What Is Axis Deviation and What Are the Causes?

Axis deviation is a finding on an electrocardiogram (EKG) that shows the general direction of the heart’s electrical activity. It is an observation, not a specific disease or diagnosis. The heart’s electrical current normally flows in a particular direction to make it beat. When this current’s general direction shifts outside the normal range, it is called an axis deviation, which can be a clue to an underlying condition.

The Heart’s Electrical Axis Explained

The heart’s electrical system generates impulses that travel through the heart muscle in a specific pattern, causing it to contract and pump blood. The average direction of this wave of electricity during a contraction is called the mean electrical axis. An EKG measures this activity through electrodes placed on the skin, which record the signals from different angles.

The mean electrical axis is measured in degrees. A normal axis is considered to be between -30 and +90 degrees, which indicates the electrical signal is traveling through the ventricles in a typical downward and leftward direction. This range represents a healthy pattern of electrical conduction through the heart’s main pumping chambers.

Any significant shift from this normal range suggests that the path of electrical conduction has been altered. This can be due to a change in the heart’s muscle mass or a problem within the conduction system itself.

Types of Axis Deviation

When the heart’s electrical energy is directed more to the left than normal, it is called Left Axis Deviation (LAD). This is defined by an electrical axis between -30 and -90 degrees. This pattern indicates the overall electrical impulse is moving upward and to the left, away from the normal direction.

A shift in the opposite direction is Right Axis Deviation (RAD), which occurs when the axis is between +90 and +180 degrees. This means the heart’s electrical activity is pointed further to the right than normal, with electrical forces moving down and to the right.

A less common finding is extreme axis deviation, diagnosed when the axis is between -90 and 180 degrees. This suggests a more unusual electrical pattern and can be associated with specific arrhythmias or incorrect EKG lead placement.

Underlying Causes and Associated Conditions

The reason for an axis deviation relates to changes in the heart’s structure or its electrical pathways. For Left Axis Deviation, a common cause is left ventricular hypertrophy, a thickening of the muscular wall of the left ventricle. This can result from long-standing high blood pressure or conditions like aortic stenosis. Another cause is a disruption in the heart’s wiring, such as a left anterior fascicular block, which delays electrical activation in a part of the left ventricle.

Right Axis Deviation is linked to conditions affecting the right side of the heart. Right ventricular hypertrophy, a thickening of the right ventricle’s wall, is a primary cause and can develop from chronic lung diseases like COPD or pulmonary hypertension. A pulmonary embolism, a blood clot in the lungs, can cause acute strain on the right ventricle and lead to RAD. In some cases, RAD can be a normal finding in very tall, thin individuals due to the heart’s position in the chest.

The significance of an axis deviation is tied directly to its underlying cause. While some causes, like minor conduction delays or body shape, may be of little concern, others can point to serious conditions. Both LAD and RAD can be associated with damage from a previous heart attack that has altered the path of electrical conduction.

Diagnosis and Next Steps

The finding of an axis deviation on an EKG serves as a prompt for further investigation. It is a clue that tells a physician to look closer at the heart’s health to determine the root cause of the deviation.

A doctor will begin with a physical examination and a detailed review of the patient’s medical history, looking for signs and symptoms of heart or lung disease. To get a clearer picture of the heart’s structure and function, an echocardiogram is often ordered. This ultrasound of the heart can visualize the thickness of the heart walls, the function of the valves, and the size of the chambers, helping to identify issues like ventricular hypertrophy.

Treatment is not aimed at correcting the axis deviation itself, but at managing the condition that is causing it. For example, if high blood pressure is causing left ventricular hypertrophy, the focus will be on controlling blood pressure with medication and lifestyle changes. If a lung condition is causing strain on the right heart, managing the respiratory disease is the priority.

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