Bradycardia

Bradycardia
Other names	Bradyarrhythmia, brachycardia
Sinus bradycardia seen in lead II with a heart rate of about 50BPM
Pronunciation	/ˌbrædɪˈkɑːrdiə/
Specialty	Cardiology
Diagnostic method	electrocardiogram
Frequency	15% (males), 7% (females)

Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM).^[1] While bradycardia can result from various pathologic processes, it is commonly a physiologic 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.^[2] 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.^[3][4] Bradycardia is most likely to be discovered in the elderly, as age and underlying cardiac disease progression contribute to its development.^[5]

Bradycardia may be associated with symptoms of fatigue, dyspnea, dizziness, confusion, and frank syncope due to reduced forward blood flow to the brain, lungs, and skeletal muscle.^[6] The types of symptoms often depend on the etiology of the slow heart rate, classified by the anatomic location of a dysfunction within the cardiac conduction system.^[2] Generally, these classifications involve the broad categories of sinus node dysfunction (SND), atrioventricular block, and other conduction tissue diseases.^[7] However, bradycardia can also result without dysfunction of the native conduction system, arising secondary 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.^[6]

The management of bradycardia is generally reserved for patients 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.^[6] Untreated SND has been shown to increase the future risk of heart failure and syncope, sometimes warranting definitive treatment with an implanted pacemaker.^[8][7] In atrioventricular causes of bradycardia, permanent pacemaker implantation is often required when no reversible causes of disease are found.^[6][2] In both SND and atrioventricular blocks, there is little role for medical therapy unless a patient is hemodynamically unstable, which may require the use of medications such as atropine and isoproterenol and interventions such as transcutenous pacing until such time that an appropriate workup can be undertaken and long term treatment selected.^[2] While asymptomatic bradycardias rarely require treatment, consultation with a physician is recommended, especially in the elderly.^{[citation needed]}

The term "relative bradycardia" can refer to a heart rate lower than expected in a particular disease state, often a febrile illness.^[9] Chronotropic incompetence (CI) refers to an inadequate rise in heart rate during periods of increased demand, often due to exercise, and is an important sign of SND and an indication for pacemaker implantation.^[7][2]

The word "bradycardia" is from the Greek βραδύς bradys "slow", and καρδία kardia "heart".^[10]