93Impact of QTc formulae in the prevalence of short and long corrected QT intervals in a young adult cohort

Abstract

Background: QTis related to heart rate in an inverse exponential relationship. Channelopathy Expert Consensus suggest the use of Bazett equation for the correction of QT interval. However, this equation is prone to innacuracy and the ACC/AHA electrocardiogam interpretation consensus discouraged its use. Methods: We estimated the prevalence of short and long QTc intervals using different QT correction formulae (Bazett, Fridericia, Framingham and Hodges) in the “Sudden Cardiac Death Screening of Risk FactOrS” (SCD-SOS) cohort. Then, we assessed the impact of the differentQTc correction formulae on Short QT Syndrome (SQTS) and Long QT Syndrome (LQTS) probability. Results: In the 14,662 young adults from the SCD-SOS cohort, individuals with a QTc ≤ 330ms and ≤320ms were rare, and more frequently identified by the Framingham correction. The different QTc correction formulae led to a shift in SQTS-probability in 5 to 10% of individuals. Framingham and Bazett correction identified a higher percentage of individuals with higher SQTS-probability, with almost 1% of individuals presenting with a Gollob score of≥2. Intermediate-probability Individuals (score=3) were rare (<0.1%), similarly to individuals identified through the Expert Consensus criteria (0.07 to 0.1%), and no high-SQTS probability individuals (score=4) were identified in the SCD-SOS cohort. Applying the different formulae was associated with marked differences in the prevalence of prolonged QTc intervals. Using Bazett's correction, 137 individuals (0.93% of the sample) with prolonged QTc were identified, while using Fridericia and Hodges the number dropped to 23 (0.16%) and 24 (0.16%), respectively, and to 14 (0.10%) using Framingham's correction. Using corrected QTc values obtained with the different formulae suggests that 10 individuals (0.07%) are high risk using Bazett's correction, none using Fridericia, and only 1 (0.007%) using Hodges and Framingham. Interestingly, the high risk individual detected with the Hodges formula was a female with QTc =462ms, exertional syncope, family history of death by drowning in uncle aged 3, and mother with a diagnosis of LQTS. This patient's QTc was with <460ms when assessed with all remaining formulae. Conclusion: Applying different QTc correction formulae leads to significant reclassification of SQTS and LQTS-probability, and their impact on predicting the actual prognosis should be assessed. (Figure Presented).