title: Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance.
abstract: BACKGROUND
  Exercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.
  
  
  METHODS
  Free-breathing real-time CMR (1.5T Aera, Siemens) was performed in 11 athletes (5 males; median age 29 [IQR: 28-39] years) and 16 age- and sex-matched healthy volunteers (7 males; median age 26 [interquartile range (IQR): 25-33] years). All participants underwent an in-scanner exercise protocol on a CMR compatible cycle ergometer (Lode BV, the Netherlands), with an initial workload of 25W followed by 25W-increment every minute. In 20 individuals, exercise capacity was also evaluated by cardiopulmonary exercise test (CPET). Scan-rescan reproducibility was assessed in 10 individuals, at least 7 days apart.
  
  
  RESULTS
  The exCMR protocol demonstrated excellent scan-rescan (cardiac index (CI): 0.2 ± 0.5L/min/m2) and inter-observer (ventricular volumes: 1.2 ± 5.3mL) reproducibility. CI derived from exCMR and CPET had excellent correlation (r = 0.83, p < 0.001) and agreement (1.7 ± 1.8L/min/m2). Despite similar values at rest (P = 0.87), athletes had increased exercise CI compared to healthy individuals (at peak exercise: 12.2 [IQR: 10.2-13.5] L/min/m2versus 8.9 [IQR: 7.5-10.1] L/min/m2, respectively; P < 0.001). Peak exercise CI, where image acquisition lasted 13-17 s, outperformed that at rest (c-statistics = 0.95 [95% confidence interval: 0.87-1.00] versus 0.48 [95% confidence interval: 0.23-0.72], respectively; P < 0.0001 for comparison) in differentiating athletes from healthy volunteers; and had similar performance as VO2max(c-statistics = 0.84 [95% confidence interval = 0.62-1.00]; P = 0.29 for comparison).
  
  
  CONCLUSIONS
  We have developed a novel in-scanner exCMR protocol using real-time CMR that is highly reproducible. It may now be developed for clinical use for physiological studies of the heart and circulation.
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore. le.thu.thao@nhcs.com.sg.
authors.forename: Thu-Thao
authors.initials: TT
authors.lastname: Le
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.
authors.forename: Jennifer Ann
authors.initials: JA
authors.lastname: Bryant
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.
authors.forename: Alicia Er
authors.initials: AE
authors.lastname: Ting
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.
authors.forename: Pei Yi
authors.initials: PY
authors.lastname: Ho
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.
authors.forename: Boyang
authors.initials: B
authors.lastname: Su
authors.affiliation: Changi General Hospital, Singapore, Singapore.
authors.forename: Raymond Choon Chye
authors.initials: RC
authors.lastname: Teo
authors.affiliation: Siemens Healthineers, Erlangen, Germany.
authors.forename: Julian Siong-Jin
authors.initials: JS
authors.lastname: Gan
authors.affiliation: Siemens Healthineers, Erlangen, Germany.
authors.forename: Yiu-Cho
authors.initials: YC
authors.lastname: Chung
authors.affiliation: MRC London Institute of Medical Sciences, London, UK.
authors.forename: Declan P
authors.initials: DP
authors.lastname: O'Regan
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.|Duke-NUS Medical School, Singapore, Singapore.|National Heart and Lung Institute, Imperial College, London, UK.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Cook
authors.affiliation: National Heart Centre Singapore, 5 Hospital Drive, Singapore, 169609, Singapore.|Duke-NUS Medical School, Singapore, Singapore.
authors.forename: Calvin Woon-Loong
authors.initials: CW
authors.lastname: Chin
mesh_terms: D000328:Adult; D056352:Athletes; D001642:Bicycling; D001794:Blood Pressure; D002302:Cardiac Output; D000072599:Cardiorespiratory Fitness; D016022:Case-Control Studies; D005080:Exercise Test / Q000295:instrumentation; D017079:Exercise Tolerance; D005240:Feasibility Studies; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging* / Q000502:physiology; D006339:Heart Rate; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015588:Observer Variation; D010807:Physical Endurance; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012119:Respiration; D016683:Supine Position; D013997:Time Factors; D016277:Ventricular Function, Left
keywords: Cardiopulmonary exercise test; Cardiovascular magnetic resonance; Exercise physiology; Supine bike ergometer