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Performing this test can help doctors rule out malfunctions that can occur when the heart’s right and left ventricles become unbalanced.
Each year, about 50,000 people in the United States experience cardiogenic shock—a life-threatening condition, usually caused by an acute heart attack, in which The heart cannot pump enough blood for the body’s needs.
A new MIT study sheds light on how the heart responds to ventricular assist devices (VADs), which are often used to treat patients with left ventricular failure. A VAD includes a pump that helps pump blood out of the left ventricle (pictured right) and into the aorta (large pink vessel). Image credit: Jose-Luis Olivares, MIT
Many of these patients are assisted by a mechanical pump that can temporarily help the heart pump blood until it recovers enough to function on its own. However, in about half of these patients, the extra support leads to an imbalance between the left and right ventricles, which can be life-threatening.
In a new study, MIT researchers have explored why this imbalance occurs, and identified factors that make it more likely. They also developed a test that doctors can use to determine whether the disorder will occur in a particular patient, giving doctors more confidence when deciding whether to use these pumps. are called ventricular assist devices (VADs).
“As we improve the mechanistic understanding of how these technologies interact with local physiology, we can improve device efficacy. And if we have more algorithmic and matrix-based guidance, it allows clinicians to This will both improve patient outcomes and lead to more widespread use of these devices,” says Kimberly Lamberti, an MIT graduate student and lead author of the study.
Eleazer Edelman, the Edward J. Poitras Professor in Medical Engineering and Science and director of MIT’s Institute for Medical Engineering and Science (IMES), is its senior author. Paperwhich appears in Science Translational Medicine. Steven Keller, assistant professor of medicine at the Johns Hopkins School of Medicine, is also an author of the paper.
Edelman notes that “the beauty of this study is that it uses pathophysiologic insights and advanced computational analyzes to provide clinicians with straightforward guidelines for how to deal with the exploding use of these valuable mechanical devices. We use these devices increasingly in our sickest patients and now have a big strategy to improve their effectiveness.
Imbalance in the heart
To treat patients who are experiencing cardiogenic shock, a percutaneous VAD can be inserted through the arteries until it is across the aortic valve, where it is used to pump blood from the left ventricle. I help. The left ventricle is responsible for pumping blood to most of the body’s organs, while the right ventricle pumps blood to the lungs.
In most cases, the device can be removed after a week or so, once the heart is able to pump on its own. While effective for many patients, in some people the devices can disrupt the coordination and balance between the right and left ventricles, which contract and relax in sync. Studies have found that this disorder occurs in up to 43 percent of patients who receive a VAD.
“The left and right ventricles are highly coupled, so as the device disrupts flow through the system, it can expose or induce right heart failure in many patients,” Lamberti says. can do.” “It is recognized throughout the field that this is a concern, but the mechanism causing it is unclear, and there are limited metrics to predict which patients will experience it.”
In this study, the researchers wanted to learn why this failure occurs, and to help doctors predict whether it will happen to a patient. If doctors knew the right heart would also need support, they could implant another VAD that supports the right ventricle.
“What we were trying to do with this study was to predict any problems in the patient’s course, so that action could be taken before they reach the extreme state of failure,” says Lamberti.
To do this, the researchers studied the devices in animal models of heart failure. A VAD was implanted in each animal’s left ventricle, and the researchers analyzed several different metrics of heart function as the device’s pumping speed increased and decreased.
The researchers found that the most important factor in how the right ventricle responded to VAD implantation was how the pulmonary vascular system — the network of blood vessels that carry blood between the heart and lungs — increased blood volume and flow through the VAD. Adapted to changes in .
The system was able to handle this extra flow if it could adjust its resistance (the slow rate of steady blood flow through the vessels) and compliance (the slowing of large blood volume pulses in the vessels).
“We found that in a healthy state, compliance and resistance can change very quickly to accommodate changes in volume caused by the device. But with progressive disease, the ability to adapt decreases, ” says Lambert.
A dynamic test
The researchers also showed that measuring and adapting this pulmonary vascular compliance may offer a way to predict how a patient will respond to left ventricular support. Using a dataset of eight patients who received a left-sided VAD, the researchers found that those measurements correlated with right-sided heart status, therefore predicting how well the patients adapted to the device. , confirmed the results with animal studies.
To perform this test, doctors routinely place the device on and then increase the speed while measuring the compliance of the pulmonary vascular system. The researchers determined a metric that could assess compliance using only the VAD itself and the pulmonary artery catheter that is commonly implanted in these patients.
“We designed this method to dynamically test the system while maintaining cardiac support,” says Lamberti. “Once the device is started, this quick test can be run, which will tell the clinicians whether the patient may need the right heart support.”
The researchers now hope to expand on these findings with additional animal studies and continue to collaborate with the manufacturers of these devices in the future, hoping to conduct clinical studies to test whether the test provides such information. will provide that will be valuable to physicians.
“Currently, few metrics are used to predict device tolerability. Device selection and decision-making are often based on the empirical evidence of clinicians at each institution. This understanding is expected to allow clinicians to determine will allow to identify which patients are intolerant to device support and provide guidance to best treat each patient based on the exact heart condition,” says Lamberti.
Written by Ann Trafton.
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