Early in the pandemic, epidemiologists made a striking observation. Compared to the general population, people with cardiovascular disease (CVD) were more than twice as likely to contract severe forms of COVID-19. In the last six months, death rates from COVID-19 have dropped significantly, but CVD remains a major predictor of poor outcome. What have we learned about heart disease and COVID-19 in that time?
Pre-existing heart conditions and poor metabolic health increase risk of severe COVID-19
As I described in a blog post back in April, some health conditions, like diabetes, increase risk of severe COVID-19 by suppressing the immune system; others, like asthma, increase risk by weakening the lungs. However, in the early months of the pandemic it was not entirely clear how CVD increased the risk of severe COVID-19. We now have two explanations.
The first is that pre-existing heart conditions, such as damaged heart muscle or blocked heart arteries, weaken the body’s ability to survive the stress of the illness. A person with a vulnerable heart is more likely to succumb to the effects of fever, low oxygen levels, unstable blood pressures, and blood clotting disorders — all possible consequences of COVID-19 — than someone previously healthy.
A second explanation relates to poor underlying metabolic health, which is more common in those with heart disease. Poor metabolic health refers to diseases such as type 2 diabetes or prediabetes and obesity, which themselves cause inflammation and risk of blood clots, compounding the effects of COVID-19 and increasing the likelihood of devastating complications of COVID-19.
How does COVID-19 cause heart damage?
The SARS-CoV-2 virus can damage the heart in several ways. For example, the virus may directly invade or inflame the heart muscle, and it may indirectly harm the heart by disrupting the balance between oxygen supply and demand. Heart injury, which may be measured by elevated levels of the enzyme troponin in the bloodstream, has been detected in about one-quarter of patients hospitalized with severe COVID-19 illness. Of these patients, about one-third have pre-existing CVD.
Inflammation of the heart muscle
The majority of people with COVID-19 will have mild symptoms and recover fully. However, about 20% will develop pneumonia, and about 5% will develop severe disease. In the severe form of COVID-19, the body’s immune system overreacts to the infection, releasing inflammatory molecules called cytokines into the bloodstream. This so-called “cytokine storm” can damage multiple organs, including the heart.
Inflammation of the heart muscle, called myocarditis, typically occurs only in patients with advanced COVID-19 disease. Myocarditis can result from direct heart invasion by the virus itself, or more commonly by inflammation caused by cytokine storm. When this occurs, the heart may become enlarged and weakened, leading to low blood pressure and fluid in the lungs. While this severe form of myocarditis is rare, recent studies have suggested that a milder form of heart muscle inflammation may be much more common than previously recognized. A recent study showed that asymptomatic heart inflammation was seen on magnetic resonance imaging in up to three-quarters of patients who had recovered from severe COVID-19.
Increased oxygen demand and decreased oxygen supply lead to heart damage
Fever and infection cause the heart rate to speed up, increasing the work of the heart in COVID-19 patients who develop pneumonia. Blood pressure may drop or spike, causing further stress on the heart, and the resulting increase in oxygen demand can lead to heart damage, especially if the heart arteries or muscle were unhealthy to begin with.
Heart damage is most often caused by heart attacks, which result from the formation of a blood clot in a vulnerable heart artery, blocking delivery of oxygen to the heart muscle. COVID-19-related inflammation raises the risk of this type of heart attack by activating the body’s clotting system and disrupting the blood vessel lining. When inflamed, this lining loses its ability to resist clot formation. These blood clots in the large and small arteries of the heart cut off its supply of oxygen. The increased clotting tendency can also lead to blood clots in the lungs, which can cause a drop in blood oxygen levels. Severe pneumonia drops blood oxygen further. When the oxygen demand exceeds the supply, the heart muscle is damaged.
Finding a silver lining and lowering risk through healthy lifestyle
People with CVD who adopt healthy behaviors can strengthen their defenses against COVID-19 while also reducing the long-term risk from cardiovascular disease itself. This means plenty of physical activity and following a healthy diet like the Mediterranean diet. Cook at home when you can, and walk outdoors with friends if your gym is temporarily closed. Purchase an inexpensive and easy-to-use monitor to measure your blood pressure at home. And continue to follow the CDC’s safety guidelines to wear masks, physically distance, and avoid large gatherings.