Cardiology > Pacemakers and Implantable Cardioverter-Defibrillators 

Background 

I) Definition 

A pacemaker is an implantable medical device that delivers electrical impulses to the heart to maintain an adequate heart rate and rhythm in patients with bradyarrhythmias or conduction system disease. It functions by sensing intrinsic cardiac electrical activity and stimulating the myocardium when it fails to generate or conduct impulses effectively. Modern devices can be single-chamber, dual-chamber, or biventricular (cardiac resynchronization therapy, CRT), depending on the indication. 

II) Classification/Types 

By Number of Chambers: 

• • Single-chamber: One lead in the right atrium or ventricle 

• • Dual-chamber: Leads in both the right atrium and right ventricle 

• • Biventricular (CRT): Leads in the right atrium, right ventricle, and coronary sinus for left ventricular pacing 

By Mode of Function (NBG Code): 

• • AAI, VVI, DDD, etc., where: 

• • First letter: Chamber paced (A=atrium, V=ventricle, D=dual) 

• • Second letter: Chamber sensed 

• • Third letter: Response to sensing (I=inhibited, T=triggered, D=dual) 

By Indication: 

• • Permanent pacemaker (PPM): Long-term rhythm support 

• • Temporary pacemaker: Short-term support in acute settings 

• • Implantable cardioverter-defibrillator (ICD) with pacing: For patients at risk for sudden cardiac death 

Pathophysiology 

The heart’s native conduction system may be compromised due to aging, ischemia, fibrosis, or congenital defects. Pacemakers restore synchronous contraction by replacing or supplementing intrinsic electrical activity. Dysfunction can arise if the device fails to detect (sense) intrinsic activity or fails to depolarize (capture) the myocardium after a stimulus. Both scenarios can result in bradycardia, hypotension, or syncope, necessitating urgent evaluation and intervention. 

Epidemiology 

• • Over 200,000 pacemakers are implanted annually in the U.S. 

• • Prevalence increases with age, especially >70 years 

• • Sick sinus syndrome and atrioventricular (AV) block are the most common indications 

• • Pacemaker malfunction occurs in ~5–10% of patients over the device’s lifetime 

Etiology 

I) Indications for Pacing 

• • Symptomatic sinus node dysfunction 

• • High-grade AV block (Mobitz type II, complete heart block) 

• • Bifascicular block with syncope 

• • Chronotropic incompetence 

• • Post-cardiac surgery conduction delays 

• • Heart failure with electrical dyssynchrony (CRT) 

II) Causes of Pacemaker Dysfunction 

Failure to Sense: 

• • Lead dislodgment 

• • Improper lead placement 

• • Lead fracture 

• • Low intrinsic signal amplitude 

• • Oversensing of muscle activity or artifacts 

Failure to Capture: 

• • Lead dislodgment 

• • Fibrosis at lead-myocardial interface 

• • Battery depletion 

• • Low output settings 

• • Electrolyte disturbances (e.g., hyperkalemia) 

• • Drug toxicity (e.g., Class I/III antiarrhythmics) 

Other Malfunctions: 

• • Oversensing (e.g., electromagnetic interference, myopotentials) 

• • Undersensing (missing intrinsic beats) 

• • Battery depletion or generator failure 

• • Twiddler’s syndrome (patient manipulation of device) 

Clinical Presentation 

I) History (Symptoms) 

• • Fatigue, dizziness, lightheadedness 

• • Palpitations or irregular heartbeat 

• • Syncope or near-syncope 

• • Exertional intolerance 

• • Intermittent chest discomfort 

II) Physical Exam (Signs) 

• • Bradycardia or pauses on pulse exam 

• • Irregular heart rhythm 

• • Cannon A waves in neck (AV dyssynchrony) 

• • Device pocket tenderness (infection) 

• • EKG showing failure to pace, sense, or capture 

Differential Diagnosis (DDx) 

• • Sinus node dysfunction or AV block without device failure 

• • ICD malfunction or shock delivery issues 

• • Myocardial infarction or ischemia 

• • Electrolyte abnormalities 

• • Vasovagal syncope 

• • Medication-induced bradycardia (e.g., beta blockers) 

Diagnostic Tests 

Initial Work-Up 

• • 12-lead ECG: Assess pacing spikes, capture, and sensing 

• • Chest X-ray: Lead positioning, pneumothorax 

• • Device interrogation: Analyze lead impedance, thresholds, battery status 

• • Labs: Electrolytes, renal function, digoxin level 

• • Telemetry monitoring: Continuous rhythm assessment 

Advanced Testing 

• • Echocardiography: Evaluate chamber size, function, and dyssynchrony 

• • Holter monitoring: Intermittent malfunction 

• • Electrophysiologic testing: Unexplained syncope or complex arrhythmia 

Treatment 

I) Acute Management 

• • For symptomatic bradycardia (failure to pace/capture): 

• • • Atropine 0.5 mg IV q3–5 min (max 3 mg) 

• • • Transcutaneous pacing or transvenous temporary pacing 

• • • Correct underlying cause: electrolytes, drug toxicity 

• • For device malfunction: 

• • • Emergency device interrogation 

• • • Reprogram pacemaker settings 

• • • Replace battery or leads if malfunction confirmed 

II) Chronic Management 

• • Reposition or replace dislodged or fractured leads 

• • Optimize pacing thresholds 

• • Device reprogramming for undersensing or oversensing 

• • Upgrade to CRT if indicated in heart failure 

Medications 

Device Therapy 

• • Permanent Pacemaker (PPM): For bradyarrhythmias and conduction block 

• • Cardiac Resynchronization Therapy (CRT): For heart failure with LBBB and low EF 

• • ICD-Pacemakers: For combined pacing and sudden death prevention 

• • Leadless pacemakers: Newer option for selected patients with fewer complications 

Patient Education, Screening, Vaccines 

• • Avoid electromagnetic interference (strong magnets, MRI unless MRI-safe) 

• • Educate on recognizing signs of device failure 

• • Inform about battery lifespan and routine follow-ups 

• • Encourage lifestyle changes to reduce cardiac burden 

• • Ensure up-to-date vaccinations to prevent cardiac infections 

Consults/Referrals 

• • Electrophysiology: For device implantation and troubleshooting 

• • Cardiology: For underlying structural heart disease or heart failure 

• • Infectious Disease: In case of device-related infections 

• • Surgery: For extraction of infected or malfunctioning devices 

Follow-Up 

Short-Term 

• • Device interrogation within weeks of implant 

• • Monitor for lead dislodgment or early complications 

• • Evaluate wound healing at pocket site 

Long-Term 

• • Routine device checks every 3–12 months 

• • Monitor battery life and pacing thresholds 

• • Regular EKGs and symptom tracking 

• • Periodic imaging to assess cardiac function 

Prognosis 

• • Excellent long-term outcomes with appropriate device placement and management 

• • Most patients regain normal activity and quality of life 

• • Malfunction is rare but potentially serious—prompt identification and correction are key 

• • CRT has been shown to reduce mortality and hospitalizations in heart failure