Diagram of myocarditis inflammation of the heart

Myocarditis is inflammation of the myocardium, most often caused by infection of the myocardium with a virus. It is also a recognized side effect of mRNA vaccines (Comirnaty from Pfizer-BioNTech and Spikevax from Moderna. What are the symptoms? The causes? The diagnosis? The treatments?

[Mis à jour le jeudi 14 octobre à 16h11] The myocardite is a inflammation of the myocardium, most often caused by infection of the myocardium with a virus. Viral infections, such as Covid, are a common cause of myocarditis, which can lead to hospitalization, heart failure or even sudden death. The Medicines Agency (ANSM) has been informed of the suspension of vaccination with Spikevax (Moderna) in Denmark and Sweden, as well as in Finland, in those under 18 or 30 years old depending on the country, after the occurrence of cases of myocarditis. As a reminder, cases of myocarditis and pericarditis have already been reported in France and Europe after the use of an mRNA vaccine (Comirnaty of Pfizer BioNTech and Spikevax of Modern), most often after the 2nd dose and in young men. The European Medicines Agency (EMA) then concluded that these effects can occur very rarely after vaccination and are now included in the package inserts of the vaccines. On the other hand, they do not call into question the benefit / risk ratio of vaccines against Covid-19. The available data suggest that the course of myocarditis after vaccination is similar to the typical course of these conditions, usually improving with rest or treatment. What are the symptoms, the treatments and the chances of recovery from myocarditis ? Which warning signs after vaccination ? Infos.

The myocardite is inflammation of the myocardium, most often caused by infection of the myocardium with a virus. The myocardium forms the main mass of the heart. It is a striated, thick, hollow muscle capable of rhythmically and involuntarily contracting. By contracting, the myocardium allows blood to circulate in the blood vessels and nourish the various organs of the body. Inflammation of the myocardium caused by a virus destroys the cells that make up the myocardium and thus decreases its capacity for contraction and its capacity to provide blood supply. Gradually, the heart is therefore no longer able to pump blood. The inflammation can spread throughout the heart muscle or be limited to one or a few areas. In this case, the symptoms will be mild and the rapid and appropriate management may allow a cure. In contrast, extensive inflammation throughout the heart can lead to severe heart failure, severe heart rhythm disturbances and sometimes sudden death.

Diagram of a healthy heart and myocarditis © Viktoriya Kabanova – 123RF

In France, since the start of monitoring, 238 severe cases of myocarditis, inflammation of the myocardium (the muscle that allows the heart to contract), were observed, including 33 in people under 19, according to data from theANSM in mid-September. They mainly occurred within 14 days of vaccination, more often after the second dose and in young men. The data analyzed in France and internationally confirm theexistence of a causal association between the Comirnaty vaccine and myocarditis. Myocarditis is now part of the side effects listed in the SPC for the Comirnaty vaccine. French data indicate that myocarditis is, for the great majority, resolving and not severe.

79 serious cases of myocarditis were reported on September 24 by the ANSM, including 9 in children under 19. The signal is now officially recognized in Europe and included in the SPC for mRNA vaccines including Moderna since September. Vaccination with Moderna was suspended at Denmark, Sweden and Finland, in those under 18 or 30 depending on the country, after the occurrence of cases of myocarditis.

After Pfizer: 33 cases of myocarditis have been reported in children under 19 years of age. Since June 15, 2021, vaccination in the youngest subjects (12-18 years old) is possible with the Comirnaty vaccine. As of September 16, 2021, more than 4.5 million of them received at least one injection. In total, 591 cases including 206 serious have been reported after vaccination. No signal was identified in the youngest subjects. “Based on the data, the adverse reaction profile in 12-18 year olds is similar to that of adults.”

After Moderna: 9 of myocarditis have been reported in people under 19 years of age. Since July 28, 2021, vaccination in the youngest subjects (12-18 years) is possible with the Spikevax vaccine. x. As of September 16, 2021, more than 285,000 of them have received at least one injection. In total, 65 cases including 18 serious have been reported after vaccination. the time to onset after the completion of the Moderna injection was less than 72 hours for 51 cases (78.5%). No signal was identified in the youngest subjects. In view of the data, the profile of adverse reactions in patients aged 12-18 years is similar to that of adult patients, estimates the ANSM.

