A wide complex tachycardia (WCT) is either of ventricular origin (ventricular tachycardia), of supraventricular origin with aberrant conduction (SVT with aberrancy), of supraventricular origin and is conducted down a bypass tract such as in Wolff-Parkinson-White syndrome (WPW), or is due to a pacemaker malfunction. The most common cause of WCT is ventricular tachycardia (VT), which accounts for 80% of all cases of WCT.^[1][2] Supraventricular tachycardia (SVT) with aberrancy accounts for 15% to 20% of WCTs. SVTs with preexcitation and antidromic atrioventricular reentrant tachycardia account for 1% to 6% of WCTs.^[3]

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• STEMI
• Unstable angina

• AV reentrant tachycardia
• Pre-excitation syndrome
• Supraventricular tachycardia
• Ventricular tachycardia

• Congestive heart failure
• Hypokalemia
• Hypomagnesemia
• STEMI

• Arrhythmogenic right ventricular dysplasia
• Hypertrophic cardiomyopathy
• Long QT syndrome
• Myocarditis
• Short QT syndrome
• Short QT syndrome type 1
• Short QT syndrome type 2
• Short QT syndrome type 3
• Short QT syndrome type 4
• Short QT syndrome type 5

• Supraventricular tachycardia (SVT) with aberrant ventricular conduction is either new or due to a preexisting left or right bundle branch block or a preexisting nonspecific intraventricular conduction delay (IVCD). The underlying supraventricular rhythm that is aberrantly conducted can be any one of the following rhythms:

• Atrial flutter with 2:1 conduction and occasional 1:1 conduction
• Automatic junctional tachycardia
• AV nodal reentrant tachycardia
• AV reentrant tachycardia using a bypass tract
• Intraatrial reentrant tachycardia
• Paroxysmal atrial tachycardia
• SA nodal reentrant tachycardia
• Sinus tachycardia

The diagnosis of rapid antegrade conduction down a bypass tract due to ventricular pre-excitation such as Wolff-Parkinson-White syndrome (WPW) should be considered if

• There is intermittent present of a delta wave
• There is intermittently a short PR interval

A paced rhythm as a cause of wide complex tachycardia is infrequent. This diagnosis is suggested in the following scenarios:

• A pacemaker is in place and there is a LBBB pattern with superior left axis deviation, however, depending on the site of pacing this pattern can vary significantly
• A wide complex tachycardia is due to an SVT and the pacemaker is tracking sensed atrial activity and is pacing the ventricles rapidly as result
• Pacemaker-mediated tachycardia in which there is retrograde conduction which triggers atrial activity during ventricular pacing
• Runaway pacemaker syndrome in which the pacemaker fires at a rate of nearly 2000 bpm and captures intermittently
• Sensor induced tachycardia in which case the pacemaker fires at a rate of nearly 160-180 bpm in response to electrocautery, noise, vibration, limb movement or other stimuli