CCRN · Cardiovascular · 7 min read
Pacemakers, ICDs and Temporary Pacing
- Analyze pacemaker pacing codes, settings, and troubleshooting steps for failure to pace, capture, and sensing.
- Implement safe clinical practices for temporary transcutaneous, transvenous, and epicardial pacing.
- Manage implantable cardioverter-defibrillators (ICDs) during emergencies, magnet application, electrocautery, and end-of-life care.
Pacemaker Coding and Modes of Operation
In critical care, understanding pacemaker nomenclature is essential for evaluating whether an implanted or temporary device is functioning as intended. The NASPE/BPEG generic pacemaker code provides a standardized framework: the first letter denotes the chamber paced, the second letter denotes the chamber sensed, and the third letter denotes the response to sensing. Knowing these designations allows the critical care registered nurse to anticipate the device's behavior on the bedside monitor.
Different pacing modes provide varying levels of physiological support. DDD mode senses and paces both atria and ventricles. When atrial activity can be appropriately tracked and pacing and sensing are effective, DDD pacing can preserve atrioventricular synchrony and improve hemodynamics, but it does not guarantee hemodynamic stability. In contrast, VVI pacing mode senses and paces only the ventricle and inhibits its pacing output whenever an intrinsic ventricular depolarization is sensed.
Asynchronous pacing modes, such as AOO, VOO, and DOO, deliver pacing stimuli at fixed rates regardless of intrinsic cardiac electrical activity. Because these modes ignore the heart's native rhythms, they do not inhibit in response to sensed beats. In ventricular-only pacing modes, loss of atrioventricular synchrony can lead to pacemaker syndrome, causing hypotension and symptoms of reduced cardiac output, with retrograde atrial activation and cannon A waves.
| Pacing Mode | Chamber Paced | Chamber Sensed | Response to Sensing | Clinical Features |
|---|---|---|---|---|
| DDD | Atrium and Ventricle | Atrium and Ventricle | Inhibits and Triggers | DDD pacing can preserve atrioventricular synchrony and atrial contribution to ventricular filling when atrial activity is appropriately tracked and pacing and sensing are effective. |
| VVI | Ventricle | Ventricle | Inhibits | Paces ventricle; inhibits output when intrinsic ventricular activity is detected. |
| VOO / DOO | Ventricle (VOO) or Both (DOO) | None | None (Asynchronous) | Delivers fixed-rate stimuli regardless of intrinsic electrical events. |
Common mistakes
- Assuming chest wall twitching during transcutaneous pacing indicates cardiac mechanical capture, rather than confirming capture with a central pulse or arterial line waveform.
- Delaying chest compressions or external defibrillation during cardiac arrest to wait for an implanted ICD to deliver an internal shock.
- Increasing the millivolt (mV) setting when trying to correct undersensing, which actually makes the pacemaker less sensitive and worsens the problem.
- Assuming temporary epicardial wire identities based on where they exit the skin instead of verifying them against the operative record and local labeling.
Key points
- The NASPE/BPEG code describes the chamber paced (first letter), chamber sensed (second letter), and response to sensing (third letter); DDD can preserve AV synchrony when atrial activity can be appropriately tracked, while VVI provides ventricular pacing with inhibition.
- Transcutaneous pacing requires confirmation of mechanical capture via a central pulse or arterial line, along with prompt prescribed analgesia and sedation.
- Wear nonconductive gloves when handling epicardial wires, insulate exposed wire tips in nonconductive containers, and identify wires via the operative report.
- Adjust sensitivity settings accurately: lower mV values increase sensitivity to treat undersensing, whereas higher mV values decrease sensitivity to treat oversensing.
- Treat loss of capture by immediately checking patient stability, securing connections, and increasing output (mA) within protocol, while evaluating for causes like lead dislodgement or hyperkalemia.
- Clinical magnets suspend tachyarrhythmia therapies in most ICDs without altering bradycardia pacing, but they switch many permanent pacemakers to asynchronous pacing.
- Support patients holistically under the Synergy Model by addressing phantom shocks and trauma, and coordinating ordered ICD deactivation when therapies no longer align with end-of-life goals.
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