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Recurrent syncope

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Q1: What does his ECG show?

His admission ECG (fig 1 in questions) shows sinus rhythm, a major prolongation of the QTc interval (660 ms in S2), and a 2/1 atrioventricular block.

Figure 1

 Lead S2 of the ECG obtained at day 6 under β block.

Q2: What diagnosis would you consider?

The diagnosis is long QT syndrome (LQTS) complicated by 2/1 atrioventricular block.

Q3: What investigations would you consider?

The differential diagnosis includes congenital and acquired long QT syndrome. Information about medication taken is critical for the diagnosis of drug induced QT prolongation. QT prolongation in the course of other diseases (electrolyte disturbances, myocardial dysfunction, neurological conditions…) should also be excluded by history, physical examination, laboratory and imaging studies (blood analysis, echocardiography…). In this case, no acquired causes of QT prolongation was shown or suspected. A family history of sudden death at a young age, a family or personal history of deafness, and QT prolongation on the ECG of the patient’ relatives commonly lead to the proper diagnosis of congenital LQTS. Genetic testing for known mutations in DNA samples from studied patients is becoming more accessible in specialised centres. Identification of an LQTS gene mutation confirms the diagnosis; however, a negative result on genetic testing is of limited diagnostic value because many patients with familial LQTS have mutations of yet unknown genes.

Q4: How would you treat this patient?

β Blocker is the present treatment of choice for congenital LQTS. The impaired conduction is classically functional and because of sinus intervals shorter than ventricular refractoriness. If the block is functional in nature, it will disappear after QT interval shortening under β block. In this case, treatment with oral nadolol (50 mg/m2/day) and temporary pacing was begun, with no recurrence of syncopal events. The 2/1 atrioventricular block persisted despite QTc interval shortening (460 ms in S2) (fig 1). β Blocker treatment was continued and permanent transvenous ventricular pacing was established, with a lowest rate setting of 90 beat/min. At one year follow up, the child remains symptom free.

Discussion

Congenital LQTS is an inherited disorder characterised by a prolongation of the QT interval on the surface ECG. This cardiac disease is potentially lethal because of polymorphic ventricular tachyarrhythmias leading to recurrent syncope or sudden cardiac death.

LQTS is occasionally complicated by a 2/1 atrioventricular block.1 This impaired conduction is classically functional and because of sinus intervals shorter than ventricular refractoriness. However, investigations in some cases have also reported abnormal His-Purkinje system refractoriness and histological abnormalities within the conduction system.1 Such abnormalities may be responsible for the persistence of the atrioventricular block in this case.

LQTS with conduction disorders is rare and has a very poor prognosis despite different treatment modes.2 This form usually manifests during early life. Most of the cases are sporadic, and de novo mutations1 or homozygous expression of mutations in several genes coding for cardiac ion channels3 were suggested.

References

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