This is complementary to a recent previous post.

A dialysis patient presented with pedal edema.  As a screen for hyperkalemia, an ECG was recorded:

QRS duration is 183 ms.  What do you think?

A previous ECG was immediately found at a time when the K was 6.1 mEq/L:

QRS duration is 167 ms, but a previous ECG with a normal K had a QRS of 184 ms. What do you think?

This shows how subtle hyperkalemia can be, and yet still be diagnostic.

See the two side-by-side here:

                        Previous, with K 6.0 mEq/L                                            This Visit

Notice how the ST segment is flatter on the right than on the left (see especially lead V4).  Such a flat ST segment is part of what makes the T-wave peaked, as the rise of the T-wave from a flat ST segment is very steep.

My previous post showed the failure to recognize such a subtle sign of hyperkalemia and the subsequent v fib arrest.

In RBBB, a QRS duration greater than 175 ms should make you strongly suspect hyperK (see this link!).  In this case, in the past, there actually had been such a long QRS in the presence of a normal K, so this case was an exception.

The patient’s K was 7.1 mEq/L.