Cardiac implantable electronic devices (CIEDs) are battery-powered medical devices used to treat a variety of cardiac disorders and include permanent pacemakers (PPMs), automated implantable cardioverter defibrillators (AICDs), and cardiac resynchronization therapy devices (CRTs). CIEDs are used to monitor and control arrhythmias (PPMs, AICDs, CRTs) and improve systolic function (CRTs). Complications of CIEDs may result from implantation or device-related malfunctions. Device malfunctions are divided into pacing malfunctions (e.g., oversensing, undersensing) and cardioversion malfunctions (e.g., lack of appropriate shocks, inappropriate shocks). Management of typically involves and treatment of underlying or resulting arrhythmias.
Types of CIEDs
- Permanent pacemakers (PPMs): capable of pacing the heart to maintain an adequate heart rate in bradyarrhythmia
- Automated implantable cardioverter defibrillators (AICDs)
- Cardiac resynchronization therapy devices (CRTs): capable of pacing both RV and LV to improve cardiac output in heart failure and pace the heart to maintain an adequate heart rate in bradyarrhythmia
|Comparison of PPMs, AICDs, and CRTs|
|Basic types|| |
Pulse generator: a thin metal case containing a power source to produce electrical impulses and a programmable computer
- Size: ∼ 5 cm across
- Battery life is usually 5–10 years depending on use (e.g., pacing rate, shock frequency). 
- Leads with electrodes for pacing, sensing, and defibrillating
- Electrodes sense the heart's electrical activity and transmit it to the pulse generator.
- The pulse generator identifies arrhythmias.
- Electrodes transmit electrical impulses from the pulse generator to the myocardium to pace or cardiovert.
- Leads are inserted into the right ventricle and, in some cases, the right atrium, usually transvenously via the cephalic, axillary, or subclavian vein.
- In biventricular pacemakers, the lead to stimulate the left ventricle is inserted into the coronary sinus.
- In most cases, the generator is implanted on the patient's nondominant side between the pectoral muscle and the muscle fascia.
- Purpose: A magnet may be placed over the pulse generator for diagnostic and/or therapeutic purposes.
- Device effect 
A PPM is a CIED that contains a pulse generator and at least one pacing lead, preventing bradycardia and asystole. Other CIEDs (e.g., AICDs, CRTs) often include pacemaker functions. PPM implantation can be preceded by in acute cases.
Types of PPMs
- Single-chamber pacemaker: one lead, usually in the right ventricle
- Dual-chamber pacemaker: two leads, one in the right atrium and one in the right ventricle
- Other CIEDs with pacemaker functions
- Cardiac rhythm monitoring
- Antibradycardia pacing
- Both of the following requirements must be met for minimum PPM functioning:
- Combination PPM and AICD devices: may also have functions (see “AICDs”)
Indications for PPMs 
- Sinus node dysfunction (SND)
- AV block
- Other causes of syncope: selected patients with carotid sinus syndrome
Pacemaker nomenclature 
NBG code: PPMs and CIEDs with pacemaker function are classified using a 5-letter system
- 1st letter: chamber(s) that are paced, i.e., A = atrium, V = ventricle, D = dual
- 2nd letter: chamber(s) that are sensed, i.e., A = atrium, V = ventricle, D = dual
- 3rd letter: device's response to sensing native beats, i.e., I = inhibited, T = triggered, D = dual 
- The 4th and 5th letters are less commonly communicated and denote device programmability and any functions, respectively.
- DDD pacemaker (most common): senses and paces both chambers; can inhibit impulses to either chamber if native atrial or ventricular beats are sensed
- VVI pacemaker: senses and paces the ventricle; can inhibit impulses to the ventricle if a native ventricular beat is sensed
ECG findings of normal pacemaker function 
- Pacemaker spike: a narrow upward deflection usually with an amplitude of < 5 mm
- Ventricular depolarizations that indicate
- Fusion beats (e.g., fusion of native beat and PPM beat) and capture beats may be preset.
DDD pacemaker: Pacemaker spikes can occur before P waves and QRS complexes.
- No intrinsic electrical activity: results in sequential AV pacing with a paced P wave followed by a paced QRS complex
- AV block with intrinsic sinus node activity: a normal P wave followed by a paced QRS complex
- No sinus node activity with normal AV conduction: paced P wave followed by a normal QRS complex
- VVI pacemaker: paced QRS complexes and dissociated P waves
- CRT device: two pacing spikes followed by a paced QRS complex
ECG findings of can vary depending on the type of CIED.
Types of AICDs
- Transvenous AICD: leads implanted into the right ventricle ± right atrium via the cephalic, axillary, or subclavian vein; multifunction device
- Subcutaneous AICD: subcutaneous lead positioned along the left parasternal margin; single function device 
- Combined AICD and CRT: See “CRT-D.”
Specific functions may vary by device depending on programming and patient needs.
- All AICDs
- Transvenous AICDs
- Subcutaneous AICDs: defibrillation only
All modern transvenous AICDs are capable of in addition to , , and .
Indications for AICDs 
The primary goal of AICDs is to prevent sudden cardiac death from ventricular tachyarrhythmias. Consult a cardiologist and/or electrophysiologist and use shared decision-making to determine if an AICD should be implanted, taking the patient's risk factors into account.
