Assessment of the Physiological Adaptations to Chronic Hypoxemia in Eisenmenger Syndrome.

Abstract

Eisenmenger syndrome is characterized by severe and lifelong hypoxemia and pulmonary hypertension. Despite this, patients do surprisingly well and report a reasonable quality of life. The aim of this study was to investigate whether these patients undergo adaptation of their skeletal and cardiac muscle energy metabolism which would help explain this paradox. Ten patients with Eisenmenger syndrome and eight age- and sex-matched healthy volunteers underwent symptom-limited treadmill cardiopulmonary exercise testing, transthoracic echocardiography and (31) P magnetic resonance spectroscopy of cardiac and skeletal muscle. Five subjects from each group also underwent near infrared spectroscopy to assess muscle oxygenation. Despite having a significantly lower peak VO2 , patients with Eisenmenger syndrome have a similar skeletal muscle phosphocreatine (PCr) recovery, a measure of oxidative capacity, when compared to healthy controls (34.9 s ± 2.9 s vs. 35.2 s ± 1.7 s, P = .9). Furthermore their intracellular pH falls to similar levels during exercise suggesting they are not reliant on early anaerobic metabolism (0.3 ± 0.06 vs. 0.28 ± 0.04, P = .7). While their right ventricular systolic function remained good, the Eisenmenger group had a lower cardiac PCr/ATP ratio compared to the control group (1.55 ± 0.10 vs. 2.17 ± 0.15, P < .05). These results show that adult patients with Eisenmenger syndrome have undergone beneficial physiological adaptations of both skeletal and cardiac muscle. This may, in part, explain their surprisingly good survival despite a lifetime of severe hypoxemia and adverse cardiopulmonary hemodynamics.