How is a bundle branch block diagnosed?
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In normal cardiac conduction, impulses travel equally down the left and right bundles, with the septum activated from left to right and the formation of small Q waves in lateral leads Show
 1) Conduction delay means impulses travel first via the right bundle branch (black arrow) 2) Septum is activated from right-to-left (yellow arrows) 3) Overall depolarisation vector is directed towards lateral leads (red arrow) ECG QRS MorphologyQRS Morphology in the Lateral LeadsThe R wave in the lateral leads may be either “M-shaped”, notched, monophasic, or an RS complex QRS Morphology in V1The QRS complex in V1 may be either:
1) rS complex in V1 (tiny R wave, deep S wave) 2) Characteristic lateral lead morphology in V5-6 3) Note appropriate discordance in V1 with ST elevation and upright T wave What about the ST elevation?
Causes of Left Bundle Branch BlockIt is unusual for LBBB to exist in the absence of organic disease. Causes are varied and include:
New LBBB in the context of chest pain was once considered a “STEMI-equivalent” and part of the criteria for thrombolysis. However, more up-to-date data suggests that chest pain patients with new LBBB have little increased risk of acute myocardial infarction at the time of presentation. Practice has now evolved to examining for excessive discordance or concordant ST segment changes indicative of infarction. ECG Examples of LBBBExample 1Broad notched R waves are best appreciated in leads aVL and I here. There is absence of Q waves in leads V5-6. Example 2 LBBB with AF. Note deep S waves in leads V1-3 and tall broad R waves laterally. Appropriate discordance is present. Example 3 Incomplete LBBBIncomplete LBBB is diagnosed when typical LBBB morphology is associated with a QRS duration < 120ms. Differential Diagnosis
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cite ECG LIBRARYElectrocardiogram EKG Library Robert ButtnerMBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner Ed BurnsEmergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library | How is bundle branch block diagnosis?A bundle branch block is usually diagnosed with an electrocardiogram. Your doctor also may want to test the health and function of your lung. Testing may also include blood work.
What are the diagnostic criteria for a left bundle branch block?A QRS duration of 120 ms (0.12 s) or more is required to diagnose a complete left bundle branch block. 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. ST-T changes always occur in the presence of LBBB.
Can echocardiogram detect bundle branch block?Abnormal heart rhythm caused by bundle branch block can be diagnosed with an electrocardiogram (ECG) or echocardiogram. Treatment of the disorder may be unnecessary, but in severe cases a pacemaker and/or management of underlying heart disease may be required.
Should I be concerned about a bundle branch block?How serious is a right bundle branch block? If you have no symptoms and no heart disease, a right bundle branch block is not serious. But if you've already had heart failure or a heart attack along with right bundle branch block, it puts you at a higher risk of death.
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