Hyperkalemia: Causes, ECG Changes, and Management
Hyperkalemia (serum K⁺ >5.0 mEq/L) is a life-threatening electrolyte imbalance commonly tested on the USMLE. It affects cardiac conduction, leading to fatal arrhythmias if untreated. Understanding its causes, ECG findings, and emergency management is crucial for both the exam and clinical practice.
Pathophysiology of Hyperkalemia
Potassium is primarily an intracellular ion, regulated by the Na⁺/K⁺ ATPase, kidneys, and acid-base balance. Disruptions in these mechanisms can lead to hyperkalemia through:
Decreased renal excretion (most common cause)
Increased potassium release from cells
Shift of K⁺ from intracellular to extracellular space
Causes of Hyperkalemia (Mnemonic: MACHINE)
Hyperkalemia results from impaired excretion, increased intake, or shifts.
| Category | Causes |
|---|---|
| M (Medications) | ACE inhibitors, ARBs, K⁺-sparing diuretics, NSAIDs, β-blockers |
| A (Acidosis) | Metabolic acidosis (H⁺ shifts K⁺ out of cells) |
| C (Cellular destruction) | Hemolysis, tumor lysis syndrome, rhabdomyolysis |
| H (Hypoaldosteronism) | Addison’s disease, Type IV RTA |
| I (Intake - Excessive) | Potassium supplements, salt substitutes |
| N (Nephrons - Renal failure) | CKD, AKI, dialysis patients |
| E (Excretion impairment) | Hypoaldosteronism, urinary obstruction |
Clinical Presentation of Hyperkalemia
Hyperkalemia may be asymptomatic or present with life-threatening cardiac and neuromuscular symptoms.
| System | Symptoms |
|---|---|
| Cardiac | Palpitations, bradycardia, arrhythmias |
| Neuromuscular | Weakness, flaccid paralysis, hyporeflexia |
| Gastrointestinal | Nausea, vomiting, ileus |
ECG Changes in Hyperkalemia (Mnemonic: Peaked T-Waves Can Quickly Die)
ECG findings correlate with serum potassium levels.
| Serum K⁺ Level (mEq/L) | ECG Changes |
|---|---|
| 5.5 - 6.5 | Peaked T waves |
| 6.5 - 7.5 | Prolonged PR interval, flattened P waves |
| 7.5 - 8.5 | Widened QRS complex |
| >8.5 | Sine wave pattern, ventricular fibrillation, asystole |
⚡ USMLE Tip: Hyperkalemia-induced sine waves are a pre-terminal sign requiring immediate treatment.
Key Diagnostic Tests for Hyperkalemia
| Test | Findings in Hyperkalemia |
|---|---|
| Serum K⁺ | >5.0 mEq/L |
| ECG | Peaked T-waves, widened QRS |
| ABG | Metabolic acidosis (if cause is acidosis) |
| Renal Function Tests | Elevated creatinine in renal failure |
| Aldosterone levels | Low in hypoaldosteronism |
Emergency Management of Hyperkalemia
Treatment depends on severity and ECG changes.
Immediate Cardiac Stabilization (If ECG Changes Present)
Calcium gluconate (IV) – Stabilizes cardiac membrane, prevents arrhythmias
Shift K⁺ into Cells (Temporary Fix)
Insulin + Dextrose (IV) – Drives K⁺ into cells
Beta-agonists (Albuterol nebulizer) – Increases Na⁺/K⁺ ATPase activity
Sodium bicarbonate – If metabolic acidosis is present
Eliminate Excess Potassium (Definitive Treatment)
Loop diuretics (furosemide) – Increases K⁺ excretion
Kayexalate (Sodium polystyrene sulfonate) – Binds K⁺ in the gut
Dialysis – Last resort for severe refractory hyperkalemia
Special Considerations in Hyperkalemia
| Patient Group | Consideration |
|---|---|
| Renal Failure | Dialysis is often needed |
| Acidosis-related | Treat underlying acidosis (e.g., DKA) |
| Patients on ACE inhibitors/ARBs | Monitor potassium regularly |
| Tumor Lysis Syndrome | Prevent with IV fluids and allopurinol |
Key Takeaways for USMLE
✔ Hyperkalemia is most commonly caused by renal failure and medications (ACE inhibitors, K⁺-sparing diuretics).
✔ ECG changes progress from peaked T waves → widened QRS → sine wave.
✔ Calcium gluconate stabilizes cardiac membranes, but insulin/dextrose shifts K⁺ intracellularly.
✔ Definitive treatment includes diuretics, potassium binders, or dialysis.
For a visual breakdown of hyperkalemia management, visit kingofthecurve.org for exclusive KOTC science concept images!
Final Thoughts
Hyperkalemia is a high-yield topic for USMLE, especially in renal and cardiovascular questions. Understanding its ECG changes and emergency treatment can help save lives in real-world clinical settings.
Boost Your USMLE Score with KOTC!
✅ Exclusive science visuals for fast learning
✅ Adaptive Q-Bank with hyperkalemia case-based questions
✅ Daily quizzes & gamified learning
🚀 Start now at kingofthecurve.org and ace your USMLE!
Frequently Asked Questions (FAQs)
-
Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.
-
Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.
-
Set short-term goals, seek support from mentors, and reward yourself for small achievements.
-
Regular exercise improves focus, reduces stress, and enhances overall mental clarity.
-
KOTC offers personalized learning tools, gamification features, and adaptive question banks to help students stay on track without burnout.
