Table 2.
Definitions
| Clinical characteristics |
| Clinical ventricular tachycardia (VT) : VT that has occurred spontaneously based on analysis of 12‐lead electrocardiogram (ECG) QRS morphology. |
| Hemodynamically unstable VT : causes hemodynamic compromise requiring prompt termination. |
| Idiopathic VT : used to indicate VT that is known to occur in the absence of clinically apparent structural heart disease (SHD). |
| Idioventricular rhythm : three or more consecutive beats at a rate of up to 100 per minute that originate from the ventricles independent of atrial or atrioventricular (AV) nodal conduction. Although various arbitrary rates have been used to distinguish it from VT, the mechanism of ventricular rhythm is more important than the rate. Idioventricular rhythm can be qualified as “accelerated” when the rate exceeds 40 bpm. |
| Incessant VT : continuous sustained VT that recurs promptly despite repeated intervention for termination over several hours. |
| Nonclinical VT : VT induced by programmed electrical stimulation (PES) that has not been documented previously. |
| Nonsustained VT : terminates spontaneously within 30 seconds. |
| PVC : premature ventricular complex; it is an early ventricular depolarization with or without mechanical contraction. We recommend avoiding the use of the terms “ventricular premature depolarization” and “premature ventricular contraction” to standardize the literature and acknowledge that early electrical activity does not necessarily lead to mechanical contraction. |
| Presumptive clinical VT : similar to a spontaneous VT based on rate, limited ECG, or electrogram data available from ICD interrogation, but without the 12‐lead ECG documentation of spontaneous VT. |
| PVC burden : the amount of ventricular extrasystoles, preferably reported as the % of beats of ventricular origin of the total amount of beats over a 24‐hour recording period. |
| Repetitive monomorphic VT : continuously repeating episodes of self‐terminating nonsustained VT. |
| Sustained VT : continuous VT for 30 seconds, or which requires an intervention for termination (such as cardioversion). |
| VT : a tachycardia (rate >100 bpm) with 3 or more consecutive beats that originates from the ventricles independent of atrial or AV nodal conduction. |
| VT storm : three or more separate episodes of sustained VT within 24 hours, each requiring termination by an intervention. |
| VT Morphologies |
| Monomorphic VT : a similar QRS configuration from beat to beat (Figure 1A). Some variability in QRS morphology at initiation is not uncommon, followed by stabilization of the QRS morphology. |
| Monomorphic VT with indeterminate QRS morphology : preferred over ventricular flutter; it is a term that has been applied to rapid VT that has a sinusoidal QRS configuration that prevents identification of the QRS morphology. |
| Multiple monomorphic VTs : more than one morphologically distinct monomorphic VT, occurring as different episodes or induced at different times. |
| Pleomorphic VT : has more than one morphologically distinct QRS complex occurring during the same episode of VT, but the QRS is not continuously changing (Figure 1B). |
| Polymorphic VT : has a continuously changing QRS configuration from beat to beat, indicating a changing ventricular activation sequence (Figure 1C). |
| Right bundle branch block (RBBB)‐ and left bundle branch block (LBBB)‐like VT configurations : terms used to describe the dominant deflection in V1, with a dominant R wave described as “RBBB‐like” and a dominant S wave with a negative final component in V1 described as “LBBB‐like” configurations. |
| Torsades de pointes : a form of polymorphic VT with continually varying QRS complexes that appear to spiral around the baseline of the ECG lead in a sinusoidal pattern. It is associated with QT prolongation. |
| Unmappable VT : does not allow interrogation of multiple sites to define the activation sequence or perform entrainment mapping; this could be due to hemodynamic intolerance that necessitates immediate VT termination, spontaneous or pacing‐induced transition to other morphologies of VT, or repeated termination during mapping. |
| Ventricular fibrillation (VF): a chaotic rhythm defined on the surface ECG by undulations that are irregular in both timing and morphology, without discrete QRS complexes. |
| PVC Morphologies |
| Monomorphic PVC : PVCs felt reasonably to arise from the same focus. Slight changes in QRS morphology due to different exit sites from the same focus can be present. |
| Multiple morphologies of PVC : PVCs originating from several different focal locations. |
| Predominant PVC morphology : the one or more monomorphic PVC morphologies occurring most frequently and serving as the target for ablation. |
| Mechanisms |
| Focal VT : a point source of earliest ventricular activation with a spread of activation away in all directions from that site. The mechanism can be automaticity, triggered activity, or microreentry. |
| Scar‐related reentry : arrhythmias that have characteristics of reentry that originate from an area of myocardial scar identified from electrogram characteristics or myocardial imaging. Large reentry circuits that can be defined over several centimeters are commonly referred to as “macroreentry.” |
Abbreviations: AV, atrioventricular; ECG, electrocardiogram; ICD, implantable cardioverter defibrillator; LBBB, left bundle branch block; PES, programmed electrical stimulation; PVC, premature ventricular complex; RBBB, right bundle branch block; SHD, structural heart disease; VT, ventricular tachycardia.