Cardiac MRI

Abstract

Background-Accurate measures are critical when attempting to distinguish normal from pathological changes in cardiac function during exercise, yet imaging modalities have seldom been assessed against invasive exercise standards. We sought to validate a novel method of biventricular volume quantification by cardiac MRI (CMR) during maximal exercise. Methods and Results-CMR was performed on 34 subjects during exercise and free-breathing with the use of an ungated real-time (RT-ungated) CMR sequence. ECG and respiratory movements were retrospectively synchronized, enabling compensation for cardiac cycle and respiratory phase. Feasibility of RT-ungated imaging was compared with standard exercise CMR imaging with ECG gating (gated); accuracy of RT-ungated CMR was assessed against an invasive standard (direct Fick); and reproducibility was determined after a second bout of maximal exercise. Ventricular volumes were analyzed more frequently during high-intensity exercise with RT-ungated compared with gated CMR (100% versus 47%; P<0.0001) and with better interobserver variability for RT-ungated (coefficient of variation=1.9% and 2.0% for left and right ventricular stroke volumes, respectively) than gated (coefficient of variation=15.2% and 13.6%; P<0.01). Cardiac output determined by RT-ungated CMR proved accurate against the direct Fick method with excellent agreement (intraclass correlation coefficient, R=0.96), which was highly reproducible during a second bout of maximal exercise (R=0.98). Conclusions-When RT-ungated CMR is combined with post hoc analysis incorporating compensation for respiratory motion, highly reproducible and accurate biventricular volumes can be measured during maximal exercise. (Circ Cardiovasc Imaging. 2013;6:329-338.)

Can Intensive Exercise Harm the Heart?

“…Cardiac outputs of 40 L/min or more have been recorded in elite endurance athletes, 38,39 and this promotes significant stretching of the atria. During ventricular systole, the residual atrial volume and rapid venous inflow fill the atria with >200 mL to maintain these massive outputs.…”

Improving the physiological realism of experimental models

“…Real-time exercise cardiac magnetic resonance (Ex-CMR) imaging with compensation for respiratory translation enables cardiac volumetric quantification of both ventricles during free breathing and maximal exercise. Cardiac outputs determined using this technique correlate very strongly with invasive Fick measures but the reproducibility is arguably better with Ex-CMR [90]. Furthermore, although echo-cardiographic images cannot be acquired in all subjects, the accuracy of measures that can be obtained are reasonably impressive [91].…”

The Role of Exercise Testing in the Modern Management of Pulmonary Arterial Hypertension

“…This technique needs to be evaluated with imaging performed during exercise to assess its full value. The feasibility of such measurements has been illustrated in other conditions [64].…”

“…It is more accurate than TTE in measuring CO [64] and similarly provides information on right ventricular function, resting values of which have been shown to be superior to PVR for predicting prognosis [65]. However, unlike TTE it cannot provide information on pressure and a significant minority of subjects fail to tolerate the test because of claustrophobia [66].…”