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ECG - Left Bundle Branch Block LBBB
Related Subjects: |ECG Basics |ECG Axis |ECG Analysis |ECG LAD |ECG RAD |ECG Low voltage |ECG Pathological Q waves |ECG ST/T wave changes |ECG LBBB |ECG RBBB |ECG short PR |ECG Heart Block |ECG Asystole and P wave asystole |ECG QRS complex |ECG ST segment |ECG: QT interval |ECG: LVH |ECG RVH |ECG: Bundle branch blocks |ECG Dominant R wave in V1 |ECG Acute Coronary Syndrome |ECG Crib sheets
📖 About
- 📉 ECG: Left Bundle Branch Block (LBBB)
- ⚠️ Usually pathological and warrants further assessment
- 🫀 Left bundle branch supplies the left ventricle
🧬 Aetiology (mechanism)
- ➡️ Right ventricle depolarises first
- ⬅️ Left ventricle depolarises second (via slower myocyte-to-myocyte conduction)
- ⏱️ Total depolarisation is delayed ➝ widened QRS complex
📊 ECG Appearance
- ⏱️ QRS duration > 0.12 s (≥3 small squares)
- 📉 Deep S wave with “W” pattern in V1–V3
- 📈 RsR’ with “M” pattern in V6
- 🧠 Aide memoire: WI(LL)IAM (W in V1, M in V6 for LBBB)
⚠️ Important: A new LBBB with chest pain is a STEMI equivalent ➝ treat as an emergency.
Prolonged QRS, absent q wave in V5/V6, with prominent ST-T changes
🩺 Causes of LBBB
- ❤️ Acute MI (STEMI/NSTEMI), Ischaemic heart disease
- 💪 Left Ventricular Hypertrophy (LVH)
- 🔒 Aortic valve disease (esp. aortic stenosis)
- 🔥 Myocarditis
- 🫀 Cardiomyopathies (dilated, hypertrophic)
- ⚡ Right ventricular pacemaker
🩻 Clinical Features
- ⏳ Delayed LV activation ➝ asynchronous contraction
- 🔊 A2 closes after P2 ➝ paradoxical splitting of the 2nd heart sound (heard on expiration)
- 📉 Often associated with impaired LV systolic function
🛠️ Management
- 📋 Usually pathological ➝ investigate for underlying structural or ischaemic heart disease
- 🚨 New LBBB + chest pain = STEMI equivalent ➝ urgent reperfusion pathway
- 🔍 Chronic/asymptomatic LBBB: consider echocardiogram to assess LV function
💡 Teaching Pearls
✔️ LBBB makes interpretation of ST segments/T waves difficult - standard STEMI criteria cannot be applied. ✔️ Use Sgarbossa criteria if suspecting STEMI in a patient with LBBB. ✔️ Chronic LBBB is strongly linked with LV dysfunction and may be an indication for cardiac resynchronisation therapy (CRT).
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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