Pacemaker response to magnet placement

Pacemaker manufacturer		Magnet mode designation	Explanation
Biotronik		AUTO (DEFAULT)	If normal conditions, 10 asynchronous events at 90 bpm, then returns to original programmed mode (ie, synchronous pacing) at the lower rate limit. If battery is at ERI, 10 asynchronous events at 80 bpm in VOO mode, then either VDD (dual-chamber) or VVI (single-chamber) with pacing at 11% below the lower rate limit. For any dual-chamber mode, the AVd shortens to 100 milliseconds for the 10 asynchronous events.
		ASYNCH	Asynchronous pacing at 90 bpm if normal conditions. At ERI, 80 bpm (single-step change) in VOO mode regardless of original programming. For any dual-chamber pacing mode, the AVd shortens to 100 milliseconds while the magnet is in place.
		SYNCH	If normal conditions, pacing in original programmed mode, without rate responsiveness. Pacing is at lowest available rate (LRL, sleep rate, or hysteresis rate). If battery is at ERI, then either VDD (dual chamber) or VVI (single chamber) with pacing at 11% below the lower rate limit.
Boston Scientific (includes Guidant Medical CPI)		ASYNCH (DEFAULT)	If normal conditions, asynchronous pacing with 100 millisecond AVd at 100 bpm. If ERI, 85 bpm (single-step change). The Insignia and Altrua models have an intermediate step (90 bpm) at ERN. Most models shorten the pulse width to 50% on the third paced ventricular event (TMT). For Triumph and Prelude models, refer to Medtronic pacemakers, below.
		OFF	No change; magnet is ignored. OFF is also the magnet mode after a "power on reset," or activation of "safety core," which can occur secondary to EMI.
		EGM mode	No change in pacing. Magnet application initiates data collection.
Intermedics (purchased by Guidant in 1998, now Boston Scientific, but special programmer needed)			Five asynchronous events at 90 bpm (regardless of battery voltage), then 60 additional asynchronous events at LRL if normal conditions, 90 bpm if ERI, and 80 bpm if EOL. The fifth paced event is emitted at 50% of the originally programmed pulse width (TMT). After the 64th asynchronous event, the magnet is ignored.
Medtronic		Conventional transvenous pacemakers (including cardiac resynchronization therapy – pacemakers)	Asynchronous pacing based on programmed mode at 85 bpm if normal conditions*, 65 bpm if at ERI.
Medtronic		Leadless intra-cardiac pacemakers (ie, “Micra” and “Micra AV”)	No magnet response.
MicroPort (Sorin / ELA Medical)			Asynchronous pacing at 96 bpm gradually declining to 80 bpm at ERI. Sorin/ELA pacemakers take eight additional pacing cycles (the final two cycles are at LRL with long AVd) upon magnet removal.
Abbott (St. Jude Medical [SJM], Pacesetter)	"SJM" radiograph logo; standard transvenous pacemaker	Battery test (DEFAULT)	Asynchronous pacing at 100 bpm (older models 98.6 bpm) gradually decreasing to 85 bpm (older models 86.3) at ERI.
		OFF	No magnet response.
		Event snapshots	No change in pacing. Magnet application causes pacemaker to collect data. Identity and Entity models lack this feature.
		Event snapshots + battery test	For a magnet placed on the device for two seconds, pacing mode and rate are unchanged, and the device stores an electrogram. If the magnet is placed for =5 seconds, the battery test mode (refer to above) is activated. Identity and Entity models lack this feature.
	Pacesetter radiograph logo; standard transvenous pacemaker	Battery test (DEFAULT)	Asynchronous pacing, and the rate depends upon specific model. In general, a pacing rate of less than 90 bpm should prompt further evaluation.
		OFF	No magnet response.
		VARIO mode (present in some models)	VARIO results in a series of 32 asynchronous pacing events. The rate of the first 16 paces reflects battery voltage, gradually declining from 100 bpm to 85 bpm at ERI. The next 15 paces are used to document ventricular pacing capture safety margin. The rate will be 119 bpm with gradually declining pacing voltage. The 16th pace of this group is at no output. The next pace restarts the 32-event sequence. The 32-event sequence repeats while the magnet remains in place.
	"Nanostim" leadless intra-cardiac pacemaker	On (DEFAULT)	Asynchronous pacing at 100 bpm for eight cycles, then 90 bpm if normal conditions; 65 bpm if ERI.
	"Nanostim" leadless intra-cardiac pacemaker	OFF	No magnet response.

