ECG Features

• Mean ventricular (QRS) axis between +110° and +180° in adults with a mean QRS duration <120 ms
• Typically rS complexes in I and aVL, along with qR complexes in II, aVF, and III
• Absence of other causes of right axis deviation (e.g. lateral myocardial infarction, dextrocardia, right ventricular hypertrophy)

Note: The entire left bundle conduction system of the heart is made up of an left anterior and posterior fascicle. The left posterior fascicle supplies fibers to the posterior and inferior wall of the left ventricle. It is shorter and thicker than the left anterior fascicle and receives dual blood supply from both the left and right coronary arteries. Multivessel coronary artery disease is the most common cause of left posterior fascicular block.