer should be contacted regarding programming for the upper rate.

In general, rate responsiveness and other “enhancements” (hysteresis, sleep rate, atrioventricular search, etc.) should be disabled by programming because many of these can mimic pacing system malfunction (see Figure 25-2).^40–42 Note that for many CPI Boston Scientific devices, the physician’s manual recommends increasing the pacing voltage to “5 volts or higher” in any case in which the monopolar electrosurgical unit (ESU) will be used. In 1986, Levine et al⁴³ noted an increase in the amount of energy required to pace the ventricle (i.e., a pacing threshold increase) in the setting of intrathoracic surgery and mono-polar ESU use. Both Pili-Floury et al¹³ and Rozner et al³⁰ have reported increases in atrial (Rozner only) and ventricular (both reports) pacing thresholds after operations involving pacemaker (but not ICD) cases in which the monopolar ESU was used, large volume and blood shifts were observed, or both. Although many of the operations were thoracic explorations, no pacing threshold changes were noted for these cases. No cardiopulmonary bypass cases were in these cohorts.

Figure 25-2 A, The search feature “managed ventricular pacing” mimics pacing system malfunction. This is a patient with a sinus rate of 50 and a native PR interval of nearly 500 milliseconds. Her Medtronic pacing device was set to AAIR-DDDR (called managed ventricular pacing [MVP]), which does not pace the ventricle in response to an atrial event until a native QRS is not conducted (dropped). The next atrial event will be followed by an immediate (60-millisecond) paced QRS. Two such events (marked X) are shown after the third and seventh P waves. The subsequent paced QRS morphology axis is nearly orthogonal to the sensing axis, which is labeled (but might not actually be) lead 2, depending on the placement of the actual leads. MVP does not permit two consecutive dropped QRS events, and if two of any four QRS events are dropped, the pacing device paces in DDD mode for at least 1 minute before resuming MVP. However, because oversensing from monopolar electrosurgery can convince a pacing device that ventricular systoles are present, a patient with atrioventricular nodal disease undergoing surgery with monopolar electrosurgery could demonstrate many dropped QRS events. B, The feature “search hysteresis” mimics pacemaker malfunction. This patient has a single-chamber VVI pacemaker set to a lower rate of 70/min. It was placed for complete atrioventricular block. This programmable feature causes the pacemaker to delay pacing every 256th event for 1400 milliseconds (equal to a rate of 50/min). This delay in pacing is shown between the third and fourth QRS complexes. From top to bottom, the tracings are lead II, lead V5, the invasive arterial pressure, and the central venous pressure. Hysteresis (where the pacemaker delays pacing after an intrinsic event) and search hysteresis often confuse caregivers regarding pacemaker malfunction (called pseudomalfunction). This electrocardiographic tracing could also result from ventricular oversensing, usually related to the T wave.

Special attention must be given to any device with a minute ventilation (bioimpedance) sensor (Box 25-5), because inappropriate tachycardia has been observed secondary to mechanical ventilation,^44,45 monopolar “Bovie” ESU,^44,46,47 and connection to an electrocardiographic (ECG) monitor with respiratory rate monitoring.^48,49

Intraoperative (or Procedure) Management

No special monitoring or anesthetic technique is required for the patient with a pacemaker. However, ECG monitoring of the patient must include the ability to detect pacemaker discharges. Often, noise filtering on the ECG monitor must be changed to permit demonstration of the pacemaker pulse, and devices such as a nerve stimulator can interfere with detection and display of the pacemaker pulses.⁵⁰

In addition, patient monitoring must include the ability to ensure that myocardial electrical activity is converted to mechanical systoles. Mechanical systoles are best evaluated by pulse oximetry plethysmography or arterial waveform display. Some patients might need an increased pacing rate during the perioperative period to meet an increased oxygen demand. A pulmonary artery catheter (PAC), an esophageal Doppler monitor, or a transesophageal echocardiogram can be used to evaluate pacing frequency and its relation to cardiac output. In addition to blood pressure and systemic vascular resistance, the monitoring of acid-base status might be needed to determine adequacy of cardiac output.

With respect to anesthetic technique, no studies have championed one over another. Nevertheless, a number of reports of prolongation of the QT interval with the use of isoflurane or sevoflurane have been published. Halothane appears to reduce this interval.^51–55 No interactions have been reported for enflurane or desflurane.

