Cardiomyopathies

Cardiomyopathy refers to disease of the heart muscle.

The term cardiomyopathy can be very confusing in clinical practice. In very simple terms it means disease of the heart muscle. However, many conditions can affect heart muscle from common cardiovascular diseases (e.g. hypertension, coronary artery disease) to rare genetic conditions.

Consequently, a number of definitions have been proposed over the years to help differentiate these many causes and their pathophysiological mechanisms.

Definition

In 2008, the European Society of Cardiology (ESC) proposed a new definition for cardiomyopathy as

‘A myocardial disorder in which the heart muscle is structurally and functionally abnormal, in the absence of coronary artery disease, hypertension, valvular disease and congenital heart disease sufficient to cause the observed myocardial abnormality’

Thus, cardiomyopathy is a disease of heart muscle that cannot otherwise be explained by common cardiovascular diseases or congenital heart disease.

Classification

The cardiomyopathies are classified based on morphological and functional phenotypes. This means what they look like structurally (e.g. dilated, thickened) and how they behave physiologically (e.g. impaired contraction, abnormal filling).

• Hypertrophic cardiomyopathy (HCM)
• Dilated cardiomyopathy (DCM)
• Restrictive cardiomyopathy (RCM)
• Arrhythmogenic cardiomyopathy (ACM)
• Unclassified cardiomyopathies

Each phenotype listed above is then further divided into familial and non-familial causes.

• Familial (inherited): cardiomyopathy phenotype that develops due to a genetic variant (mutation)
• Non-familial (acquired): cardiomyopathy phenotype that develops due to a clear acquired cause (e.g. sarcoidosis, amyloid)

These cardiomyopathy phenotypes may be limited to the heart or form part of a systemic disease process (e.g. sarcoidosis).

There are many causes of cardiomyopathy that can be genetic, acquired, or mixed.

Each cardiomyopathy phenotype has a large list of both inherited and acquired causes. Some conditions may present as more than one cardiomyopathy phenotype. For example, amyloidosis of the heart can cause both hypertrophic or restrictive cardiomyopathy.

Acquired causes

This refers to a large number of causes that may include

• Drugs (e.g. chemotherapy, hydroxychloroquine)
• Infections (e.g. Coxsackie virus, Brucellosis, Lyme disease)
• Systemic diseases (e.g. amyloidosis, sarcoidosis)
• Radiation
• Malignancy
• Alcohol
• Many others

Inherited causes

This refers to a genetic cause when a patient inherits an abnormal copy of a gene known as a variant or mutation. Alternatively, they may develop a de novo variant (a new mutation not inherited from the paternal or maternal line).

The abnormal gene often encodes important structural cardiac proteins such as sarcomere proteins or intercalated disc proteins. In these cases, cardiomyopathy often presents as the lone abnormality. These commonly have an autosomal dominant inheritance. Examples include beta-myosin heavy chain, troponin, or desmoplakin mutations.

In other cases, the abnormal gene may cause a widespread genetic disease involving multiple organs of which cardiomyopathy is one component of the disease spectrum. Examples include Myotonic dystrophy, Fabry disease, or Glycogen storage disease.

The diagnosis of cardiomyopathy is usually determined by the echocardiography findings.

Formal echocardiography (ECHO) is used to make a diagnosis of cardiomyopathy. An echo can help define the morphological and functional features of each cardiomyopathy phenotype. An ECHO also helps to exclude other causes of heart muscle disease such as valvular disease. In certain cases, a cardiac MRI or CT can provide more detailed information to better classify suspected cardiomyopathy.

HCM is defined as increased ventricular wall thickness or mass not caused by pathologic loading conditions.

In HCM, there is increased ventricular mass in the absence of ‘loading’ conditions such as hypertension or valvular disease. In the adult population, the prevalence of HCM is estimated at 1 in 500.

Aetiology & pathophysiology

HCM is commonly due to an abnormal gene that encodes one of the sarcomere proteins needed for myocardial contraction. The most common mutation is in the gene that encodes the beta myosin heavy chain and the inheritance is usually autosomal dominant.

Hypertrophy (i.e. thickening) may occur in any of the left ventricular segments but commonly involves the interventricular septum and is usually asymmetrical. Abnormal hypertrophy can have numerous pathological consequences:

• Left ventricular outflow obstruction: hypertrophy narrows the outflow tract from the ventricle to the aorta. In addition, it causes movement of the mitral valve anteriorly during systole (known as systolic anterior motion of the mitral valve). This collectively causes obstruction to blood flow during systole.
• Mitral regurgitation: abnormal movement of the mitral valve distorts its physiological function leading to blood regurgitating during systole.
• Diastolic dysfunction: fibrosis and hypertrophy limit the compliance of the ventricle leading to abnormal filling during diastole. This alters filling pressure as the heart is unable to properly relax to fill with blood.
• Systolic dysfunction: a decrease in myocardial contractility that is measured as a reduction in the left ventricular ejection fraction (amount of blood the left ventricle pumps out with each contraction).
• Arrhythmias: due to remodelling patients are at risk of both atrial and ventricular arrhythmias and there is an increased risk of sudden cardiac death.

