A dialysis patient presented with progressive weakness over 3 days. He denied chest pain or shortness of breath. He also had a history of cardiomyopathy, DM, and HTN.
Here is his emergent ECG:
|It is slow and regular. There are no P-waves.
So it is junctional rhythm or a right bundle escape, mimicking LBBB
(Or it is sinus with a hidden P-wave).At first glance, it appears to have Left Bundle Branch Block (LBBB), with rS in right precordial leads and wide monophasic R-wave in I, aVL, V5 and V6.
The ST segment in V2 is excessively proportionally discordant, at 5 mm divided by S-wave of 20 mm = 25%.
Third criterion positive in modified Sgarbossa!
Is this LAD occlusion in the presence of LBBB?
As in yesterday’s case of RBBB: Is this just right bundle branch block?, The QRS is too long.
The computer measurement of 218 ms is correct.
Moreover, the T-waves are very peaked.
A previous ECG was found and was normal.
Thus, this ECG is diagnostic of hyperkalemia.
There may be an underlying sinus pacemaker, but it is impossible to tell because the atrium does not depolarize and thus no P-wave is visible
Remember that hyperkalemia causes PseudoSTEMI STE in V1 and V2.
See this case:
In this case today, that pseudoSTEMI pattern is added to a pseudo-LBBB to result in a modified Sgarbossa false positive morphology!
LBBB and QRS duration
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.
The clinicians recognized this as hyperkalemia. The lab result was too high to measure (greater than 9.4 mEq/L).
The patient received albuterol x 6, calcium gluconate x 5 g, D50 (50 ml) x 2, 5 units regular insulin, 40 mg furosemide, and 50 mL of Na bicarb.
It turns out he had been told several days earlier that his K was low and so he had eaten several baked potatoes. Baked potatoes have about 926 mg of K (boiled potatoes have 296 milligrams, and an average banana has 426 mg). KCl is 74 mg per mEq, so the number of milliequivalents is far less, but a dialysis patient eating many baked potatoes is sufficient to substantially raise the K.
After dialysis, this was the followup ECG:
|Normal, except V1 and V2 are recorded too high on the chest (fully negative P-wave in V1, negative P-wave in V2) and there is slight ST depression.