Postexercise recovery of the spatial QRS/T angle as a predictor of sudden cardiac death Tuomas Kenttä, MSc,* Jari Viik, PhD, † Mari Karsikas, MSc, ‡ Tapio Seppänen, PhD, ‡ Tuomo Nieminen, MD, PhD, § Terho Lehtimäki, MD, PhD, ¶ Kjell Nikus, MD,** Rami Lehtinen, PhD, †† Mika Kähönen, MD, PhD, ‡‡ Heikki V. Huikuri, MD, PhD* From the *Division of Cardiology, Institute of Clinical Medicine, University of Oulu, Oulu, Finland, † Department of Biomedical Engineering, Tampere University of Technology and Biosensing Competence Centre, Tampere, Finland, ‡ Information Processing Laboratory, Technical Department, University of Oulu, Oulu, Finland, § Division of Cardiology, Helsinki University Central Hospital, Helsinki, Finland,  Department of Pharmacological Sciences, University of Tampere, Tampere, Finland, ¶ Department of Clinical Chemistry, University of Tampere, Tampere, Finland, **Department of Cardiology, Heart Center, Tampere University Hospital, Tampere, Finland, †† Tampere Polytechnic, University of Applied Sciences, Tampere, Finland, and ‡‡ Department of Clinical Physiology, University of Tampere and Tampere University Hospital, Tampere, Finland. BACKGROUND Postexercise measurement of heart rate (HR) re- covery and QT interval dynamics provides prognostic information in various patient populations. OBJECTIVE The purpose of this study was to assess whether the measurement of the spatial relationship between the depolariza- tion and repolarization wavefronts (total cosine R-to-T [TCRT]) during the postexercise recovery phase would yield prognostic information. METHODS The population consisted of 1297 patients (56  13 years; 67% men) who performed a clinically indicated bicycle stress test. The exercise-recovery hysteresis of TCRT was quantified from the 12-lead exercise electrocardiogram by measuring the TCRT/HR loop area bounded by the exercise and first 3-minute postexercise recovery curves. The HR-corrected TCRT/HR hysteresis was calculated by dividing the area with the HR decrement during the first 3 minutes of recovery. HR recovery was measured at 1 minute postexercise recovery. End points were cardiac death and sudden cardiac death. RESULTS During an average follow-up of 45  12 months, 74 patients died (5.7%); 35 (2.6%) were cardiac deaths and 24 (1.9%) were sudden cardiac deaths. Reduced TCRT/HR loop area and TCRT/HR hysteresis were associated with cardiac mortality (P .001). After adjustments for clinical variables, including ejec- tion fraction, TCRT/HR loop area remained an independent pre- dictor of cardiac death (hazard ratio 5.6; 95% confidence interval 1.6 –19.1; P = .007) and sudden cardiac death (10.7; 95% con- fidence interval 1.4 – 83.7; P = .024). HR recovery did not remain a significant predictor in the multivariate analysis. CONCLUSIONS Attenuated hysteresis of the depolarization and repolarization wavefronts during postexercise recovery is associ- ated with an increased risk of cardiac and sudden cardiac death. Analysis of repolarization dynamics from exercise electrocardio- gram represents a promising tool for risk stratification. KEYWORDS Hysteresis; Exercise; Recovery; Electrocardiogram; Re- polarization ABBREVIATIONS CHD = coronary heart disease; C-index = con- cordance index; ECG = electrocardiogram; HR = heart rate; HRR = heart rate recovery; IDI = integrated discrimination im- provement; LVEF = left ventricular ejection fraction; NRI = net reclassification index; SCD = sudden cardiac death; TCRT = total cosine R-to-T (Heart Rhythm 2012;9:1083–1089) © 2012 Heart Rhythm Society. All rights reserved. Introduction The risk of sudden cardiac death (SCD) has been shown to be increased immediately after vigorous exercise. 1 There- fore, cardiac electrical behavior has been widely studied in the postexercise recovery phase, and it has been shown to carry prognostic information in several studies. 2–6 Delayed heart rate recovery (HRR), measured during the first min- utes of postexercise recovery phase, is one of the most well-known predictors of mortality. 2 Although the measure- ment of ventricular repolarization from the standard 12-lead electrocardiogram (ECG), by means of corrected QT inter- val and T-wave morphology measurements, has also pro- vided prognostic information, 7,8,9 the predictive value of postexercise dynamics of ventricular repolarization has not been extensively studied. Currently, only T-wave alternans This study was supported in part by the Finnish Foundation for Car- diovascular Research, Sigrid Juselius Foundation, Tampere University Hospital Medical Fund, Tampere Tuberculosis Foundation, and the Finnish Funding Agency for Technology and Innovation. Address for reprint requests and correspondence: Mr Tuomas Kenttä, MSc, Division of Cardiology, Institute of Clinical Medicine, University of Oulu, PO Box 5000, FI-90014 Oulu, Finland. E-mail address: tuomas.kentta@oulu.fi. 1547-5271/$ -see front matter © 2012 Heart Rhythm Society. All rights reserved. http://dx.doi.org/10.1016/j.hrthm.2012.02.030