Axis

Blocks

LAFB

• Left axis deviation (usually between -45 and -90 degrees)
• Small Q waves with tall R waves (= ‘qR complexes’) in leads I and aVL
• Small R waves with deep S waves (= ‘rS complexes’) in leads II, III, aVF
• QRS duration normal or slightly prolonged (80-110 ms)
• Prolonged R wave peak time in aVL > 45 ms
• Increased QRS voltage in the limb leads

LPFB

• Right axis deviation (> +90 degrees)
• Small R waves with deep S waves (= ‘rS complexes’) in leads I and aVL
• Small Q waves with tall R waves (= ‘qR complexes’) in leads II, III and aVF
• QRS duration normal or slightly prolonged (80-110ms)
• Prolonged R wave peak time in aVF
• Increased QRS voltage in the limb leads
• No evidence of right ventricular hypertrophy
• No evidence of any other cause for right axis deviation