Perioperative Management of Permanent Pacemakers (PPMs) and Automatic Implantable Cardioverter-Defibrillators (AICDs)

Key action points in the perioperative management of permanent pacemakers (PPMs) and automatic implantable cardioverter-defibrillators (AICDs) include the following:

• Understand the indication for which the patient requires a cardiac implantable electronic device (CIED)
• If the patient already has a device in place, determine whether he or she is pacer-dependent 
• Determine the type of CIED, the mode in use, and the integrity of the device
• Assess the potential for intraoperative electromagnetic interference (EMI)
• Understand when it is appropriate to use a magnet, to interrogate, or to reprogram the device
• Ensure that alternative methods of pacing and defibrillating are available perioperatively
• Understand perioperative factors that may affect PPM/AICD function
• Understand the perioperative management of novel CIEDs (leadless pacemakers and subcutaneous implantable cardioverter-defibrillators [ICDs])

Understanding pacemaker terminology

CIED is a general term that may be applied to any permanent cardiac rhythm management device. CIEDs are divided into two broad categories, PPMs and AICDs (or, more simply, ICDs). In this article, CIED is used to refer to both PPMs and AICDs.

CIEDs can also be categorized according to the number of chambers upon which the device acts, as follows:

• Single-chamber devices (either atrium or ventricle)
• Dual-chamber devices (both atrium and ventricle)

Additional CIED parameters include the following:

• Sensitivity - The voltage (mV) above which the device detects a native electric deflection on electrocardiography (ECG) and perceives a chamber depolarization (either atrial or ventricular)
• Threshold - The minimum current (mA) provided by device pacing that is required to elicit chamber depolarization
• Capture - The successful depolarization of the atrium or ventricle in response to pacing

CIED pacing modes are labeled according to a five-letter coding system. ^[1] For the purposes of this article, however, only the letters in the first four positions of the code are relevant, as follows:

• Position I - Chamber(s) paced (O=none, A=atrium, V=ventricle, D=dual [A+V])
• Position II - Chamber(s) sensed (O=none, A=atrium, V=ventricle, D=dual [A+V])
• Position III - Response to sensing (O=none, T=triggered, I=inhibited, D=dual [T+I])
• Position IV - Rate modulation (O=none, R=rate modulation)

Finally, pacing can be categorized as synchronous or asynchromous, as follows:

• Synchronous (demand) pacing refers to any pacing mode with a value of A, V, or D in position II (sensing chamber), which represents device pacing that is contingent on the native cardiac rhythm
• Asynchronous pacing refers to a pacing mode with O in position II, which represents device pacing irrespective of the native rhythm

Uncertainties surrounding perioperative CIED management

Advances in the development of CIEDs over the past two decades have led to growing acceptance of the use of these devices in increasingly complex patient populations. Indeed, an analysis of PPM trends from 1993 to 2009 revealed a 56% increase in the implantation rate despite concurrent increases in patient age and comorbidities. ^[2]

The increase in implantation notwithstanding, a 2011 survey of American Society of Anesthesiologists (ASA) members revealed substantial disagreement regarding various perioperative CIED management practices, suggesting an opportunity for improving awareness regarding the implications of CIEDs for surgical patients. ^[3]

The ASA Practice Advisory for Perioperative Management of Patients with CIEDs was published in 2011 with the goal of standardizing practices and increasing provider agreement in management strategies. ^[3]  A 2020 update to the practice advisory reflected increased consistency in management practices. ^[4]  This article outlined a practical approach to evaluating and managing patients with PPMs and AICDs who present in the perioperative period.

