What precautions should be taken when evaluating an electrocardiogram (ECG) from patients on selective serotonin reuptake inhibitors (SSRI)?

Precautions When Evaluating ECGs from Patients on SSRIs

When evaluating ECGs from patients on SSRIs, clinicians should monitor for QT interval prolongation, particularly with citalopram, which poses the highest risk among SSRIs for QTc prolongation even at recommended doses. 1

QT Interval Prolongation Risk with SSRIs

SSRIs generally have a better cardiovascular safety profile than tricyclic antidepressants, but they still carry some risk of QT interval prolongation:

• Citalopram: Presents the highest risk of QTc prolongation among SSRIs 1, 2

  • FDA recommends maximum dose of 20 mg/day in patients >60 years old or those with hepatic impairment 3
  • QTc prolongation occurs in a dose-dependent manner (mean increase of 12.8 ms) 1
  • Even at the restricted dose of 20 mg in patients >60 years, QTc prolongation remains clinically significant 1

• Other SSRIs: Generally cause less QTc prolongation than citalopram 1

  • Sertraline, fluoxetine, fluvoxamine, and paroxetine show less QTc prolongation in comparative studies 2
  • However, case reports exist of QTc prolongation with sertraline overdose 4 and paroxetine 5

Monitoring Recommendations

Baseline Assessment

• Obtain baseline ECG before initiating SSRIs in patients with:
  • Pre-existing cardiac disease
  • Congenital long QT syndrome
  • Bradycardia
  • Electrolyte abnormalities (hypokalemia, hypomagnesemia)
  • Recent acute myocardial infarction
  • Uncompensated heart failure 3
  • Concomitant use of other QT-prolonging medications 6

Follow-up Monitoring

• For citalopram specifically:

  • Obtain follow-up ECG after initiation or dose increases 3
  • Consider discontinuation if QTc >500 ms or increase of ≥60 ms from baseline 6

• For other SSRIs:

  • Routine ECG monitoring is not mandatory in the absence of cardiac risk factors 7
  • Selective monitoring based on risk factors is appropriate 6

Risk Stratification

Patients can be stratified into risk groups:

• High-risk: Baseline QTc ≥500 ms (or ≥550 ms with wide QRS) or on combination QT-prolonging therapies 6
• Low-risk: No cardiac history, normal baseline QTc, no concomitant QT-prolonging medications 6

Special Considerations

Drug Interactions

• Monitor closely when SSRIs are combined with:
  • Class I or III antiarrhythmic medications (e.g., quinidine, amiodarone, sotalol)
  • Antipsychotics (e.g., chlorpromazine, thioridazine)
  • Certain antibiotics (e.g., moxifloxacin)
  • Other QT-prolonging medications 3
  • CYP2D6 inhibitors (e.g., quinidine, fluoxetine, paroxetine) when used with thioridazine 6

Electrolyte Monitoring

• Check serum potassium and magnesium levels:
  • At baseline for high-risk patients
  • Periodically during treatment
  • Correct abnormalities before initiating treatment 3

Overdose Situations

• All drug overdose victims should have ECG assessment for QT prolongation, regardless of the specific drug 6
• Citalopram overdose particularly warrants cardiac monitoring due to higher risk of QTc prolongation 2
• Serotonin syndrome is common in SSRI overdose (14% incidence) 2

Warning Signs on ECG

Be vigilant for these ECG findings that may precede torsades de pointes:

• QT-U distortion
• T wave alternans
• Enhanced U waves
• Polymorphic ventricular premature beats
• Short-long-short cycle length sequences 6

Action Points When QTc Prolongation Is Detected

If QTc exceeds 500 ms or increases by ≥60 ms from baseline:

1. Consider alternative pharmacotherapy
2. Assess for drug-drug interactions
3. Check for bradyarrhythmias or electrolyte abnormalities
4. Ensure external defibrillator availability
5. Restrict patient transport from monitored settings 6

In conclusion, while SSRIs as a class are relatively safe from a cardiac perspective, citalopram carries the highest risk of QTc prolongation. Individualized ECG monitoring based on risk factors and specific SSRI choice is the most prudent approach to ensure patient safety.