Cardiac implantable electronic devices

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 CIED malfunctions typically involves CIED interrogation and treatment of underlying or resulting arrhythmias.

See also “Implantable loop recorders” and “Mechanical circulatory support devices.”

Types of CIEDs

• Permanent pacemakers (PPMs): capable of pacing the heart to maintain an adequate heart rate in bradyarrhythmia
• Automated implantable cardioverter defibrillators (AICDs)
  • Capable of delivering shocks to terminate ventricular tachyarrhythmia
  • Transvenous AICDs are also capable of pacing the heart to maintain an adequate heart rate in bradyarrhythmia.
• 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
  • Cardiac resynchronization therapy pacemaker (CRT-P): biventricular pacemaker only
  • Cardiac resynchronization therapy defibrillator (CRT-D): biventricular pacemaker and AICD

Comparison of PPMs, ICDs, and CRTs

Structure

• 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). ^[1][2]
• Leads with electrodes for pacing, sensing, and defibrillating
  • Proximal end: connected to the pulse generator
  • Distal end: anchored to the myocardium
    • Single-chamber PPM: usually right ventricle
    • Dual-chamber PPM: right ventricle and right atrium
    • ICD: right ventricle with or without right atrium
    • CRT: right atrium, right ventricle, and coronary sinus

Basic functions

• 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.

Implantation

• 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.

Magnet placement

• Purpose: A magnet may be placed over the pulse generator for diagnostic and/or therapeutic purposes.
• Indications
  • Pacemaker-mediated tachycardia
  • Bradycardia due to oversensing
  • Asynchronous pacing due to undersensing
  • Inappropriate AICD shocks
• Device effect ^[3][4]
  • PPM and CRT-P: reverts to a fixed pacing rate
  • AICD and CRT-D
    • Disables tachyarrhythmia interventions
    • Pacing unaffected

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 temporary cardiac pacing 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
  • Combined PPM and AICD: See “Transvenous AICDs.”
  • Biventricular pacemaker: See “Cardiac resynchronization therapy.”

Functions

• All PPMs
  • Cardiac rhythm monitoring
  • Antibradycardia pacing
    • Pacing of the heart if the heart rate drops below a preset threshold
    • Achieved by delivering an electrical impulse to stimulate myocardial contraction
  • Both of the following requirements must be met for minimum PPM functioning:
    • Electrical capture: a pacemaker spike with corresponding ventricular depolarization
    • Mechanical capture: a cardiac contraction and pulse resulting from electrical capture
• Combination PPM and AICD devices: may also have antitachycardia pacing functions (see “AICDs”)

Indications for PPMs ^[5]

• Sinus node dysfunction (SND)
  • SND with symptomatic bradycardia
  • Symptomatic chronotropic incompetence
  • Symptomatic bradycardia due to tachycardia-bradycardia syndrome
  • Selected patients with sinoatrial exit block and significant symptoms
• AV block
  • High-risk AV block
  • AV block with symptomatic bradycardia
  • Permanent Afib with symptomatic bradycardia
  • Certain AV blocks resulting from neuromuscular disease or infiltrative cardiomyopathy
• Other causes of syncope: selected patients with carotid sinus syndrome

Pacemaker nomenclature ^[1][3][6]

• NBG code: PPMs and CIEDs with pacemaker function are classified using a 5-letter system
  • 1^st letter: chamber(s) that are paced, i.e., A = atrium, V = ventricle, D = dual
  • 2^nd letter: chamber(s) that are sensed, i.e., A = atrium, V = ventricle, D = dual
  • 3^rd letter: device's response to sensing native beats, i.e., I = inhibited, T = triggered, D = dual ^[6]
  • The 4^th and 5^th letters are less commonly communicated and denote device programmability and any antitachycardia pacing functions, respectively.
• Examples
  • 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 ^[1]

ECG findings depend on device type and the heart's intrinsic electrical activity.

• Pacemaker spike: a narrow upward deflection usually with an amplitude of < 5 mm
• Ventricular depolarizations that indicate electrical capture
  • Paced ventricular beats: wide QRS, often with LBBB morphology, followed by T wave
  • Ventricular depolarizations triggered by paced atrial beats: may appear normal if the His-Purkinje conduction system is intact
• 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 electrical capture can vary depending on the type of CIED.

An AICD (or ICD) is a CIED consisting of a pulse generator and leads that can sense VF and VT and deliver a shock to restore sinus rhythm.

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 ^[7]
• Combined AICD and CRT: See “CRT-D.”

Functions

Specific functions may vary by device depending on programming and patient needs.

