Bradycardia (aka bradyarrhythmia) is a slow heart rate
Dx
Resting HR<60bpm in adults
Relative bradycardia is heart rate that, although not actually below 60bpm, is still considered too slow for the patient's current medial condition
Sx
Usually asymptomatic, until the rate is <50bpm
Fatigue
Weakness
Diziness
Fainting, at very low rates
Cause
Physiological:
During sleep, a slow HR between 40-50bpm is common and considered normal
Highly trainted athletes may have athletic heart syndrome, a very slow resting HR that occurs due to sport adaptation, and helps prevent tachycardia during training
Cardiac, which includes Acute/chronic ischemic heart disease, Vascular heart disease, Valvular heart disease, or Degenerative primary electrical disease. Causes include:
Disorders of the SA node (aka sick sinus syndrome), which may have disordered automaticity or impaired conduction of the impulse from the sinus node into the surrounding atrial tissue (an exit block).
Disorders of the AV node, which may have impaired conduction in the AV node, or anywhere below it (e.g. Bundle of His). AV blocks are clinically more significant than SA blocks
Noncardiac, including:
Drugs, including beta blockers, which can slow the heart rate and decrease how forcefully it contracts
Recretional drug use/abuse
Metabolic or endocrine issues, especially in the thyroid
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