The 2011 Heart Rhythm Society (HRS)/ASA expert consensus statement on perioperative management of CIEDs also recommended that the procedural team ask the patient’s CIED team for advice in order to mitigate perioperative risks. ^[5] The Department of Anesthesiology and Pain Medicine and the Division of Cardiology at the University of Washington described their development of a training program for a small group of anesthesiologists to interrogate CIEDs, devise a management plan, and perform preoperative and postoperative programming and device testing whenever necessary. ^[6]

Addressing the problem

Pacemaker technologies, the patient comorbidities that warrant their use, and various perioperative variables make the anesthetic management of patients with CIEDs a remarkably complex subject with significant potential for perioperative complications. ^[7] However, employment of a systematic approach to understanding the patient’s underlying pathology, the characteristics of the device type, perioperative factors, and appropriate interventions will facilitate the development of a safe and effective anesthetic plan for monitoring, diagnosing, and treating potential complications.

Evaluating patient pathology and pacer dependence

Indication for CIED use

Determining the patient’s underlying electrophysiologic pathology and the specific indication for CIED implantation is the critical first step in formulating a perioperative management plan. The most common indication for PPM placement is symptomatic bradycardia due to sinoatrial (SA) or atrioventricular (AV) node dysfunction, the etiology of which is vast and beyond the scope of this article. AICDs are indicated in patients who have a history of—or are at risk for developing—life-threatening tachyarrythmias, most commonly due to structural heart disease or dilated cardiomyopathy.

Pacer dependence vs independence

One of the most important steps during the process of evaluating a patient with a CIED for surgery is determining whether he or she is pacer-dependent—in other words, knowing what would happen to the patient if the pacemaker stopped working. This is crucial for anticipating electrophysiologic complications perioperatively. A patient whose cardiac output is reliant on a paced rhythm (ie, who is pacer-dependent) will not tolerate prolonged periods of CIED dysfunction; thus, alternative methods of pacing must be immediately available.

The first step in determining pacer dependence is to obtain a preoperative ECG. Because most patients are either completely (near 100%) or rarely (< 1%) dependent on their CIED, the presence or absence of pacing spikes on the ECG is strongly suggestive of their baseline pacing requirements. Additionally, the CIED interrogation report contains information on the percentage of the time that the patient requires pacing and can be used to confirm ECG-based findings. Finally, direct interrogation of the device can be performed to determine a patient’s baseline pacing requirements.

Understanding characteristics of CIED

Type

With the myriad of CIED brands and models currently available, it is imperative to understand how each specific device responds to perioperative interventions.

The most important initial distinction to make is between PPMs and AICDs. PPMs sense and pace the atrium, the ventricle, or both, whereas AICDs have the additional function of cardioversion and defibrillation when clinically appropriate. A major reason why making this distinction perioperatively is important is that EMI and magnet placement affect the two device types differently (see below). For example, EMI can lead to inappropriate sensing in PPMs, but it can also result in inappropriate cardioversion or defibrillation in AICDs.

Various methods may be employed to identify the type of CIED present. A detailed history from a reliable historian often yields the answer quickly and should be the first step taken. Many patients have retained their device ID card, which contains the brand name, implant date, and serial/model numbers. A phone call to the brand representative or an online search of the serial number may yield the needed device information, as may office or procedural notes from the patient’s cardiologist and interrogation reports of the device.

Finally, radiography or computed tomography (CT) of the chest can be used to identify the device type and brand. Various articles and smartphone applications are available to guide the identification of CIEDs through radiographic images. ^[8]

Mode

An understanding of the mode to which the CIED is set not only provides valuable information regarding the patient’s native conduction system but also facilitates perioperative management. For example, a PPM set to AAI suggests that conduction through the AV node remains intact, whereas a PPM set to VVI suggests a conduction defect at the AV node. A device set to DDD may suggest a partial AV nodal defect but is indicative of the presence of a dual-chamber CIED.

Functional integrity

Assessing the integrity of the CIED’s leads and battery is another crucial step in the perioperative management of the surgical patient. A pacer-dependent patient with defective sensing, pacing, or battery function would be better served by a visit to the electrophysiologist before undergoing an elective procedure. Information about a CIED's functional integrity can be obtained from the pacer interrogation report or by placing a telephone call to the service representative.

