Hypokalemia and ECG: The essential mnemonic device for remembering cardiac signs
Hypokalemia, defined by a potassium deficit in the blood plasma when the blood potassium level is less than 3.5 mmol/L, is a hydroelectrolytic disorder whose major severity lies in the potential occurrence of cardiac rhythm disorders that can be life-threatening. These cardiac abnormalities are crucial to identify, particularly by electrocardiogram (ECG).
Why is an electrocardiogram essential in cases of hypokalemia?
Hypokalemia may remain asymptomatic in some patients, especially if it is moderate or develops gradually. However, even moderate hypokalemia (greater than 3 mmol/L) increases the risk of arrhythmias in patients with ischemic heart disease or those treated with digoxin. Clinical signs are not specific, but cardiac rhythm or conduction disorders should be prioritized. Therefore, ECG is an essential tool for visualizing the impact of hypokalemia on the electrical activity of the heart.
The electrocardiographic changes typical of hypokalemia
The electrocardiogram of a person with hypokalemia may show several diffuse changes, the appearance of which depends on the degree of hypokalemia. These successive signs include:
- ST segment depression.
- T-wave collapse or inversion.
- The increase in amplitude of the physiological U wave, which can induce a fictitious modification of the 'QT' interval. This U wave occurs after the T wave and can sometimes merge with it, giving a T wave with an atypical appearance.
- The widening of the QRS complexes.
- The appearance of rhythm disorders, whether supraventricular (such as atrial fibrillation or flutter) or ventricular (ventricular extrasystoles, ventricular tachycardia, torsades de pointes, or ventricular fibrillation).
A mnemonic to memorize the ECG signs of hypokalemia
Given the variety and complexity of these ECG changes, a mnemonic device can be very useful for remembering them. The mnemonic specifically mentioned in the sources for hypokalemia is:
"You're flattening Hugh Grant under this tornado"
Decoding the mnemonic: how to remember ECG changes?
This mnemonic helps link the changes observed on the ECG to an easy-to-remember sentence. Here's how each part of the sentence corresponds to the electrocardiographic signs:
- « T'aplatis » refers to the flattened or inverted 'T' wave.
- « Hugh Grant » (or just 'Hugh', which sounds like 'U') indicates the appearance or increase of the 'U' wave. The name 'Grant' may also evoke the prolongation of the QT interval (although the U wave may give an impression of QT prolongation, the mnemonic associates it with the U wave and QT prolongation distinctly).
- « Under this » refers to the ST segment depression.
- « tornado » alludes to potentially severe ventricular rhythm disorders (such as torsades de pointes or ventricular fibrillation) that may occur.
By using this simple method, it becomes easier to remember the main electrocardiogram changes in the presence of hypokalemia and thus recognize this potentially serious condition.
