Left axis deviation is a condition whereby 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

QRS complex

The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...

 positive in lead I and negative in leads aVF and II.

Cause

Common causes of LAD include left ventricular hypertrophy

Left ventricular hypertrophy

Left ventricular hypertrophy is the thickening of the myocardium of the left ventricle of the heart.-Causes:While ventricular hypertrophy occurs naturally as a reaction to aerobic exercise and strength training, it is most frequently referred to as a pathological reaction to cardiovascular...

, left anterior fascicular block

Left anterior fascicular block

Left anterior fascicular block is a cardiac condition, distinguished from left bundle branch block.It is caused by only the anterior half of the bundle of His being defective...

 (or hemiblock) and inferior myocardial infarction

Myocardial infarction

Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

. Less commonly LAD may be a normal variant, particularly in obese or stocky individuals, or it may be associated with Wolff-Parkinson-White Syndrome

Wolff-Parkinson-White syndrome

Wolff–Parkinson–White syndrome is a disorder of the heart in which the ventricles of the heart contract prematurely due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles...

 or an Ostium Primum atrial septal defect

Atrial septal defect

Atrial septal defect is a form of congenital heart defect that enables blood flow between the left and right atria via the interatrial septum. The interatrial septum is the tissue that divides the right and left atria...

.

Left ventricular hypertrophy (LVH) is generally recognised as a cause of LAD, although some sources claim that LVH does not cause LAD.