Makindo Medical Notes

Sinus bradycardia is a slow but regular heart rhythm originating from the sinoatrial (SA) node. A heart rate below 60 beats per minute is considered bradycardic, although it may be a normal finding in well-trained athletes or during sleep. In other contexts, it can cause symptoms such as presyncope or syncope.

About

• Severe sinus bradycardia can lead to reduced cardiac output, potentially causing dizziness, presyncope, or syncope.

ECG Features

• There is a P wave before every QRS complex, indicating sinus rhythm.
• P wave and QRS complexes occur at a rate of less than 60 beats per minute.

Common Causes

• Physiological: Increased vagal tone in athletes, during sleep, or in young, healthy individuals.
• Cardiac Ischaemia: Inferior wall ischaemia/infarction can impact the SA node’s function.
• Medications: Digoxin, beta-blockers, and certain calcium channel blockers (e.g., diltiazem, verapamil), especially when used in combination, can lower heart rate.
• Metabolic/Endocrine Disorders: Hypothyroidism and cholestatic jaundice can contribute to bradycardia.
• Neurological Factors: Raised intracranial pressure may lead to a reflex bradycardia alongside hypertension (Cushing’s triad).
• Other: Elderly patients may develop bradycardia due to sick sinus syndrome or hypothermia.

Investigations

• Immediate Assessment: 12-lead ECG to confirm sinus bradycardia and look for ischaemic changes; check troponin levels if ischaemia is suspected.
• Laboratory Tests: U&E (electrolytes), LFTs (liver function tests), and TFTs (thyroid function tests) to identify reversible metabolic or endocrine causes.

Management

• Asymptomatic or Mild Cases: No treatment may be necessary if bradycardia is physiological (e.g., in athletes) or if the patient is stable and without symptoms.
• Identify and Remove Reversible Causes: Review medications that can slow the heart rate and discontinue or adjust as necessary. Correct metabolic or endocrine disturbances.
• If Symptomatic (Presyncope/Syncope):
  • Ensure patient safety: Have them lie flat, elevate their legs, and check blood pressure.
  • Atropine IV may be given to increase heart rate if they are haemodynamically compromised.
  • Check and correct electrolyte imbalances.
  • Consider IV isoprenaline (isoproterenol) infusion or temporary pacing if the patient does not respond to initial measures.
• Acute Coronary Syndrome: If chest pain or ischaemic ECG changes are present, urgent coronary intervention (PCI) may be required.