Left Axis Deviation in Adults

Definition and Classification

The American College of Cardiology and Circulation define the normal QRS axis in adults as between +30° and +90° 1, 2, 3
Left axis deviation is defined as a QRS axis less than +30°, according to the American Heart Association, as published in Circulation 2, 3
Moderate left axis deviation ranges from -30° to -45°, as stated by the American College of Cardiology 2, 4
Marked left axis deviation ranges from -45° to -90° and is often associated with left anterior fascicular block, according to the American College of Cardiology 1, 4

The American College of Cardiology states that left axis deviation may be associated with various cardiac conditions, but can also be a normal variant, especially with increasing age 4, 5
The presence of left axis deviation alone has limited diagnostic value and should be interpreted in the context of other clinical and ECG findings, as recommended by the American Heart Association 5
Common causes of left axis deviation include left ventricular hypertrophy, as reported by the American College of Cardiology 4, 5
Left anterior fascicular block is a cause of left axis deviation, requiring additional criteria beyond axis deviation, according to the American College of Cardiology 6

For a QRS axis of -22°, the American College of Cardiology recommends considering additional ECG abnormalities that might indicate underlying pathology 4, 5
Assessing for other criteria of left anterior fascicular block, such as qR pattern in lead aVL, R-peak time in lead aVL ≥45 ms, QRS duration <120 ms, is suggested by the American College of Cardiology 6

Overdiagnosis of left axis deviation as a primary diagnosis rather than a finding that requires clinical correlation is a common pitfall, as warned by the American College of Cardiology 5
Failing to consider age-related changes in QRS axis is another common pitfall, according to the American College of Cardiology 5

The American College of Cardiology suggests that left ventricular hypertrophy (LVH) criteria with left axis deviation (LAD) indicates a chronic process, as LVH develops gradually over time, in adults with known chronic conditions such as hypertension or valvular disease 7
The American College of Cardiology indicates that left anterior fascicular block (LAFB) criteria, such as a qR pattern in aVL, R-peak time ≥45 ms in aVL, and QRS duration <120 ms, suggests a conduction system abnormality that is typically chronic, in patients with LAD 8
The American College of Cardiology recommends considering LAD potentially new if there are additional acute ECG changes, such as ST-segment elevation/depression, new T-wave inversions, or new bundle branch block patterns, in patients presenting with acute clinical symptoms 8

The American College of Cardiology notes that the QRS axis naturally shifts leftward with increasing age, making mild LAD more common in older adults and potentially a longstanding finding, with a normal adult range of +30° to +90° 7
The American College of Cardiology states that in children, LAD is distinctly abnormal, with a normal pediatric axis range of 10° to 110° in ages 1-5 years, suggesting a congenital or acquired structural abnormality if present 8

The American College of Cardiology recommends examining leads I and aVF to quickly determine the quadrant of the axis, with lead I positive + aVF positive indicating a normal axis (0° to +90°) 9
The American College of Cardiology states that lead I negative + aVF positive indicates right axis deviation (+90° to +180°) 10
For precise axis calculation, the axis is perpendicular to the lead with the most isoelectric (equiphasic) QRS complex, or alternatively, use the lead with the tallest net QRS deflection, as the axis points toward this lead 10

The American College of Cardiology defines left axis deviation as any axis less than -30°, with moderate LAD ranging from -30° to -45° and marked LAD ranging from -45° to -90° 10
Marked LAD (-45° to -90°) often indicates left anterior fascicular block 10

The American College of Cardiology states that in neonates, normal axis ranges from 60° to 190°, and LAD is distinctly abnormal 9
In children aged 1-5 years, the normal axis range is 10° to 110° 9
In children aged 5-8 years, the normal axis may extend to 140° 9
In children aged 8-16 years, the normal axis range extends to 120° 9

The American College of Cardiology recommends evaluating for left anterior fascicular block using criteria such as qR pattern in lead aVL, R-peak time in lead aVL ≥45 ms, and QRS duration <120 ms when marked LAD (-45° to -90°) is present 10, 11