Cardiac pacemakers
A cardiac pacemaker is an implantable pulse generator and lead system that senses intrinsic cardiac activity and paces whenever the heart rate falls below a programmed threshold. It treats symptomatic bradycardia and high-risk conduction disease such as complete heart block; permanent pacemaker implantation, chosen by device type and pacing mode, is definitive first-line treatment once reversible causes are excluded.
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What this article covers
- Overview
What it is: an implantable pulse generator with transvenous leads, or a self-contained leadless capsule, that senses intrinsic cardiac activity and paces whenever the native rate or conduction falls below a programmed threshold.
- Epidemiology
Typical recipient: most first-time recipients are older adults with age-related conduction system fibrosis.
- Risk factors
Age-related fibrosis: progressive fibrosis of the sinus node and His-Purkinje axis is the dominant risk factor.
- Pathophysiology
Sinus node dysfunction: age-related fibrosis of the sinoatrial node and atrial myocardium impairs impulse generation, producing sinus bradycardia, pauses, chronotropic incompetence, and, with…
- Clinical features
Symptoms: lightheadedness, presyncope or syncope, exertional intolerance, dyspnea, fatigue, and progressive heart failure reflect a rate that cannot meet demand; because the same rhythm can be…
- Differential diagnosis
Physiologic sinus bradycardia: seen in athletes and sleep, but the rate rises appropriately on exertion, unlike pathologic sinus node dysfunction.
- Diagnosis
What establishes the indication: a pacemaker is indicated once bradycardia or a conduction disturbance correlates with symptoms after reversible causes are excluded, or when the rhythm meets a Class…
- Management
First, stabilize unstable symptomatic bradycardia: atropine 0.5 mg IV every 3 to 5 minutes, maximum 3 mg.
- Complications
Early, within 30 days: vascular injury, pocket hematoma, pneumothorax, lead dislodgement, and extracardiac stimulation; later, lead fracture or insulation defect causes intermittent failure to pace or sense.
- Prognosis
Symptomatic sinus node dysfunction: pacing produces marked improvement when fatigue is truly pathologic rather than deconditioning.
- Prevention
Screen for reversible causes first: correct hypothyroidism, hyperkalemia, and offending medications, since removing the cause can obviate a permanent device.
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Related articles
- Atrioventricular blocks
Atrioventricular block is impaired conduction between atria and ventricles, graded first-degree, second-degree (Mobitz I and II), and third-degree (complete). The key distinction is nodal versus infranodal disease: Mobitz I is usually benign, whereas Mobitz II and complete block are infranodal, unstable, and require pacing.
- Bradycardia
Bradycardia is a heart rate below 60 per minute, ranging from a benign physiologic finding to symptomatic sinus node dysfunction or high-grade atrioventricular block. Management is driven by symptoms and stability: unstable patients receive atropine and then transcutaneous pacing or a chronotropic infusion, and durable symptomatic conduction disease is treated with a permanent pacemaker.
- Sinus node dysfunction
Sinus node dysfunction (sick sinus syndrome) is failure of the sinoatrial node to generate or transmit impulses appropriately, causing sinus bradycardia, pauses, arrest, or the brady-tachy syndrome. Diagnosis rests on correlating symptoms with ECG or ambulatory monitoring, and symptomatic irreversible disease is treated with a permanent pacemaker.
- Sinus bradycardia
Sinus bradycardia is a sinus rhythm below 60 per minute with normal P-wave morphology and a normal PR interval. It is most often a benign physiologic finding in fit or sleeping people, and treatment is needed only when it is symptomatic or reflects a reversible cause such as drugs, ischemia, or hypothyroidism.
- Atrial fibrillation
Atrial fibrillation is a supraventricular tachyarrhythmia with disorganized atrial activation and an irregularly irregular ventricular response, the most common sustained arrhythmia and a major cause of stroke. Diagnosis is by ECG showing no discrete P waves with irregular RR intervals, and management addresses rate or rhythm control, stroke prevention by CHA2DS2-VASc-guided anticoagulation, and the underlying cause.
- Syncope
Syncope is a transient loss of consciousness from global cerebral hypoperfusion with spontaneous complete recovery. The central task is separating benign reflex and orthostatic causes from dangerous cardiac syncope, using history, examination, and ECG, since cardiac syncope carries a risk of sudden death; treatment is directed by mechanism, from reassurance and hydration for reflex syncope to a pacemaker, ICD, or structural intervention for cardiac syncope.
- Infective endocarditis
Infective endocarditis is microbial infection of the endocardium, usually a heart valve, producing vegetations that cause valve destruction, embolism, and systemic infection. Diagnosis uses the modified Duke criteria combining blood cultures and echocardiography, and treatment is prolonged targeted intravenous antibiotics with surgery for complications.