A new aspect related to SARS-CoV-2 virus, related to its affect on the heart, that is potentially concerning from the clinical point of view has come up recently. The virus can affect the heart with conditions like myocarditis, the inflammation of the heart, arrhythmias which is the disruption of the heart rhythm and necrosis of heart cells that can mimic a heart attack. Significantly, these conditions are reported to have emerged in the mild or asymptomatic cases as well.
However, the exact way the disease affects the heart is yet to be ascertained. Two possibilities that emerges in this regard are— a direct attack of the virus in the cells of the heart and asserting its effect in an indirect way, that is, through an overreacting immune inflammation.
The SARS-CoV-2 virus uses the Angiotensin Converting Enzyme 2 (ACE2) protein as its entry point to a human cell, where the spike protein on the surface of the virus gets attached to the ACE2 receptor. The heart apparently is one of the organs of our body that has a high level of ACE2 in it. SARS-CoV-2 genomic RNA has been found to be very high in the lungs, nevertheless its presence beyond lungs is found in kidney, heart and liver in a substantial amount. In an autopsy study carried out in Germany, the viral copies were found in a substantial amount in 16 out of 22 patients who succumbed to the disease. In another autopsy study, carried out in in a series of 39 patients that succumbed to COVID-19, it was found that 31% of them had a significantly higher viral load, above 100 copies, in their heart.
Studies have shown the ability of the novel coronavirus to invade the cardiomyocytes, the cells that build up the heart muscle. Most of these studies are conducted on Induced Pluripotent Stem Cells (iPSCs)-derived cardiomyocytes. The iPSCs are lab derived stem cells that have the same properties as the embryonic stem cells. These stem cells can eventually differentiate into all cell types of the body except the cells in extra embryonic tissues like the placenta cells. The pluripotent stem cells have the hallmark of differentiating into other cell types. The heart muscle cells derived from the iPSCs are used in studies of variety of cardiac diseases nowadays. To look for SARS-CoV-2 infectivity in the heart muscle cells, the iPSC derived cardiac cells are used.
One such study has shown that the virus has a remarkable ability to infect the heart muscle cells that lead to the fragmentation of these cells. Also, some of these findings are verified in autopsy specimens of patients with COVID-19 severity. On the other hand, a different study showed that within 72 hours of infection in the heart muscle cells by the virus, the heart ceased to beat. This happened as the viral infection led to the apoptosis of the heart cells, the process of programmed cell death.
Besides directly infecting the heart cells, findings have revealed that immune response elicited by the virus infection can also lead to heart injury. The virus is found to be resent in the endothelial cells as well, which line up the blood vessels that carry blood to the heart. The immune response overreaction in the endothelial cell infection is found to be another dimension of the virus’s effect on the heart.
Recent MRI and ECG reports from COVID-19 patients have also raised concern about cardiac issues related to the disease. For example, in a cohort study of 100 patients that recovered from COVID-19, 78 were reported to have developed cardiac abnormalities. Interestingly, among these, asymptomatic patients are also included. Out of 18 asymptomatic patients, 12 developed cardiac issues. Again, 60 patients got myocardial inflammation which is a consistent phenomenon in myocarditis.
Another large cohort study consisting 1,216 patients from 69 countries across six continents also reported cardiac abnormalities. Out of these patients, 667—more than half—had abnormalities in the ECG reports.
These reports are now concerning medicos and it is speculated that there could be far more prevalence of heart issues than was thought, because asymptomatic patients can also develop these complication, which comprises at least 30-40% of the total infections worldwide. Moreover, asymptomatic individuals could also have lung abnormalities which are found in patients with symptoms.
There are reports of athletes who recovered from COVID-19 to have succumbed due to cardiac failure. A recent study done in the Ohio State University reported that several athletes that were asymptomatic along with those had mild symptoms were having myocarditis.
The recent findings of heart-related issues in COVID-19 has raised concerns about the limitations in the fundamental understanding of the disease and the virus as well. The findings highlight that cardiac issues related to COVID-19 may have affected more people than it was thought previously. With the reports suggesting that even the asymptomatic and those with mild symptoms could develop cardiac abnormalities, this concern grows further.
Alongside, there remains the pressing question—what leads to the pathogenesis in some of the patients? Is it due to an over reactive immune response of an individual, or is it due to the development of an auto immune condition or whether we need some other explanations is what remains to be clarified.