What is the recommended workup for sinus tachycardia?

Workup for Sinus Tachycardia

The workup for sinus tachycardia should focus on identifying and treating the underlying cause through targeted history, physical examination, and laboratory testing, rather than extensive cardiac evaluation, since sinus tachycardia is almost always a physiological response to an underlying condition. 1, 2

Initial Clinical Assessment

Determine Hemodynamic Stability First

• Immediately assess for acute altered mental status, ischemic chest pain, acute heart failure, hypotension, or shock 2
• Check oxygenation status with pulse oximetry and look for tachypnea, intercostal retractions, or suprasternal retractions 2
• Ensure continuous vital sign monitoring and establish IV access if the patient appears unstable 2

Focused History and Physical Examination

• Identify physiological causes: hypovolemia/shock, hypoxemia, fever/infection, anemia, pain, anxiety, or emotional stress 1, 2
• Screen for pathological causes: hyperthyroidism, heart failure, pulmonary embolism, myocardial ischemia, or myocarditis 1, 2
• Review medications and substances: stimulants (caffeine, alcohol, nicotine), prescribed drugs (salbutamol, aminophylline, atropine, catecholamines), recreational drugs (amphetamines, cocaine, ecstasy, cannabis), and anticancer agents (doxorubicin, daunorubicin) 1

Laboratory and Diagnostic Testing

Essential Laboratory Studies

• Complete blood count to evaluate for anemia or infection 1, 2
• Thyroid function tests (TSH, free T4) to exclude hyperthyroidism 1, 2
• Basic metabolic panel to assess for electrolyte abnormalities and volume status 2
• Arterial blood gas or pulse oximetry if hypoxemia is suspected 2

Electrocardiographic Evaluation

• 12-lead ECG during tachycardia: Confirm sinus origin with normal P-wave morphology (positive in leads I, II, aVF; negative in aVR; axis 0-90 degrees) 1
• 12-lead ECG during sinus rhythm: Essential to exclude pre-excitation or other baseline abnormalities 1
• Look for T-wave changes or conduction disturbances that might suggest myocarditis 1

When to Perform Echocardiography

• Perform echocardiogram if myocarditis is suspected based on clinical signs (gallop rhythm, ECG abnormalities disproportionate to fever) 1
• Consider echocardiography if heart failure or structural heart disease is suspected clinically 2
• Do not routinely perform echocardiography for uncomplicated sinus tachycardia with an identifiable reversible cause 1, 2

Special Considerations for Inappropriate Sinus Tachycardia (IST)

Diagnostic Criteria for IST

• Resting heart rate >100 bpm or average 24-hour heart rate >90 bpm 3, 4
• Symptoms (palpitations, chest pain, fatigue, dyspnea, presyncope) associated with the tachycardia 3, 4
• All secondary causes of tachycardia must be excluded before diagnosing IST 1, 3

Additional Workup for Suspected IST

• 24-hour Holter monitoring to document average heart rate and exclude paroxysmal arrhythmias 5
• Distinguish IST from postural orthostatic tachycardia syndrome (POTS) with orthostatic vital signs, as treatment differs significantly 2
• Consider cardiac autonomic reflex function testing to support the diagnosis 6

Critical Pitfalls to Avoid

• Never attempt to normalize heart rate in compensatory tachycardia (e.g., hypovolemia, anemia, hypoxemia), as cardiac output depends on the elevated rate and suppressing it can cause hemodynamic collapse 2
• Do not diagnose IST without excluding all reversible causes including medications, substances, infection, anemia, and hyperthyroidism 1, 3
• Distinguish IST from POTS before initiating rate control, as suppressing sinus rate in POTS causes severe orthostatic hypotension 2
• Avoid overlooking diabetic ketoacidosis in diabetic patients presenting with sinus tachycardia 5

Age-Specific Considerations

Neonatal Population

• Upper normal limit is 166 bpm in the first week and 179 bpm in the first month (98th percentile) 1
• Newborns may transiently reach heart rates up to 230 bpm during normal activity 1
• Common causes include fever, infection, anemia, pain, dehydration, neonatal hyperthyroidism, and drugs transmitted through placenta or breast milk 1