Provocation Testing in Congenital Long QT Syndrome: A Practical Guide.

Congenital long QT syndrome (LQTS) is a hereditary cardiac channelopathy with an estimated prevalence of 1 in 2500. A prolonged resting QT-interval corrected for heart rate (QTc) remains a key diagnostic component; however, the QTc value may be normal in up to 40% of genotype positive LQTS patients and borderline in a further 30%. Provocation of QTc prolongation and T-wave changes may be pivotal to unmasking the diagnosis and useful in predicting genotype. LQTS provocation testing involves assessment of repolarization during and following exercise, in response to changes in heart rate or autonomic tone, with LQTS patients exhibiting a maladaptive repolarization response. We review the utility and strengths and limitations of four forms of provocation testing - stand-up test, exercise stress test, epinephrine challenge and mental stress test - in diagnosing LQTS and provide some practical guidance for performing provocation testing. Ultimately, exercise testing when feasible, is the most useful form of provocation testing when considering diagnostic sensitivity and specificity.