When a patient shows up in the emergency room with chest pain, worried that he may be in the throes of a heart attack, it’s not uncommon for him to be sent home a few hours later with the assurance that his heart seems to be functioning just fine. Unfortunately, it’s also not uncommon for some of these patients to show up again only a few days later, this time in an ambulance after a massive heart attack.
Until now, there has been no way to tell who is most vulnerable until it’s already too late. Now, researchers at the Scripps Translational Science Institute in San Diego have found a blood marker that should allow them to pinpoint those who are most at risk and lessen or even prevent a future attack.
The problem with tests available today in the ER is that they can only tell whether damage has already been done: Blood tests look for proteins associated with injured heart tissue, and electrocardiograms can determine whether the heart muscle cells are functioning abnormally. But they can’t determine if a small blood clot that may have been causing the pain has already dissolved, or whether an artery that’s slowly cracking is about to give way.
“These vulnerable arteries are the precursor to many forms of heart attack and stroke, but we had no way to get at the artery that was unstable” says Eric Topol, director of the Scripps institute and the cardiologist who led the new study. Prior work had shown that the unstable arteries don’t just suddenly burst open, but crack, heal over, and crack again. Rather, he says, “it occurs over a number of days or even weeks, and cells from the unstable artery are being shed into the bloodstream.”
So Topol and his colleagues went looking for the cells that might tell them whether a patient had arteries in crisis. They found that, in blood samples from heart-attack patients, the cells being sloughed off blood-vessel walls were large and distorted, compared to the same type of cells in healthy volunteers. The irregular cells could be found in a simple blood sample, using an automated microscope and methods that, while expensive and cumbersome, could be used in a clinic.
Since the first study was finished, the researchers have gone a step further and found a molecular marker expressed on these misshapen cells that should be even simpler to test for. “We can get a molecular signal of an artery that’s cracking, and that gives us a lead time of days to weeks before the event will occur,” Topol says. They’re about to start testing the new method in a larger trial, and hope it will lead to a standard assay that could help avert serious events before they occur. Patients who test positive for the marker would receive a dose of intensive anti-clotting, blood thinning medication to make sure they don’t progress to a heart attack.
That’s just the start, as far as Topol is concerned. “The longer-range plan, also in the works, is to take this molecular signature and embed a nanosensor in the bloodstream, so that people at high risk are under surveillance,” he says. The embedded sensor would pick up the molecular marker and communicate with their smartphones to let them know when they should seek care.