Viral infections, like Covid, are a common cause of myocarditis, an inflammation of the heart muscle (myocardium) that can lead to hospitalization, heart failure, and sudden death. Posted on March 27, 2020 in Journal of American Medicine Association (JAMA), a study had shown that severe acute respiratory syndrome, one of the symptoms of a novel coronavirus infection, appeared to affect the myocardium and cause myocarditis. The authors of the study also recalled that viruses of the coronavirus family are able to affect the cardiovascular system. In addition, French, Italian, British and Belgian doctors had reported cases of inflammatory syndromes in children aged 10 to 15 years. In France, the alert was given by the Necker Hospital which reported 25 cases of children admitted to intensive care and who presented inflammatory syndromes of the heart, lungs or digestive system “frequently associating a circulatory failure with elements in favor of a myocardite“, details Dr Damien Bonnet, coordinator of the M3C Necker network (reference center for complex congenital heart diseases) in Paris in an article by Free noon. These symptoms suggest Kawasaki disease, an essentially infantile pathology, rare but which nevertheless represents the first cause of heart disease acquired in childhood in industrialized countries. In the acute phase, we can observe myocarditis and / or pericarditis, an inflammation of the membrane covering the heart. Left untreated, these inflammations can increase the risk of heart failure, cardiac arrhythmias and heart attacks.

Inflammation of the myocardium usually occurs in three phases:

  • Virus infection phase, which can last a few days.
  • Autoimmune phase, which can range from a few weeks to a few months.
  • Phase in which the first signs of heart failure appear. Because the cells in its walls are inflamed or destroyed, the heart is no longer able to pump blood.

In the vast majority of cases, myocarditis is caused by a viral infection that attacks heart muscle cells. It is generally viruses of the Coxsackievirus or Adenovirus family that are responsible for myocarditis. It can also be associated with another bacterial pathology like Lyme disease, Bartonellosis or diphtheria. In rare cases, it can result from toxic reaction following the taking of a drug, substances such as alcohol, cocaine, lead, arsenic or even following a snake or scorpion bite. In this case, myocarditis is called “hypersensitivity myocarditisIn very rare cases, myocarditis can occur after certain chemotherapy, radiation therapy or electrocution.

The ANSM recommends that people receiving Covid vaccines contact a doctor immediately if symptoms suggestive of myocarditis occur. These symptoms include a shortness of breath, from palpitations (strong, sometimes irregular heartbeat), and chest pain.

What symptoms after the Covid vaccination?

The ANSM recommends that anyone vaccinated against Covid presenting symptoms such as shortness of breath (dyspnea), chest pain, palpitations (strong, heartbeat) or irregular heartbeat to seek medical attention promptly.

First symptoms of myocarditis

The clinical signs of myocarditis vary in nature and severity, and are not necessarily specific to this pathology. In the less severe forms, the person does not feel any symptoms. On the other hand, certain inflammations of the myocardium can be characterized by flu-like symptoms :

  • fever
  • headache
  • stiffness and pain in the joints
  • great fatigue
  • diarrhea
  • sore throat…

Symptoms of severe myocarditis

In the most severe cases, symptoms of cardiac origin may occur:

  • chest pain and chest pain (with palpitations and a feeling of constant tightness)
  • swollen legs (edema)
  • discomfort and difficulty in breathing (dyspnea)
  • heart failure and shortness of breath even at rest
  • heart rhythm disturbances (rapid or irregular heartbeats, etc.)

Symptoms of fulminant myocarditis

In the case of a so-called fulminant myocarditis, the inflammation quickly progresses to serious heart failure (respiratory distress, even cardiac arrest) which requires urgent care and sometimes the implementation of circulatory assistance or heart transplant.

The diagnosis of myocarditis is first based on questioning (presence of symptoms listed above, medical or family history …) and a complete physical examination, performed by a doctor. If the latter suspects myocarditis, he can prescribe to his patient carrying out more in-depth examinations to detect inflammatory signals and identify the presence of a virus in the blood such as an electrocardiogram (ECG), blood samples (C-reactive protein level, sedimentation rate or white blood cells), an echocardiogram, cardiac MRI, coronary angiography (to eliminate the track of a possible myocardial infarction due to the obstruction of a coronary artery) or even a myocardial biopsy.

Treatment of viral myocarditis is based on symptom management, with medication (such as antivirals), combined with close monitoring of the patient and resting. Treatment for heart failure includes diuretics and nitrates to relieve symptoms. At the same time, it is recommended to avoid significant efforts and to restrict the consumption of alcohol and tobacco.

Healing and recovery of cardiac functions usually occurs after several months. There is a risk of long-term sequelae, the prognosis of which can only be given on a case-by-case basis. In the most severe cases of heart failure, a transplant may be necessary.

Sources :

  • Etude Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data — United States, March 2020–January 2021, CDC, 31 août 2021
  • Feedback on the PRAC of July 2021. ANSM.
  • Montreal Heart Institute
  • The practitioner’s journal, Orphanet.
  • Study “Potential Effects of coronaviruses of the cardiovascular system”, published in Jama, Cardiology on March 27, 2020.
  • Update on COVID-19 vaccine surveillance – ANSM

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