Evaluation of Supraventricular Tachycardia

Diagnostic Approach

The American College of Cardiology recommends obtaining a 12-lead ECG immediately during tachycardia to establish the diagnosis and guide management, as this is the single most critical step that determines all subsequent treatment decisions 1, 2
The American Heart Association suggests that a narrow QRS duration (<120 ms) confirms SVT, while a wide QRS duration (≥120 ms) requires differentiation from ventricular tachycardia 3
The presence of P waves buried in the QRS suggests AVNRT, while P waves in the early ST segment suggest AVRT 4, 3
A regular rhythm suggests AVNRT, AVRT, or atrial tachycardia, while an irregular rhythm suggests atrial fibrillation or atrial flutter with variable conduction 3
A short RP interval (<90 ms from QRS onset to P wave) indicates typical AVNRT or AVRT, while a long RP interval suggests atrial tachycardia 4

The American College of Cardiology notes that "neck pounding" or "shirt flapping" is highly specific for AVNRT due to cannon A-waves from atrial contraction against a closed tricuspid valve 4
Syncope is uncommon in SVT (4% of presentations) but more frequent in elderly patients, and when present, warrants urgent cardiology referral 4, 5
A 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 5
Driving history is relevant, as 57% of SVT patients experience episodes while driving, and 14% have syncope while driving 4, 3
Elderly patients with AVNRT are more prone to syncope despite slower tachycardia rates compared to younger patients 4

The American College of Cardiology recommends obtaining transthoracic echocardiography in all patients with documented sustained SVT to exclude structural heart disease that cannot be detected by physical examination or ECG alone 5
Ambulatory monitoring with a 24-hour Holter monitor is useful if arrhythmias occur several times per week, while an event recorder or loop recorder is more useful for less frequent arrhythmias 5
An implantable loop recorder may be considered for rare symptoms (<2 episodes per month) associated with severe hemodynamic instability 5

The American College of Cardiology recommends immediate referral to cardiac electrophysiology for pre-excitation (delta waves) on resting ECG with any history of palpitations, as these patients are at risk for sudden death 5
Wide complex tachycardia of unknown origin requires immediate referral, as misdiagnosis as SVT when VT is present can be fatal 3, 5, 6
Syncope during tachycardia or with exercise suggests hemodynamically significant arrhythmia and requires immediate referral 5, 6
Documented sustained SVT requires referral for catheter ablation, which has a 94.3-98.5% single-procedure success rate 5
Drug resistance or intolerance to pharmacologic therapy, as well as patient preference to be free of drug therapy, are also indications for referral 5