Polymorphic Ventricular Tachycardia, Ischaemic Ventricular Fibrillation, and Torsade de Pointes: Importance of the QT and the Coupling Interval in the Differential Diagnosis
abstract
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Access this abstract nowAIMS
Distinctive types of polymorphic ventricular tachycardia (VT) respond differently to different forms of therapy. We therefore performed the present study to define the electrocardiographic characteristics of different forms of polymorphic VT.
METHODS AND RESULTS
We studied 190 patients for whom the onset of 305 polymorphic VT events was available. The study group included 87 patients with coronary artery disease who had spontaneous polymorphic VT triggered by short-coupled extrasystoles in the absence of myocardial ischaemia. This group included 32 patients who had a long QT interval but nevertheless had their polymorphic VT triggered by ectopic beats with short coupling interval, a subcategory termed 'pseudo-torsade de pointes] (TdP). For comparison, we included 50 patients who had ventricular fibrillation (VF) during acute myocardial infarction ('ischaemic VF' group) and 53 patients with drug-induced TdP ('true TdP' group). The QT of patients with pseudo-TdP was (by definition) longer than that of patients with polymorphic VT and normal QT (QTc 491.4 ± 25.2 ms vs. 447.3 ± 55.6 ms, P < 0.001). However, their QT was significantly shorter than that of patients with true TdP (QTc 564.6 ± 75.6 ms, P < 0.001). Importantly, the coupling interval of the ectopic beat triggering the arrhythmia was just as short during pseudo-TdP as during polymorphic VT with normal QT (359.1 ± 38.1 ms vs. 356.6 ± 39.4 ms, P = 0.467) but was much shorter than during true TdP (581.2 ± 95.3 ms, P < 0.001).
CONCLUSIONS
The coupling interval helps discriminate between polymorphic VT that occurs despite a long QT interval (pseudo-TdP) and polymorphic arrhythmias striking because of a long QT (true TdP).
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Polymorphic Ventricular Tachycardia, Ischaemic Ventricular Fibrillation, and Torsade de Pointes: Importance of the QT and the Coupling Interval in the Differential Diagnosis
Eur Heart J 2021 Mar 10;[EPub Ahead of Print], R Rosso, A Hochstadt, D Viskin, E Chorin, AL Schwartz, O Tovia-Brodie, A Laish-Farkash, O Havakuk, L Gepstein, S Banai, S ViskinFrom MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
In this important study, the authors define polymorphic ventricular tachycardia (PVT) as a VT with a changing QRS pattern that terminates spontaneously (and may cause syncope) or deteriorates to ventricular fibrillation (VF), causing cardiac arrest. They subclassify the PVT into separate groups because they respond to different treatments. Torsade de pointes (TdP), defined as PVT caused by a long QT syndrome (LQTS), may respond to beta-blocker therapy, intravenous magnesium, and cardiac pacing, whereas PVTs not associated with QT prolongation, such as PVT of Brugada syndrome, short QT syndrome, and idiopathic VF, are resistant to those therapies but responsive to quinidine.
They studied the onset of 305 PVTs in 190 patients, including 87 patients with coronary artery disease in whom short-coupled extrasystoles triggered PVT in the absence of myocardial ischemia. This group included 32 patients who had a long QT interval but still had short-coupled extrasystoles trigger the PVT, a subcategory they termed “pseudo-TdP.” They compared that group with 50 patients who had VF during acute myocardial infarction and 53 patients with drug-induced true TdP. The QT of patients with pseudo-TdP was longer (by definition) than that of patients with PVT and normal QT, but shorter than that of patients with true TdP. Importantly, the coupling interval of the ectopic beat triggering the arrhythmia was just as short during pseudo-TdP as during polymorphic VT with normal QT but was much shorter than during true TdP.
The take-home message for clinicians is that the coupling interval initiating PVT helps discriminate between PVT that occurs despite a long QT interval (pseudo-TdP, short coupling interval) and PVT because of a long QT (true TdP, longer coupling interval). Distinguishing these types of PVT becomes important because the short-coupled type responds to quinidine during arrhythmic storms, a drug which would be contraindicated for the true TdP.