ECG Changes in Hyper/Hypokalemia

ECG Changes in Hyperkalemia and Hypokalemia

Hyperkalemia
Key Concept: T Wave Amplitude

The height of the T wave is directly related to potassium levels. In limb leads, the normal T wave height is less than 5 mm, and in chest leads, it's less than 10 mm. The amplitude and morphology of the T wave can provide valuable insights into the patient's potassium balance.

  • Hyperkalemia (Elevated Potassium): T wave amplitude increases, becoming tall and peaked.

  • Hypokalemia (Low Potassium): T wave amplitude decreases, potentially becoming flattened or inverted.

Early ECG Finding: Tall Tented T Waves

The earliest ECG finding in hyperkalemia is tall, tented T waves. These are distinct from hyperacute T waves, which have a relatively rounded edge and are associated with myocardial infarction or acute coronary syndromes. Tall tented T waves are characteristically pointed, and their height can often exceed that of the R waves. This change reflects the altered repolarization process due to elevated potassium levels.

ST Segment Elevation

Following the T wave changes, ST-segment elevation can occur. Hyperkalemia is included in the mnemonic "elevation," which helps in remembering the potential causes of ST-segment elevation on an ECG. The ST-segment elevation in hyperkalemia is usually more subtle compared to that seen in myocardial infarction.

P Wave Changes and PR Interval Prolongation

In hyperkalemia, the repolarization vector becomes more prominent, while the depolarization vector becomes less prominent. This shift results in:

  • Decreased P Wave Amplitude: The P wave becomes smaller and may even disappear altogether as potassium levels rise to 7 mEq or higher. This is because hyperkalemia affects atrial depolarization.

  • Prolonged PR Interval: The PR interval is prolonged due to the slowing of atrial depolarization. This is a result of the altered potassium gradient affecting the conduction speed in the atria.

QRS Complex Broadening

Elevated potassium levels slow the heart's electrical conduction, leading the QRS complex to broaden. This widening indicates a delay in ventricular depolarization.

Sine Wave Pattern

As hyperkalemia worsens, particularly when potassium levels reach 8 mEq or higher, the broad QRS complex merges with the T wave, creating a sine wave pattern. This is a critical, life-threatening sign, indicating severe derangement of cardiac conduction.

Diastolic Arrest

Hyperkalemia can ultimately lead to diastolic arrest, which is a primary cause of death in these patients. Before reaching this stage, patients may experience arrhythmias such as ventricular fibrillation, which can then deteriorate into a flat line and diastolic arrest.

  • Key Difference: Hyperkalemia leads to diastolic arrest, while hypercalcemia (calcium levels of 13-15) can cause systolic arrest, characterized by a prolonged contraction of the heart.

ECG Changes Summary in Hyperkalemia

  • Increased T wave height, leading to tall, tented T waves.

  • ST-segment elevation, though typically less pronounced than in myocardial infarction.

  • QRS broadening, indicating slowed ventricular depolarization.

  • PR prolongation, due to delayed atrial depolarization.

  • P wave disappearance, at higher potassium levels.

  • Sine wave pattern, in severe hyperkalemia.

Treatment of Hyperkalemia

First-Line Management: Calcium Gluconate

The first-line treatment for hyperkalemia is intravenous calcium gluconate or calcium chloride, which antagonizes the effect of potassium on the heart. Calcium administration helps to stabilize the myocardial cell membranes, counteracting the relaxation caused by potassium. It's important to note that calcium does not decrease serum potassium levels but protects the heart from the effects of hyperkalemia.

Insulin Drip

To actively lower potassium levels, an insulin drip is typically used. Insulin causes a redistribution of potassium, moving it from the extracellular to the intracellular space at a rate of approximately 0.5 to 1 mEq per hour. This method is efficacious for reducing potassium levels in life-threatening situations, providing a relatively quick reduction in serum potassium.

Salbutamol Nebulization

Salbutamol, a beta-2 adrenergic agonist typically used in COPD and asthma, can potentiate the action of insulin, further assisting in sending potassium inside the cells. This is often used as an adjunct therapy to insulin.

