Around 1.500 people die every year from influenza infection in Denmark, numbers show from the Danish Health Authority. When influenza virus runs in your system, the chances of arterial thrombosis increases. Especially patients already suffering from heart disease, are at large risk of experiencing deterioration of their condition.

At Herlev and Gentofte Hospital, medical doctor and PhD student Kristoffer Grundtvig Skaarup is currently canvassing all patients hospitalized with influenza infection.

“I knock on the door at the wards with patients hospitalized with influenza infection, and in my experience, most people are very positive about participating in my study."

The study investigates the damage which a severe influenza infection may cause the heart.

Testing during and post hospitalization

Patients participating in this study get an ultrasound of their heart and lungs. Kristoffer Grundtvig Skaarup also takes blood samples which he examines for troponin and BNP levels. Troponin is a marker for potential muscle damage of the heart, and BNP is a powerful plasma marker released in the body when the heart is strained. High levels of BNP may be a sign of heart failure.

Kristoffer Grundtvig Skaarup also analyses a number of inflammation markers in the blood sample to see whether there is a correlation between the severity of the infection and possible cardiac effects.

“I invite every patient who survives an influenza infection to the exact same examination two months after they have been discharged from the hospital. At this second examination, I check whether the cardiac parameters are the same or whether they have improved. Comparing data during and post hospitalization may indicate whether the virus infection have affected the heart,” explains Kristoffer Grundtvig Skaarup.

The heart loses pumping power 

American population surveys conducted since the 1930s show an increase in heart disease when patients are infected by influenza virus. Accounts of individual patients’ courses of influenza infection in American studies suggest that the heart pump loses power during an influenza infection. This increases the risk of cardiac thrombosis. However, it is still uncertain what precisely happens with the heart during an influenza infection and this uncertainty is what Kristoffer Grundtvig Skaarup grapples with in his research. The study also focuses attention on whether influenza infection affects the heart directly or whether the sinner sooner is inflammation in general.

“During the pandemic, I studied patients with COVID-19 using the same methods as in my influenza study. In a few years from now, I may be able to answer whether all kinds of infections affect the heart or if it is specifically related to the influenza infection,” says Kristoffer Grundtvig Skaarup.

He explains that a scientific study on mice has shown scar tissue formation on the heart specifically caused by influenza infection. In other words, this animal study has indicated that an influenza infection in itself strains the heart.

May alter the treatment of influenza infection

Kristoffer Grundtvig Skaarup’s study may shed light on whether we should modify the clinical practice of patients with influenza infection so that severe instances of influenza infections with cardiac effects may be prevented more efficiently than it is today.

“If the results of my PhD study show a continued effect on the heart, it may be useful to examine the patients’ heart function at hospitalization. It would enable us to identify patients at high risk of developing a severe course with cardiac complications as a consequence,” states Kristoffer Grundtvig Skaarup.

According to Kristoffer Grundtvig Skaarup, the high number of people receiving an influenza vaccine in Denmark has had a significant impact on the number of patients experiencing a severe course. During the influenza season in 2020 and 2021, around 75 % of the Danish population above the age of 65 was vaccinated against influenza. 27 % of the collective Danish population has received the vaccine during the influenza season this winter, numbers show from SSI. According to Kristoffer Grundtvig Skaarup, the relatively high support for the vaccine programme may inspire other countries where support for vaccine programmes is typically lower.

“Influenza infection may prove be the last straw for people with a fragile health condition – particularly for patients with cardiovascular disease. I look forward to providing the exact answer of why that is”, concludes Kristoffer Grundtvig Skaarup.