What is the initial lab workup for a patient presenting with palpitations?

Initial Laboratory Workup for Patients Presenting with Palpitations

The initial laboratory evaluation for a patient presenting with palpitations should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, fasting blood glucose (glycohemoglobin), lipid profile, liver function tests, and thyroid-stimulating hormone. 1, 2

Essential Initial Diagnostic Tests

• Complete blood count to assess for anemia which can precipitate palpitations 2
• Serum electrolytes including calcium and magnesium to identify electrolyte disturbances that can trigger arrhythmias 2
• Thyroid-stimulating hormone to rule out hyperthyroidism as a common cause of palpitations 2
• Blood urea nitrogen and serum creatinine to assess renal function 1
• Fasting blood glucose or glycohemoglobin to identify hypoglycemia or diabetes 1, 2
• Liver function tests to evaluate hepatic function 1
• Urinalysis for basic screening 1
• 12-lead electrocardiogram to identify any underlying arrhythmias or structural abnormalities 1, 2, 3

Cardiac-Specific Testing

• A 12-lead ECG is essential as the first diagnostic test for all patients with palpitations 3
• Chest radiograph (posterior-anterior and lateral) should be performed during initial evaluation 1
• Two-dimensional echocardiography with Doppler should be considered if there is suspicion of structural heart disease 1, 3
• Brain natriuretic peptide (BNP) and high-sensitivity troponin may be considered if cardiac cause is suspected 2

Monitoring Strategy Based on Symptom Frequency

• For frequent episodes (daily or near-daily): 24-48 hour Holter monitoring 2, 3, 4
• For less frequent episodes: Event recorder or wearable loop recorder 2, 3
• For rare episodes: Implantable loop recorder may be considered 2, 3
• Exercise testing when palpitations are triggered by exertion 3

Considerations for Laboratory Testing

• Laboratory tests should be targeted based on clinical assessment rather than ordering comprehensive panels without clinical indication 2
• The American College of Cardiology recommends against ordering excessive laboratory tests that are unlikely to yield diagnostic information 2
• The diagnostic yield of laboratory testing is highest when directed by findings from history, physical examination, and ECG 3, 5

Special Populations and Considerations

• Patients with pre-excitation on resting ECG and history of paroxysmal regular palpitations should be referred to electrophysiology 3
• Patients with structural heart disease require more intensive evaluation 3
• Palpitations associated with syncope, dizziness, or near-syncope should be considered potentially more serious 5
• Patients with hypertrophic cardiomyopathy and palpitations should have more frequent monitoring 3

Common Pitfalls to Avoid

• Assuming palpitations are non-cardiac in patients with psychiatric disorders - cardiac causes must still be ruled out 6
• Relying solely on Holter monitoring for infrequent palpitations - this has low diagnostic yield 5
• Failing to consider medication side effects or stimulant use as potential causes 5
• Overlooking the need for extended monitoring in patients with infrequent but concerning symptoms 3

The diagnostic approach should be systematic, starting with basic laboratory tests and ECG, then proceeding to more specialized cardiac monitoring based on symptom frequency and clinical suspicion of underlying cardiac disease 7, 4.