The nurse caring for a client with a serum calcium of 6.8 mg/dL. What would the nurse expect the change on the electrocardiogram (ECG)?
A. None. This is a normal calcium level.
B. Prolonged QT interval.
C. Shortened ST segment.
D. Widened T wave.
Correct Answer: B. Prolonged QT interval.
The normal serum calcium level is 8.6 to 10 mg/dL. A serum calcium level lower than 8.6 mg/dL indicates hypocalcemia. Electrocardiographic changes that occur in a client with hypocalcemia include a prolonged ST or QT interval. The ECG hallmark of hypocalcemia remains the prolongation of the QTc interval because of lengthening of the ST segment, which is directly proportional to the degree of hypocalcemia or, as otherwise stated, inversely proportional to the serum calcium level. The exact opposite holds true for hypercalcemia.
Option A: High and low levels of ionized serum calcium concentration can produce characteristic changes on the electrocardiogram. These changes are almost entirely limited to the duration of the ST segment, with no change in the QRS complexes or T waves.
Option C: The ST segment on an electrocardiogram (ECG) normally represents an electrically neutral area of the complex between ventricular depolarization (QRS complex) and repolarization (T wave). However, it can take on various waveform morphologies that may indicate benign or clinically significant injury or insult to the myocardium.
Option D: A widened T wave occurs with hypercalcemia. On electrocardiography (ECG), characteristic changes in patients with hypercalcemia include shortening of the QT interval. ECG changes in patients with very high serum calcium levels include the following: slight prolongation of the PR and QRS intervals; and T wave flattening or inversion.