Ventricular Tachycardia Differential Diagnoses

Updated: Dec 05, 2017
  • Author: Steven J Compton, MD, FACC, FACP, FHRS; Chief Editor: Jeffrey N Rottman, MD  more...
  • Print
DDx

Diagnostic ConsiderationsPacemaker-generated tachycardiaSupraventricular tachycardia

In addition to the conditions listed in the differential diagnosis (see below), other problems to consider in the differential diagnosis of ventricular tachycardia (VT) include the following:

  • Ventricular fibrillation (VF)
  • Supraventricular tachycardia (SVT) or atrial tachycardia (AT) with aberrant conduction
  • Electrocardiographic (ECG) lead motion artifact (see the image below)
    At first glance, this tracing suggests rapid polym At first glance, this tracing suggests rapid polymorphic ventricular tachycardia. It is actually sinus rhythm with premature atrial complex and a superimposed lead motion artifact. Hidden sinus beats can be observed by using calipers to march backward from the final two QRS complexes. This artifact can be generated easily with rapid arm motion (eg, brushing teeth) during telemetry monitoring.
  • Inappropriate rate-responsive pacing
  • Dual-chamber pacemaker tracking of AT
  • Pacemaker failure
  • Pacemaker syndrome
  • Premature ventricular contraction
  • Multifocal AT
  • Wolff-Parkinson-White syndrome
  • Accelerated idioventricular rhythm

VF is a disorganized, rapid ventricular rhythm that varies in interval and waveform. It may be difficult to distinguish from rapid, polymorphic VT. Sudden death accounts for approximately half of all deaths from cardiovascular disease and is generally caused by VT and VF. [1, 2]

Accelerated idioventricular rhythm is defined as an enhanced ectopic ventricular rhythm with at least three consecutive ventricular beats that is faster than the normal intrinsic ventricular escape rhythm (≤40 beats/min) but slower than VT. However, there is a potential definitional overlap with accelerated idioventricular rhythm and an automatic VT of 100-120 beats/min.

Permanent pacemakers occasionally generate rapid rhythms. The most common cause is tracking of atrial tachyarrhythmias, such as atrial flutter or atrial fibrillation (AF). The pacemaker typically paces around the programmed maximum tracking limit, which is often set at 120-140 beats/min in older patients (see the image below). If a pacemaker programmer is not available, a magnet placed over the pacer generator deactivates atrial sensing temporarily and allows for the diagnosis of the atrial arrhythmia.

Ventricular pacing at 120 beats/min. Newer pacemak Ventricular pacing at 120 beats/min. Newer pacemakers use bipolar pacing. If a smaller pacing stimulus artifact is overlooked, an erroneous diagnosis of ventricular tachycardia may result. Because leads are most commonly placed in the right ventricular apex, paced beats will have a left bundle-branch block morphology with inferior axis. Causes of rapid pacing include (1) tracking of atrial tachycardia in DDD mode, (2) rapid pacing due to the rate response being activated, and (3) endless loop tachycardia. Application of a magnet to the pacemaker will disable sensing and allow further diagnosis. Sometimes “pacing spike detection” must be programmed “ON” in the electrocardiographic system to make the spike apparent.

Wide-complex conduction during SVT can mimic VT. The two most common forms are atrioventricular (AV) reentrant tachycardia (AVRT) and AV nodal reentrant tachycardia (AVNRT) with aberrant conduction.

AVRT can be either orthodromic or antidromic, depending on the direction of conduction through the AV node. All antidromic AVRTs cause wide-complex tachycardia as a result of ventricular activation outside of the His-Purkinje system, and some orthodromic AVRTs conduct with wide QRS complexes as a result of functional or preexisting bundle-branch block, bystander accessory pathway conduction, or intraventricular conduction delay (see the images below).

Note the retrograde P waves in this electrocardiog Note the retrograde P waves in this electrocardiogram.
Retrograde P waves are also observed in this elect Retrograde P waves are also observed in this electrocardiogram.

Aberrantly conducted SVT circuits can mimic VT, but careful analysis of the ECG can allow discrimination of VT from aberrant SVT in most cases.

Historically, the use of adenosine to distinguish VT from regular wide QRS complex SVT has been discouraged because, in theory, it could precipitate VF. Wide QRS complex tachycardia should be presumed to be VT if the diagnosis is unclear. [40]

However, a retrospective observational study in 197 consecutive patients with regular wide QRS complex tachycardia found that adenosine was useful and safe as a diagnostic agent for making this differentiation. [41] Adenosine produces transient AV nodal blockade and thus should terminate reentrant SVTs, which involve the AV node as a pathway, but not most VTs.

Adenosine should not be used for irregular wide QRS complex tachycardia, because that dysrhythmia may involve AF in the presence of an accessory pathway (see the image below). In such cases, adenosine may allow conduction of rapid atrial fibrillatory impulses exclusively through an amenable accessory tract and thereby cause very rapid, intolerable ventricular rates and eventuate in the induction of VF. [42, 43]

Preexcited atrial fibrillation. The patient has an Preexcited atrial fibrillation. The patient has an accessory atrioventricular connection. Atrial fibrillation has been induced. Conduction over an accessory pathway results in a wide QRS complex, mimicking ventricular tachycardia.

 

Differential Diagnoses