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September 25, 2018 Circulation. 2018;138:e272–e391. DOI: 10.1161/CIR.0000000000000549 e280 CLINICAL STATEMENTS AND GUIDELINES Table 5. Table of Definitions of Commonly Used Terms in this Document Term Definition or Description Ventricular tachycardiaS2.2.2-2 Cardiac arrhythmia of ≥3 consecutive complexes originating in the ventricles at a rate >100 bpm (cycle length: <600 ms). Types of VT: Sustained: VT >30 s or requiring termination due to hemodynamic compromise in <30 s. Nonsustained/unsustained: ≥3 beats, terminating spontaneously. Monomorphic: Stable single QRS morphology from beat to beat. Polymorphic: Changing or multiform QRS morphology from beat to beat. Bidirectional: VT with a beat-to-beat alternation in the QRS frontal plane axis, often seen in the setting of digitalis toxicity or catecholaminergic polymorphic VT Monomorphic VT Polymorphic VT Bidirectional VT Torsades de pointesS2.2.2-2 Torsades de pointes is polymorphic VT that occurs in the setting of a long QT interval and is characterized by a waxing and waning QRS amplitude. It often has a long-short initiating sequence with a long coupling interval to the first VT beat and may present with salvos of NSVT. The twisting of the points, although characteristic, may not always be seen, especially if the episode is nonsustained or if only a limited number of leads are available. Torsades de pointes can result from bradycardia including high-grade AV block that leads to a long-short sequence initiating torsades de pointes. Ventricular flutterS2.2.2-2 A regular VA ≈300 bpm (cycle length: 200 ms) with a sinusoidal, monomorphic appearance; no isoelectric interval between successive QRS complexes. Ventricular fibrillationS2.2.2-2 Rapid, grossly irregular electrical activity with marked variability in electrocardiographic waveform, ventricular rate usually >300 bpm (cycle length: <200 ms). Sudden cardiac arrestS2.2.2-2 SCA is the sudden cessation of cardiac activity such that the victim becomes unresponsive, with either persisting gasping respirations or absence of any respiratory movements, and no signs of circulation as manifest by the absence of a perceptible pulse. An arrest is presumed to be of cardiac etiology unless it is known or likely to have been caused by trauma, drowning, respiratory failure or asphyxia, electrocution, drug overdose, or any other noncardiac cause. Sudden cardiac deathS2.2.2-2 Sudden and unexpected death occurring within an hour of the onset of symptoms, or occurring in patients found dead within 24 h of being asymptomatic and presumably due to a cardiac arrhythmia or hemodynamic catastrophe. VT/VF stormS2.2.2–3 VT/VF storm (electrical storm or arrhythmic storm) refers to a state of cardiac electrical instability that is defined by ≥3 episodes of sustained VT, VF, or appropriate shocks from an ICD within 24 h. Primary prevention ICDS2.2.2-2 ICD placement with the intention of preventing SCD in a patient who has not had sustained VT or SCA but who is at an increased risk for these events. Secondary prevention ICDS2.2.2-2 ICD placement in a patient with prior SCA, sustained VT, or syncope caused by VA. Structural heart disease* This term encompasses IHD, all types of cardiomyopathy, valvular heart disease, and adult congenital heart disease. Cardiac channelopathyS2.2.2–4 Arrhythmogenic disease due to a genetic abnormality that results in dysfunction of a cardiac ion channel (eg, long QT syndrome, catecholaminergic polymorphic VT). *The definition of this term may differ across publications. Refer to the entry for the definition used in this document. AV indicates atrioventricular; ICD, implantable cardioverter-defibrillator; IHD, ischemic heart disease; NSVT, nonsustained ventricular tachycardia; SCA, sudden cardiac arrest; SCD, sudden cardiac death; VA, ventricular arrhythmia; VF, ventricular fibrillation; and VT, ventricular tachycardia. Downloaded from http://ahajournals.org by on October 7, 2026