Preprint Exercise stress in healthy adults: normal ranges for real time cardiac magnetic resonance imaging, 2023, Schweitzer et al.

[SNT Gatchaman]

Exercise stress in healthy adults: normal ranges for real time cardiac magnetic resonance imaging
Ronny Schweitzer; Antonio de Marvao; Mit Shah; Paolo Inglese; Peter Kellman; Alaine Berry; Ben Statton; Declan P O'Regan

Background:
Real-time (RT) exercise cardiac magnetic resonance imaging (exCMR) is an emerging approach for cardiac stress testing as part of a comprehensive cardiovascular imaging assessment. It has advantages over alternative approaches due to its high spatial resolution and use of non-pharmacological stress. As access to exCMR increases, there is a need to establish reference ranges in healthy adults for clinical interpretation.

Methods:
We analysed data from 162 healthy adults who had no known cardiovascular disease, did not harbour genetic variants associated with cardiomyopathy, and who completed an exCMR protocol using a pedal ergometer. Participants were imaged at rest and after exercise with left ventricular parameters measured using commercial software by two readers. Prediction intervals were calculated for each parameter.

Results
Exercise caused an increase in heart rate (64±9 bpm vs 133±19 bpm, P < 0.001), left ventricular end-diastolic volume (140±32 ml vs 148±36 ml, P < 0.001), stroke volume (82±18 ml vs 102±26 ml, P < 0.001), ejection fraction (59±6% vs 69±7%, P < 0.001), and cardiac output (5.2±1.2 l/min vs 10.0±3.1 l/min, P < 0.001), with a decrease in left ventricular end-systolic volume (58±18 ml vs 46±16 ml, P < 0.001). There was an effect of gender and age on response to exercise across most parameters. Measurements showed moderate to excellent intraand inter-observer agreement.

Conclusion:
In healthy adults, an increase in cardiac output after exercise is driven by a rise in heart rate with both increased ventricular filling and emptying. We establish normal ranges for exercise response, stratified by age and gender, as a reference for the use of exCMR in clinical practice.

Link | PDF (Preprint: MedRxiv)

 

[SNT Gatchaman]

Exercise was performed using a MR-conditional variable resistance supine ergometer attached to the scanner table. Participants were asked to grip the handles of the ergometer and coached to keep their torso as stationary as possible during exercise to minimize bulk movement. The target heart rate (HR) for each participant was calculated as 85% of the maximal HR using Fox’s formula (220 - age in years).

Following resting RT imaging, the participants were instructed to start exercising while maintaining a cadence of 70 80 rpm, with an initial minimal workload for 1 minute. While the participants continued to exercise in the bore of the MR scanner, the workload was increased by 25 W every minute until the participant reached their target HR or until they reported leg exhaustion. The free-breathing RT imaging began immediately following the cessation of exercise in order to minimise movement artefacts and ECG mis-triggering.

Our cohort demonstrated a robust response to supine exercise with almost a 100% increase in cardiac output. Overall, EDV showed only a modest and variable increase on exercise, while there was a significant rise in HR and decrease in ESV. Older adults, with a reduced HR response and less systolic reserve, relied on greater ventricular filling to maintain exercise CO. Higher HR in younger adults during exercise, with decreased filling time, could account for the limited increase in EDV during physical activity. 25 In the oldest age groups, a decline in diastolic relaxation could also contribute to a blunted rise in CO. 26 Men had higher indexed resting and exercise volumes than women and a greater absolute and relative response to exercise. 27 The rise in HR was similar between genders, and a higher exercise SV in men was achieved through greater left ventricular emptying. We also demonstrated that it was feasible to incorporate exCMR into a full clinical protocol, including tissue characterisation and late enhancement, that could be completed within 60 minutes with a low technical failure rate. Although confined to healthy volunteers, this shows how exCMR could be incorporated into routine CMR practice.

 

[SNT Gatchaman]

I think this would be an interesting technique to apply in ME and in POTS to see if there is any significant abnormality in cardiac function when confined to the supine position, without orthostatic effects. A second-day assessment to capture any PEM effects would also be required.