What are the ECG (electrocardiogram) findings in hyperkalemia?

ECG Findings in Hyperkalemia

The first indicator of hyperkalemia is typically the presence of peaked T waves (tenting) on the electrocardiogram (ECG), which progressively develops into flattened or absent P waves, prolonged PR interval, widened QRS complex, deepened S waves, and merging of S and T waves as serum potassium rises. 1

Progressive ECG Changes Based on Severity of Hyperkalemia

Hyperkalemia produces a sequence of characteristic ECG changes that correlate with increasing potassium levels:

1. Early/Mild Hyperkalemia (>5.0 to <5.5 mEq/L):

   • Peaked T waves (tenting) - the earliest and most recognizable sign
   • Shortened QT interval

2. Moderate Hyperkalemia (5.5 to 6.0 mEq/L):

   • Flattened or absent P waves
   • Prolonged PR interval
   • Widened QRS complex

3. Severe Hyperkalemia (>6.0 mEq/L):

   • Further QRS widening
   • Deepened S waves
   • Merging of S and T waves
   • Development of sine-wave pattern
   • Idioventricular rhythms
   • Progression to asystolic cardiac arrest 1

Additional ECG Manifestations

• Conduction Abnormalities: Hyperkalemia can cause various degrees of heart block due to its effect on cardiac conduction tissue
• Bradyarrhythmias: Severe sinus bradycardia and junctional rhythm may occur 2
• Atrial Arrhythmias: Atrial bigeminy has been reported even with moderate hyperkalemia 2

Clinical Pitfalls and Caveats

1. Absence of Typical ECG Changes: An important caveat is that absent or atypical ECG changes do not exclude the presence of life-threatening hyperkalemia 3. Some patients may have severe hyperkalemia without classic ECG manifestations.

2. Peaking T Waves: While this is the most widely recognized ECG sign, it is actually rarely a manifestation of life-threatening hyperkalemia 4. More advanced changes (QRS widening, sine waves) are more concerning.

3. Cardiac Arrest Risk: Hyperkalemia can progress to cardiac arrest, especially when K+ levels exceed 6.5 mmol/L. In one study, hyperkalemia was directly responsible for sudden cardiac arrest in hospitalized patients with acute kidney injury 1.

4. Concurrent Conditions: The presence of other electrolyte abnormalities (especially hypomagnesemia) can exacerbate ECG changes and clinical manifestations of hyperkalemia.

5. Rapid Progression: ECG changes can progress rapidly, especially with acute rises in potassium levels, requiring immediate intervention when severe changes are observed.

Risk Factors for Severe Manifestations

Patients at highest risk for severe ECG manifestations and mortality from hyperkalemia include:

• Those with acute kidney injury (AKI) on normal baseline renal function (higher mortality than AKI superimposed on CKD) 5
• Patients with metabolic acidosis (common precipitating factor) 5
• Those with multi-organ failure at time of hyperkalemia diagnosis 5
• Patients with malignancy, infection, or bleeding as underlying conditions 5

Monitoring and Management Implications

When ECG changes suggestive of hyperkalemia are observed, especially QRS widening or sine-wave patterns, immediate treatment is warranted to prevent progression to cardiac arrest. The American Heart Association recommends:

• Calcium administration (calcium chloride or gluconate) to stabilize myocardial cell membranes
• Interventions to shift potassium into cells (insulin with glucose, sodium bicarbonate)
• Measures to promote potassium excretion (diuretics, potassium binders, dialysis) 1

Continuous cardiac monitoring is essential for patients with moderate to severe hyperkalemia due to the risk of sudden arrhythmias and cardiac arrest.