❤️ CardiologyCardiovascularStudentInternResident

Symptomatic Bradycardia & Heart Block

Also known as: bradyarrhythmia · complete heart block · AV block

A slow heart rate or atrioventricular conduction block causing symptoms — dizziness, syncope, fatigue or heart failure. Complete (third-degree) heart block is dangerous and may need pacing.

Source · Reviewed 2026-08-15 · v1.0— AI-assisted draft — verify against the cited guideline before clinical use.

⚕️ Education only — not medical advice. Verify against the latest official guideline and your local protocol; confirm every drug dose against the cited source before clinical use.

Who gets it

Degenerative conduction disease (elderly), ischaemia/MI (especially inferior), drugs (beta-blockers, calcium blockers, digoxin), electrolyte disturbance, high vagal tone and hypothyroidism.

Red flags — escalate / refer

Haemodynamic instability, syncope, ischaemic chest pain, heart failure, or Mobitz II / complete heart block → urgent, prepare to pace.

Work-up / diagnosis

1A 12-lead ECG to classify the block (first-degree, Mobitz I/II, third-degree) with continuous monitoring.
2Electrolytes, thyroid function, a drug review and assessment for ischaemia (troponin).

Management — overview

Treat reversible causes — stop the offending drug, correct electrolytes, treat ischaemia.
Unstable → IV atropine first, then a chronotropic infusion or transcutaneous/transvenous pacing.
Mobitz II and complete heart block usually need pacing (temporary then permanent).

In-depthFull dosing & advanced protocol

Drug dosing

IV atropine

First drug for unstable bradycardia

Adult dose: Per resuscitation protocol
Route: Intravenous

Caution: Often ineffective in Mobitz II/complete block (block is below the AV node) — pace.

ICMRStandard Treatment Workflows (STWs), India — Dept. of Health Research & ICMR (2022+) ↗

Chronotropic infusion / pacing

Bridge to, or definitive, pacing

Adult dose: Isoprenaline/adrenaline infusion; transcutaneous then transvenous pacing
Route: IV / device

WHOWHO Model List of Essential Medicines (electronic EML) (2025 (24th)) ↗

Know when atropine won't work

In infranodal block (Mobitz II, complete block) atropine usually fails — move to pacing.
Inferior-MI-related block is often transient; anterior-MI block is ominous.
A wide-complex escape rhythm is slow and unreliable.

ICMRStandard Treatment Workflows (STWs), India — Dept. of Health Research & ICMR (2022+) ↗

References

Guidelines change. If something here is out of date, tell us — we keep these current.

🚩 Report outdated / suggest update

More protocols

Acute Coronary Syndrome (incl. STEMI)Acute myocardial ischaemia — STEMI, NSTEMI or unstable angina. STEMI needs immediate reperfusion: “time is muscle”.Acute Heart FailureRapid onset or worsening of heart-failure symptoms — breathlessness, orthopnoea and oedema, often with pulmonary congestion. Relieve congestion and find the trigger.Hypertensive EmergencySevere blood-pressure elevation (usually >180/120 mmHg) WITH acute target-organ damage (brain, heart, kidney, retina). Needs controlled IV lowering — distinct from asymptomatic severe hypertension ('urgency').

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👤 Who gets it

🚩 Red flags — escalate / refer

🔎 Work-up / diagnosis

🧭 Management — overview

💊 Drug dosing

IV atropine

Chronotropic infusion / pacing

📈 Know when atropine won't work

📚 References

More protocols

👤 Who gets it

🚩 Red flags — escalate / refer

🔎 Work-up / diagnosis

🧭 Management — overview

💊 Drug dosing

IV atropine

Chronotropic infusion / pacing

📈 Know when atropine won't work

📚 References

More protocols

Who gets it

Red flags — escalate / refer

Work-up / diagnosis

Management — overview

Drug dosing

Know when atropine won't work

References

Who gets it

Red flags — escalate / refer

Work-up / diagnosis

Management — overview

Drug dosing

Know when atropine won't work

References