Bradycardia & Heart Block

Bradycardia is a frequent on-call review, especially overnight, and ranges from completely benign to immediately life-threatening.

Your role is not just to treat a slow heart rate, but to decide:

👉 Is this patient perfusing adequately?
👉 Is this physiological or pathological?
👉 Does this need urgent pacing?

Many unnecessary escalations happen — but equally, dangerous blocks are sometimes missed.

What counts as bradycardia?

Generally:

Heart rate <60 bpm

But clinically important bradycardia is usually:

👉 HR <50 with symptoms
or
👉 any HR causing instability

Remember: some patients normally sit at 40–50 bpm.

Rate alone does NOT determine severity.

Common causes on NHS wards

Always think broadly.

Physiological

  • Athletes
  • Sleep
  • High vagal tone

Medications (VERY common)

  • Beta-blockers
  • Digoxin
  • Amiodarone
  • Diltiazem / verapamil
  • Opioids
  • Sedatives

Always check drug chart early.

Acute medical causes

  • Inferior MI
  • Electrolyte disturbance (↑K+ especially)
  • Hypoxia
  • Hypothermia
  • Raised ICP (rare but important)
  • Sepsis (late stage)
  • Hypothyroidism

First step = A–E assessment

Do not stare at the ECG first.

Assess:

  • BP
  • Mental state
  • Chest pain
  • Breathlessness
  • Perfusion
  • Urine output

🚨 Unstable bradycardia (emergency)

Signs:

  • Hypotension
  • Syncope
  • Chest pain
  • Acute heart failure
  • Reduced consciousness
  • Shock

👉 Call senior + crash team early

This may need pacing.

Immediate investigations

  • ECG (essential)
  • Bloods:
    • U&E
    • Potassium
    • Magnesium
    • Troponin
    • TFTs (non-urgent)
  • Review medications
  • Check temperature
  • Consider ABG if unwell

ECG: recognising heart block (practical approach)

You do NOT need perfection — just recognise danger patterns.

1️⃣ Sinus bradycardia

  • Normal P before every QRS
  • Regular rhythm

Often benign.

Treat cause, not rate.

2️⃣ First-degree AV block

  • Long PR interval
  • All beats conducted

Usually harmless → observe.

3️⃣ Second-degree AV block

Mobitz I (Wenckebach)

  • Progressive PR prolongation
  • Dropped beat

Often benign.

Mobitz II ⚠️

  • Sudden dropped QRS
  • Fixed PR interval

Dangerous → may progress to complete block.

Escalate early.

4️⃣ Complete heart block (Third-degree)

  • P waves independent of QRS
  • Very slow ventricular rate

🚨 Pacing usually required

This is a cardiology emergency.

Immediate management (stable patient)

If stable:

  • Stop rate-limiting drugs
  • Correct electrolytes
  • Treat underlying cause
  • Monitor closely
  • Repeat ECG

Often no drugs needed.

Unstable bradycardia treatment (ALS principles)

First-line:

Atropine 500 micrograms IV
Repeat every 3–5 min (max 3 mg)

If atropine fails:

  • Transcutaneous pacing
  • Adrenaline infusion
  • Isoprenaline infusion

👉 ICU/CCU involvement early.

Do not manage alone.

When to call cardiology urgently

  • Mobitz II block
  • Complete heart block
  • Symptomatic bradycardia
  • Post-MI bradycardia
  • Persistent HR <40
  • Syncope related to rhythm
  • Failure to respond to atropine

Indications for urgent pacing (know these)

Think pacing if:

  • Complete heart block
  • Symptomatic high-grade AV block
  • Haemodynamic compromise
  • Asystolic pauses
  • Drug-resistant bradycardia

Common on-call mistakes

  • Treating numbers instead of symptoms
  • Missing medication causes
  • Ignoring hyperkalaemia
  • Delayed escalation in complete block
  • Over-treating asymptomatic patients
  • Not reviewing ECG personally

Always look at the ECG yourself.

Practical ward mindset

When bleeped:

“HR is 38 — please review”

Ask immediately:

  1. Are they symptomatic?
  2. Is BP okay?
  3. What does ECG show?
  4. Any rate-limiting drugs?
  5. Could this need pacing?

Take-home concept

Bradycardia is dangerous only when perfusion is affected or conduction is failing.

Assess the patient first.
Identify the rhythm.
Escalate early when conduction block is suspected.