• All AICDs
  • Cardiac rhythm monitoring
  • Delivery of an electrical shock to the myocardium
• Transvenous AICDs
  • Defibrillation
  • Synchronized cardioversion
  • Antitachycardia pacing: a pacing algorithm that paces the heart faster than the native heart rate to terminate VT without the use of an electrical shock
  • Antibradycardia pacing
• Subcutaneous AICDs: defibrillation only

All modern transvenous AICDs are capable of antibradycardia pacing in addition to synchronized cardioversion, defibrillation, and antitachycardia pacing.

Indications for AICDs ^[8]

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.

Primary prevention

Selected patients with an expected survival of > 1 year and any of the following:

• Arrhythmogenic right ventricular cardiomyopathy
• Hypertrophic obstructive cardiomyopathy (see “Treatment of HCM” for details)
• Cardiac channelopathies (e.g., congenital long QT syndrome, Brugada syndrome)
• Severe congestive heart failure (see “AICDs in heart failure” for specific indications) ^[9]
• Neuromuscular disorders (e.g., Duchenne muscular dystrophy, Becker muscular dystrophy)
• Cardiac sarcoidosis

Secondary prevention

All patients with an expected survival of > 1 year, an irreversible cause of ventricular tachyarrhythmias, and any of the following: ^[8]

• Sudden cardiac arrest (e.g., due to Vfib)
• Unstable VT
• Stable sustained VT
• Inducible VT and/or Vfib on an EP study AND underlying:
  • Unexplained syncope and ischemic heart disease
  • NSVT due to previous MI or LVEF ≤ 40%
• See “AICD for VT” for more information.

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

All CRT devices have leads implanted in the right atrium, right ventricle, and coronary sinus.

• Cardiac resynchronization therapy-pacemaker (CRT-P): biventricular pacemaker only
• Cardiac resynchronization therapy-defibrillator (CRT-D): biventricular pacemaker PLUS an AICD

All CRTs are biventricular pacemakers.

Functions

• All devices
  • Cardiac rhythm monitoring
  • Biventricular pacing (cardiac resynchronization)
    • Electrodes stimulate the right and left ventricles in a coordinated manner to achieve synchronous contractions.
    • Improves outcomes in heart failure (see “CRT in HF” for details)
• CRT-P
  • Antibradycardia pacing
  • Cardiac resynchronization
• CRT-D
  • Antibradycardia pacing
  • Cardiac resynchronization
  • Defibrillation

Indication for CRTs

• Indicated in patients with congestive heart failure who meet certain criteria, e.g., LVEF ≤ 35% and a wide QRS complex ^[9]
• See “CRT in HF” for detailed indications.

During implantation ^[10][11]

• Pneumothorax
• Hemothorax
• 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 ^[10][11]

• 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
• Upper extremity DVT
• Venous stenosis
• Infection (see “Device-related infections”)
• Twiddler syndrome (uncommon)
  • Caused by the accidental or deliberate manipulation of the pulse generator, resulting in lead coiling and retraction
  • Consequences
    • Failure to detect abnormal rhythms
    • Failure to capture
    • Stimulation of noncardiac structures (e.g., the diaphragm, pectoral muscle)
• Tricuspid valve dysfunction

Lead displacement and lead fracture are common underlying causes of various CIED malfunctions.

CIED malfunction ^[1][3]

• Related to pacing
  • Oversensing
  • Undersensing
  • Failure to capture
  • Pacemaker output failure
  • Pacemaker-related tachycardias
• Related to cardioversion
  • Lack of appropriate shock (i.e., failure to terminate Vtach or Vfib)
  • Inappropriate shocks

Pacemaker syndrome

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 dual-chamber pacemaker in patients with severe symptoms

CRT complications ^[11]

• 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 ^[1][3]

All patients

• 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 CIED interrogation, 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”).

Unstable patients

• All patients: Place defibrillator or pacing pads in AP configuration or > 10 cm from the pulse generator. ^[3]
• 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 CIED interrogation.
  • Identify the underlying CIED malfunction based on ECG and clinical evaluation, e.g., oversensing, undersensing, failure to capture, pacemaker-related tachycardia, problems with AICD shock delivery
  • Determine if a temporizing measure (e.g., magnet placement, transcutaneous pacing) is indicated.

Consider magnet placement for unstable patients with undersensing, oversensing, pacemaker-related tachycardia, or inappropriate shocks due to AICD malfunction.

Begin transcutaneous pacing for unstable patients with failure to capture or pacemaker output failure.

