Bradycardias

Bradycardia is a condition characterized by a slower than normal heart rate. In adults, a resting heart rate below 60 beats per minute is commonly used as a threshold, although athletes and some healthy individuals may have lower rates without symptoms. Bradycardias can arise from problems with the sinus node (sinus bradycardia), problems in conduction between the atria and ventricles (atrioventricular block), or from systemic diseases or medications that slow heart rate.

Common causes include aging of the cardiac conduction system, high vagal tone in athletes, hypothyroidism, electrolyte disturbances, hypothermia, sleep apnea, myocardial infarction, myocarditis, and medications such as digitalis, beta-blockers, or calcium channel blockers.

Symptoms vary from none to dizziness, fatigue, lightheadedness, syncope, or shortness of breath, especially if the heart cannot maintain adequate blood flow. Diagnosis relies on electrocardiography and monitoring. An ECG can show sinus bradycardia, prolonged PR interval, or varying degrees of AV block. Additional tests may include thyroid function tests, metabolic panels, or Holter monitoring.

Management depends on the cause and symptoms. In stable patients with no symptoms, observation and treatment of underlying conditions may suffice. In symptomatic or unstable bradycardia, immediate supportive care is needed, often including atropine, temporary pacing, or hemodynamic support. If drug-induced, stopping the causative medication is important. For chronic, symptomatic bradycardia or high-grade AV block, cardiovascular implantable devices such as pacemakers are commonly indicated.

Prognosis depends on the underlying cause and the presence of symptoms; proper diagnosis and treatment reduce risks of syncope and heart failure, while athletes may have benign bradycardia that requires no intervention.