EKG- Disorders of Axis

I. Problem/Condition.

Right Axis Deviation

Axis is determined by evaluation of all limb leads on an ECG. However, the most common strategy in evaluating axis is looking at leads I and AvF. If positive deflection is noted in both of these leads the axis is normal. Right axis deviation is noted when lead I is negative and lead AvF is positive indicating vector predominance towards the right axis.

Left Axis Deviation

Left axis deviation is noted when lead I is positive and lead AvF is negative indicating vector predominance towards the left axis.

II. Diagnostic Approach.

A. What is the differential diagnosis for this problem?

Right Axis Deviation

Cardiac – See Table I.

Table I.
Cardiac:
Differential diagnosis Other important EKG clues
Normal variant in thin adults
Right Atrial Enlargement increase amplitude of P wave in lead II
Right Bundle Branch Block Rsr’ noted in leads V1V2
Right Ventricular Hypertrophy tall R waves in V1V2 and deep S waves in V5V6, I and aVL
Lateral Wall Myocardial Infarction Acute, ST elevation in leads I and aVL, Chronic, q waves in lead I and aVL
Left Posterior Fascicular Block negative QRS complex in lead I, positive QRS complex in aVF
Dextrocardia reverse R wave progression in precordial leads, negative p wave and QRS complex in lead I
Preexciation Syndromes wide or narrow QRS complexes, QRS duration usually less than 0.12ms, delta wave

Pulmonary – See Table II.

Table II.
Pulmonary:
Differential diagnosis Other important EKG clues
Inspiratory variation
Cor Pulmonale evidence of RVH and RAE on ECG (see above)
Pulmonary Hypertension with Right Ventricular Hypertrophy tall R waves in V1V2 and deep S waves in V5V6, I and aVL
Pulmonary Embolism incomplete or complete RBBB, evidence of RAE and atrial arrhythmias
Emphysema ECG findings can be seen if progression to Cor Pulmonale (see above)

Left Axis Deviation

Cardiac – See Table III.

Table III.
Cardiac:
Differential diagnosis Other important EKG clues
Normal Variant
Left Ventricular Hypertrophy Sum of S wave in V1 and R wave in V5 or V6 ≥3.5 mV (35 mm) R wave in aVL ≥1.1 mV (11 mm); or 13mm is used
Left Bundle Branch Block QRS duration greater than or equal to 120 ms, Broad notched or slurred R wave in leads I, aVL, V5, and V6 and an occasional RS pattern in V5 and V6, ST and T waves usually opposite in direction to QRS complex
Left Anterior Fascicular Block positive QRS complex in lead I, negative QRS complex in AvF
Inferior MI ST segment elevation in II, III, and aVF
Hyperkalemia peaked symmetrical T waves

Other:

Mechanical shifts during expiration.

Elevated diaphragm, such as in pregnancy, ascites, abdominal tumor.

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A disorder of axis as it pertains to findings on EKG should be carefully evaluated. Patient history is helpful but may not aid in the underlying cause of axis disorders. Generally, disorders of axis do not present as life threatening emergencies, however, it may be a subtle indicator of something more ominous. History and physical exam should be the first steps in the evaluation of axis disorders and as indicated further workup and studies may be warranted.

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Although not a dangerous finding in and of itself, axis deviation may be an indication of a serious underlying condition. A careful history to elicit acute cardiac injury is therefore of utmost importance. Other historical data that may contribute to the differential diagnosis would include cardiac and pulmonary risk factors, congenital heart disease and tobacco abuse.

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Cardiovascular and pulmonary examination may provide additional evidence to support the differential developed through careful history taking.

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The 12-lead EKG can provide additional data to support a cardiac or pulmonary cause of axis deviation. Cardiac enzymes may be elevated with acute cardiac injury. Electrolyte abnormalities may be elucidated from a serum basic metabolic panel. A chest radiograph may provide evidence of chronic pulmonary disease. When a pulmonary embolus is suspected, further imaging may be required to confirm the diagnosis (covered in more detail in the Pulmonary Embolism chapter).

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The criteria for each diagnosis are covered in detail in accompanying chapters.

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The EKG is a cost-effective tool in this context.

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Typically, disorders of axis do not require immediate care unless it is accompanied by an acute medical problem such as MI. Axis disorders should be evaluated and referred to a specialist if needed.

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Common pitfalls should be considered with a specific diagnosis. Details can be found in representative chapters.

Harrigan, RA, Jones, K.. “ABC of clinical electrocardiography: Conditions affecting the right side of the heart”. BMJ. vol. 324. 2002 May 18. pp. 1201-1204.

Khan, MG.. Rapid ECG Interpretation. 2008.

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