This is a somewhat overcomplicated concept and is frequently irrelevant to clinical practice. There are only three main areas where identifying cardiac axis has clinical relevance. The first is when trying to decide whether there may be ventricular tachycardia present on the ECG. An abnormal cardiac axis may help one to conclude that this is VT rather an SVT. Secondly, when an accessory pathway is present, it helps to localise the position of the pathway within the heart. This fact is useful largely to electrophysiologists rather than the rest of the profession. Finally, when the patient has RBBB, if a left axis or a right axis deviation is present, this represents abnormality of both bundle branches and may precede complete heart block or asystole in the future.
An easy way of establishing axis is to look at lead I, II and III.
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