This interesting and instructive ECG was contributed by Jason Roediger, ECG Guru Extraordinaire, and one of the experts featured on our '"Ask the Experts" page. It is an excellent example of acute inferior wall M.I. with left bundle branch block. Left bundle branch block normally displays ST elevation and depression in a "negative concordance" pattern. That is, when the QRS complex is negative, we may expect ST elevation. When the QRS is positive, ST depression is seen. In this ECG, there is clearly ST elevation in Leads II, III, and aVF, and the ST segments have a distinct coved upward appearance. This shape signals to the experienced ECG interpreter that there is an acute injury.
Unfortunately, the normal deviations of the ST segment seen in left bundle branch block can make diagnosis of acute M.I. difficult. For a good example of a left BBB without acute M.I., please refer to the ECG archives on this site. Often, students are taught that it is IMPOSSIBLE to see an acute M.I. in the presence of LBBB. This is not true, as this ECG clearly illustrates. See the March 4, 2012 blog post on the ECG Guru regarding this topic.
This is a good example of wide complex tachycardia that must be evaluated for V Tach vs supraventricular rhythm with left BBB.
There is an irregular rhythm. When the rate is fast, it is important to look at a longer strip, as sometimes fast rates will cause the rhythm to look regular. We know that monomorphic V Tach is not irregular, so that tells us that we are looking at atrial fibrillation.
The ECG criteria for left bundle branch block is met here: 1) supraventricular rhythm (atrial fib), 2) wide QRS, and 3) negative QRS in V1 and positive QRS in Leads V6 and I.
With wide complex tachycardia, there is always a chance of ventricular tachycardia, and the patient should be treated as V tach until proven differently. For more on determining whether a WCT is V tach or SVT with ventricular conduction delay, go to this LINK.
Today, we are revisiting an ECG from the archives, with a NEW comment from Dr Ken Grauer. This ECG is worth a second look because it is a very good example of the left bundle branch block pattern. It's also a good ECG to use when discussing treatment of wide-QRS tachycardias.
This ECG demonstrates a wide complex tachycardia with classic signs of LBBB: wide QRS, QRS negative in V1 and positive in V6 and Lead I, and supraventricular rhythm. P waves are difficult, if not impossible, to discern for sure. The machine does give a P wave axis and PR interval. When evaluating a wide complex tachycardia, the patient's hemodynamic stability will initially determine treatment. All WCTs should be treated as V TACH until proven otherwise. The presence of a typical LBBB pattern makes LBBB very likely, but is not a sure thing. This patient was confirmed to have LBBB when the rate slowed, the P waves became visible, and the QRS complexes did not change.
