What is the most likely diagnosis and appropriate management for a 25‑year‑old male teacher with episodic tachycardia and chest discomfort, normal electrocardiogram, normal chest radiograph, normal thyroid‑stimulating hormone and electrolytes, negative home sleep study (apnea‑hypopnea index 2.5), and event monitors showing sinus rhythm with rare premature atrial and ventricular beats?

Most Likely Diagnosis: Inappropriate Sinus Tachycardia

This 25-year-old male teacher with episodic tachycardia (heart rate range 49-168 bpm), normal cardiac workup including negative structural disease, normal thyroid function, and event monitors showing predominantly sinus rhythm with rare PACs/PVCs most likely has inappropriate sinus tachycardia (IST) or a stress-related sinus tachycardia, and requires reassurance, lifestyle modification, and consideration of empiric beta-blocker therapy rather than further invasive testing. 1

Diagnostic Reasoning

Key Clinical Features Supporting Benign Diagnosis

• Sinus tachycardia accelerates and terminates gradually (not abruptly), which distinguishes it from paroxysmal supraventricular tachycardia (PSVT) that has sudden onset and termination characteristic of AVNRT or AVRT 1

• The patient's symptoms worsen at home but not at work, suggesting an anxiety or stress-related component rather than a primary cardiac arrhythmia 1

• All four patient-triggered events correlated with sinus rhythm, indicating that his perceived palpitations occur during normal rhythm rather than during true arrhythmia 1, 2

• Rare PACs/PVCs (<1%) are benign findings in young patients without structural heart disease and do not require treatment 1, 2

Exclusion of High-Risk Diagnoses

• No evidence of PSVT (AVNRT/AVRT): These would show regular palpitations with abrupt onset/termination, and the patient would likely respond to vagal maneuvers 1

• No pre-excitation on ECG rules out Wolff-Parkinson-White syndrome, which would require immediate electrophysiology referral due to sudden death risk 1, 2

• No sustained SVT documented on either 7-day or 30-day monitoring despite capturing symptomatic episodes 1, 2

• Normal structural evaluation (chest x-ray clear, normal sleep study) excludes structural heart disease and sleep apnea as contributors 1, 2

Appropriate Management Strategy

Immediate Steps

• Discontinue all caffeine, alcohol, and nicotine immediately as these are common triggers for sinus tachycardia 2

• Review all medications and supplements for stimulants or QT-prolonging agents that may provoke tachycardia 2, 3

• Assess for dehydration and ensure adequate hydration, as volume depletion can cause compensatory sinus tachycardia 2

Medical Therapy

• Initiate empiric beta-blocker therapy (metoprolol or atenolol) after confirming the absence of significant bradycardia (his minimum heart rate of 49 bpm is acceptable) 2

• Beta-blockers are the preferred first-line agent for suppressing inappropriate sinus tachycardia and reducing symptom burden 2

• Avoid Class I or III antiarrhythmic drugs (flecainide, propafenone, sotalol, amiodarone) without documented sustained arrhythmia due to significant proarrhythmic risk 2

Non-Pharmacologic Interventions

• Teach and encourage vagal maneuvers (Valsalva maneuver preferred over carotid massage) to perform during symptomatic episodes, though these are unlikely to terminate sinus tachycardia 2

• Address psychological stressors: Given that symptoms worsen at home and the patient is a 7th grade teacher (a high-stress occupation), consider screening for anxiety or panic disorder 1, 4

• Implement lifestyle modifications: regular exercise, adequate sleep, stress reduction techniques, and avoidance of large meals that can trigger tachycardia 2

When to Refer to Cardiology/Electrophysiology

Mandatory Referral Criteria (NOT Met in This Case)

• Pre-excitation on baseline ECG with history of paroxysmal palpitations 1, 2

• Wide complex tachycardia documented on any rhythm strip 2

• Syncope or presyncope during palpitations 1, 2, 3

• Severe symptoms (marked dyspnea, chest pain, hemodynamic compromise) during episodes 2

• Drug resistance or intolerance after trial of beta-blocker therapy 1, 2

Optional Referral Criteria

• Patient preference for definitive cure rather than lifelong medication (though this patient has no documented sustained arrhythmia requiring ablation) 2

• Frequent episodes interfering with daily activities despite optimal medical therapy 2

Critical Pitfalls to Avoid

• Do not order additional prolonged monitoring (implantable loop recorder) in this patient, as two extended monitors have already captured symptomatic episodes showing benign sinus rhythm 2

• Do not dismiss the patient's symptoms as "anxiety" without addressing them: Even though palpitations correlate with sinus rhythm, the symptoms are real and warrant treatment with beta-blockers and lifestyle modification 2

• Do not rely on automatic ECG interpretation systems, as they are unreliable and commonly suggest incorrect diagnoses 1

• Recognize that monitoring showing no arrhythmia does not exclude all pathology, but in this case with multiple captured symptomatic episodes all showing sinus rhythm, further monitoring is not indicated 2

Follow-Up Plan

• Reassess in 4-6 weeks after initiating beta-blocker therapy to evaluate symptom response 2

• Consider exercise stress testing only if palpitations are clearly triggered by exertion, which is not the case here (symptoms worsen at rest/home) 2

• No further ambulatory monitoring is indicated unless new symptoms develop (syncope, presyncope, or severe dyspnea) 2

• Reassurance is appropriate for this young patient with no structural heart disease, normal thyroid function, and benign monitoring findings 2