From the Guidelines
Left axis deviation on an EKG is a significant finding that warrants further evaluation to determine the underlying cause, as it can be associated with various cardiac pathologies, including left ventricular hypertrophy, left anterior fascicular block, and certain congenital heart defects. This condition occurs when the heart's electrical axis shifts leftward beyond -30 degrees, which can be identified by a predominantly negative QRS complex in lead aVF and a predominantly positive QRS in lead I. According to the American Heart Association electrocardiography and arrhythmias committee, council on clinical cardiology 1, the recognition of biventricular hypertrophy by ECG has a low sensitivity, and the presence of left axis deviation may be an indicator of underlying left ventricular hypertrophy.
When encountering left axis deviation on an EKG, a thorough history and physical examination, additional cardiac imaging like echocardiography, and possibly cardiac stress testing depending on clinical context are recommended. Management depends entirely on the underlying cause rather than treating the axis deviation itself. For example, if left axis deviation is due to hypertensive heart disease, controlling blood pressure with appropriate medications would be indicated, as suggested by the aha/accf/hrs recommendations 1. It is essential to note that left axis deviation represents an electrical phenomenon resulting from altered ventricular depolarization pathways, often reflecting structural or functional changes in the heart's conduction system or myocardium.
Some key points to consider when evaluating left axis deviation on an EKG include:
- The presence of prominent S waves in V5 or V6, right axis deviation, unusually tall biphasic R/S complexes in several leads, and signs of right atrial abnormality, which may indicate the presence of right ventricular hypertrophy in addition to left ventricular hypertrophy 1
- The presence of combined tall R waves and deep S waves in leads V2 to V, with combined amplitude greater than 60 mm (6.04 mV), which suggests the presence of left ventricular hypertrophy in patients with congenital heart defects and right ventricular hypertrophy 1
- The importance of considering the clinical context and underlying cause of left axis deviation when determining the appropriate management strategy.
From the Research
Left Axis Deviation on EKG
- Left axis deviation (LAD) is a common ECG abnormality that can be a marker of underlying structural heart disease 2.
- In patients with left bundle branch block (LBBB), LAD is associated with a poor response to cardiac resynchronization therapy (CRT) 3.
- The presence of LAD in patients with LBBB is independently associated with a poor left ventricular (LV) remodelling non-response, with an odds ratio of 0.21 [95% CI 0.06-0.77] (p = 0.02) 3.
Causes and Associations
- Left anterior fascicular block is one of the commonest causes of left axis deviation and has specific ECG criteria for its diagnosis 2.
- Patients with LBBB and LAD have more scar tissue, hypertrophy, and less activation delay compared to those with normal axis 3.
- A high scar tissue burden is more pronounced in non-responders to CRT, with a mean scar tissue burden of 1.4 ± 0.6 vs. 1.0 ± 0.5 (P = 0.01) 3.
Diagnostic Evaluation
- Echocardiography is the primary imaging modality used for the clinical evaluation of left ventricular (LV) diastolic function, and can be used to estimate LV filling pressure 4.
- The estimation of LV filling pressure using echocardiography can be useful for evaluating patients with dyspnea of unknown etiology, as well as those with heart failure with preserved ejection fraction 4.