Study Population

A prospective study involving 15 healthy, nonelite volunteers participating in the 2009 Manitoba Half Marathon was performed. Subjects aged 18 to 40 years who completed the race were included. Patients with histories of coronary artery disease, hypertension, smoking, elevated lipids, diabetes, and/or contraindication to undergo CMR were excluded.

Cardiac Biomarkers

Myoglobin, CK, and cTnT were evaluated at three separate time points: (1) 1 week before the race, (2) immediately after the race, (3) and 1 week after the race. Myoglobin and CK levels were determined using a Roche Elecsys and a Roche 917 analyzer, respectively (Roche Diagnostics GmbH, Mannheim, Germany). Quantitative determination of cTnT levels was performed using a third-generation Roche Elecsys assay.

Echocardiography

All subjects underwent baseline transthoracic echocardiographic (TTE) imaging 1 week before the race, immediately following the race, and 1 week after race completion. Following completion of the half marathon, each patient was immediately transferred to the study hospital for performance of the TTE exam. The transfer time from the half marathon site to the study hospital was 10 min. All TTE studies were performed immediately upon arrival at the study hospital. All patients underwent TTE imaging using a GE Vivid 7 (GE Healthcare, Milwaukee, WI) at each time point. Left ventricular (LV) and left atrial cavity dimensions indexed to body surface area were determined from two-dimensional images in accordance with the guidelines of the American Society of Echocardiography. RV cavity dimensions, RV fractional area change (FAC), and tricuspid annular plane systolic excursion (TAPSE) were also determined. Continuous-wave Doppler was used to measure the peak velocity across the tricuspid valve, and the maximal pulmonary arterial systolic pressure was estimated using the simplified Bernoulli equation.

Real-time three-dimensional TTE imaging was performed using a dedicated broadband, wide-angle, matrix-array transducer to acquire the entire RV cavity within the pyramidal scan volume. Acquisition of full-volume data sets was triggered to the R wave of every cardiac cycle to allow for an acquisition time of four heartbeats during an adequate breath hold. The subvolumes were automatically stitched to a sequence of full three-dimensional volumes covering the entire right ventricle and stored digitally for offline analysis using TomTec software (TomTec Imaging Systems, Unterschleissheim, Germany), as previously described.

CMR

CMR was performed on all study participants at baseline and within 24 hours of completion of the half marathon using a 1.5-T scanner (Avanto; Siemens Medical Solutions, Erlangen, Germany). Specifically, following acquisition of the TTE images after the half marathon, each participant underwent CMR on an hourly basis, until all 15 studies were completed. Cine balanced steady-state free-precession short-axis images then encompassed the entire left ventricle from the base to the apex (stack of 10 sequential short-axis slices; repetition time, 64 ms; echo time, 1 ms; flip angle, 80°; slice thickness, 8 mm; interslice gap, 1.6 mm; matrix size, 192 × 132) to obtain the LV ejection fraction. To evaluate for myocardial edema, dark-blood T2-weighted turbo spin-echo short-axis images were obtained (repetition time, 1800–2100 ms; echo time, 74 ms; slice thickness, 8 mm; interslice gap, 4 mm; matrix size, 256 × 175). Late gadolinium enhancement images were obtained after 10 min of 0.2 mmol/kg injection of gadolinium diethylenetriamine pentaacetic acid (Magnevist; Schering AG, Berlin, Germany) using a T1-weighted inversion recovery–prepared multislice true fast imaging with steady-state precession sequence with magnitude and phase-sensitive reconstruction. Images were acquired sequentially in the short axis, followed by horizontal and vertical long-axis images (repetition time, 700 ms; echo time, 1.0 ms; flip angle, 40°; slice thickness, 8 mm; interslice gap, 1.6 mm; matrix size, 192 × 144). Quantitative analysis was performed using dedicated computer software (CMR ⁴² release 3.1.2; Circle Cardiovascular Imaging, Calgary, AB, Canada).

Statistical Analysis

Data are summarized as mean ± SD, number (percentage), or median (interquartile range). Paired Student’s t tests were used to compare continuous variables. Chi-square and Fisher’s exact tests were applied to compare categorical variables. One-way analysis of variance (nonparametric with Dunn testing) was used to compare baseline, immediate, and 1-week postrace cardiac biomarker and echocardiographic values. Linear regression analysis and Bland-Altman plots were used to compare RV volumes and RVEF between the various imaging modalities. The Bland-Altman method is a plot of the differences of the data on a chart with mean difference ± 1.96 × standard deviation of the differences. The 95% agreement limits are ±1.96 × standard deviation of the differences. Agreement between intraobserver and interobserver variability of the LV volumes and LV ejection fraction between the imaging modalities was computed from the absolute differences between repeated measurements using the Mann-Whitney U test. P values < .05 were considered statistically significant. SAS version 8.01 (SAS Institute Inc., Cary, NC) was used to perform the analysis.