Monopolar “Bovie” electrocautery (ESU) use remains the principal intraoperative issue for the patient with a pacemaker. Between 1984 and 1997, the FDA was notified of 456 adverse events with pulse generators, 255 from electrocautery, and a “significant number” of device failures.⁵⁶ Monopolar ESU is more likely to cause problems than bipolar ESU, and patients with unipolar electrode configuration are more sensitive to EMI than those with bipolar configurations. Coagulation ESU will likely cause more problems than nonblended “cutting” ESU.⁵⁷ Magnet placement during electrocautery might allow reprogramming of an older (pre-1990) generator; however, newer generators are relatively immune to such effects. In fact, most devices from Boston Scientific, as well as St. Jude, cannot be reprogrammed in the presence of a magnet. Note, however, that strong EMI can produce an electrical reset or a detection of battery depletion, which might change the programming mode or rate, or both. If monopolar electrocautery is to be used, then the current return pad should be placed to ensure that the electrocautery current path does not cross the pacemaking system. For cases such as head and neck surgery, the pad might be best placed on the shoulder contralateral to the implanted device. For breast and axillary cases, the pad might need to be placed on the ipsilateral arm with the wire prepped into the field by sterile plastic cover. Procedures with special pacing ramifications are shown in Box 25-6.

The use of an ultrasonic cutting device, commonly called a harmonic scalpel, has been championed to prevent EMI while providing the surgeon with the ability to both cut and coagulate tissue. A number of case reports demonstrate successful surgery without EMI issues in these patients.^58–61

At this time, MRI deserves special mention. In general, MRI has been contraindicated in pacemaker and ICD patients.^62,63 However, a landmark article showing that MRI could be conducted safely in some patients has led to performance of MRI evaluations in these patients.⁶⁴ Nevertheless, not all MRI sequences and energy levels have been studied, and judicious monitoring and caution are advised.^65,66 Medtronic Corporation is testing a pacing generator and lead system called Enrhythm MRI SureScan (current model is EMDR01), which has special programming modes and leads for MRI scanning.⁶⁷ It is already approved in several European countries.

Pacemaker Failure

Pacemaker failure has three causes: (1) failure of capture, (2) lead failure, or (3) generator failure. Failure of capture because of a defect at the level of the myocardium (i.e., the generator continues to fire but no myocardial depolarization takes place) remains the most difficult problem to treat. Myocardial changes that result in noncapture include myocardial ischemia/infarction, acid-base disturbance, electrolyte abnormalities, or abnormal levels of antiarrhythmic drug(s). Note that temporary pacing (transvenous, transcutaneous, transthoracic, or transesophageal) might inhibit pacemaker output at voltages that will not produce myocardial capture.⁶⁸ Sympathomimetic drugs generally lower pacing threshold. Outright generator or lead failure is rare.

Temporary Pacemakers

Several techniques are available to the anesthesiologist to establish reliable temporary pacing during the perioperative period or in the intensive care unit.⁶⁹ Cardiovascular anesthesiologists are more likely than the generalists to routinely use temporary transvenous or epicardial pacing in their practices. Temporary cardiac pacing can serve as definitive therapy for transient bradyarrhythmias or as a bridge to permanent generator placement.

The various forms of temporary pacing include many transvenous catheter systems, transcutaneous pads, transthoracic wires, and esophageal pacing techniques. This section reviews the indications for temporary cardiac pacing and discusses the techniques available to the anesthesiologist. Many of the references in this section are older because temporary pacing is a well-established technique and not many advances have taken place since the early 1990s. Table 25-2 summarizes these techniques.

Regardless of temporary modality, most implanted pacemakers or ICDs need to be reprogrammed when placing any temporary pacing device. Electrical energy entering the body from a temporary pacing device can be sensed by the permanent device on the atrial lead, the ventricular lead, or both. Energy sensed on a ventricular lead can result in an inappropriate shock from an ICD or pacing inhibition from a pacemaker or ICD. Pacing inhibition in a pacing-dependent patient will produce asystole. If energy enters the cardiac rhythm management device on the atrial lead in a dual-chamber device, then rapid ventricular pacing might result (intrinsic atrial rate plus temporary atrial rate). The cardiac rhythm management device might “detect” an atrial arrhythmia condition, resulting in ventricular pacing only, which might produce untoward hemodynamics.