Trace 3 Farzad
A 54-year-old female presents to the ED with 2 days of palpitations associated with muscle cramping and upper extremity paresthesias. The patient is found to have normal vital signs and the following ECG was obtained. What is the most likely cause of the patient’s symptoms based solely on this ECG?
Answer is C: Hypocalcemia
This ECG demonstrates a prolonged QT-interval. Although the ECG machines calculation of the QT-interval is typically accurate, clinicians can quickly evaluate clinically significant QT-interval prolongation by checking to see where the T-wave ends in relation to the R-R interval. If you draw an imaginary line midway between two consecutive R waves, the T-wave should normally end before ½ the R-R wave distance. Beware of a prolonged QT-interval when the T-wave ends after ½ the R-R wave distance as seen in this ECG.
The differential diagnosis for a prolonged QT-interval includes: electrolyte abnormalities, medications, hypothermia, cardiac ischemia, increased intracranial pressure, and congenital causes. Many of these etiologies cause QT-interval prolongation because of abnormal T-waves that lengthen the T-wave and thus the QT-interval. In this case, the T wave itself is normal in size and the QT-interval prolongation is due to a long ST-segment. Only two conditions cause QT-prolongation specifically by prolongation of the ST-segment; hypocalcemia, and hypothermia. This patient had normal vital signs and was found to have significant hypocalcemia that resulted in her symptoms and ECG abnormalities. Her symptoms and QT-interval improved with calcium supplementation.
Prolongation of the ST-segment contributing to a prolonged QT-interval is the hallmark ECG change in hypocalcemia. Only hypocalcemia and hypothermia do this so when the temperature is normal, consider hypocalcemia!
Check out the following resource for more information about hypocalcemia and prolonged QT-intervals:
ECG Weekly – August 8, 2016: https://ecgweekly.com/2016/08/amal-mattus-ecg-case-of-the-week-august-8-2016/