Hearts need oxygen. Heart attacks are the most dramatic example of this hunger, when blocked coronary arteries starve muscles of the oxygen they need to keep beating. Less sudden is heart failure, when lagging levels of oxygen consumption can mean the heart doesn’t pump blood through the body as well as it should.
Determining how much oxygen the heart is or isn’t using can help detect heart failure, important in designing treatment in early stages of a condition that affects 1 in 4 Americans over a lifetime. There are other ways to reach a diagnosis: blood tests, electrocardiograms, echocardiograms, stress tests, and chest X-rays as well as the CT scans, coronary angiograms, and biopsies of heart muscle.
Zeroing in on oxygen has been hard but is important. Current tests to measure it require inserting a catheter in the space called the coronary sinus, or using PET scans to see radioactive tracers circulating there. But new research published Wednesday in Science Translational Medicine may offer a quicker, less invasive way to quantify how much oxygen the heart is using, and how efficiently, during a cardiac MRI scan.
The appeal of such testing is growing, with promising results in people with a common type of heart failure that improves with obesity drugs.
Tested first in pigs and then in 22 patients who’d had heart attacks, the experimental approach used a special form of an MRI to measure oxygen without needles or catheters, without radiotracer injections and radiation exposure, and without patients needing to hold their breath during a cardiac catheterization scan. The researchers knew that MRIs are sensitive to blood oxygen level signals, but capturing them was the challenge. They had to overcome imaging issues, correct for signal noise, and account for movement from beating hearts.
They succeeded, calibrating oxygen consumption in three minutes with results validated against older, more invasive techniques in the small trial. The team took a page from neuroimaging, adapting a test seeking a blood oxygen level–dependent signal in the brain.
“A cardiac MRI scan is a routine clinical procedure that people can order,” said study co-author Hsin-Jung Yang. “This is a three-minute add-on, without contrast agent, without breath-holding.”
Yang and his team envision their test being part of a longer cardiac MRI test ordered to assess the heart’s function and structure. Patients would lie inside that long tube while magnets and radio waves combine to produce images intended to show damage after a heart attack or find valve disease. Oxygen use would be one more readout.
Yang, an associate professor of biomedical sciences at Cedars-Sinai Medical Center and a faculty member of the Biomedical Imaging Research Institute at Cedars-Sinai, talked with STAT in more detail about this development. The conversation has been edited for length and clarity.
Why is measuring oxygen so important?
The heart is a pump that utilizes oxygen and nutrition every minute, every second. And how it’s using oxygen is actually very important to reflect its health, particularly in conditions like heart failure and also diabetes and hypertension. Those patients are more subject to cardiometabolic illness when the heart doesn’t function well and cannot pump as much blood as you need into your whole body.
How is oxygen use estimated now?
Currently, you can measure this through a catheter sent into the heart. And that cannot routinely be done everywhere. MRI is something that you have in all major hospitals. Because it doesn’t take contrast agents, you can do this in lower-risk populations. You can repeat it to really monitor therapy response, too.
You make it sound so easy. What were some of the challenges to overcome?
There’s a lot of technical difficulties because the heart is consistently moving, right? So we did motion-insensitive or motion-resolved kinds of images. On top of that, we did a quantification model, applying a physical model to the signal. Instead of just seeing bright or dark, we now can measure the oxygenation numbers in the heart. And that is where the actual difference is: the blood when it’s more oxygenated, it’s more dark. We know the number and we color-coded it.
How do you hope to help people with heart failure?
There are two types of heart failure: heart failure with reduced ejection fraction, or HFrEF, and heart failure with preserved ejection fractions, or HFpEF. Ejection fraction is how much of the blood in the heart’s ventricular chamber you can pump out. When that number is lower than 50%, we call it reduced ejection fraction. In that condition, you will feel symptoms like fatigue, not be able to climb stairs, and so on.
Now a fast-growing population has preserved ejection fraction, a big topic that everyone is first, trying to understand more, and second, trying to find therapies for it. GLP-1 drugs and SGLT2 drugs to treat that HFpEF population show very promising results. That’s now in the clinical guidelines for drugs that are usually used to address metabolic abnormalities like diabetes. And that’s also the key trigger of why we’re doing this.
We wanted to directly see the metabolism in the heart.
Is anyone else exploring this question?
Another route is metabolite imaging. There are different metabolites in the mitochondria that also reflect metabolic abnormalities. One of the labs in Cedars-Sinai next to us is doing that. We’re in close collaboration.
Who are the patients you think might benefit?
Metabolic syndrome is a big thing in the country. People with obesity, diabetes, hypertension — those are key populations that we have the chance of doing earlier identification. I think that is where the impact can translate the most.
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