When heart rate is less than 60/min in sinus rhythm.

Causes of Sinus Bradycardia

1. Physiological (due to increased vagal tone)—

–– Athlete.
–– Sleep.
–– Occasionally, healthy elderly.

2. Pathological—

–– Hypothyroidism.
–– Hypothermia.
–– Raised intracranial pressure.
–– Drugs (digoxin, β-blockers, verapamil).
–– Acute inferior myocardial infarction.
–– Obstructive jaundice.
–– Sick sinus syndrome.
–– Electrolyte imbalance (hypokalemia).

Causes of Bradycardia

• Sinus bradycardia due to any cause.
• Sick sinus syndrome.
• Second degree heart block (Mobitz type II).
• Complete heart block.
• Nodal rhythm.
• Idioventricular rhythm.
• Drugs (β-blocker, digoxin).
ECG Findings
• Heart rate—<60/minute.
• P, QRS and T- normal.
• Rhythm—regular.


Treatment of primary cause.