Signs of inappropriate sensing and capture include the following:

• Absence of pacing spikes when the native heart rate is below the pacer lower limit (oversensing)
• Presence of aberrant pacing spikes when the native heart rate is above the lower limit (undersensing)
• Presence of pacing spikes without corresponding atrial or ventricular depolarizations (noncapture) as observed on ECG or telemetry

Additionally, CIEDs with depleting battery lives frequently convert to safe mode or end-of-life mode to conserve power, and such conversion may manifest as loss of rate-adaptive therapy and a lower-than-expected paced rate.

If the aforementioned defects are suspected, the patient may require further interrogation, sensitivity or output adjustments, battery replacement, or some combination thereof.

Intervening to manage and minimize electromagnetic interference

Evaluation of EMI potential

After the properties of the patient’s CIED properties are determined (see above), perioperative management of the device is largely driven by the potential for EMI.

There are various potential sources of EMI in the perioperative setting (eg, radiofrequency ablation [RFA], magnetic resonance imaging [MRI], lithotripsy, radiation therapy, and electroconvulsive therapy [ECT]), but the most common cause for concern is electrocauterization above the level of the umbilicus. CIEDs set to synchronous modes (ie, with the sensing function turned on) are susceptible to misinterpretation of electrocautery use as native cardiac rhythm. This may result in inappropriate sensing, shocking, or both, as illustrated by the following examples:

• Inappropriate sensing - A pacer-dependent patient with a PPM set to DDD for complete heart block presents for excision of a chest-wall tumor; if the pacemaker remains in synchronous pacing mode, it may interpret Bovie artifact as native QRS waves and become inhibited, thereby exposing the patient to the underlying heart block and resulting in inadequate cardiac output
• Inappropriate shocking - A non-pacer-dependent patient with an AICD for a history of dilated cardiomyopathy presents for excision of a chest-wall tumor; if the defibrillator function remains on, the AICD may interpret Bovie artifact as ventricular fibrillation (VF) and defibrillate the patient inappropriately

In cases where there is concern about EMI affecting the CIED, appropriate interventions must be employed to avoid inappropriate sensing and shocking. Close attention must be paid to the ECG, pulse oximetry, and the arterial waveform (when applicable) in the presence of EMI to ensure the preservation of perfusing rhythms. Various measures may be employed to mitigate EMI and ensure appropriate CIED function (see below).

Magnet therapy

One of the most common CIED interventions in the intraoperative period is placement of a magnet over the device. This is typically effective, but to avoid harming the patient, it is imperative to have a clear understanding of the effects of the magnet on the CIED and to know when to pursue further workup.

As noted (see above), knowing whether the patient has a PPM or an AICD is crucial because the two device types respond differently to magnet therapy. Whereas placing a magnet over a PPM generally converts it to asynchronous pacing at a preset rate, placing a magnet over an AICD generally turns off its defibrillator function without affecting its pacemaker function (ie, does not convert it to asynchronous pacing). Thus, a pacer-dependent patient with an AICD remains vulnerable to inappropriate sensing due to EMI despite magnet therapy, and internal reprogramming is required before surgery. Furthermore, different CIED brands vary in terms of their specific responses to magnet therapy. ^[9]

If magnet therapy on a PPM yields no response, the possibility of malpositioning or a depleted battery should be considered. A lower-than-expected paced rate after magnet placement over a PPM is consistent with low battery life and may warrant additional interrogation. Additionally, certain AICDs (eg, those from St Jude Medical [now Abbott, Abbott Park, IL] and Boston Scientific [Marlborough, MA]) may be programmed to ignore magnet therapy, in which case the defibrillator function will remain active despite magnet placement.

When AICDs are deactivated, either via magnet therapy or through internal reprogramming, external defibrillator pads must be placed on the patient to ensure the availability of antitachycardic therapy.

