Signs and symptoms: 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.
Bradycardia is not necessarily problematic. People who regularly practice
sports may have sinus bradycardia, because their trained hearts can pump enough
blood in each contraction to allow a low resting heart rate.
Sinus bradycardia is a sinus rhythm of less than 60 bpm. It is a common
condition found in both healthy individuals and those who are considered well
conditioned athletes.
Causes: This rhythm may be caused by one of the following:
o Increased vagal tone.
o Sleep
o Hypothermia
o Hypothyroidism
o Intrinsic disease of the SA node (E.g. sick sinus syndrome).
o An effect of drugs, such as the use of digitalis, beta-blockers, quinidine, Adenosine, Calcium channel blocker.
o Seizure.
o It could also be a normal finding in a healthy, well-conditioned person.
o It may be secondary to infections like Diphtheria, acute rheumatic fever, viral myocarditis.
o Increased intracranial pressure.
o Rhodotoxin poisoning.
Diagnosis: ECG Characteristics
• Rate: Less than 60 beats per minute.
• 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.
Reference:
1. Davidson’s Principle and Practice of Medicine, 21st edition.
2. Wikipedia the free encyclopedia.
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