Electrocardiogram in Andersen-Tawil syndrome. New electrocardiographic criteria for diagnosis of type-1 Andersen-Tawil syndrome

Abstract

Andersen - Tawil syndrome (ATS) is an autosomal - dominant or sporadic disorder characterized by ventricular arrhythmias, periodic paralysis, and distinctive facial and skeletal dysmorphism. Mutations in KCNJ2, which encodes the α-subunit of the potassium channel Kir2.1, were identified in patients with ATS. This genotype has been designated as type-1 ATS (ATS1). KCNJ2 mutations are detectable in up to 60 % of patients with ATS. Cardiac manifestations of ATS include frequent premature ventricular contractions (PVC), Q-U interval prolongation, prominent U-waves, and a special type of polymorphic ventricular tachycardia (PMVT) called bidirectional ventricular tachycardia (BiVT). The presence of frequent PVCs at rest are helpful in distinguishing ATS from typical catecholaminergic polymorphic ventricular tachycardia (CPVT). In typical CPVT, rapid PMVT and BiVT usually manifest during or after exercising. Additionally, CPVT or torsade de pointes in LQTS are faster, very symptomatic causing syncope or often deteriorate into VF resulting in sudden cardiac death. PVCs at rest are quite frequent in ATS1 patients, however, in LQTS patients, PVCs and asymptomatic VT are uncommon which also contributes to differentiating them. The article describes the new electrocardiographic criteria proposed for diagnosis of type-1 Andersen-Tawil syndrome. A differential diagnosis between Andersen-Tawil syndrome, the catecholamine polymorphic ventiruclar tachycardia and long QT syndrome is depicted. Special attention is paid on the repolarization abnormalities, QT interval and the pathologic U wave. In this article, we aim to provide five new electrocardiographic clues for the diagnosis of ATS1.

Fig. (1)

“U on P” sign (black arrow). “U on P” sign (U-wave masquerading P-wave) ; the P-wave during sinus tachycardia is inscribed on the U-wave of the preceding beat.

Fig. (2)

Pseudo “Tee - Pee sign” (black arrow). Pseudo “Tee-pee sign” during a PVC, there is a prolongation of the descending limb of the T+U-wave. In ATS1, the QT interval can appeared prolonged and difficult to quantify because of a prominent U-wave. In order to properly determine the QT interval, the tangent technique should be carefully applied.

Fig. (3)

Post- extrasystolic “pseudo – LQTS pattern” (arrows). This is detected in a sinus beat following a PVC. The fusion of T+U-waves can mimic LQTS. This pattern is not observed in the subsequent sinus beats.

Fig. (4)

U-wave visible in the inferior limb leads (arrows).

Fig. (5)

Increased U-wave amplitude after “adrenaline test” in an ATS1 patient. Adrenaline administration increases the U-wave amplitude. The ratio U-wave / T-wave amplitude becomes > 1 after the adrenaline administration when compared to the usual ratio < 1 before the administration of the inotropic drug.