# Pacemakers and ICDs: Perioperative Management

## Cardiac Implantable Electronic Devices (CIEDs): Overview

### Pacemakers

Pacemakers are implanted to treat bradyarrhythmias such as sick sinus syndrome and AV block, to provide rate support in chronotropic incompetence, and in the form of cardiac resynchronization therapy (CRT-P) to treat heart failure with ventricular dyssynchrony.

### Implantable Cardioverter-Defibrillators (ICDs)

ICDs are used for both primary and secondary prevention of sudden cardiac death. They detect and treat ventricular tachyarrhythmias through a tiered response that includes antitachycardia pacing, cardioversion, and defibrillation. Most modern ICDs also incorporate full pacing capabilities. CRT-D devices combine biventricular pacing with defibrillation capability.

### Device Identification

Device identification can be accomplished through several means. Most patients carry a manufacturer ID card. A chest X-ray reveals lead positions and pulse generator location, and the manufacturer can often be identified from the header shape. However, the device interrogation report is the most reliable source of information. Common manufacturers include Medtronic, Abbott (formerly St. Jude), Boston Scientific, and Biotronik.

## NBG Pacemaker Code

### Five-Position Code

The NBG code describes pacemaker function across five positions. Position I indicates the chamber paced (A for atrium, V for ventricle, D for dual). Position II indicates the chamber sensed (A, V, D, or O for none). Position III describes the response to sensing (I for inhibit, T for trigger, D for dual). Position IV indicates rate modulation capability (R for rate responsive, O for none). Position V describes multisite pacing, though this is rarely used clinically.

### Common Modes

**VVI** mode paces and senses the ventricle, inhibiting output when a native beat is detected; this is single-chamber demand pacing. **DDD** mode paces and senses both chambers, maintaining AV synchrony. **AAI** mode paces and senses the atrium, inhibiting when a native P wave is detected. **Asynchronous modes** (DOO, VOO, AOO) deliver pacing without sensing, which eliminates the risk of EMI-induced pacing inhibition -- this is why they are used perioperatively.

<image>Educational diagram showing the NBG pacemaker code with each of the five positions explained. Below, three common pacing modes (VVI, DDD, AOO) are illustrated with corresponding ECG tracings showing pacing spikes and the resulting cardiac complexes, with annotations explaining the sensing and pacing behavior of each mode.</image>

## Preoperative Assessment

### Essential Information to Obtain

The preoperative assessment must establish the device type (pacemaker vs. ICD vs. CRT), manufacturer and model, indication for implantation, current programming (mode, rate, thresholds), battery status and estimated longevity, lead integrity and thresholds, and most critically, the patient's underlying rhythm and pacemaker dependency.

### Defining Pacemaker Dependency

A patient is pacemaker-dependent when there is no reliable intrinsic cardiac rhythm without the device. This includes patients with complete heart block, those who have undergone AV node ablation, and those with no viable escape rhythm. An interrogation report showing 100% ventricular pacing does not by itself confirm dependency, as this may simply reflect a programmed lower rate that exceeds the patient's intrinsic rate. Determining dependency preoperatively is critical because EMI-induced pacing inhibition in a dependent patient causes asystole.

### Preoperative Device Interrogation

Interrogation should ideally be performed within 6-12 months for pacemakers and within 6 months for ICDs. More recent interrogation is warranted if clinical or device concerns exist. The interrogation must be performed by trained personnel, whether from a device clinic, electrophysiology lab, or an industry representative.

## Electromagnetic Interference (EMI)

### Sources in the OR

The most common and most problematic source of EMI in the operating room is **monopolar electrocautery**. Other sources include radiofrequency ablation, MRI (which has separate management protocols), nerve stimulators and evoked potential monitoring, lithotripsy (which should be avoided in ICD patients), and electroconvulsive therapy.

