The following is a summary of “Phenotypes of Overdiagnosed Long QT Syndrome,” published in the 2023 February issue of Cardiology by Bains, et al.
Individuals with Long QT Syndrome (LQTS) are likelier to experience arrhythmic syncope, seizures, sudden cardiac arrest, or sudden cardiac death (SCD). The overdiagnosis of LQTS may be attributed to increased public and physician knowledge of the warning symptoms associated with LQTS and an increase in electrocardiographic screening programs. For a study, researchers sought to pinpoint the diagnostic errors that underlie the ongoing overdiagnosis of LQTS.
Electronic medical data were examined for individuals who initially had LQTS diagnosed externally but were later deemed to have normal results. In addition, data were extracted to get information on the referral, clinical background, and outcomes of genetic and cardiologic tests.
About 290 out of 1,841 (16%) patients with an initial diagnosis of LQTS (174 [60%] female; mean age at first Mayo Clinic evaluation, 22 ± 14 years; mean QTc interval, 427 ± 25 milliseconds) were ultimately disregarded as having normal results. The most common factor leading to an incorrect or excessive diagnosis of LQTS was a prolonged QTc interval brought on by vasovagal syncope (n = 87; 30%), which was then followed by a genetic test result that appeared to be positive for a variant in one of the key LQTS genes but was later determined not to be clinically significant (n = 68; 23%).
In addition, patients were given incorrect diagnoses because of a positive family history of SCD that was thought to be unrelated to LQTS (n = 46; 16%), an isolated or temporary QT prolongation (n = 44; 15%), or incorrect QTc interpretation due to the inclusion of U-waves (n = 40; 14%).
Vasovagal syncope, “pseudo”-positive genetic test results in LQTS-causative genes, family history of SCD, transient QT prolongation, and incorrect interpretation of the QTc interval are the 5 main determinants of discordance between a previous diagnosis of LQTS and full diagnostic reversal or removal. The knowledge raised awareness and offered crucial guidance to lessen the burden of overdiagnosed LQTS.
Reference: jacc.org/doi/10.1016/j.jacc.2022.11.036