This is a good example of sinus rhythm with left bundle branch block. There is some irregularity due to a PAC at the beginning. The QRS is wide at 144 ms (.14 seconds). There is also first-degree AV block, with a prolonged PR interval of 228 ms. The criteria for diagnosis of left BBB are: wide QRS, supraventricular rhythm, and a negatively-deflected QRS in V1 with a positive QRS in Leads I and V6.
Years ago, I was tasked with introducing 12-lead ECG interpretation to firefighter/paramedics who had been using ECG for rhythm monitoring for years. Some were eager to add to their skills, others - not so much. The feeling was, we have been doing just fine as we are. When finally convinced that they could interpret STEMI with a 12-lead, many were content to use the 12-lead ECG only for that.
This ECG offers a good example of the left bundle branch block pattern. * The QRS is wide at 144 ms. * There is a supraventricular rhythm - in this case, normal sinus rhythm with beat number two a PAC, and a slightly prolonged PR interval. * The QRS is negative in V1 and positive in V6 and also Lead I. This satisfies the ECG criteria for left bundle branch block.
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