Even the mild form of COVID-19 tends to cause an imbalance in the cardiovascular system and requires attention

People who have had COVID-19, even mild cases, tend to have cardiovascular imbalances in the short and medium term and need to undergo rehabilitation. This was the finding of a study of 130 volunteers conducted at the Federal University of São Carlos (UFSCar) in Brazil, with the support of FAPESP.

According to data published in the journal Scientific Reports, participants tested up to six weeks after infection showed a dramatic decrease in heart rate variability (HRV), i.e. the time variation between each heartbeat. Those tested between two and six months or between seven and 12 months after infection showed gradual improvements, but without reaching the level of the control group (consisting of people not infected with SARS-CoV-2).

HRV is considered a good indicator of health because it signals the heart’s ability to adapt to physiological demands. Thus, the lower the index, the worse the heart rate adjustments and adaptation to environmental stressors (situations of flight, distress and fear) and physiological stressors (systemic inflammation, characteristic of COVID-19, for example).

“This study reinforces the need for rehabilitation programs even for people who have had mild COVID-19 and haven’t been hospitalized. The participants were on average 40 years old and some had risk factors for cardiovascular disease such as high cholesterol, smoking, diabetes, obesity and high blood pressure. Apparently, COVID-19 increased this cardiovascular imbalance and, consequently, the risk of disease,” says Audrey Borghi Silva, coordinator of the Cardiopulmonary Physiotherapy Laboratory (LACAP) at the Federal University of São Carlos (UFSCar).

The impact of COVID-19 on cardiac autonomic control has been demonstrated in several studies. “Our research helps to confirm this impact and shows that it can also occur in young or middle-aged people who have had mild COVID-19 and haven’t had to be hospitalized,” highlights Aldair Darlan Santos-de-Araújo, a researcher at UFSCar and first author of the article.

Mismatch

In addition to lower heart rate variability, the researchers observed a predominance of the sympathetic nervous system over the parasympathetic nervous system in volunteers infected with SARS-CoV-2. These are the two sides of the autonomic nervous system, which controls the body’s involuntary functions such as blood pressure and body temperature. While, among other functions, the parasympathetic system slows down the heart when necessary, it is the sympathetic system’s job to increase the heart rate in situations of danger and fear, for example.

“Proper cardiovascular function requires a balance between these two mechanisms, and what we observed is that the negative impact of COVID-19 infection in these individuals caused an imbalance in the autonomic nervous system,” says Santos-de-Araújo. “The observed pattern – of reduced heart rate variability and a predominance of the sympathetic nervous system [or reduced parasympathetic activity] – indicates not only reduced global autonomic modulation but also suggests a greater likelihood of adverse cardiovascular outcomes.”

In addition, the researchers point out that the results suggest a possible transitional phase in cardiac autonomic recovery since the individuals studied in the group with the longest recovery time since diagnosis showed better behavior of this sympathetic-parasympathetic balance.

“This transient effect can be seen more clearly in the group assessed earlier [up to six weeks after infection], which had worse heart rate variability, which improved progressively over time but did not reach the levels seen in the group of uninfected participants,” explains Santos-de-Araújo.

The study also showed that dyspnea (shortness of breath) was the most common symptom among individuals with worse cardiac autonomic modulation, but it was not the only one. “In the group of individuals monitored in the period closest to infection, we observed a higher percentage of cough [47%], fatigue [50%], headache [56%], ageusia [loss of taste, 53%], anxiety [62%], runny nose [50%], and a higher prevalence of unvaccinated individuals [44%],” says Santos-de-Araújo. 

About FAPESP

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the state of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration.