From the Guidelines
To interpret right and left axis deviation on an ECG, it is crucial to understand that the normal cardiac axis ranges from -30° to +90°, with left axis deviation occurring between -30° and -90° and right axis deviation between +90° and +180°, as noted in the guidelines by 1 and 1.
Determining Axis Deviation
To determine the axis, one should look at leads I and aVF. The rules are as follows:
- If both leads are positive, the axis is normal.
- If lead I is positive and lead aVF is negative, it indicates left axis deviation.
- If lead I is negative and lead aVF is positive, it suggests right axis deviation.
- If both leads are negative, it's indicative of extreme right axis deviation.
Clinical Implications
Left axis deviation is commonly associated with conditions such as left anterior fascicular block, left ventricular hypertrophy, inferior myocardial infarction, and certain congenital heart defects, as discussed in 1. On the other hand, right axis deviation is often seen in right ventricular hypertrophy, left posterior fascicular block, pulmonary embolism, and specific congenital heart defects, with the electrocardiographic diagnosis of right ventricular hypertrophy requiring right axis deviation and prominent anterior forces in the right precordial leads, as emphasized by 1.
Diagnostic Considerations
The axis deviation provides critical diagnostic clues about underlying cardiac conditions, reflecting changes in the heart's electrical conduction pathway or structural abnormalities that alter the direction of depolarization through the ventricles. Therefore, understanding and correctly interpreting axis deviation is essential for diagnosing and managing cardiac patients, considering the information from 1 and 1 for a comprehensive approach to ECG interpretation.
From the Research
Axis Deviation on ECG
Axis deviation on an electrocardiogram (ECG) can indicate various cardiac conditions. The axis refers to the overall direction of the electrical activity in the heart.
Types of Axis Deviation
- Left Axis Deviation: This occurs when the electrical axis of the heart shifts to the left, often indicating left ventricular hypertrophy (LVH) 2. LVH can be diagnosed using a combination of limb and precordial lead voltage criteria and/or other non-voltage ECG criteria.
- Right Axis Deviation: This occurs when the electrical axis of the heart shifts to the right, often indicating right ventricular hypertrophy (RVH) 3, 4. RVH can be a complication of chronic lung disease, and treatment is targeted at correcting hypoxia and improving pulmonary gas exchange and mechanics.
Determinants of Axis Deviation
- Right Ventricular Hypertrophy: RVH is an important determinant of right ventricular infarction complicating acute inferior left ventricular infarction 4. The thickness of the right ventricular free wall is a strong predictor of right ventricular infarction.
- Left Ventricular Hypertrophy: LVH can be diagnosed using ECG criteria, but the sensitivity of these criteria can be reduced in the presence of bundle branch block 2. A combination of limb and precordial lead voltage criteria and/or other non-voltage ECG criteria is often required for an accurate diagnosis.