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Axis Deviation Chapter 5

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**Definition Electrical axis...**

The general direction in the frontal plane or toward which lead the QRS complex is predominately oriented ...the mean direction of depolarization through the frontal plane of the heart

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**Mean QRS Axis Calculation**

Lead II

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**Mean QRS Axis Calculation**

General rules the mean QRS axis points midway between any two leads that show tall R waves of equal height the mean QRS axis is oriented at right angles (90°) to any lead showing a bi-phasic complex

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**Mean QRS Axis Calculation**

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**Mean QRS Axis Calculation**

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**Mean QRS Axis Calculation**

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**Mean QRS Axis Calculation**

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**Mean QRS Axis Calculation**

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**Normal versus Deviation**

Left 3 ? 1 ? 2 ? Right + 90∘

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Axis Deviation Left Right

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**Axis Deviation Criteria**

LEAD I LEAD II (or Lead aVF or III) Normal Positive LAD Negative RAD Intermediate axis

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**Axis Deviation RAD = If R wave in III > R wave in II**

LAD = If R wave in aVL > I; and deep S wave in III

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Axis deviation ? ?

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Axis deviation ?

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Axis deviation ?

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What is the axis? Right

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What is the axis? Left

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What is the axis? Normal

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What is the axis? Left

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What is the axis? Normal

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What is the axis? Right

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**Causes of Left Axis Deviation**

FYI • left anterior hemiblock • Q waves of inferior myocardial infarction • artificial cardiac pacing • emphysema • hyperkalaemia • Wolff-Parkinson-White syndrome - right sided accessory pathway • tricuspid atresia • ostium primum ASD • injection of contrast into left coronary artery note: left ventricular hypertrophy is not a cause left axis deviation

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**Causes of Right Axis Deviation**

FYI • normal finding in children and tall thin adults • right ventricular hypertrophy • chronic lung disease even without pulmonary hypertension • anterolateral myocardial infarction • left posterior hemiblock • pulmonary embolus • Wolff-Parkinson-White syndrome - left sided accessory pathway • atrial septal defect • ventricular septal defect

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