ECG Case 114: Atrial Fibrillation with LBBB

ECG Interpretation

  • Broad complex tachycardia
  • Irregular rhythm, rate 130–200/min
  • No clear P waves but irregular baseline, best seen in lead VL
  • QRS complex duration 160 ms, with ‘M’ pattern in lead V6, indicating left bundle branch block (LBBB)

Atrial fibrillation with LBBB
Atrial fibrillation with LBBB

Clinical Interpretation

The marked irregularity of rhythm, coupled with the irregular baseline glimpsed in one beat in lead VL, shows that this is atrial fibrillation with LBBB.

Criteria for Discriminating Ventricular Tachycardia from SVT with Aberration
Criteria for Discriminating Ventricular Tachycardia from SVT with Aberration

What to do ?

Aortic valve disease is commonly associated with LBBB. An echocardiogram is needed, to ensure that there is no significant aortic stenosis – in which case vasodilators must be used with extreme caution.

The heart failure can be treated with diuretics, and digoxin will control the ventricular rate. Even at the age of 80 years, aortic valve replacement might be considered.