Shareen Jaijee and colleagues in the UK discovered that cardiac MRI during exercise can be used to detect depleted right ventricular (RV) reserves when healthy subjects are deprived of oxygen and in patients with pulmonary arterial hypertension (PAH) under normal oxygen conditions even if they have normal RV function at rest. Click through the slides for details on the study and a few clinical take home points.
PAH and Right Ventricular Function. Low right ventricular (RV) function is a potent predictor of mortality in PAH. RV response to exercise is emerging as a better indicator of ventricular-arterial coupling vs resting hemodynamics.
The Study. Patients with a diagnosis of Group 1 PAH were recruited from the Pulmonary Hypertension Service at Imperial College Healthcare NHS Trust (London) and compared with healthy controls. Biventricular function, volume, mass, and flow were determined using real time cardiac magnetic resonance imaging data obtained while patients exercised and were at rest.
Normal Subjects: Exercise Effect Significant. During non-hypoxic exercise normal subjects increased their CI by 2.5 times the resting value, at individualized workloads, with significant increases of HR, SVi, biventricular EF, and RVSVi/RVESVi. Left atrial size at rest was significantly reduced by hypoxia (24.1 ± 5.4cm2 to 21.0 ± 9.3cm2, P<0.05) but right atrial size was unchanged (24.8 ± 5.9cm2 vs 25.0 ± 5.4cm2, P=0.621).
PAH Subjects. No Overall RVEF Response to Exercise. There were no significant differences in resting indexed RV volumes and function, HR, and CI between patients and normal subjects.
Take Home Points
Right ventricle is susceptible to dysfunction during periods of hypoxia in both patients with PAH and in healthy subjects.
Hypoxia causes mildly impaired contractile reserve selectively affecting the right ventricle while still allowing augmented contractility in the left ventricle during exercise.
Authors: Sildenafil may reverse the negative impact of hypoxia on RV contractility during exercise in some subjects.
Fixed pulmonary vascular resistance in PAH limits the ability to compensate during exercise.
Counsel patients with preserved ejection fractions at rest that exercise may unmask poor RV contractile reserve and should be undertaken cautiously.