What is the electrocardiogram (ECG) axis?

From the Guidelines

The ECG axis refers to the overall direction of electrical activity in the heart as recorded by an electrocardiogram, specifically measuring the average direction of ventricular depolarization in the frontal plane. The concept of the ECG axis is rooted in the idea of the heart vector, which is a stationary, time-dependent single-dipole source that can be represented by a vector, as described by Einthoven et al 1. This vector is projected onto the lead axes to explain the voltage in any lead. The normal cardiac axis typically falls between -30 and +90 degrees, with most healthy adults having an axis between 0 and +75 degrees.

Key Points to Consider

• Determining the axis helps clinicians identify various cardiac abnormalities such as left axis deviation (less than -30 degrees), which may indicate left ventricular hypertrophy or left anterior fascicular block, or right axis deviation (greater than +90 degrees), which might suggest right ventricular hypertrophy or right bundle branch block.
• To calculate the axis, one examines the QRS complexes in different leads, particularly leads I and aVF, as the placement of electrodes on the torso and the resulting tracings are known as leads 1.
• The axis can shift due to heart disease, conduction abnormalities, or even non-cardiac factors like pregnancy or changes in body position, emphasizing the importance of considering the patient's overall clinical context.
• Understanding the cardiac axis is essential for proper ECG interpretation and can provide valuable diagnostic information about the heart's electrical conduction system and structural abnormalities, as supported by the recommendations for the standardization and interpretation of the electrocardiogram by the American Heart Association Electrocardiography and Arrhythmias Committee 1.

Clinical Implications

• Accurate determination of the ECG axis is crucial for identifying potential cardiac issues and guiding further diagnostic and therapeutic interventions.
• Clinicians should be aware of the factors that can influence the ECG axis, including electrode placement, torso inhomogeneities, and the patient's clinical context, to ensure accurate interpretation of the ECG results.

From the Research

Definition of ECG Axis

The ECG axis refers to the overall direction of the electrical activity of the heart as recorded by an electrocardiogram (ECG).

• It is an important aspect of ECG interpretation, as it can provide information about the orientation of the heart's electrical activity and help diagnose various cardiac conditions.
• The ECG axis is typically measured in degrees, with the normal range being between -30° and +100°.
• Deviations from this normal range can indicate various cardiac conditions, such as left or right axis deviation.

Factors Influencing ECG Axis

Several factors can influence the ECG axis, including:

• The position of the heart in the chest
• The orientation of the electrical conduction system of the heart
• The presence of any cardiac conditions, such as bundle branch blocks or ventricular hypertrophy
• The effects of certain medications, such as beta-blockers 2, 3, 4, 5

Relationship with Beta-Blockers

Beta-blockers, which are commonly used to treat cardiac arrhythmias, can also affect the ECG axis.

• Studies have shown that beta-blockers can reduce the incidence of sudden cardiac death, prolong survival, and ameliorate symptoms caused by arrhythmias in patients with cardiac disease 4.
• However, the effect of beta-blockers on the ECG axis is not well-established, and more research is needed to fully understand this relationship.
• Some studies suggest that beta-blockers may have different effects on the ECG axis depending on their selectivity for beta(1)- and beta(2)-receptors 4.

Limitations of Current Evidence

There are no research papers that directly address the question of what an ECG axis is, as the provided studies focus on the use of beta-blockers in treating cardiac arrhythmias.

• However, the information provided can still be useful in understanding the relationship between beta-blockers and the ECG axis, as well as the importance of considering the ECG axis in the diagnosis and treatment of cardiac conditions.
• Further research is needed to fully understand the ECG axis and its relationship with beta-blockers 2, 3, 6, 4, 5