The effect(s) of appropriately placing a magnet over a pacemaker are shown, assuming normal battery and lead function. Column 1 shows the pacemaker manufacturer. Where a manufacturer has multiple responses, Column 1 is subdivided. If the magnet response is programmable, then Column 2 shows the various magnet modes available. The first mode shown is the default. A device reset from EMI might produce some other mode (ie, magnet mode disabled). Column 3 shows the effect on pacing therapy for the magnet mode shown in Column 2. Unless otherwise specified, asynchronous pacing takes place, without rate responsiveness, in the chambers originally programmed. Thus, a dual-chamber program would result in DOO pacing; a single-chamber program would result in VOO (unless an atrial device, which would be AOO) pacing; and a biventricular, dual-chamber device would be DOOOV.
Caution for Medtronic transvenous pacemakers: All Medtronic transvenous pacemakers except Enrhythm P1501, EMDR series, Revo, Advisa, and Ensura suspend magnet detection for up to 60 minutes following removal of the programming head after an interrogation session, unless specific programming action (which requires multiple "button" depressions) is taken prior to removing the programming head.
Caution for all dual-chamber pacemakers: An electrical fault or exposure to strong EMI could cause a "power on reset" or "safety core event" (BSC - Boston-labeled devices), causing the pacemaker to switch to VVI pacing only, regardless of prior pacing programming. For a dual-chamber pacemaker with a bad RV lead and programmed to atrial pacing only (AAI, AOO) in a pacing-dependent patient, this event could result in patient injury or death.
For further explanation of terms, refer to UpToDate topics on modes of cardiac pacing and cardiac pacing nomenclature.

bpm: beats/minute; ERI: elective replacement indicator (the device should be replaced promptly - the US Food and Drug Administration [FDA] requires pacemakers to perform safely for at least three months from onset of ERI); VOO: ventricular asynchronous pacing, no sensing; VDD: ventricle paced, atrium and ventricle sensed, and either inhibition or tracking of the pacemaker in response to a sensed beat; VVI: ventricle paced, ventricle sensed, and pacemaker inhibited in response to a sensed beat; AVd: atrioventricular delay (for dual-chamber pacing; note that this is a programmed value, although the AVd can be shortened during the first 3 to 15 events upon magnet placement; note that a short AVd can reduce stroke volume and produce untoward hemodynamics in some patients); LRL: lower rate limit (the programmed lower rate, or set point, of the pacemaker); ERN: elective replacement near (the device should be undergoing monthly checks [IFI]); TMT: threshold margin test (This is the emission of a single pacing pulse [except VARIO - refer to St. Jude Medical – Pacesetter Logo] at a lower amplitude or pulse width to demonstrate adequacy of pacing output relative to pacing threshold. Typically, this is the third or fifth pacing pulse, and failure to capture [pace] on this event suggests an inadequate safety margin for capture. Properly programmed atrial-only pacemakers are unlikely to demonstrate this feature.); EMI: electromagnetic interference; EGM: electrogram; EOL: end of life (the device should be replaced immediately); AOO: asynchronous A pacing; AAI: atrium paced, atrium sensed, and pacemaker inhibited in response to sensed atrial beat; ERT: elective replacement time (Same as ERI for Boston Scientific pacemakers [Guidant, CPI labels also]. At ERT, rate-responsive programming is cancelled. At three months post-ERT, only single-chamber operation continues.); SSI: single-chamber, inhibited mode (If implanted for ventricular pacing, then SSI = VVI. For an atrial pacemaker, SSI = AAI.).
* Some Medtronic pacemakers deliver the first three or five asynchronous beats in magnet operation at 100 bpm. The first three asynchronous paces of the Adapta, Versa, Sensia, and Relia models are at 100 bpm (the amplitude of the last of the three 100 bpm paced beats is reduced by 20%). The first five asynchronous paces of the Azure, Astra, Percepta, Serena, and Solara models are at 100 bpm. Other models (ie, EnRythm, Revo, Advisa, Ensura, Viva) deliver all asynchronous beats in magnet response at 85 bpm (or 65 bpm if at ERI). In Azure, Astra, Percepta, Serena, Solara, EnRythm, Revo, Advisa, Ensura, and Viva devices, a magnet suspends tachyarrhythmia detection. When the magnet is removed, the device returns to its programmed operation.

Original figure modified for this publication. Rozner MA. Implantable cardiac pulse generators: Pacemakers and cardioverter-defibrillators. In: Miller's Anesthesia, 8th ed, Miller RD (Ed), Saunders, Philadelphia 2015. Table used with the permission of Elsevier Inc. All rights reserved.

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Pacemaker response to magnet placement