Differential Diagnosis of Supraventricular Tachycardia

Introduction to SVT Diagnosis

The American College of Cardiology recommends determining QRS width and hemodynamic stability to guide diagnostic approach and treatment decisions for SVT 1
The American Heart Association suggests that atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of SVT, typically with P waves hidden within the QRS complex 1

AVNRT is characterized by a regular RR interval with no visible atrial activity, and may show pseudo-R' wave in lead V1 or pseudo-S wave in inferior leads due to P waves deforming the QRS 1, 2
Atrioventricular reciprocating tachycardia (AVRT) has a P wave present in the ST segment, separated from the QRS by >70 ms, and requires an anatomically distinct accessory pathway bypassing the AV node 1, 2
Atrial tachycardia (AT) has a P wave morphology that differs from sinus rhythm, usually seen near the end of or shortly after the T wave, with a long RP interval typical (RP > PR) 1

If uncertain about the diagnosis of wide QRS-complex tachycardia, the American College of Cardiology recommends treating as ventricular tachycardia (VT) 3, 4, 5, 6
SVT with pre-existing bundle branch block should be compared to baseline ECG during sinus rhythm when available, with QRS morphology matching the baseline BBB pattern 3
SVT with AV conduction over an accessory pathway can occur during AT, atrial flutter, AF, AVNRT, or antidromic AVRT, with anterograde conduction over the accessory pathway and retrograde over the AV node 5

AV dissociation, where the ventricular rate is faster than the atrial rate, proves VT diagnosis, although only clearly discernible in 30% of VTs 3, 5, 6, 7
Fusion beats are pathognomonic for VT, representing the merger between conducted supraventricular impulses and ventricular depolarization 3, 4, 5, 7, 8
QRS width criteria, such as QRS >0.14 seconds with RBBB pattern or QRS >0.16 seconds with LBBB pattern, favor VT 3, 4, 5, 6

For hemodynamically unstable patients, immediate synchronized DC cardioversion is the first-line treatment for any unstable narrow or wide QRS-complex tachycardia 3, 4, 5, 8, 6
For hemodynamically stable narrow QRS-complex tachycardia, vagal maneuvers such as the Valsalva maneuver or carotid sinus massage should be attempted first 1, 4
Adenosine is the preferred agent for acute termination of SVT if vagal maneuvers fail, due to its rapid onset and short half-life, but is contraindicated in severe asthma and should be used with caution in certain populations 3, 4, 8

Never administer verapamil or diltiazem for wide-complex tachycardia of uncertain etiology, as it can cause severe hypotension or accelerated ventricular rate in VT or pre-excited AF 1
Obtain a 12-lead ECG before treatment when possible to avoid missing VT masquerading as SVT, and consider using esophageal electrodes to help identify P waves when not visible on surface ECG 1, 2, 3, 5, 6, 7

Circulation, 2016

Journal of the American College of Cardiology, 2003

Circulation, 2003

Journal of the American College of Cardiology, 2003