This patient presented with weakness, decreased urine output, and vomiting:
|What is the ECG diagnosis?|
There is a very long QT (computer says the QTc is 525 ms) due to a long ST segment. This is pathognomonic for hypocalcemia. The ionized Ca was 2.34 mg/dL (normal is 4.4-5.2)
The Cr was 12.1 indicating (new onset) of renal failure.
Calcium was given without much change.
The next AM the non-ionized Ca was 5.7 mg/dL (normal: 8.6-12.0).
Here was a repeat ECG:
|QTc 523. Long ST segment remains.|
Although the QT is very long, long QT due to hypocalcemia is rarely associated with Torsades de Pointes.
Comment by KEN GRAUER, MD (3/19/2019):
There are a number of ECG patterns that should immediately suggest a clinical diagnosis. This is one of them! The value of recognizing this particular ECG pattern — is that it may expedite your clinical diagnosis even before laboratory results return.
- To my reading — both of the ECGs in this case looked similar. I chose the 1st ECG — and for clarity, I’ve put it together with a user-friendly method I devised many years ago to rapidly estimate the QTc (Figure-1):
|Figure-1: The initial ECG in this case — and a rapid method for estimating the QTc (See text).|
- Applying my method to the case at hand — the rhythm in ECG #1 is regular, with an R-R interval just under 4 large boxes. Thus, the heart rate is just a bit over 75/minute (ie, 300÷4). I selected lead V3 as one of the leads where we can clearly define the onset and offset of the QT interval. I measure the QT in this lead to be ~2.4 large boxes = 480 msec. Using a correction factor of 1.1 (since the heart rate ~75/minute) — I estimate the QTc = 480 + [480 X .1 = 48) = 480 + 48 ~528 msec. For speed and ease of calculation — I usually round off values (it’s all an estimate anyway! ) — but I’ve enjoyed being able to get very close to computer-calculated QTc values by this simple correction factor method.
- Clinical correlation will typically suggest which one or more of these 3 causes of a prolonged QTc is operative for the case at hand. The patient in the case presented here had new-onset renal failure — so, assuming normal mentation and no potentially QT-altering drugs — electrolyte disturbance should be strongly suspected.