Challenges in the diagnosis of long QT syndromes

Challenges in the diagnosis of long QT syndromes

Long QT syndromes have common phenotype of delayed depolarization, caused by ion channel mutations, which in turn causes QT prolongation and a propensity for ventricular tachyarrhythmias. These arrhythmias can cause, hypotension and syncope and sometimes sudden cardiac death. Clinical features, age at onset, family history, electrocardiogram and finally genetic testing are the important steps in the evaluation of a suspected long QT syndrome. Over the years, increased awareness and improved genetic testing has caused an increase in the number of diagnosed cases of long QT syndrome, though the true prevalence may not have increased.

But the variability in the electrocardiograms is striking, with about one third of the mutation positive LQTS carriers can have a QT interval which overlaps with that of healthy normal individuals. More over various factors like age, gender, central nervous system disorders, changes in electrolytes and several medications can affect the QT interval. There is a lot of variation in the symptoms as well, with even one third of the LQTS mutations in certain families never having any symptom. Different subtypes have different risks for cardiac events and clinical signs and symptoms do not adequately differentiate the LQTS subtype, though the symptom triggers may give an indication. Similarly, the response to beta blockers may also vary depending on the sub type.