From the Guidelines
A QRS axis of +296 degrees is indeed indicative of right axis deviation, but it is not in the northwest orientation, rather it falls in the southwest quadrant. Right axis deviation is defined as a QRS axis greater than +90 degrees, and +296 degrees falls within this definition, as stated in the American Heart Association electrocardiography and arrhythmias committee guidelines 1. Specifically, +296 degrees is equivalent to -64 degrees when converted to the standard ECG coordinate system (which ranges from -180 to +180 degrees). This places the axis in the extreme right inferior quadrant, or what would be considered the southwest quadrant, not the northwest. The northwest quadrant would include axes between -90 and -180 degrees. Some key points to consider when interpreting QRS axis include:
- Normal QRS axis in adults is between 30° and 90°, with left-axis deviation being 30° and beyond, and moderate right-axis deviation being from 90° to 120°, as outlined in the guidelines 1
- Right axis deviation can be seen in various conditions including right ventricular hypertrophy, lateral wall myocardial infarction, left posterior fascicular block, or as a normal variant in tall, thin individuals
- When interpreting ECG axis, it's essential to consider the patient's clinical context and other ECG findings to determine the significance of this finding, as emphasized in the American College of Cardiology Foundation recommendations 1.
From the Research
QRS Axis Deviation
- A QRS axis of +296 degrees is considered to be indicative of extreme right axis deviation 2.
- Extreme right axis deviation is defined as a shift in QRS axis between +180° and +270° 2.
- Right axis deviation is often associated with a northwest orientation on the electrocardiogram 3, 4.
Clinical Significance
- New-onset extreme right axis deviation during myocardial infarction may be related to extensive myocardial ischemia and/or necrosis causing an "electrical escaping" with an extreme dislocation of the QRS axis 2.
- Right axis deviation can be a useful clue to evaluate myocardial ischemia in acute myocardial infarction cases 4.
- Extreme right axis deviation has been associated with severe clinical complications and higher risks in coronary artery disease 4, 2.
Electrocardiographic Interpretation
- The QRS axis can be calculated from the bipolar limb leads, unipolar limb leads, or the combination of lead I and lead aVF 5.
- The combination of lead I and lead aVF is best correlated with other methods of QRS axis calculation 5.
- Computer interpretations of QRS axis can be accurate, but physicians should be aware of axis ranges and recognize any serious computer deviations 5.