When magnets are removed after surgical procedures, PPMs and AICDs typically revert to their respective baseline settings; however, interrogation must be performed postoperatively to confirm the return of baseline CIED function. An unmonitored patient left in asynchronous pacing is at high risk for an R-on-T phenomenon, and an AICD whose defibrillator function is turned off may prove fatal in a patient requiring antitachycardic therapy.

Electrophysiology consultation

An electrophysiology consultation is always appropriate when there are uncertainties regarding perioperative management of CIEDs; however, it is particularly worthy of strong consideration in the following specific clinical scenarios:

• Preoperatively, patients who are pacer-dependent or pacer-dependent with an AICD may require additional interrogation and reprogramming, as do patients in whom magnet placement interferes with surgical exposure
• Intraoperatively, an electrophysiology consultation may be warranted if there are unexpected responses to magnet placement
• Postoperatively, interrogation must be performed if magnet therapy or antitachycardic therapy was employed intraoperatively to ensure the return of baseline CIED function

Reduction of EMI risk

If electrocauterization must be performed above the level of the umbilicus, the following specific interventions may be employed to reduce the risk of EMI affecting the CIED:

• Use of a bipolar cautery drastically reduces the risk of EMI as compared with the use of a unipolar cautery, because of the local containment of current within the cathode and anode tips of the Bovie; this may be requested after consultation with the surgeon
• If a unipolar cautery must be used, placement of the grounding pad as far away from the CIED as possible will reduce the risk of EMI; this is frequently achieved by placing the grounding pad on the lower extremities to direct the current away from the upper chest, where EMI is most likely to occur
• Using the lowest effective current amplitude and delivering the current in short bursts (as opposed to long continuous applications) will also reduce EMI risk

Managing other perioperative factors affecting CIED function

Although EMI is the major source of intraoperative alterations in CIED function, there are a number of additional factors that may also influence the operation of a CIED within the perioperative period. ^{[10, 11]}

The electrolyte and metabolic abnormalities frequently observed in the perioperative period can adversely affect CIED function and should therefore be aggressively corrected. Specifically, hyperkalemia, hyperglycemia, alkalemia, acidemia, hypoxemia, and hypercapnia increase the pacing threshold and may lead to failure to capture. Additionally, hypokalemia and hypomagnesemia may lead to hemodynamically significant arrhythmias.

Insertion of central venous catheters and pulmonary arterial catheters must be performed with caution in patients with CIEDs because of the potential for induction of arrhythmia, dislodgment of pacing electrodes, or both. Emergency medications and alternative pacing or defibrillating modalities must be readily available.

Initiation of positive-pressure ventilation (PPV) may distort the intrathoracic anatomy and lead to loss of electrode contact; therefore, verification of CIED function should be performed after PPV is initiated.

Some common anesthetic medications may also affect CIED function and should be used with caution. Drugs that induce fasciculations (succinylcholine) and myoclonus (etomidate, ketamine) should be avoided because of their potential for causing oversensing (similar to inappropriate sensing caused by EMI) and complete inhibition of a pacemaker. Nitrous oxide accumulation in the prepectoral pacemaker pocket may lead to loss of electrode contact and cause loss of sensing or capture. Other inhalational anesthetics and opioids do not alter CIED function and can be used safely.

Management of novel cardiac implantable electronic devices

Leadless pacemakers

Because leadless pacemakers have only recently been introduced into the market, perioperative management of these devices is not yet covered under expert opinions, consensus guidelines, or practice advisories.

Currently, there are two leadless pacemakers that have been approved by the US Food and Drug Administration (FDA) for clinical use in the United States: the Micra transcatheter pacemaker system (Medtronic, Minneapolis, MN) and the Aveir VR Leadless Pacemaker (Abbott, Chicago, IL). The Aveir VR succeeds the Nanostim leadless pacemaker (St Jude Medical, now Abbott), which is no longer available. The Micra and Aveir systems both consist of a single-chamber RV pacemaker; they differ with respect to differing dimensions, weight, battery capacity, and projected longevity.

Advantages of leadless pacemakers over conventional transvenous CIEDs include the avoidance of lead-associated complications (eg, thrombosis, vascular obstruction, infection, fracture, and development of tricuspid valve incompetence). Furthermore, because the entire device is embedded within the RV, complications associated with pacemaker pocket creation (eg, skin breakdown, infection, and bleeding) are also avoided. 

There are notable differences between the Micra and Aveir systems that warrant special anesthetic considerations. Perhaps the most important distinction between the two devices is their magnet responsiveness. The Micra lacks a magnet response mode and must be reprogrammed when asynchronous pacing is desired. In contrast, the Aveir system can be programmed to respond to magnet application; however, its intracardiac location renders its proper positioning challenging and its efficacy variable. During magnet-induced asynchronous pacing (VOO), the Aveir pacing rate ranges from 85 to 100 beats/min, depending on battery voltage.

The difference in longevity between the two devices is significant. The Micra is estimated to have a longevity of 4.7 years, whereas the Aveir has a projected longevity of 10.3 years under standard settings. The Aveir allows chronic retrieval, whereas the Micra cannot be explanted and must be programmed to “device off” in the event of device malfunction or at the end of service life. Furthermore, there are ongoing efforts to develop the Aveir system to include multidevice implantation and interdevice communication to enable dual-chamber sensing and pacing capabilities.

In view of the abovementioned features of the Micra and Aveir systems, it is clear that anesthetic management of these novel devices necessitates increased vigilance and coordination between the anesthesiologist and device representatives in the perioperative period. ^{[12, 13, 14]}

Subcutaneous implantable cardioverter defibrillators

The Emblem MRI S-ICD (subcutaneously implanted cardioverter defibrillator) system (Boston Scientific) received FDA approval for clinical use in the United States in 2012. The pulse generator is implanted at the sixth intercostal space at the left midaxillary line, while the electrode is tunneled from the generator to the xyphoid process, then superiorly to the manubriosternal junction.

Indications for use of the S-ICD include patients who require defibrillation therapy without need for ATP or bradycardia pacing; the device only provides sensing, detection, and defibrillation therapy and lacks permanent pacing functions. As with leadless pacemakers, advantages of S-ICDs include avoidance of lead-associated complications (eg, lead thrombosis, vascular obstruction, infection, fracture, and development of tricupsid valve regurgitation).

Also as with leadless pacemakers, guidelines for the management of S-ICDs in the perioperative setting are lacking. Although the principles of perioperative management of conventional ICDs may be applied to S-ICDs, there are differences between the two types of devices that may warrant special consideration.

For example, the recommended magnet positioning for the S-ICD system is at the upper or lower edges of the generator (confirmed by a 60-s beeping tone), as opposed to directly over the center, as in the case for conventional transvenous ICDs. In addition, given the broader sensing area of the S-ICD (over the left hemithorax) as compared with that of transvenous ICDs, it is plausible that S-ICDs may be more senstive to EMI and thus may require additional mitigation interventions to reduce EMI-related complications in the perioperative setting.

In view of the relative novelty of S-ICDs, it is advisable to involve the electrophysiology service, a device representative, or both in the perioperative management of patients with these devices who are undergoing sugery. ^{[12, 13]}

Clinical scenario

A 70-year-old male patient with a past medical history of hypertension, hyperlipidemia, coronary artery disease (CAD), and aortic stenosis who underwent a triple coronary artery bypass graft (CABG) and bioprosthetic aortic valve replacement 20 years previously presents for left-side video-assisted thoracoscopic surgery (VATS) for evaluation of a left lower pulmonary nodule. The patient has a PPM in place, implanted after his aortic valve replacement because of unresolved complete heart block. 

