What is the differential diagnosis of idiopathic spontaneous tachycardia in an adult woman without obvious precipitating factors?

Differential Diagnosis of Idiopathic Spontaneous Tachycardia in Women

The differential diagnosis of idiopathic spontaneous tachycardia in women without obvious precipitating factors should prioritize supraventricular tachycardia (specifically AVNRT), inappropriate sinus tachycardia, and postural orthostatic tachycardia syndrome, as these represent the most common causes in this demographic. 1

Primary Supraventricular Tachycardia Diagnoses

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

• AVNRT is the most common SVT and occurs in >60% of women presenting with paroxysmal tachycardia 1
• Women have twice the risk of men for developing paroxysmal SVT, with AVNRT being the predominant mechanism 1
• Mean age of symptom onset is 32±18 years, though 16% present after age 50 1
• Heart rate typically ranges 180-200 bpm but can vary from 110 to >250 bpm 1, 2
• Characterized by sudden onset palpitations, neck pulsations, shortness of breath, and dizziness 1, 2
• ECG shows pseudo R' wave in V1 and pseudo S waves in inferior leads due to P waves buried in or immediately after QRS 2

Atrioventricular Reentrant Tachycardia (AVRT)

• Second most common SVT mechanism, though frequency decreases with age 1
• Mean age of symptom onset is 23±14 years in adults 1
• Orthodromic AVRT (narrow complex) shows P waves in ST segment separated from QRS by >70 ms 2
• Requires identification of pre-excitation (delta waves, short PR interval) on baseline ECG 3
• Critical: Pre-excitation mandates immediate electrophysiology referral due to sudden death risk 3

Atrial Tachycardia

• Less common than AVNRT/AVRT but must be considered in the differential 1, 2
• Can be focal or multifocal (MAT), with MAT often associated with pulmonary disease 1, 2
• Atrial rate exceeds ventricular rate when AV block is present 1

Secondary Causes Masquerading as Idiopathic Tachycardia

Inappropriate Sinus Tachycardia Syndrome

• Persistent resting heart rate >100 bpm (often 120-130 bpm) with normal P-wave morphology preceding each QRS 3
• Disproportionate heart rate response to minimal activity 3
• Diagnosis of exclusion requiring investigation of reversible causes 3

Postural Orthostatic Tachycardia Syndrome (POTS)

• Predominantly affects women with acute onset of persistent lightheadedness and fatigue 4
• Heart rate increase ≥30 bpm (or >120 bpm) within 10 minutes of standing 4
• May follow viral illness in some cases 4
• Represents a mild form of autonomic neuropathy with excessive orthostatic catecholamine increase 4

Reversible Causes of Sinus Tachycardia

When sinus tachycardia is documented, investigate:

• Hyperthyroidism (obtain TSH, free T4) 3
• Anemia (obtain CBC) 3
• Dehydration/electrolyte abnormalities (obtain basic metabolic panel) 3
• Stimulant use (caffeine, medications, illicit drugs—obtain toxicology screen) 3
• Anxiety/panic disorder (67% of patients with unrecognized SVT fulfill criteria for panic disorder) 1

Rare but Life-Threatening Diagnoses

Idiopathic Ventricular Tachycardia

• Diagnosis of exclusion in patients without structural heart disease, metabolic abnormalities, or long QT syndrome 5, 6, 7
• Right ventricular outflow tract VT is more common in women and presents with left bundle branch block morphology 1
• Generally well-tolerated but occasional sudden deaths reported, preventing classification as truly benign 6
• Requires periodic re-evaluation to ensure no structural abnormalities develop 5

Polymorphic Ventricular Tachycardia with Normal QT

• Extremely rare presentation of spontaneous PVT without structural heart disease, electrolyte abnormalities, or catecholamine triggers 8
• Life-threatening and requires immediate recognition 8

Inherited Arrhythmia Syndromes

• Wolff-Parkinson-White syndrome (0.1-0.3% prevalence, up to 2% risk of ventricular fibrillation in asymptomatic patients) 1, 3
• Long QT syndrome, Brugada syndrome, hypertrophic cardiomyopathy (can present with asymptomatic tachycardia but carry sudden death risk) 3, 7

Diagnostic Algorithm

Step 1: Obtain 12-Lead ECG During Tachycardia and Sinus Rhythm

• Never dismiss tachycardia without ECG documentation first 3
• Look for pre-excitation (delta waves, short PR), QT prolongation, Brugada pattern, or hypertrophic cardiomyopathy features 3
• Determine if narrow complex (<120 ms) or wide complex (>120 ms) 1

Step 2: Classify Tachycardia Type

• Regular narrow complex with sudden onset/offset: AVNRT or AVRT most likely 1, 2
• Regular narrow complex with gradual onset: Sinus tachycardia or inappropriate sinus tachycardia 3
• Irregular narrow complex: Atrial fibrillation, MAT, or atrial flutter with variable block 1
• Wide complex: Assume ventricular tachycardia until proven otherwise 1

Step 3: Laboratory Evaluation

• Complete blood count, thyroid function tests, basic metabolic panel, toxicology screen 3
• Obtain these even if SVT is suspected to exclude reversible causes 3

Step 4: Structural Heart Disease Evaluation

• Transthoracic echocardiography to exclude structural abnormalities 3
• Exercise stress testing to assess for exercise-induced arrhythmias 3
• Ambulatory monitoring if episodes are paroxysmal 3

Step 5: Risk Stratification and Referral

• Immediate electrophysiology referral if pre-excitation present 3
• Consider electrophysiology referral for recurrent symptomatic SVT given high success rates (94.3-98.5%) of catheter ablation 2, 9

Critical Pitfalls to Avoid

• Never assume sinus tachycardia without ECG confirmation—SVT can occur at rates of 130 bpm 3
• Never administer verapamil or diltiazem for wide-complex tachycardia unless SVT with aberrancy is definitively proven 2
• Never use AV nodal blocking agents in pre-excited atrial fibrillation—this precipitates ventricular fibrillation 2, 9
• Never dismiss asymptomatic tachycardia as benign without obtaining baseline ECG to exclude sudden death syndromes 3
• Do not attribute symptoms to anxiety/panic disorder without excluding organic causes—54% of SVT patients are initially misdiagnosed with psychiatric conditions 1