### Effects of EMI on Pacemakers

EMI can affect pacemaker function in several ways. **Oversensing** occurs when the device interprets EMI as cardiac electrical activity and inhibits pacing output -- this is dangerous in pacemaker-dependent patients. **Inappropriate tracking** happens when EMI sensed by the atrial lead is tracked to the ventricle at the upper tracking rate. **Mode switching** occurs when the device interprets EMI as atrial tachyarrhythmia and automatically changes mode. **Reset to backup mode** (power-on-reset) can result from exposure to strong EMI fields. **Lead tip thermal injury** is rare but can cause permanent changes in pacing thresholds.

### Effects of EMI on ICDs

ICDs are susceptible to all the pacemaker effects described above, plus one additional critical concern: **inappropriate shock delivery**. When the ICD interprets EMI as ventricular tachycardia or fibrillation, it may deliver an inappropriate therapeutic shock. This is the primary perioperative concern with ICDs.

### Minimizing EMI Risk

Bipolar electrocautery should be used when possible because the current travels a shorter path. When monopolar cautery is necessary, the grounding pad should be placed so the current path is directed away from the pulse generator. The cautery should be kept as far from the device as possible, ideally more than 15 cm. Short, intermittent bursts are preferable to prolonged application. Surgery below the umbilicus generally poses low risk for thoracically implanted devices.

## Magnet Behavior

### Pacemaker + Magnet

Placing a magnet over a pacemaker switches it to an asynchronous mode (AOO, VOO, or DOO depending on the device). This eliminates sensing, so EMI cannot inhibit pacing. The magnet rate varies by manufacturer: Medtronic devices pace at 85 bpm at full battery, Boston Scientific at 100 bpm, and Abbott at a variable rate. The magnet rate can also serve as a battery status indicator, as it decreases with battery depletion. The effect is present only while the magnet remains in place and returns to the programmed mode when the magnet is removed. Magnet behavior on pacemakers is consistent and predictable across manufacturers.

### ICD + Magnet

| Manufacturer | Pacemaker Magnet Rate (full battery) | ICD Magnet Behavior |
|---|---|---|
| Medtronic | 85 bpm | Suspends therapy while magnet applied; resumes on removal |
| Boston Scientific | 100 bpm | Suspends therapy; after ~30 sec **permanently disables** tachytherapy (requires reinterrogation) |
| Abbott (St. Jude) | Variable | Suspends therapy while magnet applied; resumes on removal |

Placing a magnet over an ICD **suspends tachyarrhythmia detection and therapy** (no shocks will be delivered) but does **not** change the pacing mode, which is an important distinction from pacemaker magnet behavior. Some devices emit an audible tone when the magnet is detected. Critically, ICD magnet behavior varies by manufacturer. Medtronic and Abbott devices suspend detection only while the magnet is applied, resuming normal function when it is removed. Boston Scientific devices, after approximately 30 seconds of magnet application, permanently disable tachytherapy, which remains disabled even after the magnet is removed -- the device must be reinterrogated to re-enable therapy. Because of this inconsistency, formal reprogramming is preferred over magnet application for ICDs when possible.

<image>Split-panel illustration comparing magnet effects on pacemakers versus ICDs. Left panel shows a pacemaker switching from DDD to DOO mode with an ECG tracing demonstrating asynchronous pacing spikes. Right panel shows an ICD with tachytherapy suspended (no shock icon with a red X) but pacing mode unchanged. A warning callout highlights that ICD magnet behavior varies by manufacturer with specific examples for Medtronic, Boston Scientific, and Abbott devices.</image>

## Perioperative Management Strategy

### ASA/HRS Practice Advisory Framework

The perioperative management of CIEDs follows a systematic framework. **Step 1** is to determine the device type and function: whether it is a pacemaker only, ICD, or CRT device, whether the patient is pacing-dependent, and what the current programming is. **Step 2** assesses the surgery-specific EMI risk: high-risk scenarios include surgery above the umbilicus with monopolar electrocautery near the device, while low-risk scenarios include surgery below the umbilicus, bipolar cautery, short procedures, and procedures distant from the device. **Step 3** applies to pacemaker-dependent patients facing high EMI risk: the device should be reprogrammed to an asynchronous mode (VOO or DOO) or a magnet should be applied, with external pacing and defibrillation available as backup. **Step 4** covers non-pacemaker-dependent patients with low EMI risk: these patients may proceed without reprogramming, with minimized EMI exposure and monitoring for inappropriate inhibition. **Step 5** addresses ICD management: tachytherapy should be disabled (through reprogramming or magnet) for any surgery where EMI might trigger inappropriate shocks, external defibrillation pads should be applied in anterior-posterior configuration before induction, a defibrillator must be immediately available, and tachytherapy must be re-enabled immediately after surgery.

