cardiac axis
electrical axis of the heart
ECG axis determination
left axis deviation
right axis deviation
how to calculate cardiac axis on ECG
causes of left axis deviation
causes of right axis deviation
fascicular block ECG criteria
normal cardiac axis degrees
12-lead ECG interpretation
quadrant method ECG
hexaxial reference system
ventricular hypertrophy ECG
ECG interpretation guide
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| Cardiac Axis |
What is Cardiac Axis? Why to check? Causes? Pathology?
Determining the electrical axis of the heart is one of the most vital steps in interpreting a 12-lead ECG. It provides immediate clues about structural changes, conduction blocks, and ventricular hypertrophy.
This comprehensive guide breaks down the step-by-step methodology for calculating the cardiac axis using R-wave amplitudes, identifying axis deviations, and understanding core ECG intervals.
The average direction of spread of the depolarization wave through the ventricles as seen from the front is called the ‘cardiac axis’. The cardiac axis VR III VF normal direction or not. The direction of the axis can be derived most easily from the QRS complex in leads I, II and III. A normal 11 o’clock–5 o’clock axis means that the depolarizing wave is spreading towards leads I, II and III, and is therefore associated with a predominantly upward deflection in all these leads; the deflection will be greater in lead II than in I or III.When the R and S waves of the QRS complex are equal, the cardiac axis is at right angles to that lead. In short If QRS is primarily positive in limb leads I and II, then axis is normal.
Leads VR and II look at the heart from opposite directions. When seen from the front, the depolarization wave normally spreads through the ventricles from 11 o’clock to 5 o’clock, so the deflections in lead VR are normally mainly downward (negative) and in lead II mainly upward (positive)
The cardiac axis is sometimes measured in degrees , though this is not clinically particularly useful. Lead I is taken as looking at the heart from 0°; lead II from +60°; lead VF from +90°; and lead III from +120°. Leads VL and VR look from –30° and –150°, respectively. The normal cardiac axis is in the range –30° to +90°. If in lead II the S wave is greater than the R wave, the axis must be more than 90° away from lead II. In other words, it must be The cardiac axis and lead angles–90° VR–150°–180° +180° Right axis deviation +120° III +90° VF Limit of the normal cardiac axis 16 Left axis deviation +60° II VL–30° 0° I at a greater angle than –30°, and closer to the vertical and left axis deviation is present. Similarly, if the size of the R wave equals that of the S wave in lead I, the axis is at right angles to lead I or at +90°. This is the limit of normality towards the ‘right’. If the S wave is greater than the R wave in lead I, the axis is at an angle of greater than +90°, and right axis deviation is present.
To remember if lead I and III Reaching togather this consider as RIght Axis Deviation. And if Leaving away then Left Axis Deviation then it will Left Axis Deviation.
Causes:
Right and left axis deviation in themselves are seldom significant – minor degrees occur in tall, thin individuals and in short, fat individuals, respectively. However, the presence of axis deviation should alert you to look for other signs of right and left ventricular hypertrophy. A change in axis to the right may suggest a pulmonary embolus, and a change to the left indicates a conduction defect.
Left-axis deviation (more negative than –30°) occurs in diffuse left ventricular disease, inferior MI, and in left anterior hemiblock (small R, deep S in leads II, III, and aVF). Right-axis deviation (>90°) occurs in right ventricular hypertrophy (R > S in V1 ) and left posterior hemiblock (small Q and tall R in leads II, III, and aVF). Mild right-axis deviation is common in thin, healthy individuals (up to 110°).
Reference: ECG made easy by John R Hampton, Harrison manual of medicine, The ECG for beginners
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