![]() ![]() 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. ST-T changes: Left sided leads (V5, V6, I and aVL) shows T-wave inversions and ST segment depressions.Leads V5-V6: Broad, clumsy, completely positive and often notched R-wave.The S-wave in V1 may be notched and resemble the letter “W”. If it is missing, a QS complex appears in V1 and occasionally V2, but rarely V3. The small r-wave is missing or smaller than normal. The following ECG criteria are commonly used to diagnose LBBB: ST-T changes always occur in the presence of LBBB. In addition to prolonged QRS duration, LBBB is characterized by deep and broad S-waves in leads V1 and V2 and the broad clumsy R-waves in V5 and V6. A QRS duration of 120 ms (0.12 s) or more is required to diagnose a complete left bundle branch block. The hallmark of LBBB is the prolonged QRS duration. It is easy to diagnose left bundle branch block (LBBB). ECG criteria for left bundle branch block (LBBB) These ECGs are printed at paper speed 50 mm/s. Finally, note that there are marked difference in the ECG pattern between LBBB and RBBB. These ST-T changes are due to abnormal repolarization and they are expected to occur in both LBBB and RBBB. Also note that both left bundle branch block (LBBB) and right bundle branch block (RBBB) cause marked ST-T changes, including ST elevations, ST depressions and inverted (negative) T-waves. A QRS duration of 120 ms (0.12 s) is required to diagnose bundle branch block. As evident from these ECGs, the cardinal difference between normal conduction and bundle branch blocks is the QRS duration: bundle branch blocks are caused by dysfunctional bundle branches, which results in slow (and abnormal) activation of ventricular myocardium and thus prolonged QRS duration. These ECGs show the difference between normal conduction, left bundle branch block (LBBB) and right bundle branch block (RBBB). The hallmark of left bundle branch block (LBBB) is QRS duration ≥0,12 seconds, deep and broad S-wave in V1/V2 and broad clumsy R-wave in V5/V6. Refer to Figure 1, where the difference between normal conduction, right bundle branch block ( RBBB) and left bundle branch block (LBBB) is illustrated. Depolarization of the left ventricle will be carried out by impulses spreading from the right ventricle. Because the left bundle branch is dysfunctional, the impulse will spread (through the left ventricle) partly or entirely outside of the conduction system such impulse conduction is slow and therefore the QRS duration becomes prolonged. Left bundle branch block (LBBB) is the consequence of anatomical or functional dysfunction in the left bundle branch, causing the impulse to be blocked. doi:10.1097/HJH.Left bundle branch block (LBBB): ECG criteria and clinical implications Left ventricular hypertrophy identified by cardiac computed tomography and ECG in hypertensive individuals: a population-based study. Effect of mitral valve replacement on reduction of left atrial size. Pande S, Agarwal SK, Mohanty S, Bansal A. Changes in left atrial size in patients with persistent atrial fibrillation: a prospective echocardiographic study with a 5-year follow-up period. Endothelin-1 is associated with dilatation of the left atrium and can be an independent predictor of atrial fibrillation after mitral valve surgery. Association between diastolic dysfunction and future atrial fibrillation in the Tromsø Study from 1994 to 2010. Tiwari S, Schirmer H, Jacobsen BK, et al. ![]() Prevalence of echocardiographic left-atrial enlargement in hypertension: a systematic review of recent clinical studies. Huge left atrium accompanied by normally functioning prosthetic valve. ![]()
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