Scientists have noticed that COVID-19 can trigger serious cardiovascular problems, especially among older people who have a buildup of fatty material in their blood vessels. But now a new study has revealed why and shown that SARS-CoV-2, the virus that causes COVID-19, directly infects the arteries of the heart.
The study also found that the virus can survive and grow inside the cells that form plaque—the buildup of fat-filled cells that narrow and stiffen the arteries leading to atherosclerosis. If the plaque breaks, it can block blood flow and cause a heart attack or a stroke. The SARS-CoV-2 infection makes the situation worse by inflaming the plaque and increasing the chance that it breaks free.
This can explain long-term cardiovascular effects seen in some, if not all, COVID-19 patients.
SARS-CoV-2 virus has already been found to infect many organs outside the respiratory system. But until now it hadn't been shown to attack the arteries.
"No one was really looking if there was a direct effect of the virus on the arterial wall," says Chiara Giannarelli, a cardiologist at NYU Langone Health, in New York, who led the study. Giannarelli noted that her team detected viral RNA—the genetic material in the virus—in the coronary arteries. “You would not expect to see [this] several months after recovering from COVID.”
Mounting evidence now shows that SARS-CoV-2 is not only a respiratory virus, but it can also affect the heart and many other organ systems, says Ziyad Al-Aly, a clinical epidemiologist at Washington University in St. Louis. Al-Aly's research has shown that the risk of developing heart and cardiovascular diseases, including heart failure, stroke, irregular heart rhythms, cardiac arrest, and blood clots increases two to five times within a year of COVID-19, even when the person wasn't hospitalized.
"This important study links, for the first time, directly the SARS-CoV-2 virus with atherosclerotic plaque inflammation," says Charalambos Antoniades, chair of cardiovascular medicine at the University of Oxford, United Kingdom.
Virus triggers the inflammation in plaque
A recent study of more than 800,000 people led by Fabio Angeli, a cardiologist at University of Insubria in Varese, Italy, has shown that COVID-19 patients develop high blood pressure twice as often as others. More worrying is that the risk of cardiac diseases can also rise for patients who suffered only mild COVID symptoms.
"I saw a patient who now has a defibrillator, and she didn't even have a severe [COVID] illness," says Bernard Gersh, a cardiologist at Mayo Clinic, Rochester, Minnesota.
Wondering whether the cardiovascular damage during COVID was due to the virus directly attacking the blood vessels, the NYU team analyzed autopsied tissue from the coronary arteries and plaque of older people who had died from COVID-19. They found the virus was present in the arteries regardless of whether the fatty plaques were big or small.
"The original finding in this study is that the virus was convincingly found in the plaque in the coronary artery," says Juan Carlos Kaski, a cardiovascular specialist at St George's, University of London, who was not involved in the study.
The NYU team found that in the arteries, the virus predominantly colonized the white blood cells called macrophages. Macrophages are immune cells that are mobilized to fight off an infection, but these same cells also absorb excess fats—including cholesterol from blood. When microphages load too much fat, they change into foam cells, which can increase plaque formation.
To confirm that the virus was indeed infecting and growing in the cells of the blood vessels, scientists obtained arterial and plaque cells—including macrophages and foam cells—from healthy volunteers. Then they grew these cells in the lab in petri dishes and infected them with SARS-CoV-2.
Giannarelli found that although virus infected macrophages at a higher rate than other arterial cells, it did not replicate in them to form new infectious particles. But when the macrophages had become loaded with cholesterol and transformed into foam cells, the virus could grow, replicate, and survive longer.
"We found that the virus tended to persist longer in foam cells," says Giannarelli. That suggests that foam cells might act as a reservoir of SARS-CoV-2. Since more fatty buildup would mean a greater number of foam cells, plaque can increase the persistence of the virus or the severity of COVID-19.
Scientists found that when macrophages and foam cells were infected with SARS-CoV-2 they released a surge of small proteins known as cytokines, which signal the immune system to mount a response against a bacterial or viral infection. In arteries, however, cytokines boost inflammation and formation of even more plaque.
"We saw that there was a degree of inflammation [caused] by the virus that could aggravate atherosclerosis and cardiovascular events," says Giannarelli.
These findings also confirm previous reports that measuring inflammation in the blood vessel wall can diagnose the extent of long-term cardiovascular complications after COVID-19, says Antoniades.
"What this study has found is that plaque rupture can be accelerated and magnified by the presence of the virus," says Kaski.
Understanding heart diseases after COVID
While this new research clearly shows that SARS-CoV-2 can infect, grow, and persist in the macrophages of plaques and arterial cells, more studies are needed to fully understand the many ways COVID-19 can alter cardiac health.
"The NYU study identifies one potential mechanism, especially the viral reservoir, to explain the possible effects" says Gersh. "But It's not going to be the only mechanism."
This study only analyzed 27 samples from eight elderly deceased patients, all of whom already had coronary artery disease and were infected with the original strains of virus. So, the results of this study do not necessarily apply to younger people without coronary artery disease; or to new variants of the virus, which cause somewhat milder disease, says Angeli.
"We do not know if this will happen in people who have been vaccinated," says Kaski. "There are lots of unknowns."
It is also not clear whether and to what extent the high inflammatory reaction observed in the arteries of patients within six months after the infection, as shown in the new study, will last long-enough to trigger new plaque formation. "New studies are needed to show the time-course of the resolution of vascular inflammation after the infection," says Antoniades.
COVID patients should watch for any new incidence of shortness of breath with exertion, chest discomfort, usually with exertion, palpitations, loss of consciousness; and talk to their physician about possible heart disease.