Clinical applications of QT / RR hysteresis assessment: A systematic review

Background QT / RR hysteresis ( QT ‐hys) is an index of the time accommodation of ventricular repolarization to heart rate changes. This report comprehensively reviews studies addressing QT ‐hys as a biomarker of medical conditions. Methods This is a secondary analysis of data from a recent systematic review pertaining to methods of assessment of QT ‐hys. Articles included in the former review were filtered in order to select original articles investigating the association of QT ‐hys with medical conditions in humans. Results Nineteen articles fulfilled our inclusion criteria. Given the heterogeneity of the methods and investigated conditions, no pooled analysis of data could be implemented. QT ‐hys was mostly studied as a risk marker of severe arrhythmias, as a predictor of the long QT syndrome ( LQTS ) phenotypes and genotypes and as a marker of exercise‐induced ischemia. An increased QT ‐hys appears to be implicated in arrhythmogenesis, although the evidence in this regard relies on few human studies. An augmented QT ‐hys was reported in the LQTS , predominantly in the LQT 2 genotype, but conflicting results were obtained between studies using different methods of assessment. In addition, QT ‐hys appears to be a useful marker of stress‐induced myocardial ischemia in patients suspected of coronary artery disease. Conclusions QT ‐hys evaluation has potential clinical utility in at least some clinical conditions. Further studies of the clinical validity of QT ‐hys assessment are warranted, particularly condition specific studies based on QT ‐hys evaluation methods that provide separate estimates of QT ‐hys and QT / RR dependency.