Furosemide

Furosemide, a loop diuretic, is used to cause urinary loss of potassium (caliuresis), helping to eliminate potassium from the body. However, its effect may be limited in patients with renal insufficiency.

Hemodialysis

When all other measures fail or in cases of severe renal dysfunction, hemodialysis is the most effective treatment for acute, life-threatening hyperkalemia. It rapidly removes potassium from the body.

Key Notes on Hyperkalemia Treatment

  • Drug of Choice (First Line): Calcium gluconate (does not affect potassium values but stabilizes myocardial cell membranes).

  • Most Effective Drug (to lower K values): Insulin drip, which redistributes potassium intracellularly.

  • Chronic Hyperkalemia Treatment: Patiromer or sodium zirconium cyclosilicate (potassium binding drugs).

Chronic Hyperkalemia and ACE Inhibitors

Even in patients with chronic hyperkalemia and hypertension, ACE inhibitors should not be automatically discontinued due to their significant cardiovascular benefits, particularly in heart failure and post-MI. Patiromer or sodium zirconium cyclosilicate can be used to manage the hyperkalemia, allowing the continuation of ACE inhibitor therapy under close monitoring.

Hypokalemia
Cause of Death: Diaphragmatic Paralysis

In hypokalemia, the primary cause of death is diaphragmatic paralysis due to muscle paralysis. Severe hypokalemia can impair muscle function, including the diaphragm, leading to respiratory failure.

ECG Changes in Hypokalemia

  • Decreased T Wave Amplitude: The T wave amplitude decreases and may become absent or inverted. This reflects abnormal ventricular repolarization.

  • ST Segment Depression: ST-segment depression occurs, often indicative of myocardial ischemia or non-specific repolarization abnormalities.

  • Increased P Wave Amplitude: The P wave amplitude increases, leading to pseudo P pulmonale (P wave height > 2.5 mm in the absence of pulmonary artery hypertension). This indicates atrial enlargement or changes in atrial conduction.

  • Prominent U Waves: Prominent U waves develop, which are positive deflections following the T wave. These are thought to be related to prolonged repolarization of the Purkinje fibers.

  • Prolonged QT Interval: The QT interval is prolonged. If the T wave is absent, it may appear as a prolonged QU interval. This prolongation increases the risk of arrhythmias.

  • Prolonged PR Interval: The PR interval is prolonged, similar to hyperkalemia, due to alterations in the potassium gradient affecting conduction speed.

PR Interval Prolongation

PR interval is prolonged in both hypo- and hyperkalemia due to changes in the potassium gradient affecting conduction speed in the atria. It's a less specific finding but important to note.

Arrhythmias in Hypokalemia

Hypokalemia can lead to arrhythmias, specifically torsades de pointes, due to QT prolongation. However, the leading cause of death remains diaphragmatic paralysis, underscoring the critical impact of hypokalemia on muscle function.

Treatment of Hypokalemia

Potassium chloride (KCl) is administered, but it must be diluted in intravenous fluids to prevent thrombophlebitis and cardiac arrest. The typical rate of administration is 20 to 40 mEq per hour via a peripheral line. Higher concentrations or faster rates may require a central line due to the risk of infusion-related complications.

Correction of hypokalemia and potassium replacement formulas are discussed in the electrolyte section. Monitoring serum potassium levels and adjusting replacement rates are essential to avoid over-correction.

Key Takeaways for Hypokalemia

Remember the ECG findings and treatment of hypokalemia, as these are often tested. T wave amplitude decreases, ST segment depression, and prominent U waves develop. Prompt and careful potassium replacement is crucial to prevent life-threatening complications.

Summary of ECG Changes
Hyperkalemia

  • T Wave: Tall tented T waves.

  • ST Segment: ST elevation.

  • P Wave: Disappears.

Hypokalemia

  • T Wave: Decreased/absent, inverted.

  • ST Segment: ST depression.

  • P Wave: Pseudo P pulmonale (increased amplitude).

  • U Wave: Prominent U wave.

Common in Both

PR Prolongation: Seen in both hyper- and hypokalemia due to alteration in potassium gradients.

Treatment

  • Hyperkalemia: Calcium gluconate (acute), Patiromer (chronic).

  • Hypokalemia: Potassium chloride (KCl) with IV fluids.