- Paced chamber [O, A, V, D (A+V)]
- Sensed chamber [O, A, V, D (A+V)]
- Response to sensed event [O, Inhibited, Triggered, D (I+T)]
- Rate modulation [O, R]
- Multisite pacing [O, A, V, D (A+V)]
Note that T (Triggered) is only an option for the for 3rd letter of the pacemaker designation and is only used when the device is being tested. Inhibited means if electrical activity is sensed the pacer pulse will not fire. R will increase paced heart rate in response to sensed “exercise”. DDI only for paroxysmal afib, prevents high ventricular rate. Most pacers are in DDD or VVI mode.
Examples (from Table 1 of the Advisory below):
- AAI = atrial antibradycardia pacing; if the atria fails to fire, it is paced. Ignores PVCs.
- AOO = asynchronous A pacing
- DDD = dual-chamber antibradycardia pacing; if atria fails to fire, it is paced. If the ventricle fails to fire after an atrial event (sensed or paced) the ventricle will be paced.
- DDI = Like above, but the atrial activity is tracked into the ventricle only when the atria is paced.
- DOO = asynchronous A+V pacing
- VOO = asynchronous V pacing
- VVI = V only antibradycardia pacing; any failure of the ventricle to fire results in pacing. “There can be no A-V synchrony in someone with a VVI pacemaker and intrinsic atrial activity.”
ASA Practice Advisory Summary
If electromagnetic interference (EMI) is likely to occur, pacer functions should be set to asynchronous mode either by reprogramming or with a magnet. However, avoid routinely placing a magnet on an ICD.
- Pad and bovie tool should not pass through the pulse generator or leads
- short, irregular bursts at lowest energy possible
- use bipolar or ultrasonic (harmonic) if possible
- avoid focus of the beam near the pulse generator
- disable atrial pacing if the lithotripsy system is set to trigger on the R wave
- Remove the magnet first to reenable anti-tachycardia therapy
- Interrogate and restore pacer/ICD function. (There are case reports of perioperative events causing pacer threshold changes, safety mode reset, and appearance of the elective replacement indicator.)
- American Society of Anesthesiologists. Practice advisory for the perioperative management of patients with cardiac implantable electronic devices: pacemakers and implantable cardioverter-defibrillators: an updated report by the american society of anesthesiologists task force on perioperative management of patients with cardiac implantable electronic devices. Anesthesiology. 2011 Feb;114(2):247-61