🫀 FREE MSRA PODCAST – Atrioventricular (AV) Block: Types, Causes, and ECG Pearls
Today’s deep dive is all about heart block, also known as AV block — a classic MSRA topic!
Learn to distinguish the three types, understand the underlying mechanisms, and lock in the essential ECG patterns with memory tricks and clinical context.
🧠 Episode Summary:
🔌 What is AV Block?
A conduction abnormality where electrical signals from the atria to the ventricles are delayed or blocked.
Can be mild and silent or life-threatening depending on the degree.
⚡ **The Three Degrees (Mnemonic: “1 is slow, 2 drops, 3 disconnects”):
1️⃣ First-Degree:
• Constantly prolonged PR interval >0.2s
• Usually asymptomatic
• Often doesn’t need treatment
2️⃣ Second-Degree (Mobitz Type I – Wenckebach):
• Progressive PR lengthening → dropped beat
• Mnemonic: Wenckebach walks away
• Often benign but may cause symptoms
2️⃣ Second-Degree (Mobitz Type II):
• Fixed PR interval with sudden dropped QRS
• More serious — risk of progression to complete block
• Needs pacemaker
3️⃣ Third-Degree (Complete AV Block):
• No relationship between P waves and QRS
• Atria and ventricles beat independently
• Ventricular escape rhythm (slow!)
• Requires urgent pacemaker
📉 Causes of AV Block (Mnemonic: DAMAGED):
• D – Drugs (beta-blockers, CCBs, digoxin)
• A – Ageing (degeneration of conduction fibres)
• M – Myocardial infarction (esp. inferior MI)
• A – Autoimmune diseases (SLE, sarcoid, Lyme)
• G – Genetics (congenital AV block)
• E – Electrolytes (hyperkalaemia, hypermagnesaemia)
• D – Disease (cardiomyopathy, myocarditis, endocarditis)
🩺 Diagnosis & Investigations:
• 📈 ECG – cornerstone: look for PR intervals, dropped beats, AV dissociation
• 🕒 Holter monitor – for intermittent blocks
• 🧪 Bloods – check electrolytes, rule out drug toxicity or inflammation
• 🫀 Echo – assess structural heart disease
• 🧬 EPS – for unclear or high-grade cases
💉 Management:
• 👀 First-Degree + asymptomatic → Observation
• ⚠️ Mobitz II + Third-Degree → Pacemaker required
• 🔍 Address underlying cause (e.g. stop offending drugs, treat Lyme disease, manage MI)
🚨 Complications if Untreated:
– 💢 Bradycardia
– 🌀 Syncope and falls
– ⚡ Sudden cardiac death
– 💔 Heart failure and poor cardiac output
🧠 Exam Tip:
Spot the difference between Mobitz I vs II on the ECG.
Use the phrase:
“Wenckebach walks away (PR gets longer), Mobitz II stays steady and drops suddenly.”
📎 More MSRA resources on Atrioventricular Block:📖 Revision Notes: https://www.passthemsra.com/topic/atrioventricular-block-revision-notes/
🧠 Flashcards: https://www.passthemsra.com/topic/atrioventricular-block-flashcards/
💬 Accordion Q&A: https://www.passthemsra.com/topic/atrioventricular-block-accordion-qa-notes/
🔗 Topic Page: https://www.passthemsra.com/?post_type=sfwd-topic&p=23536&preview=true
🌐 Main Site: https://passthemsra.com
🎁 Free Resources: https://freemsra.com
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