From the Guidelines
Axis divination on an ECG is determined by the vector of the maximal QRS deflection, with a normal QRS axis in adults considered to be within 30° and 90°. To determine the axis, one can use the method described in the AHA/ACC/HRS recommendations 1, which involves identifying the QRS complexes in leads I and aVF.
- If both leads show positive QRS complexes, the axis is normal (0 to +90 degrees).
- If lead I is positive and aVF is negative, the axis is leftward (-90 to 0 degrees).
- If lead I is negative and aVF is positive, the axis is rightward (+90 to +180 degrees).
- If both leads are negative, the axis is extreme rightward or northwest (-180 to -90 degrees). For more precise determination, finding the lead with the most equiphasic QRS complex (equal positive and negative deflections) can help, as the axis will be perpendicular to that lead 1.
- Axis determination is clinically important as it can indicate various cardiac conditions, such as left axis deviation suggesting left anterior fascicular block or lateral wall MI, while right axis deviation might indicate right ventricular hypertrophy or pulmonary conditions 1.
- Extreme axis deviations warrant further investigation as they often indicate significant cardiac pathology, and it is essential to consider the age and body habitus of the patient when interpreting the QRS axis, as the normal range varies across different age groups 1.
From the Research
Axis Divination on ECG
- Axis divination, or the determination of the electrical axis of the heart, is an important aspect of electrocardiogram (ECG) interpretation.
- The electrical axis of the heart is the direction in which the electrical impulse travels through the ventricles, and it can be affected by various factors, including structural heart disease.
- Left axis deviation, in particular, is a common ECG abnormality that can be indicative of underlying heart disease, as noted in a study published in 2005 2.
- Some of the common causes of left axis deviation include:
- Left anterior fascicular block, which has specific ECG criteria for diagnosis, as discussed in the study 2
- Other structural heart diseases, which may be apparent from clinical findings
- The presence of left axis deviation on an ECG should prompt further investigation into the underlying cause, as it may have significant implications for patient management and risk assessment.