From the Guidelines
Hyperkalemia causes biphasic T waves on an ECG through its differential effects on cardiac repolarization, as evidenced by the most recent study 1. When potassium levels are elevated in the blood, the initial phase involves accelerated early repolarization in the epicardial and midmyocardial cells of the heart, while the endocardial cells are less affected. This creates a temporary voltage gradient across the myocardial wall during phase 3 of the cardiac action potential. As repolarization continues, the later phase is characterized by delayed terminal repolarization, particularly affecting the midmyocardial M cells. These sequential changes in repolarization timing across different layers of the heart muscle result in the characteristic biphasic appearance of the T wave, with an initial positive deflection followed by a negative component. This biphasic T wave morphology typically appears when serum potassium levels reach approximately 5.5-6.5 mEq/L and serves as an early ECG warning sign of developing hyperkalemia before more severe manifestations like peaked T waves, widened QRS complexes, and eventual cardiac arrest can occur, as noted in 1 and 1. Some key points to consider include:
- The severity of hyperkalemia can be classified as mild, moderate, or severe, with corresponding ECG changes, as described in 1.
- Hyperkalemia can lead to cardiac arrhythmias, including ventricular fibrillation and asystole, as reported in 1 and 1.
- Prompt recognition of biphasic T waves should trigger immediate evaluation and treatment of the underlying hyperkalemia, as emphasized in 1. It is essential to recognize that the electrocardiographic manifestations of hyperkalemia can vary among individuals and may not be predictable, as highlighted in 1. Therefore, it is crucial to consider the clinical context and laboratory results when interpreting ECG findings in patients with suspected hyperkalemia.
From the Research
Mechanism of Hyperkalemia-Induced Biphasic T Wave
The exact mechanism by which hyperkalemia causes a biphasic T wave on an electrocardiogram (ECG) is not explicitly stated in the provided studies. However, the studies do discuss the effects of hyperkalemia on the ECG and the possible mechanisms behind these changes.
Effects of Hyperkalemia on the ECG
- Hyperkalemia can cause various abnormal ECG findings, including peaked T waves, wide QRS complexes, and arrhythmias 2, 3.
- The severity of hyperkalemia can affect the presence and severity of these ECG abnormalities 2.
- In some patients, particularly those with chronic kidney disease, the ECG abnormalities may be minimal or absent despite high serum potassium levels 2, 4.
Possible Mechanisms
- Hyperkalemia can affect the cardiac action potential, leading to changes in the ECG 3.
- The peaked T wave is thought to be caused by a shortening of the action potential duration and an increase in the amplitude of the T wave 3.
- However, the studies do not provide a clear explanation for the mechanism behind a biphasic T wave in hyperkalemia.
Limitations of the Studies
- The studies primarily focus on the association between hyperkalemia and ECG abnormalities, rather than the specific mechanism behind these changes 5, 2, 4, 3.
- The studies do not provide a clear explanation for the development of a biphasic T wave in hyperkalemia, suggesting that further research is needed to understand this phenomenon.