Bradycardia

Bradycardia (from Ancient Greek βραδύς (bradús) 'slow' and καρδία (kardía) 'heart'), also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due to asymptomatic type 1 atrioventricular block. Resting heart rates of less than 50 BPM are often normal during sleep in young and healthy adults and athletes. In large population studies of adults without underlying heart disease, resting heart rates of 45–50 BPM appear to be the lower limits of normal, dependent on age and sex. Bradycardia is most likely to be discovered in the elderly, as age and underlying cardiac disease progression contribute to its development. Bradycardia may be associated with symptoms of fatigue, dyspnea, dizziness, confusion, and syncope due to reduced blood flow to the brain. The types of symptoms often depend on the etiology of the slow heart rate, classified by the anatomical location of a dysfunction within the cardiac conduction system. Generally, these classifications involve the broad categories of sinus node dysfunction (SND), atrioventricular block, and other conduction tissue diseases. However, bradycardia can also result without dysfunction of the conduction system, arising secondarily to medications, including beta blockers, calcium channel blockers, antiarrythmics, and other cholinergic drugs. Excess vagus nerve activity or carotid sinus hypersensitivity are neurological causes of transient symptomatic bradycardia. Hypothyroidism and metabolic derangements are other common extrinsic causes of bradycardia. The management of bradycardia is generally reserved for people with symptoms, regardless of minimum heart rate during sleep or the presence of concomitant heart rhythm abnormalities (See: Sinus pause), which are common with this condition. Untreated sinus node dysfunction increases the risk of heart failure and syncope, sometimes warranting definitive treatment with an implanted pacemaker. In atrioventricular causes of bradycardia, permanent...