Effect of O2-Enriched Breathing on Myocardial Uptake of 99mTc-Sestamibi

Abstract

Oxygen (<inf>O2</inf>) inhalation after acute myocardial ischaemia has long been a part of standard therapy in cardiology. It has also been demonstrated that therapeutic hyperoxia diminishes myocardial stunning. The aim of this pilot study was to investigate whether the uptake kinetics of the myocardial perfusion agent technetium-99m sestamibi (MIBI) during O<inf>2</inf>-enriched breathing is modified in comparison with the kinetics observed under conventional rest imaging performed after injection during inhalation of room air. Nine patients scheduled for coronary intervention (CI) with a documented significant stenosis (≥50%) of at least one epicardial coronary vessel and one patient with slow flow on coronary angiography were investigated. First, rest MIBI electrocardiogram-gated single-photon emission tomography (G-SPET) with 740 MBq was performed. Two days later, the tracer was injected following a 5-min period of 100% O<inf>2</inf>-supported (nasal catheter) breathing at rest (6 l/min) and a second G-SPET acquisition (O<inf>2</inf>+MIBI G-SPET) was carried out. Patients' medication was not withdrawn and was matched throughout the study. The mean elevation of arterial oxygen saturation achieved was 2.95%. No significant changes in arterial blood pressure or heart rate could be detected at any time during the procedure. Compared with the results of baseline G-SPET, on O<inf>2</inf>+MIBI G-SPET five patients scheduled for CI and the patient with slow flow showed increased tracer uptake in initially ischaemic regions without any alterations in other myocardial regions. In three of these five patients, post-CI imaging could be performed and showed increased tracer uptake in all additional areas detected previously by O<inf>2</inf>+MIBI imaging. In three patients, besides improvement in ischaemic regions, a mild reduction in tracer uptake was observed in myocardium that initially appeared normal. In one of these patients, thallium-201 rest-redistribution SPET was performed and showed an (uptake pattern more similar to that seen on O<inf>2</inf>+MIBI images than that on baseline MIBI G-SPET. In one patient, no difference in tracer uptake was observed in pre- and post-CI studies. Improvement was detected in the wall thickening images of the O<inf>2</inf>+MIBI study in seven of the ten patients. Four of these patients showed improvement in the same regions after CI. In this pilot study, it was demonstrated that MIBI injection during O<inf>2</inf>-enriched breathing can be a useful technique for enhancing the detection of viable myocardial tissue. The possible mechanisms of altered tracer kinetics are discussed.