Haemodynamic left-ventricular changes during dobutamine stress in patients with atrial septal defect assessed with magnetic resonance imaging-based pressure-volume loops

Abstract

Background: Atrial septal defect (ASD) results in a left-to-right shunt causing right-ventricular (RV) volume overload and decreased cardiac output from the left ventricle. Pressure-volume (PV) loops enable comprehensive assessment of ventricular function and might increase understanding of the pathophysiology of ASD. The aim of this study was to investigate if left-ventricular (LV) haemodynamic response to stress in patients with ASD differs from controls.

Material and methods: Patients with ASD (n = 18, age 51 ± 18) and healthy controls (n = 16, age 35 ± 13) underwent cardiac magnetic resonance (CMR) and brachial cuff pressure measurements at rest and during dobutamine stress. An in-house, validated method was used to compute PV loops.

Results: Patients had lower stroke work, potential energy and external power at rest than controls (p < 0.001; p < 0.05; p < 0.05). Stroke work and external power increased and potential energy decreased during stress in patients (p < 0.05; p < 0.0001; p < 0.01) and controls (p < 0.0001; p < 0.001; p < 0.01). Contractility and arterial elastance at rest were higher in patients than controls (p < 0.01; p < 0.01). Contractility increased during stress in both groups (p < 0.0001; p < 0.001). There was no difference between patients and controls in arterio-ventricular coupling.

Conclusion: LV haemodynamic response to stress can be assessed using noninvasive PV loops derived from CMR and brachial blood pressure. Patients with ASD had normal LV energy efficiency, in contrast to other patient groups with decreased cardiac output. Data suggest that patients with ASD had an increased inotropic level at rest with high contractility and heart rate but were able to respond with a further increase during stress, albeit to not as high a cardiac output as controls.

Keywords: atrial septal defect; cardiovascular magnetic imaging; congenital heart defect; heart failure; pressure-volume loops.

Figure 1

Flow diagram of study design. Patients were examined with cardiac magnetic resonance and brachial pressure at rest and during dobutamine stress. Left‐ventricular endocardial borders were manually delineated in all timeframes, and pressure–volume (PV) loops were derived at rest and during stress. The PV loop area represents stroke work (SW) and the grey triangle corresponds to mechanical potential energy (PE). The slope of the line from maximal ventricular elastance (Emax) and V0 represents the contractility and the negative slope of the red line between the Emax point on the PV loop and the end‐diastolic volume at zero pressure represents the arterial elastance (Ea).

Figure 2

Mean pressure–volume loops for controls (black) and patients with atrial septal defect (ASD) (blue) at rest (solid line) and stress (broken line).

Figure 3

Graphs showing differences in stress response in the left (LV) and right ventricle (RV) between patients with atrial septal defect (ASD) and controls relative to resting values. Box and whiskers show median, IQR, and min to max. Patients are marked with filled circles and controls with open circles. (a) Patients did not increase cardiac output (CO) and heart rate (HR) as much as controls but there was no difference in systolic blood pressure (SBP). (b) Left‐ventricular efficiency and external power did not increase as much in patients with ASD as in controls. Energy per ejected volume remained unchanged in both groups.