Right axis deviation with rS in I and aVL, qR in II, III and aVF, and a QRS under 0.12 s.
The posterior fascicle is blocked, so the left ventricle activates from the anterior fascicle, from above downward. That gives you right axis deviation, rS in I and aVL, qR in II, III and aVF, an R-wave peak time in aVF over 45 ms, and a narrow QRS. It's rare on its own (it usually comes with RBBB), and it's a diagnosis of exclusion: right ventricular hypertrophy, pulmonary embolism and lateral infarction must be ruled out first.
Each is a standard 12-lead: 2.5 seconds of each lead in four columns, with 10 seconds of lead II along the bottom, drawn to scale (25 mm a second, 10 mm a millivolt). The measurements are under each one.
Left axis deviation (-45° to -90°) with qR in I and aVL, rS in II, III and aVF, and a QRS under 0.12 s.
A QRS axis beyond +90°: lead I negative, aVF positive.
The ECG tool in the app gives you a new 12-lead every time and walks you through reading it: rate, QRS, axis, then where the ST is up and down. It's part of the Paramedic level, and you can try 5 ECGs a day free.
Try the 12-lead drill
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