Lecture Notes: Electrocardiography and Hypokalemia
Key Topic: Severe Hypokalemia and ECG Findings
Severe Hypokalemia is indicated by specific patterns on an ECG.
Key ECG Finding: The presence of prominent U waves which are as large or larger than the T wave.
This pattern is highly predictive of severe hypokalemia (potassium levels below 2.0).
Understanding U Waves
U waves appear as additional humps following the T wave.
Camel Humps: Large U waves can resemble what Marriot described as camel humps.
These are not minor blips but significant elevations that can be misleadingly interpreted as prolonged QT by computers.
Purists' View: It’s not truly a prolonged QT but rather T-U fusion.
Relationship Between Potassium Levels and ECG Waves
As potassium increases, T waves become larger.
As potassium decreases, T waves shrink and U waves grow.
In severe hypokalemia:
T wave may become flat.
T wave inversion occurs, leading to significant ST segment sagging.
Prominent U wave emerges, often seen in precordial leads V2, V3.
Recognizing Severe Hypokalemia Patterns
Reverse Wellens Wave: This term refers to the opposite of Wellens' sign, featuring biphasic T waves that first go down then up—indicative of hypokalemia.
Nickname: Nicola-Cam T Wave
Named by the lecturer for personal reasons, resembling a roller coaster.
Practical Application in Clinical Settings
Use the pattern as an early diagnostic tool before lab results confirm hypokalemia.
Tips for Practitioners:
Involve interns to demonstrate the finding; mocks use of ultrasound to diagnose hypokalemia.
Apply this knowledge to impress colleagues by diagnosing hypokalemia from the ECG alone.
Examples from ECG
Patterns of T wave inversion and large U waves in leads V2 and V3 strongly suggest hypokalemia.
Despite computer misdiagnosis as prolonged QT, recognize the T wave fusion with U waves.
This pattern is a red flag for increased risk of ventricular arrhythmias.
Conclusion
Recognizing these ECG patterns allows for early intervention in hypokalemic patients.
Correct interpretation of these signs can guide early treatment decisions and avoid misdiagnosis.