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Factors determining exercise capacity in patients with atrial septal defect: assessment of heart function with CMR during dobutamine stress
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: Q85 (2015)
Patients with left to right shunting of blood through an atrial septal defect (ASD) have decreased exercise capacity. This study hypothesized that central factors influence exercise capacity, namely systemic and pulmonary cardiac output and right ventricular (RV) function during stress as well as left atrial pressure (LAP) and pulmonary artery pressure (PAP). Previous studies have found varying effects of stress and increased heart rate on the degree of shunting. The purpose of the study was therefore to determine if atrial shunting ratio changes during stress and examine if central factors can explain decreased exercise capacity in ASD patients.
Eighteen patients with ASD and 16 healthy volunteers underwent cardiac magnetic resonance at rest and during 20 µg/kg/min dobutamine infusion and 0.25-0.75 mg atropine injection, aiming for an increase in heart rate to at least 70% of age-predicted maximal pulse. Two patients could not undergo stress CMR. Cine ssfp images were used for LV and RV volumes. Flow velocity mapping of the aorta and pulmonary trunk quantified cardiac output and shunt ratio (QP/QS) at rest and during stress. Ergospirometry was used to determine peak oxygen uptake (VO2 peak). LAP and PAP were invasively measured at rest at the time of transcutaneous closure of the ASD.
Subject characteristics are shown in table 1. In patients with ASD the shunt ratio decreased from 2.2±0.8 at rest to 1.6±0.6 (p<0.01) during dobutamine stress. On dobutamine stress systemic cardiac output increased by 81±37% and pulmonary cardiac output increased by 30±28% (p<0.001). VO2 peak correlated with cardiac output at dobutamine stress in controls (fig 1A), but only with aortic cardiac output in patients with ASD (fig 1B). VO2 peak did not correlate with QP/QS in patients (p=0.22 at rest and p=0.29 at stress). VO2 peak correlated with RV end systolic volume during stress in controls (p<0.01) but not in patients (p=0.56). There was no correlation between VO2 peak and LAP or PAP at rest (p=0.45 and p=0.71 respectively).
The shunting ratio in ASD patients decreases during dobutamine stress. This is explained by proportionally larger increase in systemic flow compared to shunting flow. Exercise capacity in patients is related to the capacity to maintain a high systemic cardiac output during stress but not to the degree of shunting, RV function at stress or to LAP or PAP at rest.
The Swedish Heart-Lung Foundation.
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Stephensen, S.S., Steding-Ehrenborg, K., Thilén, U. et al. Factors determining exercise capacity in patients with atrial septal defect: assessment of heart function with CMR during dobutamine stress. J Cardiovasc Magn Reson 17, Q85 (2015). https://doi.org/10.1186/1532-429X-17-S1-Q85
- Right Ventricular
- Exercise Capacity
- Pulmonary Artery Pressure
- Atrial Septal Defect
- Dobutamine Stress