Sinus Bradycardia
Definition and scope
Sinus bradycardia is a rhythm originating from the sinoatrial node with a ventricular rate < 60 bpm in adults. In the emergency department the priority is to distinguish physiological/asymptomatic bradycardia from pathological/symptomatic bradycardia, identify reversible causes, and institute urgent treatment when there is haemodynamic compromise (Resuscitation Council UK).
Common causes
Sinus bradycardia may be physiological or pathological. Common groups include:
- Physiological causes: high vagal tone in athletes, sleep, vasovagal states, post‑prandial slowing, and therapeutic iatrogenic causes (beta‑blockers, some non‑dihydropyridine calcium‑channel blockers).
- Cardiac (intrinsic) causes: sick sinus syndrome (sinus node dysfunction), ischaemia (for example inferior myocardial infarction), myocarditis, infiltrative disease, and post‑cardiac surgery.
- Metabolic/endocrine/systemic causes: hypothyroidism, hypothermia, hyperkalaemia.
- Drugs and toxins: beta‑blockers, non‑dihydropyridine calcium‑channel blockers (verapamil, diltiazem), digoxin, organophosphates, opioids, and some antiarrhythmics.
- Neurological causes: raised intracranial pressure/brainstem compression (Cushing response).
Clinical presentation - when it matters
Bradycardia is clinically important when it causes inadequate cardiac output or reflects serious underlying pathology.
- Symptoms or signs suggesting pathological bradycardia include syncope or presyncope, dizziness, new or worsening breathlessness, chest pain, confusion, hypotension or signs of shock, and pulmonary oedema.