Mr. Jones is admitted to your unit from the ER with a serum calcium concentration of 5.2mg/dL. Which ECG change do patients with hypocalcemia often demonstrate?
A. Prolonged QT interval
B. Shortened PR interval
C. Shortened QT interval
D. Prolonged PR interval
Size Matters: Small Ca Equals Big Heart
Let’s start by reviewing low calcium:
As critical care nurses, we are concerned with those “big events”.
Here’s the deal:
Hypocalcemia impairs cardiac contractility. The result is dilatation of the heart.
Remember in second grade when you learned that the shortest distance between two points is a straight line? This is the same concept except our “vehicle” is electricity and the distance is the surface area of the heart. When the heart is bigger sized the electricity has a much larger distance to go.
So let’s put 2 and two together here:
If a low calcium level makes the heart bigger - than we are left with:
- A longer QT interval
- A longer ST segment
So What? Well -
A reduced calcium level can result in a prolonged QT interval or QTc (QT corrected) as described above.
Combine this with the fact that if your calcium is low then your magnesium will also be decreased and we are setting up our heart for the perfect storm. As a matter of fact, the odds of going into a ventricular rhythm are increased. Not just any ventricular arrhythmia -
Polymorphic ventricular tachycardia: AKA torsades de pointes. Ventricular arrhythmias result in severe hypotension and cardiogenic shock.
So a tiny little electrolyte that no one really thinks about just killed your patient.
Key point: If calcium is acutely low, let’s look at getting it fixed.
So the correct answer:
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