Measurement of blood oxygen saturation (O2 saturation) is essential for the clinical evaluation of patients with cardiovascular disease, heart failure, and pulmonary disease. With the introduction of the right heart catheter, measurements of O2 saturation in the right heart, venae cavae, and pulmonary artery became readily available and have thus contributed significantly to our hemodynamic understanding of congenital and acquired heart disease. Furthermore, the introduction of a pulmonary artery catheter, which can be implanted within minutes at the bedside, allows better monitoring for critically ill patients in the intensive care unit. In acquired heart disease, O2 saturation provides important information about systemic oxygen delivery and consumption, making it essential for evaluating heart failure patients and patients with pulmonary arterial hypertension. Nevertheless, invasive catheter implantation is associated with not insignificant risks of complications and a noninvasive method has not yet been established.
The blood oxygen level-dependent (BOLD) effect has been established in recent years as an effective method to noninvasively measure O2 saturation using T2 magnetic resonance imaging (T2-MRI). BOLD effect-based oximetry has been found to provide noninvasive information about both blood oxygenation, myocardial oxygenation, and skeletal muscle oxygenation using MRI. The principle underlying this technique exploits the dependence of the T2- relaxation time on the oxygenation of hemoglobin, as well as the different magnetic properties of hemoglobin in the oxygenated and deoxygenated states. To establish the mathematical relationship between the T2 relaxation time of whole blood and O2 saturation, a Luz-Meiboom (L-M) model describing the transverse (T2) relaxation arising from the transfer of protons between a protein and a water solution was proposed. The application of this model has improved the "classical" BOLD sequences, which were only measurable in static tissue (myocardium), minimizing the large estimation variability in flows (ventricles and vessels), allowing a more quantitative measurement. With the increasing number of patients receiving transcatheter aortic valve implantation (TAVI) as well as being diagnosed with atypical pulmonary hypertension, a large number of patients with relevant comorbidities require invasive hemodynamic evaluation. Simultaneous evaluation of central venous SO2 (ScvO2) and cardiac function is highly desirable and could allow noninvasive staging of frail high-risk patients. The first pilot clinical study of this concept was recently published.
The first aim of the investigators is to determine the precision of non-invasive O2 saturation measurement using BOLD-T2-MRI in contrast to invasive O2 saturation measurement using a right heart catheter in patients.
The secondary objective of the study is to investigate the role of BOLD measurements as a diagnostic test in patients with dyspnea at presentation, at least NYHA class 2 and an indication for cardio MRI. In these patients, BOLD measurements will be performed both at rest and during exercise. A sensitivity analysis will be performed to determine the diagnostic value of BOLD measurements in different patient populations.
