Prevalence and prognostic significance of long QT interval among patients with chest pain: selecting an optimum QT rate correction formula.

BACKGROUND Little is known about the prevalence and prognostic significance of long QT interval among patients with chest pain during the acute phase of suspected cardiovascular injury. OBJECTIVES Our aim was to investigate the prevalence and prognostic significance of long QT interval among patients presenting to the emergency department (ED) with chest pain using an optimum QT rate correction formula. METHODS We performed secondary analysis on data obtained from the IMMEDIATE AIM trial (N, 145). Data included 24-hour 12-lead Holter electrocardiographic recordings that were stored for offline computer analysis. The QT interval was measured automatically and rate corrected using seven QTc formulas including subject specific correction. The formula with the closer to zero absolute mean QTc/RR correlation was considered the most accurate. RESULTS Linear and logarithmic subject specific QT rate correction outperformed other QTc formulas and resulted in the closest to zero absolute mean QTc/RR correlations (mean±SD: 0.003±0.002 and 0.017±0.016, respectively). These two formulas produced adequate correction in 100% of study participants. Other formulas (Bazett's, Fridericia's, Framingham's, and study specific) resulted in inadequate correction in 47.6 to 95.2% of study participants. Using the optimum QTc formula, linear subject specific, the prevalence of long QTc interval was 14.5%. The QTc interval did not predict mortality or hospital admission at short and long term follow-up. Only the QT/RR slope predicted mortality at 7year follow-up (odds ratio, 2.01; 95% CI, 1.02-3.96; p<0.05). CONCLUSIONS Adequate QT rate correction can only be performed using subject specific correction. Long QT interval is not uncommon among patients presenting to the ED with chest pain.