Preoperative ECG reveals an AV-paced rhythm at 80 beats/min. Chest radiography reveals a 1 × 1 cm left-lower-lobe density and a dual-chamber PPM in the left upper chest cavity. A recent pacemaker interrogation has noted a pacing mode of DDD at 80 beats/min, 98% V-pacing, an underlying heart rate (HR) of 40 beats/min, and 7 years of remaining battery life.

After thoracic epidural placement, the patient undergoes uneventful general anesthetic induction, intubation, and placement of a left radial arterial catheter. As the surgeon makes an incision with the electrocautery, you notice flattening of the arterial line tracing with a corresponding blood pressure (BP) of 68/26 mm Hg, a pulse rate of 38 beats/min, and loss of pulse oximeter plethysmography. The ECG tracing displays Bovie artifact with no discernible QRS waves. The pressure tubing remains patent, withdrawing and flushing easily, and the transducer is at the appropriate position. You obtain a noninvasive measurement of BP, which corresponds to the arterial line pressure.

You immediately instruct the surgeon to stop use of the electrocautery. You then notice the return of the arterial line tracing, with a BP of 134/76 mm Hg and a pulse rate of 80 beats/min. The pulse oximetry tracing also returns and shows an arterial oxygen saturation (SaO₂) of 96%. The ECG shows an AV-paced rhythm at 80 beats/min. You call for a magnet to be brought into the room and place it over the PPM. The ECG now shows an AV-paced rhythm at 100 beats/min.

You then instruct the surgeon to resume incision, and the remainder of the intraoperative course proceeds without further incidents. At the end of the case, the magnet is removed, and the patient is brought to the postanesthesia care unit (PACU) after successful extubation. You give the appropriate signout and proceed to your next case. 

Approximately 1 hour later, you are called to reevaluate the patient for a nonfunctioning epidural and 10/10 pain. You notice an HR of 108 beats/min on telemetry, with atrial and ventricular spikes pacing at 100 beats/min. As you are evaluating the patient’s epidural, he suddenly goes into VF and loses consciousness. The arterial line tracing is flat, and you immediately begin chest compressions.

Defibrillator pads are placed, and the patient receives one unsynchronized defibrillation at 200 J, which is followed by the return of spontaneous circulation (ROSC). Telemetry now shows AV pacing at 100 beats/min. After reintubating the patient, you immediately request an emergency electrophysiology consultation for pacemaker interrogation and reprogramming to synchronized pacing. The patient is stabilized and transferred to the intensive care unit (ICU) for further management.

Resolution

This scenario demonstrates the deleterious effects of inappropriate sensing due to EMI in a pacer-dependent patient, the danger of leaving a patient in asynchronous pacing, and the importance of pacer reinterrogation in the postoperative period.

In this case, preoperative evaluation of the patient’s CIED was carried out appropriately. The pacemaker’s indication, type, mode, and integrity were all identified, as was the patient's pacer dependence. However, appropriate intraoperative interventions for a patient at high risk for experiencing EMI effects were not employed.

Because the patient was pacer-dependent and the pacemaker was in a synchronous pacing mode (DDD), the pacemaker interpreted Bovie artifact as native QRS above its set rate of 80 beats/min and thus was inhibited. The patient’s native underlying rhythm was subsequently unmasked and proved to generate inadequate stroke volume (hypotension), HR (bradycardia), and cardiac output.

Placement of a magnet before incision would (in most cases, with the previously discussed caveats kept in mind) have converted the pacemaker to asynchronous pacing (DOO) with a rate dependent on device brand and battery status, thereby avoiding inappropriate sensing. In addition to magnet therapy, employing a bipolar cautery device, moving the grounding pad as far away from the PPM as possible, reducing Bovie amplitude, and avoiding continuous application of current could reasonably have been considered as means of minimizing EMI risk.

