NEW YORK – Beyond echocardiograms, the current standard of practice in emergency settings for diagnosing heart attacks relies on measuring troponin levels, which can take hours. But a team of researchers from the University of Notre Dame is looking to create a diagnostic test to return results in a fraction of the time.
Described in a paper published in September in Lab on a Chip, the new technology is based on a sensor that detects microRNA to determine whether a patient is having an acute myocardial infarction (AMI), or heart attack.
According to Pinar Zorlutuna, a professor of engineering at Notre Dame, the two key innovations are the use of miRNA biomarkers to detect heart attacks and the biosensor itself. While MiRNA biomarkers have been suggested as potential indicators of AMI in the past, they couldn't be detected quickly because they required PCR instruments that had long turnaround times, she said.
With the biosensor developed by Zorlutuna and her team, the markers can be detected in low concentrations with high sensitivity, enabling its use at the point of care, she added.
The process is relatively simple, Zorlutuna said. A plasma sample from a patient is pipetted into a chamber in the device, and using microfluidics, the sample is sucked through a capillary to the sensor's circuit board.
Once on the circuit board, it passes through a sonic acoustic wave that lyses the exosomes – where miRNAs are located – in the sample without adding a lysing solution, which can potentially dilute or contaminate the sample. Those miRNAs produce early signals of a heart attack, before the cells start dying, Zorlutuna said.
The lysed exosomes are passed to the sensor unit that contains three sensor heads that correlate to three different miRNAs. Those miRNAs bind to probes on a highly-charged membrane surface within the sensor, changing the properties of the surface. A voltage reader measures the changes, which correlate to the miRNA concentration in the blood, and returns a number. If that number is below a certain threshold, the diagnosis is that patient is not having a heart attack, but a result above the threshold indicates AMI, Zorlutuna said.
In the Lab on a Chip study, which was funded by the National Institutes of Health's National Heart, Lung, and Blood Institute, four cohorts of patients were tested – one group of reference subjects with no evident coronary artery disease (CAD); one group with stable CAD; one group with ST-elevation myocardial infarction before they were treated with percutaneous coronary intervention; and one group with ST-elevation MI after being treated with percutaneous coronary intervention.
ST-elevation myocardial infarction is a very serious type of heart attack associated with high morbidity and mortality.
The team found that the three miRNA biomarkers it tested – miR-1, miR-208b, and miR-499 – were elevated in patients with CAD and those with ST-elevated MI both before and after clinical intervention. The miR-1 biomarker was found to vary significantly between the three cohorts with heart disease and is associated with early stage AMI, meaning it can likely differentiate between disease stages, the researchers wrote.
Meantime, miR-208b can differentiate between patients with disease and those without. The miR-499 biomarker didn't vary significantly between the three patient groups, so it could be "a reasonable reference control for plasma samples from patients with suspected cardiac disease," according to the paper.
Aside from finding that the sensor's results correlate with those of the gold standard, the researchers also found that the biosensor can distinguish between patients that have undergone interventions and those that haven't.
The current gold standard for AMI diagnosis is protein biomarker testing, specifically for troponin, but troponin levels only go up once cells are dying, meaning diagnosis can only occur further along in the heart attack cycle, Zorlutuna said. That process occurs between three hours and five days after a patient's symptoms begin.
The battery-powered sensor, however, acts as an earlier detector, so interventions can be made sooner, and treatments can be applied. With earlier detection, it's also possible to distinguish different stages of a patient's heart attack, which can be helpful in patients who don't know they've had a heart attack.
Another issue with troponin testing is the need for pretreatment steps, which can compromise the sensitivity of the test and result in false positives.
Zorlutuna said the biosensor can be used as another checkpoint in the decision-making process to determine if invasive treatment is necessary, and it can be used either with or instead of troponin testing.
No special technology besides the sensor is needed to run the test, and because of its portability, it can easily be performed at the point of care or in an emergency room, Zorlutuna said.
Keith March, a professor of medicine in the University of Florida Division of Cardiology, said that the sensor could also help discern whether a blood vessel is still blocked or if it's open.
March, who helped conceptualize the project and provided clinical samples, but who has not been involved with the electrical technology development, said that the ability to determine a blood vessel's blockage can help personalize treatment to a patient, particularly in an emergency where time is of the essence.
"Time is muscle," he said, meaning that the longer blood isn't flowing to the heart, the more a patient is irretrievably losing function of the heart muscle. The speed of Zorlutuna's biosensor could make sure patients aren't losing that muscle.
Her team currently has a patent pending on the device and is working with Notre Dame's Idea Center for Translational Studies to see how it can best be commercialized. The office is currently doing market analysis to see how clinicians would adopt it and whether they'd be willing to change standard practices, she said, adding the office is "looking for broader information from clinicians."
Benjamin Hoggan, the director of de-risking at the Idea Center at Notre Dame, which helps researchers at the university commercialize their technology, who was not involved with the development of the technology, said that while he thinks the tech is promising, there are a number of competing solutions available, such as Angel Medical's AngelMed Guardian system, an implantable cardiac monitory system that gives high-risk notifications based on ST segment changes.
There's a need to determine the value of the test among clinicians and see if it would lead to improved clinical outcomes, he said.
He added that the plan would be to use the device in emergency care facilities alongside echocardiograms to differentiate between coronary artery disease and AMI, and then measure the effectiveness of certain drug therapies to avoid unnecessary surgeries.
However, there are some key hurdles Zorlutuna and her team will have to overcome before the test is commercially available, Hoggan said. A blood-based emergency diagnostic like this one will require significant clinical validation and likely a long regulatory pathway through the US Food and Drug Administration, he said.
In addition, "doctor adoption will be a challenge … on trust of data, change of behavior, and the need to change [the standard of care] to reflect a faster course of action," he said.
The University of Florida's March added that another consideration for commercializing the sensor is ensuring they're manufactured "in a consistent and reliable way," so that manufacturing can be scaled up widely.
Zorlutuna's lab is testing more clinical samples to further refine the sensor, she said. It's also working on a new iteration of the device, which would include troponin testing to combine the key diagnostic tools in one instrument. That device would use the same technique but split into two channels – one with the membrane sensor for miRNAs, and one with a sensor for troponin, she said.