From the Guidelines
To determine axis deviation on an EKG, first look at leads I and aVF, and consider the age and body habitus of the patient, as the normal QRS axis shifts to the left with increasing age. The mean frontal plane electrical axis, determined by the vector of the maximal (dominant) QRS deflection, is considered to be within 30° and 90° in adults, with left-axis deviation being 30° and beyond, and moderate right-axis deviation being from 90° to 120°, and marked right-axis deviation being between 120° and 180° 1.
Key Points to Consider
- In adults, the normal QRS axis is considered to be within 30° and 90°, with left-axis deviation being 30° and beyond, and moderate right-axis deviation being from 90° to 120°, and marked right-axis deviation being between 120° and 180° 1.
- In children, there is normally a rightward QRS axis at birth that shifts gradually leftward throughout childhood, with the mean electrical axis in the frontal plane being between 60° and 190° and being termed “extreme right axis” when it is between 90° and 190° 1.
- The quadrant approach, which involves looking at leads I and aVF, provides a quick assessment, but examining all limb leads gives the most accurate determination of cardiac electrical axis.
- For more precision, find the most isoelectric lead (where QRS is equally positive and negative) and the axis will be perpendicular to that lead.
- Left axis deviation often indicates left ventricular hypertrophy or left anterior fascicular block, while right axis deviation may suggest right ventricular hypertrophy, left posterior fascicular block, or pulmonary conditions, and extreme axis deviation is typically pathological and warrants further investigation 1.
From the Research
Determining Axis Deviation based on EKG
To determine axis deviation based on an EKG, several factors need to be considered, including the QRS complex and the presence of conduction blocks.
- The QRS axis can be classified as normal, left axis deviation (LAD), or right axis deviation (RAD) based on the mean frontal plane QRS axis 2.
- Left axis deviation is typically defined as a QRS axis of less than -30°, while right axis deviation is defined as a QRS axis of greater than 90° 3, 2.
- The presence of conduction blocks, such as left bundle branch block (LBBB), can also impact the determination of axis deviation 4, 5, 3.
- In patients with LBBB, left axis deviation has been associated with a poor response to cardiac resynchronization therapy (CRT) and a higher risk of adverse outcomes 5, 3.
- Right axis deviation in patients with LBBB has also been linked to a poor prognosis, with a higher risk of death and heart failure hospitalization 3.
Clinical Implications
The determination of axis deviation based on EKG has important clinical implications, including:
- Predicting response to CRT in patients with LBBB 5, 3
- Identifying patients at higher risk of adverse outcomes, such as death and heart failure hospitalization 3, 2
- Informing the diagnosis and management of cardiac conditions, such as myocardial infarction and heart failure 4, 5, 3, 2
EKG Interpretation
When interpreting an EKG to determine axis deviation, it is essential to consider the following: