What is the recommended approach for diagnosing Supraventricular Tachycardia (SVT)?

Diagnosis of Supraventricular Tachycardia (SVT)

The cornerstone of SVT diagnosis is obtaining a 12-lead ECG during tachycardia, which should be the first diagnostic step in any patient with suspected SVT. 1

Initial Diagnostic Approach

• Obtain a 12-lead ECG during tachycardia whenever possible, but do not delay treatment if the patient is hemodynamically unstable 2, 1
• If immediate cardioversion is needed, at minimum obtain a monitor strip from the defibrillator before cardioversion 2
• A resting 12-lead ECG should be recorded even when not in tachycardia to identify pre-excitation patterns 2
• Assess the clinical history for pattern of episodes, including onset/termination characteristics, duration, frequency, and possible triggers 2
• Document response to vagal maneuvers, which can aid in diagnosis (termination suggests AVNRT or AVRT) 2, 1

ECG Analysis for Narrow QRS Tachycardia (<120 ms)

• If QRS is narrow (<120 ms), the tachycardia is almost always supraventricular 2
• When no P waves are visible and RR interval is regular, AVNRT is most likely 2
• Look for pseudo-R wave in V1 and/or pseudo-S wave in inferior leads, which are pathognomonic for AVNRT 2
• If P wave is present in ST segment and separated from QRS by 70 ms, AVRT is most likely 2
• For tachycardias with RP longer than PR, consider atypical AVNRT, PJRT, or atrial tachycardia 2
• Use adenosine or carotid massage with continuous ECG recording to help reveal the underlying mechanism 2, 1

ECG Analysis for Wide QRS Tachycardia (≥120 ms)

• If QRS is wide (≥120 ms), differentiate between SVT with aberrancy and ventricular tachycardia (VT) 2
• Always treat as VT if diagnosis cannot be easily proven as SVT, as inappropriate treatment of VT with calcium channel blockers can cause hemodynamic collapse 2, 3
• Wide QRS tachycardia can be divided into three categories 2:
  1. SVT with bundle-branch block or aberration
  2. SVT with AV conduction over an accessory pathway
  3. Ventricular tachycardia
• Look for AV dissociation or fusion complexes, which indicate VT 1
• Consider that VT accounts for >80% of wide complex tachycardias 4

Special Diagnostic Considerations

• Pre-excitation on resting ECG with history of paroxysmal regular palpitations is sufficient for presumptive diagnosis of AVRT 2
• Patients with pre-excitation and irregular paroxysmal palpitations may have atrial fibrillation, requiring immediate electrophysiological evaluation due to risk of sudden death 2, 1
• Automatic analysis systems of 12-lead ECGs are unreliable and commonly suggest incorrect arrhythmia diagnoses 2
• If P waves are not visible on standard ECG, esophageal pill electrodes can be helpful 2

Indications for Referral to Cardiac Electrophysiologist

• Presence of wide complex tachycardia of unknown origin 2
• Pre-excitation on resting ECG, even without documented tachycardia 2, 1
• Drug resistance or intolerance 2
• Patient preference to be free of drug therapy 2
• Severe symptoms such as syncope or dyspnea during palpitations 2
• All patients with Wolff-Parkinson-White syndrome (pre-excitation combined with arrhythmias) 2, 5

Additional Investigations

• Consider echocardiography to exclude structural heart disease 2
• Extended cardiac monitoring (Holter monitor or event recorder) may be needed if diagnosis remains unclear 5
• Invasive electrophysiological study may be used for both diagnosis and therapy in cases with clear history of paroxysmal regular palpitations 2, 5