Selected patients with an expected survival of > 1 year and any of the following:
- (see “Treatment of HCM” for details)
- (e.g., , )
- Severe congestive heart failure (see “ ” for specific indications) 
- Neuromuscular disorders (e.g., , )
All patients with an expected survival of > 1 year, an irreversible cause of ventricular tachyarrhythmias, and any of the following: 
A CRT device is a CIED that contains a pulse generator and leads to the atrium and both ventricles that pace the heart in a coordinated manner. Some CRTs also can deliver shocks to restore sinus rhythm.
Types of CRTs
- Cardiac resynchronization therapy-pacemaker (CRT-P): biventricular pacemaker only
- Cardiac resynchronization therapy-defibrillator (CRT-D): biventricular pacemaker PLUS an AICD
- All devices
Indication for CRTs
During implantation 
- Cardiac perforation
- Pocket hematoma
- Accidental lead placement into the LV/LA
- CRTs: coronary sinus dissection or perforation during placement of the LV pacing lead
After implantation 
- Lead displacement: the migration of a CIED lead away from its intended position, leading to dysfunction
- Lead fracture: fragmentation and discontinuity of a CIED lead, leading to dysfunction
- Venous stenosis
- Infection (see “ ”)
- Twiddler syndrome (uncommon)
- Tricuspid valve dysfunction
and are common underlying causes of various .
CIED malfunction 
Related to pacing
- Related to cardioversion
Can occur in patients with single-chamber pacemakers (e.g., VVI pacemakers)
- Symptoms: fatigue, weakness, dyspnea, lightheadedness, neck or throat pain, chest pain
- Cause: AV dyssynchrony, which can cause the atria to contract against closed mitral and tricuspid valves, resulting in loss of atrial kick and decreased cardiac output
- Management: replacement with a in patients with severe symptoms
CRT complications 
- Coronary sinus dissection or perforation during placement of the LV pacing lead
- Displacement of the left ventricular pacing lead, resulting in loss of pacing
We list the most important complications. The selection is not exhaustive.
Management approach 
- ABCDE assessment with 12-lead ECG and continuous telemetry
- Perform a cardiorespiratory examination (e.g., to assess for signs of heart failure) and inspect the pulse generator site.
- Determine the type of CIED.
- Refer for , as management depends on the type of device and complication.
- Obtain CXR to assess for lead displacement and lead fracture.
- Consider other diagnostic tests based on clinical suspicion (see “Diagnostics”).
- All patients: Place defibrillator or pacing pads in AP configuration or > 10 cm from the pulse generator. 
- Pulseless patients: Initiate ACLS.
Patients with a pulse
- Treat the presenting arrhythmia: See “Adult unstable bradycardia algorithm,” “Initial management of Vtach,” and “Management of unstable tachycardia.”
- Urgently consult cardiology for .
- Identify the underlying CIED malfunction based on ECG and clinical evaluation, e.g., , , , , problems with AICD shock delivery
- Determine if a temporizing measure (e.g., magnet placement, transcutaneous pacing) is indicated.
Consider AICD malfunction. for unstable patients with , , , or inappropriate shocks due to
Begin for unstable patients with or .
Sensing problems 
- Undersensing: typically results in asynchronous pacing
Oversensing: the sensing of inappropriate stimuli
- PPMs: Activity other than cardiac depolarizations is sensed and the device is inhibited from delivering an appropriate pulse, resulting in bradycardia.
- AICDs: Activity other than sustained ventricular tachyarrhythmias is sensed and the device delivers an inappropriate shock.
- Causes include:
- Management of unstable patients:
Pacing problems 
- Failure to capture: results in bradycardia
- Pacemaker output failure: results in bradycardia
- Management of unstable patients:
Pacemaker-related tachycardias 
- Pacemaker-mediated tachycardia: typically occurs in dual-chamber pacemakers with atrial sensing
- Sensor-driven tachycardia: typically occurs in rate-responsive dual-chamber pacemakers
Runaway pacemaker: typically occurs in older-generation single-chamber pacemakers; rare in modern devices
- Very low battery states can result in potentially lethal rapid misfiring.
- Heart rates can surpass the maximum device limit due to programming malfunction.
- Management of unstable patients:
|Overview of acute AICD complications |
|Causes to consider||Emergency intervention|
|Lack of appropriate shocks|| |
|Inappropriate shocks (i.e., oversensing)|
- All patients: Evaluate ECGs for signs of ischemia, arrhythmia, and electrolyte derangement.
- AICDs: Evaluate current cardiac rhythm to help determine if the shock was appropriate.
- Properly placed CIEDs
- Lead displacement: e.g., pacing lead tip in the SVC, retracted RV lead in the RA
- Lead fracture: discontinuity along the expected path of the lead
- Routine laboratory studies: CBC, BMP
- Additional studies based on clinical suspicion
CIED interrogation 
- Definition: placement of an external device over a CIED pulse generator to check device function and retrieve diagnostic data
- Management: The device can be reprogrammed as required.
- Interference with MRI: Despite many CIEDs now being MRI safe, an electrophysiologist or the device manufacturer should be consulted before scanning.
- Surgical patients: Consider consulting an electrophysiologist regarding temporary CIED deactivation, as surgery involving diathermy can trigger the device to stimulate the heart unnecessarily. 
- Patient education
- Driving advice
- Education about possible interactions during medical procedures and with electronic devices 
- Discussions about device deactivation during end-of-life care
- Provision of a cardiac device wallet card and medical alert bracelet
- Regular follow-up is essential.