A 37-year-old man was admitted to our department after an episode of rapid regular palpitations, triggered by emotional stress. He had no previous symptoms and was not taking any medication. There was no relevant family history. The first two electrocardiograms documented sinus rhythm and a pattern of abnormal repolarization with ST-segment elevation. The corrected QT interval (QTc) was between 428 and 468 ms (Figure 1A and B). Laboratory tests showed no abnormalities and exercise testing was normal. Holter monitoring documented intermittent QTc prolongation (maximum 580 ms), with no other abnormalities. Screening for mutations in the KCNQ1, KCNH2, SCN5A and KCNE1 genes for LQT1, LQT2, LQT3 and LQT5 variants of long QT syndrome (LQTS) revealed a c.529G>T (p.Glu177X) mutation in heterozygosity in the KCNH2 gene of LQT2 (Figure 1C). This variant has not been previously reported, but, since it produces a premature STOP codon, there is a high probability that it is actually pathogenic. The patient was discharged home on beta-blocker therapy and with information on drugs that prolong QT, to be avoided. Clinical and molecular study of first-degree relatives is currently under way.

Figure 1.

(A) and (B) The first two electrocardiograms, with corrected QT interval between 428 and 468 ms. (C) The novel mutation identified in exon 4 of the KCNH2 gene.

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LQTS patients can have intermittent QT prolongation, but they are at risk for ventricular arrhythmias that can be triggered by various stimuli and by drugs that prolong QT.

Most drugs that prolong QT act by blocking the Ikr ionic current, encoded by the KCNH2 gene. In our patient, intermittent QT prolongation was documented and a novel KCNH2 mutation was identified, enabling arrhythmia prevention therapy to be initiated.