Emergency Medicine Hub / Cardiovascular Emergencies • 3 min read • 4 sections

Pacemaker & ICD Malfunctions & Device Emergencies

Comprehensive emergency evaluation and protocolized troubleshooting for Cardiac Implantable Electronic Devices (CIEDs): interpretation of the 5-letter NASPE/BPEG pacing code; diagnostic differentiation of Failure to Pace, Failure to Capture, and Failure to Sense (undersensing vs. oversensing); emergency management of Pacemaker-Mediated Tachycardia (PMT) and Runaway Pacemaker; physical device complications including Twiddler syndrome and pocket infections; emergency application of cardiac magnets on pacemakers versus ICDs; and rapid stabilization of ICD electrical storm and inappropriate shocks.

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Magnet on ICD

Suspends tachyarrhythmia detection and INHIBITS ALL DEFIBRILLATOR SHOCKS; does NOT alter underlying pacemaker pacing mode

Magnet on Pacemaker

Converts device to ASYNCHRONOUS fixed-rate pacing (DOO or VOO, typically 85-100 bpm); terminates Pacemaker-Mediated Tachycardia (PMT)

Oversensing vs Undersensing

Oversensing (sees P/T waves or muscle twitching as QRS) -> Inhibits pacing -> Bradycardia/Asystole; Undersensing (ignores intrinsic QRS) -> Fires inappropriately -> R-on-T hazard

ICD Electrical Storm Regimen

Apply magnet to stop shocks + IV Amiodarone 150 mg + IV Esmolol infusion (or Propranolol 1 mg IV q5min) + IV Magnesium 2-4 g + deep sedation with Propofol

Runaway Pacemaker Trap

Elderly failing battery discharges at 200-400 bpm producing severe ischemia/VF -> Apply magnet immediately; if refractory, surgically snip pacemaker lead

Twiddler Syndrome

Patient unconsciously rotates generator within subcutaneous pocket, winding and dislodging transvenous leads -> CXR shows coiled leads at pocket and lead retraction

Bottom-Line Clinical Pearl

In any patient with an Implantable Cardioverter-Defibrillator (ICD) receiving recurrent, agonizing shocks (whether due to an electrical storm of refractory ventricular tachycardia or inappropriate shocks from rapid atrial fibrillation), applying a doughnut magnet directly over the ICD generator immediately suspends tachyarrhythmia detection and inhibits all further defibrillation shocks without altering the device's bradycardia pacing functions. Conversely, placing a magnet over a permanent pacemaker converts the device to an asynchronous, fixed-rate pacing mode (DOO/VOO at 85-100 bpm), which terminates pacemaker-mediated reentrant tachycardias (PMT).

1. The NASPE/BPEG Generic Pacing Code

Permanent pacemakers and ICDs utilize the standardized 5-letter NASPE/BPEG (North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group) code to describe device function and programmability:

Position I: Chamber(s) Paced	Position II: Chamber(s) Sensed	Position III: Response to Sensing	Position IV: Rate Modulation	Position V: Multisite Pacing
O = None A = Atrium V = Ventricle D = Dual (A + V)	O = None A = Atrium V = Ventricle D = Dual (A + V)	O = None T = Triggered I = Inhibited D = Dual (T + I)	O = None R = Rate responsive (accelerates pacing with accelerometer/motion)	O = None A = Atrium V = Ventricle (Bi-V/CRT) D = Dual

2. Core Pacemaker Malfunctions: Diagnosis & Management

Malfunction Type	Electrocardiographic Hallmark	Etiologies & Emergency Correction
Failure to Pace (Output Failure)	Absence of expected pacing spikes when the intrinsic heart rate falls below the programmed lower rate limit. Produces prolonged pauses, severe bradycardia, or asystole.	Etiologies: Lead fracture, lead dislodgement, battery depletion (End of Life (EOL)), cross-talk inhibition, or extreme oversensing. Action: Apply magnet (forces fixed-rate pacing). If refractory: transcutaneous or temporary transvenous pacing.
Failure to Capture	Pacing spikes are clearly visible on the surface ECG, but are NOT followed by a depolarized P-wave or wide QRS complex.	Etiologies: Lead dislodgement/perforation, exit block (fibrosis at myocardium-lead interface), severe hyperkalemia, acute myocardial infarction, or class IC antiarrhythmic toxicity. Action: Correct electrolyte derangements (calcium for hyperkalemia); programmer interrogator to increase voltage output/pulse width; external pacing.
Failure to Sense: Oversensing (Device is TOO sensitive)	Device detects electrical signals not intended to be sensed (large P-waves, tall T-waves, or skeletal muscle myopotentials from pectoral contractions) and falsely interprets them as intrinsic cardiac depolarization. Pacing is inappropriately inhibited, causing profound pauses.	Action: Place doughnut magnet over generator (suspends sensing and initiates asynchronous pacing, restoring ventricular rate immediately). Reprogram sensing threshold.
Failure to Sense: Undersensing (Device is NOT sensitive enough)	Device fails to detect intrinsic cardiac depolarizations (R-waves or P-waves). As a result, the pacemaker fires blindly and randomly at a fixed rate, completely ignoring intrinsic beats. Pacing spikes appear within intrinsic QRS complexes or on T-waves (R-on-T phenomenon).	Hazard: High risk of triggering fatal Ventricular Tachycardia or Ventricular Fibrillation via R-on-T pacing. Reprogram device to increase sensitivity (lower the millivolt detection threshold).
Pacemaker-Mediated Tachycardia (PMT)	Endless-loop reentrant tachycardia in dual-chamber (DDD) systems: a premature ventricular complex (PVC) conducts retrograde through the AV node into the atrium. The atrial lead senses this retrograde P-wave and triggers ventricular pacing, which again conducts retrograde, creating a continuous loop at the maximum tracking rate (120-160 bpm).	EMERGENCY FIX: APPLY MAGNET OVER GENERATOR! The magnet converts the DDD pacemaker to DOO mode, terminating atrial sensing and instantly breaking the reentrant loop.

