Cardiovascular · Year 1 · from Cardiovascular

Case 3: Left Bundle Branch Block

Patient Presentation

Demographics: 75-year-old male

Chief Complaint: Routine pre-operative evaluation

History of Present Illness: A 75-year-old male with history of hypertension and coronary artery disease (prior LAD stent 5 years ago) is undergoing pre-operative evaluation for elective hip replacement surgery. He denies chest pain, shortness of breath, palpitations, or syncope. He exercises regularly and can walk 2 miles without symptoms. His last stress test was 2 years ago and was normal.

Physical Examination:

  • Vital Signs: BP 138/82 mmHg, HR 68 bpm, RR 14/min, SpO2 98% on room air
  • General: Well-appearing, no acute distress
  • Cardiovascular: Regular rate and rhythm, paradoxically split S2, no murmurs
  • Lungs: Clear bilaterally

Workup

  • ECG Findings:
  • QRS duration: 160 ms (prolonged >120 ms)
  • Broad, notched R waves in lateral leads (I, aVL, V5-V6) - "M" pattern
  • Deep S waves in V1-V3
  • Absent septal Q waves in lateral leads
  • ST-segment and T-wave changes discordant to QRS (appropriate)
  • Left axis deviation
  • ECG Interpretation:
  • Rate: 68 bpm
  • Rhythm: Normal sinus rhythm
  • Axis: Left axis deviation (-45°)
  • Intervals: PR 180 ms, QRS 160 ms
  • Conclusion: Left bundle branch block (LBBB)
  • Comparison: New compared to ECG 2 years ago (which showed normal QRS duration)
  • Echocardiogram ordered: LVEF 40%, septal dyskinesis, mild LV dilation

Diagnosis

New left bundle branch block with newly reduced ejection fraction - requires further evaluation for ischemia

ECG Correlation: LBBB occurs when conduction through the left bundle is blocked:

  • Septal depolarization reversed: Right-to-left instead of left-to-right (loss of septal Q waves)
  • LV depolarization delayed: Impulse travels through myocardium, not Purkinje fibers
  • Prolonged QRS: >120 ms due to slow muscle conduction
  • Secondary repolarization changes: ST/T wave changes opposite to QRS direction (appropriate discordance)

Paradoxically split S2 occurs because delayed LV activation causes A2 to occur after P2. New LBBB can indicate underlying coronary artery disease, cardiomyopathy, or conduction system disease.

Treatment

  1. Cardiology consultation for new LBBB with reduced EF
  2. Stress testing unreliable for ischemia detection in LBBB → proceed to coronary angiography
  3. Initiate guideline-directed medical therapy for heart failure (ACE inhibitor, beta-blocker)
  4. Consider cardiac resynchronization therapy (CRT) if EF remains ≤35% with LBBB on optimal medical therapy
  5. Postpone elective surgery pending cardiac workup

Clinical Image

Image Description: 12-lead ECG demonstrating left bundle branch block with characteristic findings: QRS >120 ms, broad notched R waves in I, aVL, V5-V6, deep S waves in V1-V3, and appropriate discordance of ST-T changes.

Source: Wikimedia Commons - Left bundle branch block ECG License: CC BY-SA 3.0 URL: https://commons.wikimedia.org/wiki/File:LBBB_ECG.png

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