Can lithium cause bradycardia (abnormally slow heart rate)?

Lithium-Induced Bradycardia: Recognition and Management

Yes, lithium can cause bradycardia, and this is a documented adverse effect that can occur even at therapeutic levels. The FDA drug label specifically lists "sinus node dysfunction with severe bradycardia (which may result in syncope)" among lithium's cardiovascular adverse reactions 1.

Mechanism and Presentation

Lithium-induced bradycardia can manifest through several mechanisms:

• Direct effect on cardiac conduction system, particularly the sinus node
• T-wave changes and AV-block have been reported
• Can occur at therapeutic lithium levels, not just in toxicity
• May present as junctional escape rhythm in severe cases

Risk Factors and Incidence

Bradycardia risk is increased in patients with:

• Pre-existing cardiac disease
• Concomitant use of other medications affecting heart rate (beta-blockers, calcium channel blockers)
• Renal impairment (leading to increased lithium levels)
• Electrolyte abnormalities
• Advanced age

According to a retrospective study of lithium overdose cases, cardiac complications were reported in 5.7% of hospitalized patients, with bradycardia being the most common cardiac manifestation (62% of cardiac complications) 2.

Clinical Presentation

Patients with lithium-induced bradycardia may present with:

• Asymptomatic bradycardia detected on routine examination
• Fatigue, dizziness, lightheadedness
• Pre-syncope or syncope in severe cases
• Confusion or altered mental status (especially in elderly)
• Symptoms may occur even after a single dose in sensitive individuals 3

Diagnosis

When bradycardia is detected in a patient on lithium:

1. Obtain serum lithium levels (though bradycardia can occur even at therapeutic levels)
2. Perform ECG to evaluate for bradyarrhythmias, AV blocks, or T-wave changes
3. Check electrolytes, renal function, and thyroid function (lithium can cause hypothyroidism)
4. Consider other causes of bradycardia (medications, electrolyte abnormalities, hypothyroidism)

Management

For lithium-induced bradycardia:

1. Discontinue lithium if bradycardia is symptomatic or severe (HR <45 bpm)

2. For acute symptomatic bradycardia:

   • Atropine 0.5-1 mg IV (may be repeated every 3-5 min to maximum 3 mg) 4
   • If unresponsive to atropine, consider temporary pacing or pharmacologic agents:
     • Dopamine 5-20 mcg/kg/min IV
     • Isoproterenol 1-20 mcg/min IV (avoid in suspected ischemia)
     • Epinephrine 2-10 mcg/min IV 4

3. Monitor cardiac rhythm until resolution

4. Consider alternative mood stabilizers in consultation with psychiatry

Prognosis

• Most cases of lithium-induced bradycardia are reversible upon discontinuation of lithium 5
• Resolution typically occurs within days of lithium discontinuation
• Rarely, permanent sinus node dysfunction may occur requiring pacemaker implantation 6

Special Considerations

• Patients with bipolar disorder requiring mood stabilization will need alternative medications if lithium is discontinued
• Careful monitoring is required when initiating lithium therapy, even before therapeutic levels are reached 3
• Lithium can cause other cardiac effects including T-wave changes and QT interval alterations 4
• Patients with heart failure or ischemic heart disease may be more susceptible to bradycardia effects

Prevention

• Baseline ECG before starting lithium therapy
• Regular monitoring of lithium levels to maintain within therapeutic range
• Periodic ECG monitoring, especially in patients with cardiac risk factors
• Prompt evaluation of any cardiac symptoms in patients taking lithium

Lithium-induced bradycardia is a recognized adverse effect that clinicians should be vigilant about, especially when initiating therapy or in patients with cardiac risk factors. While often reversible with lithium discontinuation, it can occasionally lead to serious complications requiring intervention.