QTc Behavior During Exercise and Genetic Testing for the Long-QT Syndrome

The quest to facilitate the diagnosis of the long-QT syndrome (LQTS) and even to predict genotype is neverending. The study by Sy et al1 published in the current issue of Circulation adds a new piece to the puzzle and has the potential to be very useful.Article see p 2187Since the early days,2 diagnosis of the long-QT syndrome (LQTS) has undergone several levels of progressive upgrade. Initially, the diagnosis was made only in the presence of multiple factors, such as very bizarre T waves and marked prolongations of the QT interval in a child or teenager or abrupt loss of consciousness during emotional or physical stress, and it also required one of the few medical doctors who had heard about LQTS. The first attempt to provide diagnostic criteria for LQTS came in 19853 and, in their simplicity, they are still useful now for a first assessment (Table 1). As the disease became better known, as was bound to happen given its prevalence (1 in 2 000),4,5 a new set of more specific diagnostic criteria to discriminate between subjects likely or unlikely to be affected by LQTS was proposed and provided a quantitative score.6View this table:Table 1. 1985 LQTS Diagnostic CriteriaThose criteria, subsequently referred to as the “Schwartz criteria,” were developed before the genetic revolution, which has progressively led to the identification of 13 LQTS disease-causing genes.7 As a consequence, a lot of weight was placed on the actual duration of the QT interval. By the early 1990s, it had been recognized8 that the highest risk was for patients who had already suffered 1 cardiac event. It was thus essential not to miss the diagnosis in these patients; hence, weight was given to previous symptoms. Also, it was obvious that the disease had …