Right axis deviation

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The hexaxial reference system is a diagram that is used to determine the heart's electrical axis in the frontal plane.
A very slight right axis deviation, possibly due to height and not a posterior block, approximately 110° from lead I+. One can tell the rough angle by which lead is isoelectric (or biphasic); in this case lead I is most biphasic and thus we know the axis is roughly perpendicular to this lead. However, the downstroke of lead I is slightly larger than the upstroke so we know it is slightly more than 90°.

In electrocardiography, Right axis deviation (RAD) is a heart condition wherein the electrical conduction of the heart has an electrical axis greater than +90° (or sometimes greater than +105°) on a 12-lead ECG. When the axis is extremely deviated to the right (i.e. between 180 degrees and -90 degrees) the condition may be termed extreme right axis deviation or northwest deviation).

RAD can be indicative of increased workload of the right ventricle (i.e. right ventricular hypertrophy). Examples include COPD, pulmonary arterial hypertension, or large pulmonary embolism. In the latter, for example, a clot in the pulmonary arteries requires more work of the right ventricle to push blood past it.

Alternatively, RAD can be reflective of loss of muscle power of the left ventricle, such as in left-sided myocardial infarction.

Conduction abnormalities can also cause RAD, left posterior fascicular block being an example of this.

Finally, anatomy can be the source of RAD. For instance, slight RAD is relatively common in tall, slim individuals, as the apex of the heart generally becomes more vertically aligned. Furthermore, RAD can be seen in individuals with situs inversus, a rare medical condition where the visceral organs are flipped across a vertical axis.

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