A patient arrived after PEA arrest, with ROSC after intubation and chest compressions.
Here is the initial 12-lead ECG:
|What is the appropriate therapy?
This ECG is all but diagnostic of hyperkalemia. There is an irregular, slow, wide complex rhythm. Is it ventricular escape? (no, because it is irregular and there appear to be conduced P-waves). Or atrial fib with slow ventricular response? (no, because it is irregular and there appear to be conducted P-waves).
Because you can see some conducted atrial activity in lead II across the bottom, you know that it is of supraventricular origin. So then it is clear that there is Right Bundle branch block (RBBB). However, it is extremely wide (the computer measured it at 193 ms, and I think this is correct), much wider than RBBB should be. Also, you can see peaking of the T-waves in many leads.
The physicians did not recognize this, but they did think to give calcium empirically. The K returned at 7.1 mEq/L and complete therapy for hyperK was given.
Here is the ECG after therapy:
|Probable junctional rhythm
QRS of 133 ms by computer (looks correct)
See more similar cases here:
QRS duration in RBBB and LBBB
RBBB by definition has a long QRS (at least 120 ms). But very few are greater than 190 ms. Literature on this is somewhat hard to find, but in this study of patients with RBBB and Acute MI, only 2% of patients with pre-existing RBBB had a QRS duration greater than 200 ms. This study only reported durations in 10 ms intervals up to 150 ms, but one might extrapolate from it that approximately 10% of patients with baseline RBBB have a QRS duration greater than 160 ms. 193 ms would be quite unusual.
The point of this is that if you see BBB with a very long QRS, you must suspect hyperkalemia or sodium channel blockade (e.g, flecainide). Then of course the peaked T-waves should tip you off. Unless a patient has severe hypercalcemia (this should be evident by a short QT on the ECG as seen at the bottom of this post), or severe hyperphosphatemia (which is very unusual), treatment with calcium is harmless if you read an ECG falsely positive for hyperkalemia.
So don’t wait for the laboratory K or you might be resuscitating a cardiac arrest (see the case at this post with ECGs #3 and #4 of this post).
How about LBBB?
In this study of consecutive patients with LBBB who were hospitalized and had an echocardiogram, 13% had a QRS duration greater than 170 ms, and only 1% had a duration greater than 190 ms.
Hypercalcemia (courtesy of K. Wang)
|Notice the very short QT interval, and very short ST segment