Background
Patients with acute myocardial ischemia receive oxygen as a standard measure of care to maintain or improve the myocardial oxygen supply. In 1975 Neil et al. were able to show that higher oxygen concentration reduces myocardial blood flow. However, since the oxygen concentration in the blood was significantly increased it was/is assumed that the higher oxygen supply outweighs the decrease in perfusion. Oxygenation-Sensitive (OS) Cardiovascular Magnetic Resonance (CMR) is a newer technology that uses the paramagnetic deoxyhemoglobin in the blood as an endogenous contrast. An drop in tissue oxygenation (drop in oxyhemoglobin) results in an increase in deoxyhemoglobin, which results in an drop in SI in OS-images. Vice versa an increase in tissue oxygenation results in an increase in OS-SI. Therefore, OS-CMR can assess myocardial tissue oxygenation changes non-invasively, free of contrast and free of radiation. While other diagnostic modalities only give information on myocardial oxygenation with surrogate parameters that may indicate ischemia OS-CMR gives local functional information of the myocardial oxygen supply. Studies have been performed using OS-CMR for the detection of coronary artery disease. More recently breathing maneuvers that change systemic blood gases have been suggested as a vasoactive stimulus to detect coronary artery disease and measure changes to the myocardial oxygen supply. Guensch et al. were able to show that hypercapnia and the combination of hypercapnia and hypoxia lead to a increase of myocardial oxygenation that can only be explained by an increase blood flow. However, hypocapnia resulted in a decrease in myocardial oxygenation in healthy volunteers. In a porcine model the investigators were able to show that the increase in systemic oxygen supply resulted in a decrease in myocardial blood flow in healthy and swine with an acute coronary artery stenosis, but a decrease in myocardial oxygenation was only observed in the animals with a coronary artery stenosis (Abstract Guensch et al: Administration of exogenous oxygen may worsen myocardial ischemia, ESC 2014, accepted). The impact of hyperoxia as well as hypocapnia and hypercapnia in humans with a chronic coronary artery disease is poorly investigated. As the administration of oxygen is part of the treating guidelines in acute myocardial ischemia and in certain situations (e.g. anesthesia) higher oxygen concentrations are maintained for safety reasons, it is important to further investigate the role of higher oxygen concentrations in coronary artery disease. Further the investigators want to shed light on transient states of hypocapnia and hypercapnia induced by voluntary breathing. Because OS-CMR is a safe diagnostic tool (no radiation, no contrast, no pharmacologic vasodilator required) and can give insight on the oxygenation changes of the heart is it ideal to test the hypothesis. Therefore the investigators want to invite patients with a known coronary stenosis (confirmed by previous coronary angiography) scheduled for a percutaneous coronary intervention (staged PCI) or coronary artery bypass surgery to participate in this study prior to the intervention and compare the MRI results to healthy volunteers. All participants will perform hyperventilation with a consecutive breath-hold as well as inhale oxygen for 3-5 minutes while the breathing maneuver is being repeated. For the patients the results will then be compared to the findings of coronary angiography (QCA, reduction in lumen-diameter of the vessel).
Objective
With this study the investigators want to investigate whether the administration of oxygen, as well as performing breathing maneuvers (hyperventilation, breath-holding) have a negative or positive effect on the oxygenation of myocardium subtended to arteries diseased of coronary artery disease, as opposed to healthy subjects.
Methods
CAD-patients with a known coronary pathology that are scheduled for a PCI or coronary bypass surgery will be recruited for the CMR exam prior to the coronary intervention. A i.v. line will be placed for safety reason. During short breath-holds oxygenation-sensitive baseline images and cardiac function images will be acquired. The subjects will then be asked to hyperventilate for one minute with 20-30 breaths/min. Immediately after a maximal breath-hold will be performed in end-expiration as long as the subject can comfortably bear. During the entire breath-hold oxygenation sensitive images will be recorded. Whenever the subject feels the need to breath, he/she can immediately do so and signal the technician with a call bell. After recovery the subject will breath oxygen 12-15L/min through a mask for 3-5 min after which oxygenation sensitive images as well as function images will be repeated. The hyperventilation-breath-hold will be repeated with oxygen. Healthy volunteers will undergo the same protocol.
