What are the appropriate initial laboratory tests for patients presenting with palpitations?

Initial Laboratory Tests for Patients Presenting with Palpitations

For patients presenting with palpitations, the appropriate initial laboratory tests should include complete blood count, serum electrolytes (including calcium and magnesium), thyroid-stimulating hormone, and fasting blood glucose, along with a 12-lead electrocardiogram. 1, 2

Primary Diagnostic Approach

Initial Evaluation

• Complete blood count (CBC) to assess for anemia which can precipitate palpitations 1
• Serum electrolytes including calcium and magnesium to identify electrolyte disturbances that can trigger arrhythmias 1
• Thyroid-stimulating hormone (TSH) to rule out hyperthyroidism as a cause of palpitations 1
• Fasting blood glucose or glycohemoglobin to identify hypoglycemia or diabetes 1
• 12-lead electrocardiogram (ECG) to identify any underlying arrhythmias or structural abnormalities 1

Additional Tests Based on Clinical Suspicion

• Blood urea nitrogen (BUN) and serum creatinine to assess renal function, especially if considering medication use 1
• Liver function tests if liver disease is suspected or if considering medications metabolized by the liver 1
• Urinalysis if systemic disease is suspected 1

Diagnostic Strategy Based on Patient Characteristics

For Patients with Suspected Cardiac Etiology

• Echocardiography should be performed if there is suspicion of structural heart disease 1
• Prolonged ECG monitoring (Holter monitor for 24-48 hours) for patients with daily palpitations 2
• Event recorder or implantable loop recorder for patients with infrequent episodes 1, 2

For Patients with Specific Presentations

• Stress testing for patients with palpitations during or after exertion 1
• Carotid sinus massage for older patients or those with palpitations during neck turning 1

Clinical Pearls and Pitfalls

Important Considerations

• Palpitations associated with dizziness, near-syncope, or syncope should be considered potentially more serious and warrant more extensive evaluation 2
• Up to 16% of patients with palpitations may have no identifiable cause despite thorough evaluation 2, 3
• Psychiatric causes account for approximately 31% of palpitations, making this an important consideration in the diagnostic workup 3

Common Pitfalls to Avoid

• Failing to check electrolytes and thyroid function, which are common reversible causes of palpitations 1
• Over-reliance on 24-hour Holter monitoring for infrequent palpitations; longer-term event recorders are more appropriate for episodic symptoms 2
• Neglecting to consider medication effects, including over-the-counter and prescription drugs that can cause palpitations 2

Monitoring and Follow-up

• For patients with recurrent unexplained palpitations who are at low risk for sudden cardiac death, an implantable loop recorder should be considered 1
• Follow-up testing should be guided by initial test results and the persistence of symptoms 1
• Despite the high recurrence rate of palpitations (75% within one year), the short-term prognosis is generally good with low mortality rates 3