What is the appropriate evaluation and management for a patient presenting with Supraventricular Tachycardia (SVT)?

Evaluation of Supraventricular Tachycardia

Initial Diagnostic Approach

Obtain a 12-lead ECG immediately during tachycardia to establish the diagnosis and guide management—this is the single most critical step that determines all subsequent treatment decisions. 1

Key ECG Features to Document

• QRS duration: Narrow (<120 ms) confirms SVT; wide (≥120 ms) requires differentiation from ventricular tachycardia 1
• P wave location and morphology: P waves buried in QRS suggest AVNRT; P waves in early ST segment suggest AVRT 1
• Regularity: Regular rhythm suggests AVNRT, AVRT, or atrial tachycardia; irregular suggests atrial fibrillation or atrial flutter with variable conduction 1
• RP interval: Short RP (<90 ms from QRS onset to P wave) indicates typical AVNRT or AVRT; long RP suggests atrial tachycardia 1

Baseline Sinus Rhythm ECG

Obtain a 12-lead ECG during sinus rhythm to identify pre-excitation (delta waves), which mandates immediate cardiology referral due to risk of sudden death. 1 Pre-excitation on resting ECG in a patient with paroxysmal palpitations is sufficient for presumptive diagnosis of AVRT without needing to document the arrhythmia first 1.

Clinical History Elements

Symptom Characterization

• Palpitations (present in 86% of patients): Abrupt onset and offset strongly suggest paroxysmal SVT 2
• Chest discomfort (47% of patients) or pressure 2
• Dyspnea (38% of patients) 2
• "Neck pounding" or "shirt flapping": Highly specific for AVNRT due to cannon A-waves from atrial contraction against closed tricuspid valve 1
• Syncope: Uncommon in SVT (4% of presentations) but more frequent in elderly patients; when present, warrants urgent cardiology referral 1

Critical pitfall: True syncope during SVT is rare (4%), but near-syncope is common. In younger patients with Wolff-Parkinson-White syndrome, syncope should raise concern for pre-excited atrial fibrillation with rapid ventricular response, which can degenerate to ventricular fibrillation—this requires immediate electrophysiology evaluation 1.

Risk Stratification Questions

• History of irregular palpitations in a patient with baseline pre-excitation strongly suggests episodes of atrial fibrillation, requiring immediate electrophysiology evaluation due to sudden death risk 1
• Driving history: 57% of SVT patients experience episodes while driving; 14% have syncope while driving 1
• Age consideration: Elderly patients with AVNRT are more prone to syncope despite slower tachycardia rates compared to younger patients 1

Diagnostic Testing Beyond ECG

Echocardiography

Obtain transthoracic echocardiography in all patients with documented sustained SVT to exclude structural heart disease that cannot be detected by physical examination or ECG alone. 1 This identifies hypertrophic cardiomyopathy, dilated cardiomyopathy, valvular abnormalities, and other structural lesions 3.

Ambulatory Monitoring

• 24-hour Holter monitor: Use only if arrhythmias occur several times per week 1
• Event recorder or loop recorder: More useful for less frequent arrhythmias 1
• Implantable loop recorder: Consider for rare symptoms (<2 episodes per month) associated with severe hemodynamic instability 1

Do not delay referral to cardiology while attempting to capture arrhythmia on ambulatory monitoring if pre-excitation is present on baseline ECG. 1

Laboratory Evaluation

• Thyroid function tests: Exclude hyperthyroidism as precipitant 4
• Complete blood count: Rule out anemia 3
• Electrolytes: Identify metabolic abnormalities 4

Mandatory Cardiology Referral Criteria

Refer immediately to cardiac electrophysiology for: 1, 3

• Pre-excitation (delta waves) on resting ECG with any history of palpitations—these patients are at risk for sudden death 1
• Wide complex tachycardia of unknown origin—misdiagnosis as SVT when VT is present can be fatal 1, 3
• Syncope during tachycardia or with exercise—suggests hemodynamically significant arrhythmia 1, 3
• Documented sustained SVT—catheter ablation is first-line therapy with 94.3-98.5% single-procedure success rates 2
• Drug resistance or intolerance to pharmacologic therapy 1
• Patient preference to be free of drug therapy 1

Additional Evaluation Considerations

Exercise Testing

Exercise testing is indicated only if arrhythmia is clearly triggered by exertion. 1 The rate of AVRT is faster when induced during exercise, though rate alone does not explain near-syncope symptoms 1.

Electrophysiology Study

Invasive electrophysiology study with subsequent catheter ablation may be used for both diagnosis and therapy in patients with clear history of paroxysmal regular palpitations, even without ECG documentation. 1 This approach is particularly appropriate when the clinical history strongly suggests SVT and the patient desires definitive therapy.

Critical pitfall: Automatic ECG analysis systems are unreliable and commonly suggest incorrect arrhythmia diagnoses—always review the 12-lead ECG manually 1.

Long-term Monitoring for Complications

Persistent tachycardia lasting weeks to months with fast ventricular response can cause tachycardia-mediated cardiomyopathy (occurs in 1% of PSVT patients), which is reversible but requires careful long-term follow-up even after recovery. 3, 2