### Rate-Adaptive Pacing

Rate-responsive modes (DDDR, VVIR) should be turned off perioperatively to prevent inappropriate rate increases triggered by surgical vibration, ventilation, or electrocautery. This is particularly important with accelerometer-based sensors and minute ventilation sensors.

## Intraoperative Monitoring

### Required Equipment

Continuous ECG monitoring capable of detecting pacing spikes is essential. Pulse oximetry with a visible plethysmograph confirms that pacing spikes are producing mechanical cardiac contractions (capture). An arterial line should be considered for hemodynamically significant cases. ICD patients require external defibrillator pads applied before induction. Transcutaneous pacing capability must be available as backup for pacemaker-dependent patients. A magnet should be immediately accessible.

### Troubleshooting Intraoperative Problems

**Loss of capture** should prompt an increase in output, evaluation for lead displacement, and checking of electrolytes (particularly hyperkalemia). **Failure to sense** (oversensing or undersensing) requires sensitivity adjustment. **Inappropriate pacing inhibition** is managed by applying the magnet or reprogramming to asynchronous mode. If an **ICD fires inappropriately**, the magnet should be applied to suspend therapy while the rhythm is evaluated.

## Postoperative Management

The device must be reinterrogated before discharge in any patient whose device was reprogrammed. ICD tachytherapy must be re-enabled as soon as the risk of electrocautery-related EMI has passed. Interrogation findings should be documented in the chart. Even when only a magnet was used without formal reprogramming, interrogation is recommended to confirm normal device function. Patients with significant intraoperative EMI exposure should be monitored for 24-48 hours.

<image>Step-by-step perioperative CIED management algorithm presented as a clinical workflow. Starting with preoperative interrogation and dependency assessment, flowing through intraoperative management decisions (reprogram vs. magnet, EMI minimization strategies, monitoring setup with external defib pads), and ending with postoperative reinterrogation and therapy re-enablement. Each decision point is clearly labeled with the rationale.</image>

## Clinical Pearls

The single most important preoperative question is whether the patient is pacemaker-dependent, as this determines the urgency of EMI management. Magnet behavior on pacemakers is predictable (asynchronous pacing), but magnet behavior on ICDs varies by manufacturer and can even be programmed off -- the response must always be verified. External defibrillation pads should be placed before induction in any patient with an ICD whose tachytherapy will be suspended. The pads should be positioned in an anterior-posterior configuration, at least 8 cm from the pulse generator. If an ICD fires intraoperatively, it is an emergency: the rhythm must be checked to confirm it is not true VF, and the magnet applied if the detection is false. Re-enabling ICD therapy postoperatively is a critical safety step; patients have died from VT/VF with a suspended ICD in the recovery room.

## References

- Practice Advisory for the Perioperative Management of Patients with Cardiac Implantable Electronic Devices: Pacemakers and Implantable Cardioverter-Defibrillators 2020. *Anesthesiology*. 2020;132(2):225-252.
- Crossley GH, Poole JE, Rozner MA, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA) Expert Consensus Statement on the perioperative management of patients with implantable defibrillators, pacemakers. *Heart Rhythm*. 2011;8(7):1114-1154.
- Rozner MA. The patient with a cardiac pacemaker or implanted defibrillator and management during anaesthesia. *Current Opinion in Anaesthesiology*. 2007;20(3):261-268.
- Schulman PM, Rozner MA. Use caution when applying magnets to pacemakers or defibrillators for surgery. *Anesthesia & Analgesia*. 2013;117(2):422-427.