From the Guidelines
Axis deviations on an ECG are abnormal directions of the heart's electrical activity that can indicate various cardiac conditions, with left axis deviation suggesting left ventricular hypertrophy, left anterior fascicular block, or inferior myocardial infarction, and right axis deviation indicating right ventricular hypertrophy, right bundle branch block, pulmonary embolism, or lateral wall myocardial infarction. The normal cardiac axis ranges from -30 to +90 degrees.
Key Points to Consider
- Left axis deviation occurs when the axis is less than -30 degrees, as noted in the study by 1, which discusses the association between left axis deviation and left ventricular hypertrophy (LVH).
- Right axis deviation, when the axis exceeds +90 degrees, can indicate right ventricular hypertrophy (RVH), as discussed in the study by 1, which highlights the challenges in detecting RVH due to the dominance of left ventricular activation vectors.
- Extreme axis deviation (beyond -90 or +180 degrees) often suggests ventricular arrhythmias or incorrect lead placement.
- To determine the axis, one can look at leads I and aVF: if both are positive, the axis is normal; if I is positive and aVF negative, it's left deviation; if I is negative and aVF positive, it's right deviation; if both are negative, it's extreme deviation.
Diagnostic Considerations
- Axis deviations are important diagnostic clues that should be interpreted alongside other ECG findings and clinical information for accurate diagnosis, as emphasized by 1 and 1.
- The use of ancillary clinical information plays a greater role in the appropriate use of the ECG for recognizing conditions like RVH, as noted in 1.
- The studies by 1 and 1 provide guidance on the interpretation of ECG changes associated with cardiac chamber hypertrophy, highlighting the importance of considering the clinical context and other diagnostic findings.
From the Research
Axis Deviations on ECG
Axis deviations on an electrocardiogram (ECG) can indicate various underlying heart conditions. The two main types of axis deviations are:
- Left axis deviation (LAD)
- Right axis deviation (RAD)
Left Axis Deviation
Left axis deviation is one of the most commonly encountered ECG abnormalities 2. Its presence should alert medical professionals to the possibility of underlying structural heart disease. Some common causes of left axis deviation include:
- Left anterior fascicular block, which has specific ECG criteria for its diagnosis 2
- Myocardial disease, which can be associated with poor response to cardiac resynchronization therapy (CRT) in patients with left bundle branch block (LBBB) 3
- Left ventricular hypertrophy, which can be detected by MRI studies in heart transplant recipients 4
Right Axis Deviation
Right axis deviation can also be an indicator of underlying heart conditions. However, the provided studies do not focus on RAD as much as LAD. One study mentions that patients with axis deviation (including RAD) had more myocardial scar tissue and severe LV hypertrophy compared to those with a normal axis 3.
Clinical Implications
Axis deviations on an ECG can have significant clinical implications. For example:
- Patients with LAD and LBBB may show less benefit from CRT compared to other LBBB patients 3
- The presence of LAD can be independently associated with a poor left ventricular remodelling non-response to CRT 3
- Axis deviations can be correlated with left ventricular hypertrophy and deviation of the left ventricular long axis in heart transplant recipients 4