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Explain this ecg
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Reading File
ECG Analysis: Left Bundle Branch Block (LBBB)
This is a teaching ECG with student annotations. Here is a full breakdown:
Technical Details
- Paper speed: 25 mm/sec | Calibration: 1 cm/mV (standard)
- Leads present: All 12 leads + rhythm strip (Lead II at bottom)
ECG Findings
| Parameter | Finding |
|---|---|
| Rate | ~75 bpm (regular) |
| Rhythm | Regular |
| Axis | Left axis deviation (Lead I positive, Leads II/III negative) |
| P waves | Difficult to isolate due to wide QRS; likely present |
| PR interval | Not reliably measurable |
| QRS duration | Markedly prolonged: ~140-160 ms (normal: 40-100 ms, written on the ECG as "QRS - 0.04 - 0.1") |
Diagnosis: Left Bundle Branch Block (LBBB)
The QRS morphology is classic:
- Lead I, aVL, V5, V6: Broad, notched, monophasic R waves - the student correctly circles the "M" shape in Lead I
- V1, V2, V3: Deep, wide QS or rS complexes - "W" shape
- Mnemonic annotated: "V1 W, V6 M" - this is part of WiLLiaM MaRRoW: LBBB = W in V1, M in V6
Secondary ST-T Changes (Normal in LBBB - "Discordance")
These are expected and do NOT indicate ischemia on their own:
- Leads with upright QRS (I, aVL, V5, V6): ST depression + T wave inversion - the student annotates "T wave -ve"
- Leads with negative QRS (V1-V3): ST elevation + upright T waves
- The student also notes "biphasic T wave" near V5/V6 - seen in the transitional zone
Answering the Written Question: "What pathological conditions can change the normal QRS interval?"
The QRS is normally 0.04-0.10 seconds (40-100 ms). Conditions that widen it beyond 120 ms:
| Cause | Mechanism |
|---|---|
| Left Bundle Branch Block (LBBB) | Depolarization must travel slowly through myocardium rather than fast conducting system |
| Right Bundle Branch Block (RBBB) | Same mechanism, right-sided |
| Wolff-Parkinson-White (WPW) | Pre-excitation via accessory pathway creates delta wave, widens QRS |
| Ventricular tachycardia / PVCs | Ectopic ventricular origin, no fast conduction |
| Ventricular paced rhythm | Pacemaker activates ventricle directly |
| Severe hyperkalemia | K+ reduces resting membrane potential, slows conduction |
| TCA overdose / Na channel blockers | Sodium channel blockade slows phase 0 depolarization |
| Severe LVH | Mild QRS widening from increased muscle mass |
Student Annotations Summary
The annotations are largely correct:
- "Left bundle branch block" - correct diagnosis
- "QRS - 0.04 - 0.1" - correct normal range
- "M" circled on Lead I - correct LBBB lateral lead morphology
- "T wave -ve" - correct discordant T wave observation
- "V1 W" and "V6 M" - correct mnemonic for LBBB
Clinical note: LBBB is always considered pathological and warrants investigation for underlying structural heart disease (cardiomyopathy, ischemic heart disease, hypertension). New-onset LBBB with chest pain is treated as a STEMI equivalent in current guidelines.
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