From the Guidelines
Leads I and aVF are primarily used to interpret cardiac axis deviation on an electrocardiogram (ECG). To determine axis deviation, first examine lead I: if the QRS complex is predominantly positive, the axis is either normal or left deviated; if negative, it indicates right deviation. Then check lead aVF: a positive QRS suggests normal or right deviation, while a negative QRS indicates left deviation. By combining these observations, you can classify the axis as normal (positive in both leads), left axis deviation (positive in I, negative in aVF), right axis deviation (negative in I, positive in aVF), or extreme axis deviation (negative in both leads) 1.
The approach of using leads I and aVF is based on the principle that these limb leads provide perpendicular views of the heart's electrical activity, with lead I representing the horizontal axis and aVF representing the vertical axis, allowing for accurate determination of the direction of electrical depolarization through the heart. This method is particularly useful in diagnosing conditions such as right ventricular hypertrophy (RVH), which often causes right axis deviation and can be associated with specific electrocardiographic patterns, including tall R waves in right precordial leads and ST-T abnormalities 1.
In clinical practice, it is essential to consider the electrocardiographic findings in the context of the patient's overall clinical presentation, as right axis deviation can occur in various conditions, including RVH, congenital heart disease, and chronic obstructive pulmonary disease 1. By combining the information from leads I and aVF with ancillary clinical data, healthcare providers can make more accurate diagnoses and develop effective treatment plans.
Key points to consider when interpreting axis deviation include:
- Leads I and aVF are the primary leads used to determine axis deviation
- The QRS complex in lead I and aVF can indicate normal, left, right, or extreme axis deviation
- Right axis deviation is often associated with conditions such as RVH and congenital heart disease
- Clinical correlation is essential to accurately diagnose and manage conditions associated with axis deviation 1.
From the Research
Interpretation of Axis Deviation
To interpret axis deviation, the following leads are used:
- The frontal plane leads (I, II, III, aVR, aVL, aVF) are used to determine the axis of the heart in the frontal plane 2, 3, 4, 5
- The precordial leads (V1-V6) are used to determine the axis of the heart in the horizontal plane 2, 3, 4
Types of Axis Deviation
There are several types of axis deviation, including:
- Left axis deviation (LAD), which is associated with left-sided cardiac disease and increased risk of mortality 2, 5
- Right axis deviation (RAD), which is associated with right-sided cardiac disease and increased risk of mortality 2
- T-axis deviation, which is associated with increased risk of cardiac events and mortality 3, 6
Leads Used to Interpret Axis Deviation
The following leads are used to interpret axis deviation:
- Lead I and aVF are used to determine the axis of the heart in the frontal plane 2, 3, 4, 5
- Lead II is used to determine the axis of the heart in the frontal plane and to diagnose left and right axis deviation 2, 3, 4, 5
- Leads V1 and V6 are used to determine the axis of the heart in the horizontal plane 2, 3, 4
Clinical Significance
Axis deviation can be an indicator of underlying cardiac disease and can be used to risk stratify patients 2, 3, 6, 4, 5