What is ACM?  (may also be referred to as ARVD, ARVD/C and ARVC)

ACM stands for arrhythmogenic cardiomyopathy. Arrhythmogenic means “causing an arrhythmia” or an irregular heartbeat. Cardiomyopathy is a general term for chronic disease of the heart muscle.

Arrhythmogenic cardiomyopathy is an inherited, rare form of heart disease that causes the muscular tissue in the right ventricle of the heart, and also sometimes in the left ventricle, to be progressively replaced by fatty, fibrous tissue which can result in irregular heart rhythms.

ACM is caused by abnormalities in heart cells that connect to each other through cell to cell contacts known as the intercalated disc, with abnormalities in a portion of the intercalated disc called the desmosome. Typically, this abnormality causes a disruption of the normal structure and function of specific desmosomal proteins, leading to a “pulling apart” of these cell to cell contacts. Over time, this “pulling apart” of the heart cells starts a process of scar and fat replacement. The loss of heart muscle cells results in fewer muscle cells than normal, and the wall of the ventricles may be thin. Often, the ventricles may become enlarged and don’t squeeze as strongly as they should. Most patients with ACM have both structural and electrical abnormalities.

This heart disease affects men, women, and children of all races. While ACM is most commonly diagnosed in adults in their 30s and 40s, both children in their teens and 20s and older people have been diagnosed with this disease. It’s extremely rare to find signs or symptoms of ACM before 12 years of age. It’s also not common to first develop signs or symptoms of ACM after the age of 60. ACM accounts for as many as 20% of sudden cardiac deaths in patients under 35 years of age.

Approximately 20% to 30% of ACM patients have a family history of ACM or of sudden death.

ACM is estimated to affect about 1 in 5,000 people. It may affect far more people due to its somewhat hidden nature and the difficulty in recognizing this heart disease; however, big advancements have been made in recognizing and diagnosing ACM earlier in patients. It’s possible to have this disease without knowing it. Although ACM is a genetic, heritable disease, genetics may not be the only factor. Other factors such as exposure to certain viruses and/or an athletic lifestyle can determine whether a person is clinically affected with ACM. This is an area of active research.

Four stages of ACM have been described. The first stage is the “concealed phase” during which time patients don’t exhibit symptoms of ACM. It may not be possible to diagnose ACM during this early “concealed phase.” The second stage is characterized by ventricular arrhythmias, or irregular heartbeats. Patients in this phase often experience palpitations, ventricular tachycardia, syncope or fainting, or sudden cardiac death. In some patients, ventricular arrhythmia s may develop before observable evidence of structural heart disease is present. Diagnosing ACM in this situation is particularly challenging. However, in the third stage, the electrical and structural abnormalities of ACM can be assessed by the ECG, echocardiogram, and cardiac MRI with emphasis on the structure and function of the right ventricle. This is followed by the final phase in which the degenerative process results in both left and right ventricle involvement. Patients may experience palpitations, light headedness, fainting, or sudden death.

The terminology for ACM has changed throughout the years. In 1982, Dr. Guy Fontaine from Paris, France, named the disease ARVD since the pathology of the heart’s right ventricle suggested a defect in development. The “D” in ARVD was for the word “dysplasia”, which is defined as an abnormal development of tissues, organs or cells. Presently, the term ARVD is now seldom used since it refers to an embryonic developmental abnormality and this is now known to be incorrect. It is now clear that the structural defects in ACM are not congenital, or present at birth, as previously thought, but actually develop progressively throughout childhood and early adulthood.

Then Dr. Fontaine indicated that many of these patients developed inflammation on the right side of the heart, possibly due to a viral myocarditis. Thus, these patients were then termed as having a cardiomyopathy superimposed on the congenital defect termed ARVC/D.

This sequence wasn’t accepted by Dr. Thiene and Dr. Basso, pathologists from Padua, Italy. In 1996, they convinced others that this disease should be called a cardiomyopathy. Therefore, the abbreviation was ARVC.

At about the same time, it was discovered that the disease commonly affects a portion of the left ventricle, also. Thus, the term ARVC for a right sided only disease was changed to arrhythmogenic cardiomyopathy, or ACM.  However, since the term ARVC/D is well recognized as the disease entity, ARVC/D is commonly used.

Clinical genetic testing for ACM is available in the United States and should be performed in certified diagnostic laboratories (see list of labs under the “Genetic Factors” page). It usually requires submitting a small blood sample.

ACM may be present in otherwise young and healthy people. Unfortunately, it has taken the lives of some young people before they could be diagnosed and treated to help protect them. However, there is good news: With appropriate treatment, many patients with ACM can live normal lives.