How to diagnose and treat a patient with symptoms suggestive of supraventricular tachycardia (SVT) but may actually have atrial fibrillation (AF)?

Distinguishing Atrial Fibrillation from Supraventricular Tachycardia

Critical First Step: Obtain a 12-Lead ECG During Tachycardia

The single most important diagnostic maneuver is obtaining a 12-lead ECG during the arrhythmia—this definitively distinguishes AF from SVT and should be prioritized above all other testing. 1

The fundamental distinction hinges on rhythm regularity:

• Regular narrow-complex tachycardia with sudden onset/termination suggests AVNRT or AVRT 1
• Irregular narrow-complex tachycardia indicates AF, atrial flutter with variable block, or multifocal atrial tachycardia 1

ECG Diagnostic Features During Tachycardia

For Atrial Fibrillation:

• Irregular R-R intervals when AV conduction is intact 1
• Absence of distinct P waves 1
• Irregular atrial activity 1

For AVNRT (Most Common SVT):

• Regular narrow QRS complex (<120 ms) with regular R-R intervals 2
• Absent or barely visible P waves (buried in QRS) 2
• Pseudo r' wave in lead V1 and pseudo S waves in inferior leads (II, III, aVF) are pathognomonic 2

For AVRT:

• Regular narrow-complex tachycardia with retrograde P waves visible after the QRS 1
• Pre-excitation (delta waves) on resting ECG when in sinus rhythm strongly suggests AVRT 1

Diagnostic Algorithm When Patient Presents With Palpitations

Step 1: Document the Rhythm

• If patient is currently symptomatic: obtain 12-lead ECG immediately 1, 3
• If symptoms occur daily: 24-48 hour Holter monitoring 3
• If symptoms occur several times per week: event recorder (superior diagnostic yield and more cost-effective than Holter) 3
• If symptoms occur less than twice monthly with severe features: implantable loop recorder 3

Step 2: Assess Rhythm Regularity and Response to Vagal Maneuvers

• Termination by vagal maneuvers (Valsalva, carotid massage) confirms reentrant tachycardia involving AV nodal tissue (AVNRT or AVRT), not AF 1, 2
• Record a 12-lead ECG during adenosine administration to observe the response—this aids differential diagnosis 2
• AF will not terminate with vagal maneuvers but may transiently slow the ventricular response 1

Step 3: Evaluate Resting ECG for Pre-excitation

• Pre-excitation (delta waves) with history of paroxysmal regular palpitations = presumptive AVRT requiring immediate electrophysiology referral 1, 2
• Pre-excitation with irregular palpitations strongly suggests AF with accessory pathway conduction—this requires immediate electrophysiological evaluation due to sudden death risk 1, 2

Critical Clinical Clues

Symptoms Favoring AVNRT Over AF:

• "Neck pounding" or "shirt flapping" sensations (cannon a-waves from atrial contraction against closed tricuspid valve) 1
• Polyuria (from atrial natriuretic peptide release due to elevated atrial pressures) 1, 2
• Sudden onset and sudden termination 1

Symptoms Less Specific:

• Palpitations, lightheadedness, chest discomfort, dyspnea, and presyncope occur with both AF and SVT 1
• True syncope occurs in approximately 15% of SVT patients but is uncommon 1

The Hidden Relationship: SVT Triggering AF

A critical pitfall: 10% of patients referred for AF ablation have an underlying SVT that triggers their AF episodes 4. This is particularly important because:

• AF often starts during an attack of PSVT rather than de novo 5
• The cumulative proportion of PSVT patients who develop AF is 13% at 3 months, 22% at 1 year, and 29% at 2 years 5
• Patients with inducible SVT are younger, have less structural heart disease, smaller left atria, and higher prevalence of paroxysmal AF (84.6% vs 24.6%) 4
• Ablation of the triggering SVT alone prevents AF recurrence in 92.3% of these patients 4

Mandatory Immediate Cardiology Referral

Refer immediately to cardiac electrophysiology for: 1, 3, 2

• All patients with Wolff-Parkinson-White syndrome (pre-excitation on ECG)
• Wide complex tachycardia of unknown origin
• Syncope during tachycardia or with exercise
• Documented sustained SVT despite normal structural evaluation
• Pre-excitation with irregular palpitations (suggests AF with accessory pathway)

Common Diagnostic Pitfalls to Avoid

• Do not rely on automatic ECG interpretation systems—they are unreliable and commonly suggest incorrect diagnoses 2
• Do not assume all irregular tachycardias are AF—consider atrial flutter with variable block and multifocal atrial tachycardia 1
• Do not dismiss the possibility of underlying SVT in patients with documented AF, especially younger patients with paroxysmal AF and minimal structural heart disease 4
• Do not start Class I or III antiarrhythmic drugs without documented arrhythmia due to significant proarrhythmic risk 3
• Recognize that persistent tachycardia for weeks to months can cause reversible tachycardia-mediated cardiomyopathy 1

Treatment Implications Once Diagnosis is Established

For Confirmed AVNRT/AVRT:

• Catheter ablation is first-line for long-term management with high success rate (<5% recurrence, <1% risk of heart block) 6, 7
• Beta-blockers or calcium channel blockers for acute management or suppressive therapy 6, 7

For Confirmed AF:

• Anticoagulation based on CHA₂DS₂-VASc score takes priority 1
• Rate control with beta-blockers or calcium channel blockers 1
• Rhythm control with antiarrhythmics or ablation for symptomatic patients 1
• Sotalol AF is specifically indicated for maintenance of normal sinus rhythm in patients with symptomatic AF/AFL who are currently in sinus rhythm, but should be reserved for highly symptomatic patients due to risk of life-threatening ventricular arrhythmias 8

For AF Triggered by SVT:

• Consider electrophysiology study to identify and ablate the triggering SVT—this may eliminate AF recurrences without requiring AF ablation 4