Differentiating SVT from VT

Initial Assessment

The American College of Cardiology and the American Heart Association recommend that when differentiating between Supraventricular Tachycardia (SVT) and Ventricular Tachycardia (VT), the QRS width is the initial distinguishing feature, with VT being the presumed diagnosis in wide complex tachycardias until proven otherwise due to its higher morbidity and mortality risk 1, 2
A narrow QRS complex (<120 ms) almost always indicates SVT, according to the American College of Cardiology 3, 4
A wide QRS complex (>120 ms) could be either VT or SVT with aberrant conduction; it should be treated as VT if the diagnosis is uncertain, as suggested by the American College of Cardiology and the American Heart Association 1, 3

The presence of AV dissociation with a ventricular rate faster than the atrial rate is pathognomonic for VT, as stated by the American Heart Association 1, 2
Fusion complexes represent a merger between conducted sinus impulses and ventricular depolarization and are pathognomonic for VT, according to the American College of Cardiology 5, 6
The Brugada criteria, which include the lack of any R-S complexes in precordial leads and an R-S interval >100 ms in any precordial lead, imply VT, as recommended by the American Heart Association 1, 2
The Vereckei algorithm, which includes an initial R wave or Q wave >40 ms in lead aVR and a notch on the descending limb at the onset of a predominantly negative QRS, implies VT, as suggested by the American Heart Association 1, 2
A QRS width >140 ms with an RBBB pattern or >160 ms with an LBBB pattern favors VT, according to the American College of Cardiology 6
QRS concordance, where all precordial leads show either positive or negative deflections, suggests VT, as stated by the American Heart Association 1, 2
An R-wave peak time ≥50 ms in lead II suggests VT, as recommended by the American Heart Association 1, 2

Hidden P waves in AVNRT may be partially hidden within the QRS complex, creating a pseudo-R wave in V1 and/or a pseudo-S wave in inferior leads, as described by the American College of Cardiology 3, 4
Visible P waves after QRS in AVRT are visible in the ST segment and separated from QRS by ≥70 ms, according to the American College of Cardiology 3, 4
The RP relationship, where a short RP (RP < PR) is typical of AVNRT or AVRT, and a long RP (RP > PR) is typical of atypical AVNRT, PJRT, or atrial tachycardia, is an important diagnostic criterion, as suggested by the American College of Cardiology 3, 4, 5
The response to adenosine, which can aid in the diagnosis of different SVT mechanisms, is a useful diagnostic tool, as recommended by the American College of Cardiology and the American Heart Association 3, 5, 6

The American College of Cardiology and the American Heart Association warn that never assuming stable vital signs rule out VT, as hemodynamic stability does not distinguish between SVT and VT 1, 3
The American College of Cardiology and the American Heart Association advise against using calcium channel blockers in undiagnosed wide complex tachycardias, as they can precipitate hemodynamic collapse in VT 1, 3
When in doubt, treating as VT is the safest approach, if the diagnosis of wide complex tachycardia is uncertain, as recommended by the American College of Cardiology and the American Heart Association 1, 3
Pre-existing bundle branch block can make SVT appear as wide complex tachycardia, as described by the American College of Cardiology and the American Heart Association 1, 3
SVT with accessory pathway conduction can present with wide QRS, especially with antidromic AVRT, as suggested by the American College of Cardiology and the American Heart Association 1, 3