Wikipedia:Imperial College/Project Page/Sandbox causes

Causes
Fascicular Block

Main article: Left Posterior Fascicular Block

Blockage of the left posterior fascicle would lead to activation of the anterior portion of the left ventricle followed by activation of the rest of the ventricle in a superior to inferior direction and directed towards the right. This would lead to right axis deviation findings on an ECG. Bifascicular block is a combination of right bundle branch block and either left anterior fascicular block or left posterior fascicular block. Conduction to the ventricle would therefore be via the remaining fascicle. The ECG will show typical features of RBBB plus either left or right axis deviation.

Lateral Myocardial Infarction

The lateral wall of the left ventricle is supplied by branches of the left anterior descending (LAD) and left circumflex (LCx) arteries. Infarction of the lateral wall will thus lead to deviation of the axis away from the site of infarction.

Right ventricular hypertrophy

Increased thickness of the right ventricle leads to right axis deviation (see above).

Pre-excitation Syndromes

Pre-excitation refers to early activation of the ventricles due to impulses bypassing the AV node via an accessory pathway. Accessory pathways are abnormal conduction pathways formed during cardiac development. An example of Pre-excitation Syndromes is Wolf-Parkinson White Syndrome. Here, the presence of a left lateral accessory pathway leads to right-axis deviation.

Ventricular Tachycardias

Fascicular tachycardia usually arises from the posterior fascicle of the left bundle branch. They produce QRS complexes of relatively short durations with a right bundle branch block pattern. Tachycardias originating in the anterior left fascicle would lead to right axis deviation.

Right ventricular outflow tract tachycardia originates from the outflow tract of the right ventricle or the tricuspid annulus. As it arises from the right ventricle, the impulse spreads inferiorly from beneath the pulmonary valve, and there right axis deviation.

Ventricular Ectopy

Ventricular ectopy is when the heartbeat is an abnormal heartbeat where the QRS complex is significantly wider. When the origin of the ectopic heartbeat is in the anterior fascicule then there is right axis deviation.