Using leads I and aVF the axis can be calculated to within one of the four quadrants at a glance.

If the axis is in the "left" quadrant take your second glance at lead II.

• both I and aVF +ve = normal axis
• both I and aVF -ve = axis in the Northwest Territory
• lead I -ve and aVF +ve = right axis deviation
• lead I +ve and aVF -ve
  • lead II +ve = normal axis
  • lead II -ve = left axis deviation

causes of a Northwest axis (no man's land)

• emphysema
• hyperkalaemia
• lead transposition
• artificial cardiac pacing
• ventricular tachycardia

causes of right axis deviation

• normal finding in children and tall thin adults
• right ventricular hypertrophy
• chronic lung disease even without pulmonary hypertension
• anterolateral myocardial infarction
• left posterior hemiblock
• pulmonary embolus
• Wolff-Parkinson-White syndrome - left sided accessory pathway
• atrial septal defect
• ventricular septal defect

causes of left axis deviation

• left anterior hemiblock
• Q waves of inferior myocardial infarction
• artificial cardiac pacing
• emphysema
• hyperkalaemia
• Wolff-Parkinson-White syndrome - right sided accessory pathway
• tricuspid atresia
• ostium primum ASD
• injection of contrast into left coronary artery

note: left ventricular hypertrophy is not a cause left axis deviation