Viral Cardiomyopathy: What's The Link Between Myocarditis And Dilated Cardiomyopathy?

Myocarditis is an inflammation of the heart’s muscle wall. This inflammation can lead to the weakening of the heart muscle, reducing its ability to pump blood. It can also cause a disruption of the normal electrical signaling in the heart, which can result in severe arrhythmias (irregular heartbeats).

What causes myocarditis?

In most cases, the cause of myocarditis is a viral infection. The most common viruses that cause myocarditis (sometimes called cardiotropic viruses) include:

• Coxsackie (A, B; the Coxsackie B virus most often associated with myocarditis)
• Influenza (A, B) virus (flu)
• Varicella-Zoster virus (chickenpox)
• Herpes simplex virus (the virus that causes oral herpes characterized by cold sores, as well as genital or anal herpes)
• Adenoviruses (a group of viruses that can cause conditions like the common cold a pink eye)
• HIV (especially in Africa)
• Hepatitis C (especially in Asia)

Many of these viruses are very common — most adults will have been exposed to at least one of them at some point. Our bodies react to infections by activating the immune system. An immune response stops the virus from spreading within the heart and usually leads to the elimination of the virus from the organism. However, the immune response itself can cause damage to the heart. Whether someone develops myocarditis depends mostly on their immune system and some risk factors. Males are affected more than females and the majority of patients are either young adults between 20 and 30 years old or children. People who suffer from malnutrition and people who exercise regularly are also at higher risk.

Other causes of myocarditis are not as frequent, especially in the United States and Europe. They include:

• Bacterial infections
• Parasitic infections (like toxoplasmosis and Trypanosoma cruzi)
• Fungal infections
• Reactions to certain drugs or chemicals
• Exposure to radiation or radiotherapy (cancer treatment)
• Immune conditions that might be associated with autoimmunity (very rarely)

What are the symptoms of myocarditis?

Myocarditis has a range of symptoms that vary among individuals and also depend on what caused it. The problem is that these symptoms are not specific — they are either symptoms characteristic of a flu or of heart problems (like heart failure and cardiac arrest). Many people don’t develop any symptoms.

Symptoms can include:

• Flu-like symptoms (feeling tired, sore throat, headache, fever). It’s estimated that these symptoms strike more than 60 percent of people with myocarditis.
• Chest pain or shortness of breath.
• Palpitations (a feeling that your heart is pounding in your chest).
• Arrhythmia (irregular heartbeat; you might feel this as your heart beating too fast or erratically).

Blood tests might show a raised white cell count (in 24 percent of patients) and increased erythrocyte sedimentation rate (in 60 percent of patients).

What is dilated cardiomyopathy (DCM)?

Cardiomyopathy is a group of heart muscle diseases. Your heart has four chambers — two upper and two lower ones. The upper chambers or atria collect the blood, passing it to the lower, pumping, chambers called the ventricles. The ventricles have thick muscle walls that enable strong contractions needed to pump blood to the rest of the body at high pressure.

How can myocarditis lead to dilated cardiomyopathy?

About one-third of myocarditis patients will develop DCM. It’s helpful to think of myocarditis as a disease happening in three distinct stages:

• Phase 1: Initial heart injury (days 0 to 3)
• Phase 2: Autoimmune response caused by the initial injury (days 4 to 14)
• Phase 3: Dilated cardiomyopathy

The link between myocarditis and DCM lies in the inflammatory response. Whenever there is a pathogen in our bodies (like viruses and bacteria), our immune system is activated. The immune response is mediated by various immune cells that communicate with each other using molecules called cytokines.

The first line of response is an innate immune response and in the case of myocarditis, it’s mediated by cells called natural killers or NK cells. Their name says it all — their goal is to kill the virus and stop it from spreading in the heart. The virus itself can cause the death of heart cells or necrosis. The effect of NK cells is beneficial, and the cytokines they produce can be both good and bad. However, they are accompanied by NK-like cells that produce perforin molecules. These molecules cause damage to heart cells, forming little pores on the their membranes that may lead to cell death. Next in line are a type of white blood cells called T-lymphocytes that also attack the virus. If these responses don’t lead to inactivation, myocarditis progresses to Phase 2.

In phase 2, the T-lymphocytes (T cells) may recognize the heart cells as their targets instead of only going after the virus. Because the body is attacking itself, this is called an autoimmune response. It damages the heart cells. The products of this damage then additionally activate T cells to degrade the heart cells. The exact mechanism that leads from this phase to DCM is still being elucidated, but the ongoing damage to the heart muscle eventually leads to dilatation. Research on this topic is important, because it might show us how to prevent heart damage and avoid DCM.

How is myocarditis treated?

Treatment for myocarditis is not always necessary. In cases where it is, the treatment depends on the individual case: the cause of myocarditis, clinical manifestations and the phase of the disease.

Some treatment options can include:

• Medications used to modify the immune response (immunomodulators).
• Medications used for the non-heart symptoms (such as flu-like symptoms). These can include drugs to lower the fever (antipyretics) and over-the-counter analgesics used to treat the pain.
• Medications used for the heart-related symptoms. The medications that will be used depend on the symptoms, but they are most commonly prescribed when heart failure happens as a complication of myocarditis or DCM. Medications for heart failure include diuretics (water tablets), ACE inhibitors (medications that reduce the workload on the heart) and medications to lower your blood pressure. Sometimes the medications used to prevent the blood from clotting- anticoagulants are also used.