Monomorphic Ventricular Tachycardia

This section will cover monomorphic ventricular tachycardia (VT) and related rhythms that originate from the ventricles. 

Things to be included:

• An overview of the various terms and classification systems used to characterize ventricular tachycardias. This includes morphologic classifications (i.e., RBBB-like, LBBB-like, monomorphic, polymorphic, pleomorphic), duration-based classification (i.e., non-sustained, sustained, incessant), etiologic classification (i.e. ischemic, idiopathic), mechanism-based classification (i.e., focal, reentrant) and classification based on response to medications (i.e. verapamil-, adenosine-, or catecholamine-sensitive). We will also review the classic causes of VT, such as ischemic heart disease, cardiomyopathy, channelopathies, drugs and electrolytes, and idiopathic VT.

• Approach to analyzing an ECG of monomorphic VT. This will include concepts such as, but not limited to:

  • How to distinguish the QRS complex in a wide complex tachycardia, which can be difficult due to the lack of a clear isoelectric baseline.

  • Using ECG features to hypothesize the underlying mechanism of a VT, which involves examining the initiation and termination.

  • How to localize the source of the VT using a 12- or 15-lead ECG. This means finding the location of the ectopic focus in automatic VTs and the exit site of the reentry circuit in a reentrant VT. There will also be a discussion on the limitations of localization, such as the possibility of a single scar being associated with multiple exit sites and VT morphologies.

  • Differentiating VT from SVT with aberrancy. This will be associated with an in-depth conversation the multiple well-known aspects that can bias a diagnosis either towards or away from VT. This includes: narrowness of the initial deflection, presence of AV dissociation or capture/fusion beats, positive precordial concordance, regularity, and morphology. 

    • We will go over some popular criteria that incorporate these elements to make a simple decision tree that clinicians can follow (such as the Brugada, Vereckei, lead II RWPT, Bayesian, Griffin, and ACC algorithms). We will also go over the sensitivities and specificities of these criteria and the downsides (i.e. lower specificity on validation studies).

    • By giving examples of rhythms that "break the rules", we will go over how there are no perfect ways to differentiate VT from SVT on the ECG alone.

• An assortment of various monomorphic ventricular arrhythmias, such as:

  • Accelerated idioventricular rhythm, a slower and fairly "benign" ventricular rhythm that is usually associated with enhanced physiologic automaticity following successful reperfusion after a STEMI or various medications (i.e. anesthetic agents). 

  • Different types of idiopathic VT, such as RVOT VT, fascicular VT, and bundle branch reentrant VT.

  • Ischemic scar-reentrant VT from various locations, related to different types of infarcts.

  • VT associated with arrhythmogenic right ventricular cardiomyopathy (ARVC).

  • Monomorphic VT with varying degrees of ventriculoatrial (VA) block, characterized by differing RP intervals for the retrograde p waves. This includes:

    • Complete VA block and AV dissociation. We will also highlight the difference between AV dissociation related to VT and AV dissociation related to a complete AV block with ventricular escape.

    • Second degree VA block, including VA Wenckebach and 2:1 VA block.

    • 1:1 VA conduction (no block).

  • Ventricular parasystole and parasystolic tachycardia, which are secondary to an ectopic pacemaker in the ventricles that may be rapidly firing and is protected from overdrive suppression from the sinus rhythm.

  • Ventricular flutter, a very rapid pre-fibrillation rhythm characterized by a sinusoidal pattern in which distinguishing the QRS complex from the ST-T complex is impossible. Ventricular fibrillation (VF) itself will be covered in the "Polymorphic VT" section.

  • Examples of the fate of VT, for example:

    • Spontaneous termination of VT.

    • VT devolving into VF.

    • VT abolished by delivering a shock.

    • VT terminated by anti-tachycardia pacing.

  • An overview of the differential diagnosis of monomorphic VT, such as:

    • SVT with aberrancy (such as bundle branch block, preexcitation, hyperkalemia or sodium channel blockers).

    • Pacemaker-mediated tachycardia.

    • Artefact.