Delayed Cardiac Recovery form Physical Exercise
Long after Repair of Tetralogy of Fallot: Assessment by Ultra-Fast MRI
, , , A.
P. Kunz ‘ AAW. Roest4, HJ. Lamb ‘ WA. Helbing 3, J. Doombos ‘ EE. van der Wall 2,4, de Roos Ia4
, ,
Depts of Radiology ‘ Cardiology 2 and Pediatry ‘ Leiden University Medical Center,
Leiden, The Netherlands and the Interuniversity Cardiology Institute of the Netherlands 4
Introduction course of stroke volume in healthy subjects decreasedto resting
Knowledge about the dynamic behavior of the cardiac system level after two minutes, stroke volume of the Fallot patients
during recovery from physical exercise can provide important remained significantly above resting level during period observed.
clinical information. A rapid decrease of the heart rate and an The difference in stroke volume recovery manifests itself also in
increase of the stroke volume has been observed in subjects who the time course of cardiac output. Four minutes after termination of
continued loadless pedaling during recovery Tom ergometer exercise, Fallot patients showed significant larger cardiac output
exercise [l]. In patients, a recently published study underlies the comparedto healthy subjects.
importance of exercise recovery by using the rate of decline in
heart rate after the cessation of exercise as a direct predictor of
mortality [2]. Recently, fast gradients and turbo-field echo-planar
MR imaging (TFEPI) were introduced, which allow reliable
assessment flow maps in great vessel in 3 - 4 seconds.
The purpose of the present study was to monitor changes in flow
through the ascending aorta during recovery from submaximal
ergometer exercisein healthy subjects and in Fallot patients. 0 50 100 150 200 250
time [set]
Methods 60
Examination protocol: Flow in the ascending aorta of 9 healthy z 50 Stroke Volume
subjects (17 f 2.4 yrs) and 5 corrected (correction >lO years ago)
tetralogy of Fallot patients (17.2 f 2.8 yrs) was studied using a
Philips ACS/NT 1.5 T system. Subjects were positioned in supine
position on a modified table top fitted with a MR-compatible
bicycle ergometer (Lode BV, The Netherlands), which allows
physical exercise during a MR examination. Individual exercise
levels were determined on the workload corresponding with 60%
of the maximal oxygen uptake, which was measured during a
maximal exercise test prior to the MR examination. Examination
of
was started by the assessment a frst flow map in the ascending
aorta at rest. Thereafter, the subjects were asked to cycle for about
lo-12 minutes at the determined workload. Subjects were then
instructed to ceasecycling and to hold their breath during a period
of 3 - 4 seconds while the first recovery flow map was assessed.
During the subsequent recovery process, 18 flow maps were
assessedin intervals of 15 second over a total period of 4:30 0 100 200
minutes. During the entire period, heart rate of the subjects was time [XC]
recorded. The applied ultra-fast sequenceconsisted of a segmented Figure 1: Heart rate, stroke volume and cardiac output during
k-space TFEPI phase contrast technique (FOV: 330 x 165 mm*, recoveryfrom ergometer exercisein healthysubjects(thick line) and
matrix size: 128 x 40, slice thickness: 10 mm, velocity encoding Fallot patients i
(thin line). Curvesaremeanfor all subjects SEM.
range: 200 cm/s, TE = 4.6 ms, TR = 13.9 ms, a = 30”, temporal * : significantdifference between healthycontrolsandpatients.
resolution: 29 ms) which allows the acquisition of a complete
Discussion
velocity map in 8 heart beats.
Data analysis: All images were quantitatively analyzed using the Ultra-fast near real-time MR flow imaging is feasible during
FLOW analytical software package. Stroke volume and cardiac physical exercise in patients. Post exercise regulation of cardiac
output were calculated and normalized to values obtained at rest. function was different in patients after total repair of tetralogy of
Fallot compared to healthy subjects. While heart rate recovery was
identical compared to healthy subjects, increased stroke volumes
Results
were observed during recovery which leads to a delayed
Figure 1 shows time courses of heart rate, stroke volume and normalization of cardiac output. This may be causedby a restricted
cardiac output of healthy subjects and Fallot patients during lung volume in these patient, leading to increased cardiac output
recovery from ergometer exercise. After cessation of exercise, and breathing rate [3] during exercise recovery to provide
heart rate exponentially recovered during a period of four minutes sufficient blood oxygenation.
to a level of 12.1 f 3.1 % above the resting heart rate in healthy Long term after correction for tetralogy of Fallot, cardiac function
controls and 10.1 f 6.0 % in the patients (ns.). No difference was is impaired, as shown by a delayed stress recovery of cardiac
found in heart rate recovery between patients and healthy subjects. fter
output. Near real-time MR flow assessment physical exercise
Both, patients and healthy subjects showed a increase in stroke may provide a new clinical tool to evaluatemyocardial condition in
volume after termination of exercise. However, a significant larger patients, and may help guiding titure therapy.
increase in stroke volume was found in the Fallot group compared
to the healthy subjects (Maximal stroke volume increase during References
recovery: Fallot patients: SV-= 35.9 * 9.7 % above rest; healthy 1. Goldberg DI, et al. JAppl Physiol48(5): 833-837 (1980).
2. Cole CR, et al. NEnglJMed341: 1351-1357 (1999).
controls: SV- = 12.2 * 3.8 % above rest; p < 0.05). While time 3. Rowe SA, et al. JACC 17 (2): 461-466 (1991).
Proc. Intl. Sot. Mag. Reson. Med. 8 (2000) 655