Study objective: Long QT syndrome has significant mortality, which is reduced with appropriate management. It is known that long QT syndrome masquerades as other conditions, including seizure disorders. We aim to evaluate a series of patients with genetically confirmed long QT syndrome to establish the frequency of delayed recognition. We also examine causes and potential consequences of diagnostic delay.
Methods: A consecutive case series of patients with long QT syndrome was identified through the Cardiac Inherited Disease Registry in New Zealand between 2000 and 2005. Detailed retrospective review of 31 cases was undertaken. The primary outcome was the time from first presentation with sudden loss of consciousness to a diagnosis of long QT syndrome. If the diagnosis was not made at the initial presentation, it was considered delayed. For the patients with a delayed diagnosis, the median duration of delay was compared between the subgroup of patients initially misdiagnosed with epilepsy and the others.
Results: Genetic mutations in 31 probands were consistent with long QT type 1 in 18 (58%) patients, long QT type 2 in 10 (32%) and long QT type 3 in 3 (10%). Median age at diagnosis was 21 years (1 day to 54 years). Thirteen patients (39%) experienced diagnostic delay after presentation with syncope or seizure: median delay 2.4 years (2 months to 23 years). Electroencephalograms were obtained in 10 patients; 5 were diagnosed with epilepsy. For those labeled epileptic, diagnostic delay was significantly longer than with other misdiagnoses: estimated median difference 9.75 years (95% confidence interval 7.6 to 20.7 years). During the delay period, 4 sudden unexplained deaths reportedly occurred in young relatives. Ten of the 13 had an ECG before diagnosis, with unrecognized pulse rate-corrected QT interval prolongation in 8 cases (range 0.47 to 0.65 seconds).
Conclusion: Delayed diagnosis of long QT syndrome is frequent. Symptoms are often attributed to alternative diagnoses, most commonly seizure disorder. Patients labeled as epileptic experience a particularly long diagnostic delay. ECGs were frequently requested, but interpretation errors were common. Given the potentially preventable mortality of long QT syndrome, emergency physicians investigating syncope and seizure should maintain a high index of suspicion.