On paper speed 50 mm/s one large square equals 100 ms and one small square equals 20 ms. Thus, on 25 mm/s 3 small squares equals 120 ms. Recall that at paper speed 25 mm/s, one large square equals 200 ms and one small square equals 40 ms. Use large squares to estimate the QRS duration as shown in this illustration. It is easy to recognize LBBB on 25 mm/s and 50 mm/s. Furthermore, the S-wave in V5/V6 is typically very broad in the presence of RBBB.įigure 4 displays how QRS duration can be calculated rapidly on 25 mm/s and 50 mm/s paper speed. RBBB is characterized by rSR’ complex in V1/V2, meaning that there are two R-waves and a large S-wave. As seen, LBBB is characterized by deep and broad S-waves in V1/V2 and broad and clumsy R-waves in V5/V6. This figure illustrates ECG patterns in LBBB and RBBB. Abnormal repolarization manifests with ST-T changes, including ST elevations, ST depressions and negative T-waves.įigure 3 compares the characteristic ECG patterns in leads V1/V2 and leads V5/V6 in the presence of left bundle branch block (LBBB) and right bundle branch block (RBBB). Abnormal depolarization manifests as an abnormal QRS complex with duration 120 ms or more. Because activation (depolarization) of the left ventricle is abnormal in the presence of LBBB, the recovery (repolarization) will also be abnormal. Left bundle branch block (LBBB) at two different paper speeds (25 mm/s and 50 mm/s). The ST-segment elevation rarely exceeds 5 mm.įigure 2 illustrates left bundle branch block at two paper speeds (25 mm/s and 50 mm/s). V1–V3 shows ST-segment elevation and positive T-waves.
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