Left axis deviation

In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II.

Common causes of LAD include left ventricular hypertrophy (LVH), left anterior fascicular block (or hemiblock) and inferior myocardial infarction. Less commonly LAD may be a normal variant, particularly in obese or stocky individuals, or it may be associated with Wolff–Parkinson–White syndrome or an ostium primum atrial septal defect.

LVH is generally recognised as a cause of LAD, although some sources claim that LVH does not cause LAD.

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