See quick 12 lead ECG interpretation
In this article an approach to EKG interpretation of bundle branch blocks is outlined. For more explicit explanations and more examples check out the separate articles right bundle branch block (RBBB) and left bundle branch block (LBBB). Though the ECG criteria differ, identifying the two types of bundle branch block can be done using a similar approach. Here are some points to consider:
1. The duration of the QRS complex is ≥ 0.12 seconds in both types of bundle branch block. Look for that on the EKG. Most likely a prolonged QRS is what will raise your suspicion of bundle branch block.
2. Think of lead V1 as “looking” at the right side of the heart. Thus this lead is where to identify RBBB. Contrary lead V5 and lead V6 are “looking” at the left side of the heart. Use these leads to possible spot LBBB. Look for characteristic EKG patterns besides QRS ≥ 0.12 sec. That is: an extra R wave in lead V1 (in RBBB) and a broad notched R wave plus an absent Q wave in lead V5-V6 (in LBBB).
3. Seek to confirm your suspicion by identifying other diagnostic criteria as the late wide/slurred S wave in lateral leads seen in RBBB and maybe ST segment or repolarization changes seen in both types of bundle branch blocks, but in different leads depending on which type is in question.
4. Remember to always analyze the ECG using a systematical approach. Think of other possible reasons to your ECG findings. Acute myocardial infarction can cause bundle branch block and wide QRS complexes are also seen in ventricular arrhythmia.
See the links below for more on conduction abnormalities.
– Mathias
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