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Two Types of T Wave Alternans in Long-QT Syndrome JUAN SHU, M.D.,∗ YIGANG LI, M.D.,† ROBERT JU,‡ and GAN-XIN YAN, M.D., Ph.D.∗ ,†,‡ From the ∗ Department of Cardiology, the First Hospital, Xi’an Jiaotong University, Xi’an, China; †Department of Cardiology, Xinhua Hospital, Shanghai Jiaotong University, Shanghai, China; and ‡Lankenau Medical Center and Lankenau Institute for Medical Research, Wynnewood, Pennsylvania, USA

clinical: electrophysiology–long-QT syndrome, clinical: noninvasive, techniques—T wave alternans A 5-year-old female child with bilateral hand syndactyly, QT prolongation, and 2:1 atrioventricular (AV) block was seen in consultation (Fig. 1). The genetic testing identified a mutation in CACNA1C gene, confirming type 1 Timothy syndrome (LQT8). During ambulatory EKG monitoring, she had two types of T wave alternans (TWA): one occurred during a steady state in which RR intervals remained relatively unchanged (type 1), whereas the other developed during transition from 2:1 AV conduction to 1:1 conduction in which a sudden change in RR intervals and aberrant conduction were associated (type 2). During type 1 TWA, there was no significant beat-to-beat variation in PP interval (or RR interval) as well as in QRS duration (Fig. 2A). In addition, there was an identifiable isoelectric interval between the end of previous T wave and P wave. Type 2 TWA, as shown in Figure 2B and C, was profound and developed likely secondary to a sudden change in heart rate and aberrant ventricular conduction from resumption of 1:1 AV conduction from 2:1 AV block during sinus arrhythmia (Fig. 2C). Type 2 TWA disappeared after a few seconds of 1:1 AV conduction from 2:1 AV block when the RR intervals remained stable and the mean QT ventricular became shorter. The relationship between QRS and QT during type 2 TWA is shown in Figure 2D. J Cardiovasc Electrophysiol, Vol. 25, pp. 910-912, August 2014. Supported by the Sharpe-Strumia Research Foundation (Yan GX) and National Natural Science Foundation of China (NSFC-81370289, Yan GX and Shu T).

Previous studies have shown that TWA may herald development of malignant ventricular arrhythmia. However, two types of TWA in our case obviously developed at different mechanisms, from which different arrhythmogenic risks would be expected. Type 1 TWA, commonly reported in the literature, is unrelated to ventricular conduction and a change in RR intervals. It is probably due to abnormal intracellular Ca2+ cycling that influences ventricular repolarization in an alternating pattern.1 Our recent basic research has shown that early afterdepolarization (EAD) alternans in left ventricular hypertrophy manifests as type 1 TWA on the ECG, which often precedes the development of EAD-initiating R-on-T ectopic beats.2 On the other hand, type 2 TWA was less commonly reported. It may occur as a consequence of an abrupt change in ventricular rate or aberrant ventricular conduction. “TWA” resulting from intermittent pre-excitation is the best illustration of activation-dependent change in T wave (Fig. 2E). A sudden change in RR intervals may also contribute importantly to type 2 TWA (Fig. 2B and C). Facilitation of TWA by an abrupt change in RR intervals in long-QT syndrome may be related to adaptation of time-dependent repolarizing currents to a new rate. Surprisingly, this female child was free of syncope and documented ventricular arrhythmias despite the fact that both types of TWA were commonly seen prior to the drug therapy. Even though, potential risks of both types of TWA to trigger TdP should not be ignored.

References

No disclosures. Address for correspondence: Juan Shu, M.D., or Gan-Xin Yan, M.D., Ph.D., Department of Cardiology, the First Hospital, Xi’an Jiaotong University, Xi’an, China; E-mail: [email protected] doi: 10.1111/jce.12427

1. Walker ML, Rosenbaum DS: Repolarization alternans: Implications for the mechanism and prevention of sudden cardiac death. Cardiovasc Res 2003;57:599-614. 2. Liu T, Patel C, Guo D, Ju R, Kowey P, Yan GX. Early after depolarization alternans manifests T wave alternans in left ventricular hypertrophy. Circulation 2013;128:A10368 [Abstract].

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Figure 1. Bilateral hand syndactyly (upper paper) and 2:1 atrioventricular (AV) block (lower panel, arrows indicating P waves) in the setting of a markedly prolonged QT interval (QTc = 643 milliseconds). For a high quality, full color version of this figure, please see Journal of Cardiovascular Electrophysiology’s website: www.wileyonlinelibrary.com/journal/jce

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Figure 2. A: Type 1 T wave alternans (TWA) in which no slow conduction or a sudden change in ventricular rate was present; B: Type 2 TWA initiated by an abrupt change in RR intervals and aberrant conductions (open arrows) occurring on the T wave of the previous beats in the presence of prolonged QT intervals; C: The type 2 TWA appeared during transition of 2:1 AV block to 1:1 AV conduction (the solid arrows indicated P waves). D: The relationship among the RR, QT intervals, and QRS duration (mean values of the tracings in panels A and B) during the type 2 TWA. E: Apparent “TWA” due to intermittent pre-excitation in a patient with a normal QT interval.

Two types of T wave alternans in long-QT syndrome.

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