The postoperative complication described above highlights the danger of unmonitored asynchronous pacing resulting in R-on-T phenomenon and underscores the absolute necessity of reinterrogating the pacemaker postoperatively, especially if the pacemaker was manipulated intraoperatively (either during surgical exposure or through magnet therapy). Magnet removal generally causes a CIED to revert to its baseline mode, but confirmation can be obtained only via formal interrogation of the device.

In this case, the PPM failed to revert to synchronous pacing, probably because of physical disturbance resulting from its proximity to the surgical field. The patient remained in asynchronous pacing (DOO at 100 beats/min) and sustained an R-on-T VF when his native HR was raised above 100 beats/min from uncontrolled pain. Even though advanced cardiac life support (ACLS) protocol was initiated immediately and ROSC was obtained in a timely manner, this complication could have been avoided with prompt reinterrogation of the device postoperatively and expeditious identification of the PPM's failure to revert to synchronous pacing.

Clinical scenario

A 57-year-old female patient with a past medical history of sick sinus syndrome, dilated cardiomyopathy with a left ventricular ejection fraction (LVEF) of 30%, and VF who has undergone AICD implantation presents for emergency open cholecystectomy to treat gallbladder rupture. Because the case is an emergency, preoperative evaluation is limited. Before induction, a V-paced rhythm at 75 beats/min is noted on telemetry. After uneventful induction, intubation, and arterial line placement, a magnet is applied to the AICD to deactivate antitachycardic therapy.

As the surgeon makes an incision with the electrocautery, you notice a decrease in HR from 75 beats/min to 44 beats/min, a loss of pacing spikes on telemetry, and a decrease in BP from 110/67 mm Hg to 85/48 mm Hg. You immediately instruct the surgeon to stop use of the electrocautery, whereupon you notice a return of a V-paced rhythm at 75 beats/min and an increase in BP to 105/75 mm Hg.

Electrophysiology consultation is obtained to reprogram the AICD to asynchronous pacing; however, in view of the emergency nature of the case, the surgeon wishes to proceed with the operation. After the surgeon switches to a bipolar cautery, you allow resumption of the procedure, and the electrophysiologist arrives 30 minutes later to reprogram the device to VOO at 75 beats/min.

Approximately 1 hour later, as the surgeon continues surgical excision of the gallbladder, the patient suddenly goes into VF with loss of arterial waveform. You initiate ACLS protocol with chest compressions and administration of epinephrine and amiodarone; however, defibrillation is delayed, because defibrillator pads were not applied before the patient was positioned and paddles were not readily available.

Resolution

This scenario, though similar in appearance to that outlined in case example 1, differs in one crucial respect, which emphasizes the importance of differentiating a PPM from an AICD.

Even though a thorough preoperative evaluation was not possible, owing to the surgical emergency, the history of sick sinus syndrome and the appearance of a paced rhythm on telemetry should indicate to the practitioner that the patient is probably pacer-dependent. Therefore, whereas application of the magnet will appropriately deactivate the AICD's defibrillation function and thus prevent inappropriate shocking, it will have no effect on the device's pacemaker function and thus will not prevent inappropriate sensing.

As in case example 1, inappropriate sensing related to electrocauterization resulted in inadequate cardiac output as the patient’s underlying sinus bradycardia was unmasked. Internal reprogramming of the device to asynchronous pacing is the appropriate intervention, along with resumption of the emergency surgical procedure while reprogramming is awaited, on the assumption that steps are taken to reduce EMI (eg, use of a bipolar cautery and minimizing current amplitude).

The failure to defibrillate the patient promptly after she experiences VF highlights the necessity of having alternative antitachycardic therapy immediately available in a patient with history of ventricular dysrhythmias and a deactivated AICD. Defibrillator pads should have been applied to the patient before the AICD was deactivated; this would have allowed transcutaneous pacing as well as immediate defibrillation. As in case example 1, it is vital to perform postoperative reinterrogation to ensure the return of antitachycardic therapy after magnet removal and reprogramming to synchronous pacing.