Author:
Kai Knudsen
Updated:
28 January, 2026
A pacemaker generates electrical impulses to the heart in a regulated and controlled manner through an electrophysiological system that can be implanted in the body or external via transcutaneous electrodes.
Pacemaker
A pacemaker consists of two parts. One part is the pacemaker device, which is an encapsulated computer with a battery. The other part consists of the electrodes, which detect the heart rhythm and, if necessary, deliver electrical impulses to make the heart contract.
Implanted pacemaker:
- A small device placed under the skin, usually near the collarbone.
- Connected to the heart with one or more leads (wires) that deliver electrical impulses directly to the heart muscle.
- Used for long-term treatment of slow or irregular heart rhythms.
- Continuously monitors and adjusts the heart rate as needed.
External (transcutaneous) pacemaker:
- A temporary device placed outside the body.
- Delivers electrical impulses through electrodes attached to the skin (usually on the chest).
- Used in emergency situations or short-term care, such as during surgery or acute heart rhythm disturbances.
- Less comfortable than implanted pacemakers due to external stimulation.
Basic Concept: Pacemaker Mode and the Three-Letter Code (ICHD)
When programming and classifying pacemakers, a standardized international nomenclature is used, commonly referred to as the three-letter pacemaker code (ICHD/NBG code). This code describes which cardiac chamber is paced, which intrinsic activity is sensed, and how the pacemaker responds to sensed events.
The code consists of three positions:
1st Letter – Chamber(s) Paced
The first letter indicates which part of the heart the pacemaker can stimulate:
- V = Ventricle
- A = Atrium
- S = Single (one chamber only)
- D = Dual (both atrium and ventricle)
Example:
A pacemaker capable of pacing both atrium and ventricle is designated D.
2nd Letter – Chamber(s) Sensed
The second letter indicates where the pacemaker detects intrinsic electrical activity:
- V = Sensing in the ventricle
- A = Sensing in the atrium
- S = Single
- O = None (no sensing)
- D = Dual (both atrium and ventricle)
Sensing allows the pacemaker to recognize the patient’s own rhythm and avoid unnecessary pacing.
3rd Letter – Mode of Response to Sensing
The third letter describes how the pacemaker reacts when intrinsic activity is detected:
- T = Triggered pacing
- I = Inhibited pacing
- O = None (no response)
- D = Dual (both inhibition and triggering)
This response mechanism is central to so-called demand pacing, where pacing is delivered only when needed.
Example: DDD Pacemaker
A common pacing mode is DDD, meaning:
- D (pacing): Paces both atrium and ventricle
- D (sensing): Senses both atrial and ventricular activity
- D (response): Can both inhibit and trigger pacing depending on sensed signals
A DDD pacemaker can maintain AV synchrony by:
- inhibiting stimulation when intrinsic rhythm is present
- pacing when intrinsic rhythm is absent
- coordinating atrial and ventricular contractions
Clinical Importance
The three-letter code is widely used to quickly describe pacemaker function and is essential in:
- preoperative anesthetic assessment
- perioperative management of pacemaker patients
- interactions with magnets and electrocautery
- evaluation of bradycardia and AV block
- selection of the optimal pacing strategy
Perioperative Management of Pacemaker Patients (CIED)
1. Purpose
The purpose of this guideline is to ensure structured and safe perioperative management of patients with cardiac implantable electronic devices (CIEDs), including pacemakers, ICDs, and CRT systems, during anesthesia and surgery.
Perioperative risk is primarily related to electromagnetic interference (EMI) from electrocautery and other equipment, which may cause pacing inhibition, inappropriate therapy delivery, or asynchronous pacing.
2. Background and Definitions
CIEDs include:
- Pacemakers (PM) – treatment of bradyarrhythmias
- Implantable cardioverter-defibrillators (ICD) – with antitachycardia therapy
- CRT-P / CRT-D – biventricular pacing for heart failure
Pacemaker modes are classified using the three-letter code (e.g., VVI, DDD) describing:
- Chamber paced
- Chamber sensed
- Response to sensing
3. Preoperative Assessment
3.1 Identify the Device
Before surgery, the following must be established:
- Device type: pacemaker, ICD, CRT
- Indication for implantation
- Implantation date and most recent interrogation
- Programmed pacing mode
- Battery status and any active alerts
3.2 Evaluate Pacemaker Dependency
Pacemaker dependency is present when the patient lacks an adequate intrinsic rhythm.
