is a heart rhythm that originates from the sinus node and has a rate of under 60bpm.
- This rhythm may be caused by one of the following:
- Rate: Less than 60.
- Rhythm: Regular.
- P waves: Upright, consistent, and normal in morphology and duration.
- P-R Interval: Between 0.12-0.20 seconds in duration.
- QRS Complex: Less than 0.12 seconds in width, and consistent in morphology.
The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope. The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms.
Sinus Bradycardia is not necessarily a bad symptom. People who regularly practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction.
Sinus Bradycardia can aid in the sport of Freediving, which includes any of various aquatic activities that share the practice of breath-hold underwater diving. Bradycardia aids in this process due to drop in blood rate pulse. These adaptations enable the human body to endure depth and lack of oxygen far beyond what would be possible without the mammalian diving reflex.