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/m2 versus 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.

Keywords: Cardiopulmonary exercise test; Cardiovascular magnetic resonance; Exercise physiology; Supine bike ergometer.

Figures

Fig. 1

Set up of the cycle ergometer in CMR scanner

Fig. 2

Exercise CMR imaging protocol

Fig. 3

Endocardial contours for volume measurements of breath-hold cine and real-time cine images

Fig. 4

Exercise Cardiac Reserve in Athletes and Healthy Volunteers. Changes in indexed LV end-diastolic volume (a), indexed LV end-systolic volume (b), indexed stroke volume (c) and cardiac index (d) during exercise in healthy volunteers and athletes. Data presented in median (dots) and interquartile range (bars)

Fig. 5

Cardiac Response to Exercise. Absolute Change in Cardiac Volumes From Baseline in Healthy Volunteers (Left) and Athletes (Right). Results are presented in box-and-whiskers plot (minimum and maximum); and median with interquartile range for line plot

Fig. 6

Scan-rescan reproducibility. Example of the exercise profile of an individual performed in the two scans (a); Bland-Altman plot of the difference in cardiac index measured between the two scans (b)

Fig. 7

Correlation and Agreement in Cardiac Index Derived from Exercise CMR and CPET. Linear regression of cardiac index values measured from CMR and derived from CPET at rest and peak exercise (a) and Bland-Altman plot of the difference between cardiac index measured from CMR and estimated from CPET, at rest and peak exercise (b)