What are the ECG changes in hyperkalemia?

ECG Changes in Hyperkalemia

Hyperkalemia produces a progressive sequence of ECG changes that begins with peaked T waves and can evolve to life-threatening cardiac arrhythmias including asystolic cardiac arrest. 1

ECG Progression in Hyperkalemia

• Initial changes (usually at serum K+ >5.5 mmol/L):

  • Peaked/tented T waves - the earliest and most common ECG finding 1, 2
  • T waves appear narrow and symmetrical with increased amplitude 2

• Moderate hyperkalemia (as K+ continues to rise):

  • Flattened or absent P waves 1
  • Prolonged PR interval 1, 2
  • Widened QRS complex 1
  • Deepened S waves 1

• Severe hyperkalemia (K+ >6.5 mmol/L):

  • Merging of S and T waves 1
  • Progressive QRS widening 1, 2
  • Development of a sine-wave pattern 1, 3
  • Idioventricular rhythms 1
  • Ventricular fibrillation or asystolic cardiac arrest 1

Clinical Significance

• ECG changes may be the first indicator of hyperkalemia before symptoms appear 1
• The presence of ECG changes, particularly QRS widening, indicates severe cardiotoxicity requiring immediate treatment 1, 4
• Not all patients develop ECG changes at the same potassium level - patients with chronic kidney disease, diabetes, or heart failure may tolerate higher levels without ECG changes 1

Risk Factors for Hyperkalemia

• Renal failure (most common cause) 1, 5
• Medications:
  • Renin-angiotensin-aldosterone system inhibitors (ACE inhibitors, ARBs, MRAs) 1
  • Potassium-sparing diuretics 1
  • NSAIDs 1
  • Beta-blockers 1

Treatment Approach Based on ECG Changes

When ECG changes are present, urgent treatment is required:

1. Stabilize myocardial cell membrane:

   • Calcium chloride (10%): 5-10 mL IV over 2-5 minutes or calcium gluconate (10%): 15-30 mL IV over 2-5 minutes 1, 6

2. Shift potassium into cells:

   • Insulin + glucose: 10 units regular insulin with 25g glucose IV over 15-30 minutes 1
   • Sodium bicarbonate: 50 mEq IV over 5 minutes 1
   • Nebulized albuterol: 10-20 mg over 15 minutes 1

3. Promote potassium excretion:

   • Diuretics (if renal function adequate): furosemide 40-80 mg IV 1
   • Sodium polystyrene sulfonate (Kayexalate): 15-50g orally or rectally 1
   • Dialysis for severe or refractory cases 1

Important Clinical Pearls

• The absence of ECG changes does not rule out dangerous hyperkalemia 1
• Patients with chronic hyperkalemia may develop tolerance to higher potassium levels 1
• ECG changes may not correlate perfectly with serum potassium levels in all patients 4, 7
• Pseudo-hyperkalemia (falsely elevated K+ due to hemolysis during blood collection) should be considered when ECG findings don't match laboratory values 1
• Rapid correction of hyperkalemia is essential when ECG changes are present to prevent progression to life-threatening arrhythmias 1, 4