An elderly woman presented to the emergency department with generalized weakness. She and her family said she did not have a fever, but had a history of frequent UTIs.
They also said she had no syncope, palpitations, pain, shortness of breath, cough or other symptoms. His vital signs were normal and an ECG was performed (shown).
The computer read it as an atrial pacemaker and an anteroseptal MI, probably recent, and came up with the diagnosis: acute MI.
What is the most likely cause of the ECG findings in this patient? Hypokalemia, pulmonary embolism, acute coronary syndrome or hypocalcemia?
The ECG showed biphasic T waves and prominent U waves in the precordial leads. He also showed flat, non-specific T waves in the lower leads and QT or QU prolongation. These findings are suspicious of hypokalemia, although descending then ascending T waves are more common with hypokalemia than ascending then descending T waves seen here.
Dr. Smith received this ECG without any clinical information and replied, “This ECG screams hypokalemia.” His additional lessons: Hypokalemia does not actually produce descending T waves as is often taught; it actually mimics descending T waves, as it can cause an ST depression followed by an ascending U wave.
Hypokalemia can also cause an apparent prolongation of the QT interval which is incredibly long, and it is usually actually a QU interval when the QT interval is incredibly long. Another common feature of hypokalemia on this ECG that is almost pathognomonic are the long, sunken (really SU) ST segments.
The correct answer, of course, is hypokalemia. U waves, nonspecific T waves, and long QT interval in a patient with generalized weakness are likely to be hypokalemia. The clinical presentation was less suggestive for pulmonary embolism, although it may cause flat or nonspecific changes in the T wave, but is unlikely to cause U waves. The clinical presentation corresponds to acute coronary syndrome and up and down T waves correspond to ACS, but U waves are unlikely (but possible) in ACS. The clinical presentation was less suggestive of hypocalcemia, although this may cause flat or nonspecific T wave changes and prolonged QT, but is unlikely to cause U waves.
The patient’s troponin-i was 0.08 ng/L at both doses four hours apart (99% URL
Hypokalemia can cause many and varied ECG findings and the degree of abnormalities can vary greatly with the degree of hypokalemia. The results of this ECG are more pronounced than you would expect with a potassium of 2.8. More serious ECG findings may be more likely when other electrolyte abnormalities are present or when the electrolyte abnormality develops more acutely.
Access links in REM reading this on our site: www.EM-News.com.
Comments? Write to us at [email protected].
Dr Pregersonis an emergency physician with Palomar Health in San Diego. He is the author of 1 Minute Emergency Medicine Consultation, The 8 in 1 Quick Reference Guide for Emergency Services, A to Z Emergency Pharmacopoeia and Antibiotics Guide, Don’t Try This at Home, and Think twice: more lessons from emergencies. Follow him on Twitter@EM1MinuteGuru, and visit his website athttps://em1minuteconsult.com. Read his past columns onhttp://bit.ly/BradyCardiaEMN. Dr. Smithis Professor of Emergency Medicine at Hennepin Healthcare, Professor of Emergency Medicine at the University of Minnesota Medical School, and Editor of Dr. Smith’s ECG Blog. (https://bit.ly/306xAeq). Follow him on Twitter@smithecgblog.