Makindo Medical Notes

🫀 Sinus bradycardia is a slow but regular rhythm from the sinoatrial (SA) node, defined as HR < 60 bpm. It can be a benign, physiological finding (e.g., in athletes or during sleep) but in other contexts may reduce cardiac output, causing dizziness, presyncope, or syncope. Always distinguish between normal adaptation and pathological bradycardia.

📌 About

• Severe sinus bradycardia may impair cardiac output → dizziness, hypotension, presyncope, syncope.
• In elderly patients, may represent sick sinus syndrome 🧓.
• Can be transient (sleep, high vagal tone) or persistent (structural heart disease, drugs).

📉 ECG Features

• Regular sinus rhythm: P wave precedes every QRS.
• Rate < 60 bpm (may drop to 30–40 bpm in sleep or athletes).
• PR interval normal unless concomitant AV nodal disease.

⚠️ Common Causes

• Physiological: ↑ vagal tone (athletes 🏃, sleep 💤).
• Ischaemia: Inferior MI → SA node dysfunction.
• Medications: Digoxin, beta-blockers, verapamil, diltiazem.
• Metabolic/Endocrine: Hypothyroidism 🦋, cholestatic jaundice, electrolyte disturbances (esp. ↑K⁺).
• Neurological: Raised ICP → Cushing’s reflex (HTN + bradycardia + irregular breathing).
• Other: Hypothermia ❄️, sick sinus syndrome in elderly.

🧪 Investigations

• Bedside: 12-lead ECG (to confirm sinus origin, exclude heart block, look for ischaemia).
• Bloods: U&E, TFTs, LFTs, troponin if ACS suspected.
• Other: Holter monitor if intermittent; consider echocardiography if structural disease suspected.

🩺 Management

• Asymptomatic: No treatment if physiological or mild (e.g., in athletes).
• Address Reversible Causes: Stop rate-limiting drugs, correct metabolic/endocrine abnormalities.
• Symptomatic (presyncope/syncope, hypotension):
  • Place patient flat, elevate legs → optimise preload.
  • Atropine IV (first-line if haemodynamically unstable).
  • If refractory → IV isoprenaline, dopamine, or temporary pacing ⚡.
  • Correct electrolytes (esp. K⁺, Mg²⁺, Ca²⁺).
• Acute Coronary Syndrome: Treat as ACS → PCI if indicated.
• Chronic Symptomatic Cases: Consider permanent pacemaker implantation (esp. sick sinus syndrome).

💡 Teaching Pearls: - Always check for **drug causes** (digoxin, BB, CCB). - In ACS, sinus bradycardia may be vagally mediated or due to inferior MI. - **Athletic bradycardia** is normal if asymptomatic and with normal chronotropic response to exercise. - Symptomatic bradycardia in the elderly often → pacemaker.