Bradycardia: slow heart rate, causes, diagnosis, and treatment

Characteristics and types

Bradycardia can arise from slowed impulse generation in the sinus node (sinus bradycardia) or from impaired conduction between heart chambers (atrioventricular block). Common patterns include first-degree, second-degree (Mobitz I and II), and third-degree (complete) heart block. Junctional bradycardia and idioventricular rhythms are other conduction-related variants. The electrocardiogram (ECG) is the primary tool for distinguishing these types.

Causes and risk factors

Causes range from normal physiological states to pathology. Well-trained athletes and people during sleep often have harmless, physiologic bradycardia. Pathological causes include intrinsic disease of the sinus node or conduction system, ischemic heart disease, myocarditis, electrolyte disturbances, hypothyroidism, and increased vagal tone. Certain medications and substances can slow heart rate; common examples include beta-blockers, some calcium-channel blockers, and digitalis — these are discussed broadly as medicines that may contribute to bradycardia.

Symptoms and diagnosis

Many people with mild bradycardia are asymptomatic. When symptoms occur they may include lightheadedness, fatigue, shortness of breath, exercise intolerance, chest discomfort, or syncope (fainting). Diagnosis relies on clinical history and ECG recordings. Holter monitors, event recorders, and in some cases electrophysiology testing help document intermittent or nocturnal bradycardia.

Treatment and management

Management depends on cause and severity. Asymptomatic, physiologic bradycardia often requires no treatment. Reversible factors — such as adjusting implicated medications or correcting metabolic disturbances — are addressed first. Symptomatic or high-grade conduction block may require acute measures (e.g., atropine in emergency settings) and long-term therapy such as implantation of a permanent pacemaker to restore adequate heart rate and prevent episodes of syncope.

History and notable facts

Recognition of slow heart rhythms expanded with the introduction of the electrocardiogram in the early 20th century and therapeutic pacing techniques in the mid-20th century. Today bradycardia is managed through a combination of lifestyle assessment, medication review, noninvasive monitoring, and device therapy when indicated. Distinguishing benign from pathologic bradycardia is central to appropriate care.