What T wave height indicates hyperkalemia?

T Wave Height as an Indicator of Hyperkalemia

The first indicator of hyperkalemia may be the presence of peaked T waves (tenting) on the electrocardiogram (ECG), though there is no specific T wave height that definitively indicates hyperkalemia. 1

ECG Changes in Hyperkalemia

Hyperkalemia causes a progressive sequence of ECG changes as serum potassium levels rise:

1. Early changes (typically seen at >5.5 mEq/L):

   • Peaked T waves (tenting), particularly in precordial leads V2-V4
   • The average T wave elevation in hyperkalemia is approximately 7 mm 2

2. Progressive changes as potassium continues to rise:

   • Flattened or absent P waves
   • Prolonged PR interval
   • Widened QRS complex
   • Deepened S waves
   • Merging of S and T waves 1

3. Severe changes (untreated):

   • Sine-wave pattern
   • Idioventricular rhythms
   • Asystolic cardiac arrest 1

Important Clinical Considerations

• T wave tenting is not a reliable indicator: Tenting occurs in only about 31% of hyperkalemia cases and can be present in 33% of patients with normal potassium levels 3

• T:R ratio may be more specific: The ratio of the tallest precordial T-wave to R-wave amplitude (T:R) is more specific (85% vs 67%) but less sensitive (24% vs 33%) than tenting for identifying hyperkalemia ≥6.0 mmol/L 3

• Age affects presentation: T wave tenting becomes less common with increasing age 3

• Severity classification:

  • Mild hyperkalemia: >5.0 to <5.5 mEq/L
  • Moderate hyperkalemia: 5.5 to 6.0 mEq/L
  • Severe hyperkalemia: >6.0 mEq/L 1

Clinical Pitfalls to Avoid

• Don't rely solely on ECG changes: ECG manifestations of hyperkalemia are variable and may be absent even in severe cases

• Beware of pseudo-hyperkalemia: High K+ level in the test tube without true hyperkalemia in the body (caused by hemolysis during sampling) 1

• Consider patient factors: Patients with chronic kidney disease, diabetes, or heart failure may tolerate higher potassium levels without ECG changes 1

• Monitor high-risk patients: Patients receiving RAAS inhibitors, potassium-sparing diuretics, NSAIDs, beta-blockers, and other medications listed in Table 1 are at increased risk 1

• Elevated T:R ratio indicates risk: An elevated T:R ratio is associated with increased risk of sudden death (hazard ratio = 8.3) 3

When hyperkalemia is suspected or confirmed, prompt treatment should be initiated based on severity, with calcium administration to stabilize cardiac membranes being the first step in severe cases or those with ECG changes 1.