What are the effects of lithium on the electrocardiogram (ECG)?

Effects of Lithium on ECG

Lithium can cause several ECG abnormalities including T-wave flattening or inversion, sinus node dysfunction, bradycardia, QT prolongation, and in rare cases, conduction blocks and Brugada pattern. These changes may occur even at therapeutic lithium levels, though the risk increases with higher serum concentrations 1, 2.

Common ECG Changes Associated with Lithium

Repolarization Abnormalities

• T-wave flattening or inversion (most common finding) 2, 3
• ST-segment changes
• QT interval prolongation (seen in 24% of lithium intoxication cases) 4

Conduction Abnormalities

• Sinus node dysfunction 1
• Bradycardia (decreased heart rate) 4
• PR interval prolongation 1, 3
• Sinoatrial blocks
• AV blocks (including Mobitz type I) 5

Severe or Rare Manifestations

• Brugada-like ECG pattern 6
• Ventricular arrhythmias 1
• Cardiac arrhythmias 1

Clinical Significance and Monitoring

Relationship to Lithium Levels

• ECG changes can occur at therapeutic lithium levels (0.6-1.2 mEq/L) 7
• Risk of significant ECG abnormalities increases with:
  • Higher serum lithium concentrations (especially >1.5 mEq/L) 1
  • Longer duration of treatment 2
  • Acute intoxication vs chronic therapy 4

Monitoring Recommendations

• Baseline ECG before initiating lithium therapy is recommended 7
• Follow-up ECGs are warranted after:
  • Initiation of lithium therapy
  • Changes in dosage
  • Addition of interacting medications 7
• More frequent monitoring for patients with:
  • Pre-existing cardiac disease
  • Elderly patients
  • Patients on medications that may interact with lithium

Clinical Implications

• Most ECG changes at therapeutic lithium levels are benign 3
• QT prolongation can become severe (>500ms) in 54% of cases with QT abnormalities, particularly in chronic intoxication 4
• Discontinuation of lithium typically leads to resolution of ECG abnormalities 6

Management Considerations

When to Be Concerned

• QTc interval exceeding 500 ms 4
• New onset of conduction blocks 5
• Development of symptomatic bradycardia
• Appearance of Brugada pattern 6

Actions to Take

• For severe ECG changes: consider dose reduction or discontinuation of lithium
• For Brugada pattern: prompt discontinuation of lithium is recommended 6
• For lithium toxicity: ECG monitoring is essential during treatment 4
• Consider alternative mood stabilizers in patients with significant cardiac conduction abnormalities

Practical Recommendations

1. Obtain baseline ECG before starting lithium therapy
2. Monitor ECG periodically, especially after dose adjustments
3. Be vigilant for ECG changes in patients with lithium levels >1.5 mEq/L
4. Pay special attention to T-wave morphology, heart rate, and QT interval
5. Consider more frequent cardiac monitoring in elderly patients or those with cardiac risk factors

While most lithium-induced ECG changes are benign at therapeutic levels, awareness of potential cardiac effects is important for safe management of patients on lithium therapy.