Which electrolyte imbalance can cause palpitations?

Electrolyte Imbalances That Cause Palpitations

Both hypokalemia and hyperkalemia are the primary electrolyte imbalances that cause palpitations and cardiac arrhythmias, with hypokalemia being the most common electrolyte abnormality encountered clinically, while magnesium abnormalities also contribute to arrhythmogenesis. 1

Hypokalemia (Low Potassium)

Hypokalemia is the most frequent electrolyte disturbance causing palpitations and arrhythmias. 1

Prevalence and Risk Factors

• Occurs in up to 20% of hospitalized patients, 40% of patients taking diuretics, and 17% of patients with cardiovascular conditions 2
• In patients presenting with ventricular tachycardia/ventricular fibrillation (VT/VF), hypokalemia (K <3.5 mmol/L) was present in 35.7% of cases, with severe hypokalemia (K <3.0 mmol/L) in 13.6% 3
• Gastrointestinal illness and recent increases in diuretic dose were strongly associated with severe hypokalemia in VT/VF patients (odds ratios of 11.1 and 21.9, respectively) 3

Arrhythmia Mechanisms

• Increases resting membrane potential and prolongs both action potential duration and refractory period, creating conditions for reentrant arrhythmias 4
• Increases automaticity and threshold potential, predisposing to automatic arrhythmias 4
• Decreases conductivity, further promoting reentrant arrhythmias 4

Clinical Manifestations

• Arrhythmias associated with hypokalemia include: premature ventricular contractions (PVCs), ventricular tachycardia (VT), torsades de pointes (TdP), ventricular fibrillation (VF), cardiac arrest, first or second-degree atrioventricular block, and atrial fibrillation 1
• Common symptoms include cardiac arrhythmias and muscle weakness or pain 2
• Patients with heart failure should maintain potassium levels ≥4 mEq/L to prevent arrhythmias 1, 5

ECG Findings

• Broadening of T waves, ST-segment depression, and prominent U waves (>1 mm) 1, 5
• U waves larger than T waves in the same lead 4
• QT interval prolongation, which can progress to QTU alternans and early afterdepolarizations 6

Hyperkalemia (High Potassium)

Hyperkalemia is one of the few potentially lethal electrolyte disturbances that can directly cause cardiac arrest. 1

Prevalence and Severity

• Affects up to 8% of hospitalized patients, mainly with compromised renal function 6
• Severe hyperkalemia (>6.5 mmol/L) occurs most commonly from renal failure or release of potassium from cells 1
• In a study of 29,063 hospitalized patients, hyperkalemia was directly responsible for sudden cardiac arrest in 7 cases 1

Progressive ECG Changes by Potassium Level

• 5.5-6.5 mmol/L: Peaked (tented) T waves, often the first indicator 1, 5
• 6.5-7.5 mmol/L: Flattened or absent P waves, prolonged PR interval 1, 5
• 7.0-8.0 mmol/L: Widened QRS complex, deepened S waves, merging of S and T waves 1, 5
• >8.0 mmol/L: Bradycardia from extremely prolonged PR and QRS intervals 1
• >10.0 mmol/L: Sine-wave pattern, idioventricular rhythms, ventricular fibrillation, asystole, or pulseless electrical activity 1

Important Caveat

ECG manifestations of hyperkalemia vary significantly among individuals and may not be predictable, requiring careful clinical correlation. 1, 5

Magnesium Abnormalities

Hypomagnesemia

• Contributes to QT prolongation and increases risk of torsades de pointes, even when magnesium levels appear normal 1, 5
• Frequently associated with hypokalemia and should be corrected concurrently 5
• Found in 7.8% of patients presenting with VT/VF 3
• Magnesium bolus or infusion is recommended for torsades de pointes regardless of baseline magnesium level 1, 5

Hypermagnesemia

• Can cause prolonged PR, QRS, and QT intervals 1, 5
• Severe cases (6-10 mmol/L) may result in atrioventricular nodal conduction block, bradycardia, hypotension, and cardiac arrest 1, 5

Calcium Abnormalities

While less commonly causing palpitations directly, calcium abnormalities affect cardiac electrophysiology 1:

• Hypocalcemia: Prolongs ST segment and QT interval 6
• Hypercalcemia: Shortens ST segment and QT interval 6
• Clinically significant effects typically occur only with extreme abnormalities 6

Monitoring Recommendations

Continuous ECG monitoring is indicated for: 1, 5

• Moderate to severe potassium or magnesium imbalances
• Any electrolyte abnormality with ECG changes on 12-lead ECG
• Patients with cardiac comorbidities and electrolyte disturbances
• During treatment of severe electrolyte abnormalities that may cause rapid shifts

Critical Clinical Pitfalls

• Do not assume normal ECG excludes significant electrolyte abnormality - ECG changes in hyperkalemia are unpredictable and variable 1, 5
• Always check magnesium when treating hypokalemia - concurrent hypomagnesemia prevents effective potassium repletion 5
• Diuretic therapy is a major risk factor - up to 56% of patients on diuretics develop hypokalemia 7
• Recent diuretic dose increases dramatically increase risk - 21.9-fold increased odds of severe hypokalemia in VT/VF patients 3
• Gastrointestinal illness compounds risk - 11.1-fold increased odds of severe hypokalemia with concurrent GI illness 3