What effect does hyperkalemia have on the heart?

Cardiac Effects of Hyperkalemia

Hyperkalemia disrupts the heart's electrical conduction system and contractile function by reducing the potassium gradient across cardiac cell membranes, leading to progressive membrane depolarization, conduction abnormalities, decreased contractility, and ultimately life-threatening arrhythmias or asystolic cardiac arrest if untreated. 1

Fundamental Mechanism of Cardiac Dysfunction

• The steep potassium gradient between intracellular and extracellular compartments is essential for cardiac excitability and contractile function 1
• Elevated extracellular potassium reduces this concentration difference, causing the resting membrane potential to become less negative (depolarization) 1
• This membrane depolarization progressively impairs both electrical conduction and mechanical contraction as potassium levels rise 1

Progressive Cardiac Effects by Severity

Mild to Moderate Hyperkalemia (5.5-6.5 mEq/L)

• Peaked T waves appear as the earliest ECG manifestation, often the first clinical sign of hyperkalemia 1, 2
• Cardiac contractility begins to decline at these levels 1

Moderate Hyperkalemia (6.5-7.5 mEq/L)

• P waves flatten or disappear entirely 1
• PR interval becomes prolonged 1, 2
• QRS complex widens progressively 1, 2
• Deepened S waves and merging of S and T waves develop 2

Severe Hyperkalemia (>7.0-8.0 mEq/L)

• Sine-wave pattern emerges on ECG, indicating imminent cardiac arrest 1, 2
• Severe depression of contractility occurs 1
• Idioventricular rhythms may appear 2
• Asystolic cardiac arrest becomes imminent without treatment 1, 2

Critical Clinical Context

The combination of impaired electrical conduction and reduced contractility explains why hyperkalemia is a potentially lethal electrolyte disturbance. 1

Individual Variability and Modifying Factors

• Potassium levels up to 6 mEq/L may be tolerated without arrhythmias, particularly in patients with chronic kidney disease, diabetes, or heart failure 3
• The threshold for cardiac toxicity varies based on: 1
  • Concurrent electrolyte abnormalities (especially calcium and magnesium)
  • Presence of structural cardiac disease
  • Rate of potassium rise (acute versus chronic)
  • Chronic kidney disease status
• Important caveat: ECG changes do not always correlate reliably with potassium levels, and severe hyperkalemia can occasionally occur without typical ECG findings 4, 5

Clinical Significance for Treatment Decisions

• The presence of any ECG changes indicates that hyperkalemia is severe enough to affect cardiac function and requires urgent treatment 1
• Hyperkalemia with potassium >6.5 mEq/L or any ECG changes constitutes a medical emergency 6
• Calcium salts (calcium chloride or calcium gluconate) should be administered immediately to stabilize the cardiac membrane potential when ECG changes are present 1, 7, 6
• Continuous cardiac monitoring is mandatory during treatment 2

Contractility Depression

• The degree of contractility impairment correlates with potassium levels, though individual variation exists 1
• This reduced contractility, combined with conduction abnormalities, creates the substrate for hemodynamic collapse 1