3. The Cardiac Magnet: Pacemaker vs. ICD Application Rules

A standard clinical doughnut magnet (or horseshoe magnet) activates an internal reed switch or Hall-effect sensor within the device generator. The physiological response differs profoundly between pacemakers and ICDs:

Device Type	Clinical Effect of Magnet Application	Clinical Indications in the Emergency Department
Permanent Pacemaker (PPM)	Converts device to ASYNCHRONOUS mode (DOO or VOO) at a fixed magnet rate (typically 85 to 100 bpm depending on manufacturer and remaining battery life). Note: When magnet is removed, device returns to previous programmed mode.	1. Terminate Pacemaker-Mediated Tachycardia (PMT) 2. Overcome severe oversensing (inhibited pacing caused by electrocautery or muscle twitching) 3. Verify capture threshold and assess remaining battery life (a magnet rate < 85 bpm often signifies battery depletion).
Implantable Cardioverter-Defibrillator (ICD)	SUSPENDS TACHYARRHYTHMIA DETECTION AND INHIBITS ALL SHOCKS! CRITICAL RULE: Magnet application on an ICD does NOT alter the bradycardia pacing function (it does NOT switch the pacemaker component to asynchronous DOO mode).	1. Inappropriate shocks (sinus tachycardia, rapid atrial fibrillation with RVR, lead fracture sending artifact noise) 2. Electrical Storm (recurrent VT/VF refractory to shocks) 3. End-of-life/palliative care deactivation to prevent agonizing terminal shocks.

4. ICD Electrical Storm: Stepwise Resuscitation Protocol

ICD Electrical Storm is defined as >= 3 distinct episodes of sustained VT or VF requiring device therapy (antitachycardia pacing [ATP] or shocks) within a 24-hour period. Recurrent high-energy shocks produce intense adrenergic discharge, worsening myocardial ischemia and triggering further dysrhythmias in a lethal positive feedback loop:

Step/Intervention	Protocol & Pharmacotherapy	Physiological Pearl
Step 1: Immediate External Magnet Application	Tape a doughnut magnet directly over the ICD generator using medical tape.	Instantly eliminates repetitive agonizing 35-joule shocks, breaking the sympathetic storm. Attach external defibrillator pads immediately for backup manual cardioversion.
Step 2: Sympathetic Blockade (First-Line)	Esmolol IV loading dose (500 mcg/kg over 1 min), then infusion at 50–300 mcg/kg/min OR Propranolol 1 mg IV every 5 minutes (up to 3-5 mg). (Non-selective beta-blockers like Propranolol cross the blood-brain barrier and block peripheral beta-2 receptors, providing superior suppression over cardioselective beta-1 blockers).	Excessive sympathetic tone is the primary driver of electrical storm; beta-blockade is the single most effective pharmacological intervention.
Step 3: Antiarrhythmic Loading	Amiodarone 150 mg IV over 10 minutes, followed by continuous infusion at 1 mg/min for 6 hours, then 0.5 mg/min. PLUS Magnesium Sulfate 2 to 4 g IV over 10-15 minutes.	Target serum potassium > 4.5 mEq/L and serum magnesium > 2.5 mg/dL to stabilize ventricular refractory periods.
Step 4: Deep Sedation & Neuromuscular Blockade	Intubate and deeply sedate with Propofol infusion (30–80 mcg/kg/min) or Midazolam.	Abolishing conscious perception and central sympathetic outflow terminates resistant electrical storm when pharmacotherapy alone fails.

The Runaway Pacemaker Emergency & The External Defibrillation Pad Trap

Beware the rare but lethal disaster of a 'Runaway Pacemaker': in older generators with severe electronic component failure or near-dead batteries, the pacing clock can malfunction, discharging spikes at an uncontrolled rate of 200 to 400 beats per minute. This drives the ventricles into a catastrophic ventricular tachycardia, acute myocardial ischemia, and ventricular fibrillation. APPLY A MAGNET IMMEDIATELY: in some models, magnet application forces the rate down to a safe fixed rate; if the runaway pacing persists, you must urgently perform a bedside cutdown over the pacemaker pocket under local anesthesia to SNIP AND TRANSECT THE PACING LEAD with sterile shears to physically break the circuit! Furthermore, when performing external manual defibrillation or cardioversion on any patient with a pacemaker or ICD, NEVER place external defibrillator pads directly over the generator: keep the pads at least 8 to 10 cm (3 to 4 inches) away (anteroposterior pad positioning is preferred). Direct electrical arcing through the generator destroys internal circuitry and causes myocardial thermal burns at the lead-tissue interface.

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