Sensing problems ^[3]

• Undersensing: typically results in asynchronous pacing
  • Failure to sense cardiac depolarizations, leading to the delivery of inappropriate pulses
  • Causes
    • Mechanical: lead displacement, lead fracture, battery depletion
    • Conditions that affect native impulses: e.g., MI, electrolyte abnormalities, antiarrhythmics, fibrosis at the lead-myocardial interface
• 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:
    • Lead displacement or lead fracture
    • Other cardiac activity: e.g., large T waves, atrial arrhythmias
    • Large myopotentials
    • Electromagnetic interference
• Management of unstable patients: magnet placement

Pacing problems ^[3]

• Failure to capture: results in bradycardia
  • Presence of pacemaker spikes without mechanical capture
  • Causes
    • Mechanical: lead displacement, lead failure, battery depletion
    • Conditions that affect the capture threshold: e.g., electrolyte abnormalities, antiarrhythmics, cardiomyopathy, MI, fibrosis at the lead-myocardial interface
• Pacemaker output failure: results in bradycardia
  • Failure of the pulse generator to generate pacing spikes when expected
  • Causes: lead displacement, lead fracture, battery depletion, electromagnetic interference
• Management of unstable patients: transcutaneous pacing

Pacemaker-related tachycardias ^{[12][13][14][15]}

• Pacemaker-mediated tachycardia: typically occurs in dual-chamber pacemakers with atrial sensing
  • Reentry tachycardia: A retrograde P wave is sensed by the atrial lead triggering a paced ventricular beat, which recreates another retrograde P wave, triggering an endless loop.
  • Cause: The first retrograde P wave is most commonly triggered by a premature ventricular contraction.
• Sensor-driven tachycardia: typically occurs in rate-responsive dual-chamber pacemakers
  • Sensors track and conduct false stimuli, leading to inappropriate tachycardia.
  • Heart rates remain under maximum device limit.
• 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: magnet placement

Cardioversion problems

Repeated AICD shocks may be appropriate, e.g, in patients with recurrent VT or electrical storm. Begin initial management of Vtach in these patients.

Diagnostics

ECG

• All patients: Evaluate ECGs for signs of ischemia, arrhythmia, and electrolyte derangement.
• PPMs
  • Evaluate for paced rhythm.
  • Compare ECG morphologies to prior ECGs, if available.
  • Use the modified Sgarbossa criteria to assess for myocardial infarction in paced rhythms.
• AICDs: Evaluate current cardiac rhythm to help determine if the shock was appropriate.

Chest x-ray

• Evaluation
  • Identify the CIED type: Determine the number of leads, locations, and whether shock coils are present.
  • Assess the pulse generator and leads for fracture or displacement.
  • Compare with previous chest x-rays, if available.
• Findings
  • Properly placed CIEDs
    • Single-chamber pacemaker or AICD : one electrode lead in the RA or RV
    • Dual-chamber pacemaker or AICD : two electrode leads, one in the RA and one in the RV
    • Biventricular pacemaker : three electrode leads, one in the RA, one in the RV, and one in the coronary sinus for LV pacing
  • 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

In contrast to pacemaker leads, AICD leads have thick shock coils that are visible on x-ray.

Laboratory studies

• Routine laboratory studies: CBC, BMP
• Additional studies based on clinical suspicion
  • Clinical features of ACS: high-sensitivity troponin
  • Clinical features of heart failure: BNP
  • Suspected device-related infection: See “Cardiac devices” in “Device-related infections.”

CIED interrogation ^[1][3]

• Definition: placement of an external device over a CIED pulse generator to check device function and retrieve diagnostic data
• Indications
  • All symptomatic patients: e.g., those with worsening cardiac function
  • Suspected device malfunction
  • Evidence of intrinsic dysrhythmia on ECG
  • Repeated AICD shocks
  • Before and after procedures with a risk of electromagnetic interference (e.g., MRI)
• Management: The device can be reprogrammed as required.

Disposition ^[1]

• PPMs
  • Admit patients with suspected device-related infection or significant device malfunction (e.g., lead fracture, battery depletion).
  • Discharge patients with reassuring CIED interrogation and an alternative cause of the symptoms.
• AICDs
  • Admit patients with multiple shocks confirmed by interrogation or single shocks thought to be secondary to myocardial infarction or heart failure.
  • Discharge all other patients with a single shock confirmed by interrogation after discussion with cardiology and expedited follow-up.

• 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. ^[17]
• Patient education
  • Driving advice
  • Education about possible interactions during medical procedures and with electronic devices ^[18][19]
• 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.