Sinus rhythm with a rate that is lower than normal
Medical condition
Sinus bradycardia is a sinus node dysfunction giving a heart rate that is lower than the normal 60100 beats per minute (bpm) in humans. Bradycardia is generally defined to be a heart rate of under 60 bpm.[1][2]
The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope.[3] The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms.
Bradycardia is not necessarily problematic. People who practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate.[4] Sinus bradycardia can also be an adaptive advantage; for example, diving seals may have a heart rate as low as 12 beats per minute, helping them to conserve oxygen during long dives.[5]
Sinus bradycardia is a common condition found in both healthy individuals and those who are considered well-conditioned athletes.[6]
Heart rates considered bradycardic vary by species; for example, in the house cat, a rate of under 120 beats per minute is abnormal. Generally, smaller species have higher and larger species lower rates.[7]
Diagnosis of sinus bradycardia can be confirmed by an electrocardiogram that shows the following characteristics:[1]
Taking a thorough medical history and physical exam by healthcare providers can also help with narrowing differential diagnosis. Any recent changes to patient's medication history, new symptoms such as chest pain, shortness of breath and palpitations, family history of sinus bradycardia, physical exam that reveals cyanosis, peripheral edema, altered mental status, dyspnea, rales and crackles are all relevant information to consider for differential diagnosis.[1]
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