From the Guidelines
Left axis deviation (LAD) is an abnormal electrical axis of the heart that points between -30 and -90 degrees on the electrocardiogram (ECG) and should prompt further cardiac evaluation to determine its underlying cause, which may include left ventricular hypertrophy, left anterior fascicular block, or other conditions 1. When evaluating LAD, it is essential to consider the clinical context and potential underlying causes. LAD can occur in individuals with left ventricular hypertrophy (LVH), and in such cases, management focuses on addressing the underlying cause, such as hypertension, through blood pressure control with appropriate medications 1.
Key Considerations
- LAD itself does not require specific treatment, but rather management of the underlying cause.
- Common causes of LAD include left ventricular hypertrophy, left anterior fascicular block, inferior myocardial infarction, and certain congenital heart defects.
- When evaluating LAD on an ECG, look for positive QRS complexes in lead I and negative QRS complexes in leads II and aVF.
- Additional testing, such as echocardiography, stress testing, or cardiac MRI, may be necessary to determine the significance and cause of the LAD, depending on the clinical context 1.
Clinical Implications
- Isolated LAD may be a normal variant in some individuals, but it should still prompt further cardiac evaluation, especially when accompanied by symptoms or other ECG abnormalities.
- The direction of the QRS axis is crucial in determining the presence of LAD, and an abnormal direction of the T-wave axis may indicate primary repolarization abnormalities 1.
- Primary and secondary repolarization abnormalities may occur concurrently, and a combination of both should be considered when evaluating LAD 1.
From the Research
Left Axis Deviation
- Left axis deviation is one of the most commonly encountered ECG abnormalities, and its presence should alert medical directors and underwriters to the possibility of underlying structural heart disease 2
- Many of the causes of left axis deviation are apparent from the clinical findings, with left anterior fascicular block being one of the commonest causes and having specific ECG criteria for its diagnosis 2
Clinical Significance
- In patients with chronic left bundle branch block, left axis deviation is associated with a greater incidence of myocardial dysfunction, more advanced conduction disease, and greater cardiovascular mortality compared to those with a normal axis 3
- Clinical variables such as greater age, exertional angina, congestive heart failure, cardiomegaly, and coronary artery disease are more frequent in patients with left axis deviation 3
- Patients with left axis deviation also have longer mean P-R, A-H, and H-V intervals and atrial and atrioventricular (A-V) nodal effective refractory periods 3
Prognosis
- The cumulative 4-year mortality rate for patients with left bundle branch block and left axis deviation approaches 75%, with a greater incidence of cardiovascular mortality compared to those with a normal axis 3
- A-V block developed in 6% of patients with left axis deviation, whereas none of the patients with a normal axis developed A-V block 3