In a 46-year-old woman presenting with palpitations and shortness of breath, who has a normal sinus rhythm on electrocardiogram (ECG) and normal bilateral breath sounds, what is the most likely diagnosis and recommended treatment?

Diagnosis and Treatment

In a 46-year-old woman with palpitations and shortness of breath but normal sinus rhythm on ECG and normal lung exam, the most likely diagnosis is paroxysmal supraventricular tachycardia (PSVT) that was not captured on the initial ECG, and the immediate next step is ambulatory ECG monitoring to document the arrhythmia during symptoms.

Diagnostic Approach

Why PSVT is Most Likely

The clinical presentation strongly suggests paroxysmal supraventricular tachycardia (AVNRT or AVRT) based on several key features 1, 2:

• Age and gender: Women in their 30s-40s are the typical demographic for AVNRT, with mean symptom onset at 32±18 years
• Symptom pattern: Palpitations with shortness of breath are classic SVT symptoms
• Normal baseline ECG: PSVT characteristically shows normal sinus rhythm between episodes

Critical Differential Considerations

While the normal ECG is reassuring, you must systematically exclude:

Cardiac causes requiring urgent evaluation:

• Atrial fibrillation (paroxysmal)
• Atrial flutter
• Ventricular tachycardia
• Mitral valve prolapse 3, 4, 3

Non-cardiac causes:

• Anxiety/panic disorder (present in 67% of patients with unrecognized SVT) 1
• Hyperthyroidism
• Inappropriate sinus tachycardia 5

Essential Diagnostic Workup

Immediate investigations 6, 7:

1. 12-lead ECG during symptoms - This is the gold standard. Encourage the patient to present immediately during an episode 7

2. Ambulatory ECG monitoring - Select based on symptom frequency 8:

   • Daily symptoms: 24-48 hour Holter monitor
   • Weekly symptoms: 7-day Holter or external loop recorder
   • Monthly symptoms: 14-30 day external loop recorder
   • Less frequent: Implantable loop recorder (diagnostic yield 90% at 1 year) 9

3. Echocardiogram 6, 7:

   • Evaluate for structural heart disease
   • Assess left atrial size and ventricular function
   • Exclude mitral valve prolapse (associated with palpitations in 45% of panic disorder patients) 3, 4

4. Laboratory tests 6:

   • Complete blood count
   • Thyroid function (TSH)
   • Electrolytes
   • Fasting glucose

Treatment Strategy

If AVNRT/AVRT is Documented

Acute management during episodes 1, 2:

• Vagal maneuvers (Valsalva, carotid massage)
• If unsuccessful: IV adenosine or calcium channel blockers

Long-term management 4, 3:

1. First-line: Lifestyle modifications

   • Eliminate caffeine, alcohol, cigarettes
   • These alone may control symptoms in many cases

2. Pharmacologic therapy

   • Beta-blockers are first-line for symptomatic control
   • Effective for palpitations, chest pain, anxiety, and fatigue associated with SVT

3. Definitive therapy

   • Refer to cardiac electrophysiologist for catheter ablation if:
     • Symptoms are frequent or severe
     • Patient desires freedom from medications
     • Drug therapy is ineffective or not tolerated 7

If Mitral Valve Prolapse is Found

Symptomatic management 3, 4, 3:

• Beta-blockers for palpitations and chest pain
• Avoid stimulants
• Event monitoring to correlate symptoms with arrhythmias

Common Pitfalls to Avoid

1. Don't dismiss as anxiety - 54% of SVT patients are initially misdiagnosed with panic disorder, especially women 1, 2

2. Don't rely on single ECG - Normal sinus rhythm between episodes is expected with paroxysmal arrhythmias

3. Don't use 24-hour Holter for infrequent symptoms - Match monitoring duration to symptom frequency 8, 9

4. Don't overlook driving safety - 57% of SVT patients experience episodes while driving; 14% have syncope while driving 2

Red Flags Requiring Urgent Cardiology Referral

• Syncope or near-syncope with palpitations 7, 1
• Family history of sudden cardiac death
• Structural heart disease on echocardiogram
• Pre-excitation pattern on ECG (suggests WPW syndrome - requires immediate electrophysiology evaluation) 7

The key is obtaining ECG documentation during symptoms - without this, you're treating blindly. Start with appropriate ambulatory monitoring based on symptom frequency, and provide reassurance while awaiting diagnosis, as most causes are benign but treatable.