Fourteen-Year Follow-up in a Teenager with Congenital Long QT Syndrome Masquerading as Idiopathic Generalized Epilepsy

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Figure 1.
Rhythm strip demonstrating prolonged QTc; bifid T wave, a hallmark of the LQT2 genotype; and T wave alternans. LQT2, congenital long QT syndrome subtype 2.
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Figure 2.
A 12-lead ECG showing an unsustained torsade de pointes with a QTc duration of 518 ms was recorded shortly after a seizure episode. QTc, corrected QT interval (measured QT/square root of RR in seconds).
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Figure 3.
Frequent runs of self-terminating polymorphic ventricular tachycardia and torsade de pointes were detected on Holter monitoring during an ictal episode.

Table 1.

Clinical Characteristics in Common Genotypes of Congenital Long QT Syndrome

Characteristic	LQT1	LQT2	LQT3
Gene muted	KCNQ1 (=KvLQT1)	KCNH2 (=HERG)	SCN5A
Current affected	I_Ks	I_Kr	I_Na
Events occurring with emotional stress	Strong association	Moderate association	Weak association
Events occurring with exercise	Strong association	Weak association	Weak association
Other triggers	Diving	Loud noise	Sleep
		Rest	Rest
Events before the age of 10 (%)	40	16	2
Events before the age of 40 (%)	63	46	18
Median age at first event (years)	9	12	16
Efficacy of β-blockade to prevent events	Strong association	Moderate association	Weak association

LQT, long QT subtype; I_Ks, slowly activating potassium-delayed rectifier; I_Kr, rapidly activating potassium-delayed rectifier; I_Na, cardiac voltage-dependent sodium channel.