PATHOGENESIS

Now I am going to describe to you, what´ s actually going on in the body during the myocarditis. The heart wall is composed of three layers – the endocardium (the inner heart layer membrane), the myocardium (the heart muscle) and the epicardium (the external heart membrane). The heart is placed in a sacculated case called the pericardium (picture 1). During myocarditis, the myocardium (heart muscle) is affected.

Picture 1: Heart wall (author: BruceBlaus)

The most common causes of myocarditis are different kinds of viruses and each of them damages the heart in different way. Less often myocarditis can be cause by bacterium, fungi, parasites, toxins, drugs or myocarditis can be a complication of another, mostly autoimmune disease, see this page). During viral myocarditis, the heart damage is developing during several successive phases and the patient can pass through up to three phases of the disease. The first phase of myocarditis is associated with viremia, when cells of the heart muscle are damaged by the virus itself. The virus affects the heart muscle cells or the cells of vessels nearby. The virus uses them for its replication and in the process, damages and destroys them. The second phase of the disease comes after several days (ca 4 days) from viremia. The immune system detects the virus and is stimulated by its presence in the heart muscle. It could sometimes induce a massive immune inflammatory response, when the immune response includes cell (white blood cells) and antibody-mediated immunity. There are several kinds of cells connected to the immune response – macrophages, activating the cytokines release (e.g. interleukins –mediating the communication between cells of immune system, and chemokines – controlling the transport of cells of immune system to the place of inflammation). Further, there are NK-cells, destroying cells affected by the virus. There are also T and B-cells, participating in the antibodies production and the elimination of heart muscle cells which have been attacked by the virus. The heart muscle is also damaged by the immune reaction, but is the price that must be paid to stop the replication of virus infection. In some cases, the immune system can “cause” the most part of the damage in the heart muscle.

 

Picture 2: Scheme of myocarditis (authors of the pictures: Thomas Splettstoesser; Wapcaplet; KGH)

  After the elimination of the virus or after the demarcation of heart muscle cells affected by virus, the immune system must “calm down” as soon as possible. There are several mechanisms participating in this situation. If the immune system did not “calm down,” it could move on to the state of chronic stimulation or autoimmune response (“self-destruction”), and could continue damaging the heart. It causes the formation of fibrosis (scars) in the heart muscle, with continuing chronic inflammation. It causes heart structural changes and a worsening of the myocardium function. It can lead to the development of other (systematic – autoimmune inflammatory) disorders. The first 90 days from viremia are the most important in the processes mentioned above and also in the process of healing the affected parts of the myocardium and in the process of inhibition of immune response. It is also the time, when myocarditis could develop to the chronic form. The immoderate immune response is the reason, why a part of the treatment is focused on the immune regulation and the suppression of the immoderate immune response. The interaction between the immune system and the virus and the activity of the virus in the heart sometimes affects the heart´s function, which could change during the acute inflammation. The changes in function are mostly observed at the left ventricle (Picture 3). The changes manifest with different disorders of heart rhythm (arrhythmias) and in some cases even with symptoms of heart failure. The pericardial effusion (accumulation of fluid between the membranes of pericardium) is observed in around one half of cases. The accumulated fluid could “press” on the heart, what makes primarily the filling of the heart with blood more difficult. The blood supply to the right atrium and right ventricle is decreased and then also adequate pumping of blood to the body. Sometimes the heart tamponade can be observed – it is cause by enormous accumulation of fluid and a noticeable worsening of the heart function. The effusion is caused by inflammation of the pericardium (pericarditis), because of that; myocarditis accompanied with the inflammation of pericardium is called myopericarditis. Vice versa, if the inflammation of the heart muscle (mostly weak) is a complication by pericarditis, we call this disease perimyocarditis. The course of myocarditis can be influenced even by genetic predisposition and gender. It was found, that myocarditis is more frequently observed at males than at females, probably because of testosterone. Sometimes, the virus is not completely destroyed by the immune system and then it remains encased in the heart muscle. Or the virus is completely destroyed, but a weak inflammation persists in the myocardium. In some cases, both the virus and the weak inflammation of the myocardium can persist in the heart. Myocarditis can progress to a chronic form, when the other attack of the disease is possible.

Picture 3: Human heart (author: Wapcaplet, Yaddah, Wnauta)

THE COURSE AND COMPLICATIONS OF MYOCARDITIS (CLINICAL PICTURE OF MYOCARDITIS)

The course of myocarditis is different for each patient. Myocarditis can even pass without early diagnosis on the part of the patient and it can seem to be a “severe” flu to the patients and doctors. Diagnosis can unfortunately be made several weeks after the basic disease; when it progress to chronic phases, alternatively long-term complications. In some cases, diagnosis of myocarditis is not made at all, when the course of the disease is light. Sometimes, myocarditis can have very dramatic course, when the heart muscle inflammation causes changes in the heart function. It sometimes leads to severe disorders of heart rhythm and symptoms of heart failure. If the diagnosis of myocarditis has been provided  to you orone of your relatives, it is essential and indispensable to strictly followe the recommendation of medical experts. Maintain a strict resting regime and absolute mental peace. For half of the patients, myocarditis is healed without any severe consequences and another attack does not happen again. In some cases, the inflammation of the myocardium progress to the chronic form, often accompanied with limitation of the heart function (see this page). Chronic myocarditis is sometimes called inflammatory cardiomyopathy. Inflammatory cardiomyopathy has the same course as dilated cardiomyopathy, when dilatation – widening of  the heart ventricles is observed. Because of the persistence of the inflammation, fibrosis and damage of the heart muscle, structural changes of heart wall shows up and there are also changes in the reduction of heart contractility and suppleness of the heart wall. It leads to heart function disorder (mostly of the left ventricle). But it does not lead to additional necrosis of heart muscle cells. However, of course, there is a possibility of another attack of acute myocarditis.

Autors of the opening picture: BruceBlaus