Common indicators:
- Complete (third-degree) AV block
- Asystole without pacing
- 90% pacing burden
Pacemaker-dependent patients require special precautions in case of EMI.
3.3 Surgical Risk Evaluation
| Risk factor | Examples |
|---|---|
| Monopolar electrocautery above the diaphragm | Thoracic or head/neck surgery |
| Proximity to generator/leads | Breast surgery |
| Pacemaker dependency | Complete AV block |
| Active ICD therapies | Risk of inappropriate shock |
4. Perioperative Principles
4.1 Electromagnetic Interference (EMI)
EMI may be misinterpreted as cardiac activity and result in:
- Inhibition of pacing → bradycardia/asystole
- Triggering → tachypacing
- Inappropriate ICD shock
Monopolar electrocautery is the most frequent cause.
Bipolar cautery is preferred whenever possible.
5. Management According to Device Type
5.1 Pacemakers (without ICD)
Low-risk procedures (no cautery above diaphragm)
- No reprogramming required
- Standard monitoring
High-risk procedures (cautery above diaphragm)
- Consider asynchronous pacing mode (VOO/DOO) in pacemaker-dependent patients
- Alternative: magnet application (device-specific)
5.2 ICDs (with or without pacing)
ICDs are sensitive to EMI and may deliver inappropriate therapy.
For procedures with EMI risk:
- Deactivate tachycardia therapies (shock/ATP) preoperatively
- Pacing function remains active but may still be inhibited
External defibrillator pads must always be applied.
6. Magnet Use
Magnet effects are device-specific:
| Device | Magnet effect |
|---|---|
| Pacemaker | Asynchronous pacing (VOO/DOO) |
| ICD | Tachytherapy suspended, pacing unchanged |
Magnets should be used only when:
- Response is known
- Continuous monitoring is ensured
7. Intraoperative Management
Required Monitoring
- ECG with pacing detection
- Pulse oximetry
- Invasive blood pressure for high-risk cases
- Immediate access to external pacing/defibrillation
Electrocautery Recommendations
- Prefer bipolar cautery
- If monopolar is required: short intermittent bursts
- Grounding pad positioned so current flow is directed away from the CIED system
8. Postoperative Management
After procedures involving EMI or device reprogramming:
- Postoperative device interrogation is mandatory
- ICD therapies must be reactivated
- Monitoring continues until normal function is confirmed
Documentation must include:
- Device type and status
- Interventions (magnet use, reprogramming)
- Confirmation of postoperative restoration
9. Emergency Algorithm: Intraoperative Pacing Failure
If bradycardia/asystole occurs:
- Stop electrocautery
- Assess pulse and hemodynamics
- Apply magnet if appropriate (pacemaker-dependent patients)
- Initiate external pacing if necessary
- Contact cardiology/CIED team urgently
10. Summary Recommendation
- Always identify the CIED preoperatively
- Assess pacemaker dependency
- EMI risk determines need for reprogramming
- ICD tachytherapy must be disabled when electrocautery is used
- External pacing/defibrillation must be immediately available
- Postoperative restoration and interrogation are mandatory in high-risk cases
- VOO = Fixed-rate ventricular pacing
- VVI = Ventricular-inhibited pacing
- AAI = Atrial-inhibited pacing
- DDD = Dual atrial & ventricular pacing
Pace
- Atrium
- Ventricle
- Dual (A+V)
- O = None
Sense
- Atrium
- Ventricle
- Dual (A+V)
- O = None
Sense Response
- Triggered
- Inhibited
- Dual (T+I)
- O = None
External Temporary PM after Heart Surgery
Blue contact – atrium, white contact – ventricle
SC electrode to positive (+) pole
EMERGENCY – asynchronous high-energy stimulation with VVO (unlock the PM first!)
Stimulation
- Atrial – normally 2-10 V (max range 0.1-18.0 V)
- Ventricle – normally 5-10 V (max range 0.1-18.0 V)
- Guideline – 5 V above capture threshold
Sensing
- Atrial – normally 0.5-1 mV (max range 0.2-20 mV)
- Ventricle – normally 2-3 mV (max range 1.0-20 mV)
- AV interval usually 150-180 ms – compare with patient’s PQ time
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