electrocardiography Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity through repeated cardiac cycles. It is an electrogram of the heart which is a graph of voltage versus time of t ...

, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II. There are several potential causes of LAD. Some of the causes include normal variation, thickened left ventricle, conduction defects, inferior wall myocardial infarction, pre-excitation syndrome, ventricular ectopic rhythms,

congenital heart disease A congenital heart defect (CHD), also known as a congenital heart anomaly, congenital cardiovascular malformation, and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at birth. A congenital he ...

emphysema Emphysema is any air-filled enlargement in the body's tissues. Most commonly emphysema refers to the permanent enlargement of air spaces (alveoli) in the lungs, and is also known as pulmonary emphysema. Emphysema is a lower respiratory tract di ...

, mechanical shift, and paced rhythm. Symptoms and treatment of left axis deviation depend on the underlying cause.

Defining left axis deviation

Cardiac axis in electrocardiography represents the sum of depolarization vectors generated by individual cardiac myocytes. To interpret the cardiac axis, one has to determine the relationship between the QRS axis and limb leads of the ECG. Usually, left ventricles makes up most of the heart muscles, so a normal cardiac axis is directed downward and slightly to the left. In a normal axis, QRS is between -30° and +90°. In contrast to that, left axis deviation (LAD) is defined as QRS axis between −30° and −90°, and right axis deviation is defined as QRS axis greater than +90°, while extreme axis deviation occurs when QRS axis is between -90° and 180°.

Determining left axis deviation

Determining the electrical axis can provide insight into underlying disease states and help steer the differential diagnosis. There are several methods to determining the ECG axis. The easiest method is the quadrant method, where one looks at lead I and lead aVF. First, examine the QRS complex in both leads I and avF and determine if the QRS complex is positive (height of R wave > S wave), equiphasic (R wave = S wave), or negative (R wave < S wave). If lead I is positive and lead aVF is negative, then this is a possible LAD. To determine a true LAD, examine QRS in lead II. If the QRS complex is positive in lead II, then this is a normal axis. On the other hand, if QRS complex is negative in lead II, then this is a LAD. Another method of determining LAD is called the Isoelectric lead, which allows for a more precise estimation of the QRS axis.

Causes

There are several potential causes of LAD. These include normal variation, left ventricular hypertrophy, conduction defects, inferior wall myocardial infarction, preexcitation syndrome, ventricular ectopic rhythms, congenital heart disease, hyperkalemia, emphysema, mechanical shift and pacemaker-generated paced rhythm. Normal variation causing LAD is an age-related physiologic change. Conduction defects such as left bundle branch block or left anterior fascicular block can cause LAD on the ECG . Pre-excitation syndrome as well as congenital heart diseases such as atrial septal defect, endocardial cushion defects can also cause LAD on ECG. Mechanical shifts that cause LAD are expiration or raised diaphragm from pregnancy, ascites (fluid accumulation in the abdomen), abdominal tumor, or enlarged

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

spleen The spleen (, from Ancient Greek '' σπλήν'', splḗn) is an organ (biology), organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The spleen plays important roles in reg ...

. Left axis deviation is a border deviation in athletes, which, if it is combined with another borderline feature such as right bundle branch block, requires further investigation in view of increased risk of

sudden cardiac death Cardiac arrest (also known as sudden cardiac arrest ''SCA is when the heart suddenly and unexpectedly stops beating. When the heart stops beating, blood cannot properly circulate around the body and the blood flow to the brain and other org ...

Signs and symptoms

Left axis deviation symptoms depend on the underlying cause. For example, if left ventricular hypertrophy is the cause of LAD, symptoms can include

shortness of breath Shortness of breath (SOB), known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that con ...

, fatigue,

chest pain Chest pain is pain or discomfort in the chest, typically the front of the chest. It may be described as sharp, dull, pressure, heaviness or squeezing. Associated symptoms may include pain in the shoulder, arm, upper abdomen, or jaw, along with n ...

(especially with exercise),

palpitations Palpitations occur when a person becomes aware of their heartbeat. The heartbeat may feel hard, fast, or uneven in their chest. Symptoms include a very fast or irregular heartbeat. Palpitations are a sensory symptom. They are often described as ...

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...

, or

fainting Syncope , commonly known as fainting or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...

. If a conduction defect such as left bundle branch block is the cause of LAD, there may not be any symptoms unless the conduction defect is caused by heart failure, in which case there can be symptoms of

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

such as shortness of breath or fatigue.

Treatment

Left axis deviation per se does not require treatment, however the underlying cause can be treated. If left ventricular hypertrophy is the cause of LAD, treatment depends on the underlying cause of the hypertrophy. If

high blood pressure Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms itself. It is, however, a major ri ...

is the cause of LVH, then treatment is targeted at lowering blood pressure and preventing further enlargement of the left ventricle by using medications such as angiotensin-converting enzyme inhibitors (ACE inhibitors),

angiotensin receptor blockers Angiotensin II receptor blockers (ARBs), formally angiotensin II receptor type 1 (AT1) antagonists, also known as angiotensin receptor blockers, angiotensin II receptor antagonists, or AT1 receptor antagonists, are a group of pharmaceuticals tha ...

(ARBs), calcium channel blockers, diuretics, and beta-blockers. If LVH is due to valvular issues such as aortic valve stenosis, surgical repair of the valve or replacement of the valve is required.

References