Collectively these pathological changes can lead to heart failure with features of breathlessness, fatigue and fluid overload. This is because of abnormal relaxation and filling, abnormal contraction and/or outflow obstruction.

Clinical features

The presentation of HCM is highly variable. The majority of patients are asymptomatic or have mild symptoms. This means a large proportion are diagnosed through screening or as an incidental finding on echocardiography.

Other patients may present with features of heart failure, arrhythmias or cardiac arrest.

Typical symptoms:

• Fatigue
• Shortness of breath
• Orthopnoea (breathlessness lying down)
• Ankle swelling
• Chest pain: typically due to microvascular angina due to an increased oxygen demand or reduced flow through small vessels
• Presyncope or syncope (transient loss of consciousness): often during exertion due to outflow obstruction
• Palpitations

Typical signs:

• Ejection systolic murmur (left ventricular outflow obstruction): harsh crescendo-decrescendo shortly after S1 and loudest at the apex and lower left sternal edge
• Mid-late systolic murmur (mitral regurgitation): occurs at the apex. Depending on the extent of mitral regurgitation and the direction of the jet regurgitating through the mitral valve it may be pansystolic
• Heave (visible or palpation pulsation)
• Thrill (palpable murmur)
• Features of heart failure: raised JVP, crackles on lung auscultation, peripheral oedema

In some cases, the physical examination may be normal.

Diagnosis

A variety of investigations may be used in the workup of suspected HCM, but the diagnosis is principally made on imaging using echocardiography or cardiac MRI. Increased left ventricular wall thickness ≥15 mm in the absence of any other identifiable cause is consistent with HCM.

An ECG is commonly done as part of the workup and typically shows a variety of ST-T wave changes due to abnormal depolarisation although a variety of findings may be present.

Management

The management of HCM is hugely complex and depends on the presence or absence of outflow obstruction, degree of heart failure and development of arrhythmias. Screening needs to be considered in families including genetic counselling.

In general, beta-blockers help reduce the outflow tract gradient and some patients may be suitable for septal myomectomy that directly removes the abnormal septum and relieves outflow obstruction.

DCM is characterised by ventricular chamber enlargement and impaired contraction.

In DCM, there is dilatation and impaired contraction of one or both ventricles that commonly manifests as heart failure with features of breathlessness, fatigue, and fluid overload. It is the third most common cause of heart failure and may present at any age but commonly in the adult years (20-60 years old).

Aetiology & pathophysiology

A huge number of conditions can cause DCM. This includes infections (e.g. parvovirus B19, coxsackievirus), drugs (e.g. Doxorubicin), pregnancy (e.g. Peripartum) and inherited causes (e.g. abnormal sarcomere genes) amongst many others. When no cause can be identified it is termed idiopathic of which an estimated 50% are familial due to inheritance of an abnormal gene that is usually autosomal dominant.

In DCM, there is progressive dilatation of the left ventricular cavity that may be associated with dilatation of the other chambers. The dilatation leads to progressive systolic dysfunction that manifests as poor myocardial contraction and features of heart failure. Patients may also develop conduction abnormalities leading to arrhythmia.

Clinical features

DCM is characterised by the development of heart failure. Typical clinical features include:

• Breathlessness
• Reduced exercise tolerance
• Fatigue
• Orthopnoa
• Paroxsymal nocturnal dyspnoea: severe, sudden shortness of breath, usually at nighttime
• Peripheral oedema
• Palpitations: due to the development of arrhythmias

Diagnosis

A diagnosis of dilated cardiomyopathy requires evidence of dilation and impaired contraction of the left ventricle or both ventricles, which can be visualised on echocardiography.

It is important to exclude common causes of dilation such as ischaemic heart disease. The term ischaemic cardiomyopathy may be used in clinical practice, but this is not a true cardiomyopathy under the current definition.

Management

Treatment of DCM essentially mirrors that of chronic heart failure. This involves the use of both prognostic medications (e.g. angiotensin receptor antagonists, beta-blockers) and medications to improve symptoms (e.g. diuretics). For more information see our notes on Heart failure.

Cardiac transplantation is more likely to be considered due to the young age of onset, whereas more common causes of heart failure (e.g. hypertension, ischaemia) typically present at an older age and with more co-morbidities.

RCM is an uncommon cardiomyopathy characterised by abnormal ventricular filling.

RCM is characterised by abnormal ventricular filling in the ventricles that are non-dilated and usually have no evidence of hypertrophy. The systolic function of the heart is usually preserved in the early stages of the disease and it manifests as diastolic dysfunction (heart failure due to abnormal filling). The epidemiology largely depends on the underlying cause that differs by geographical region.

Aetiology & pathophysiology

RCM is much less common than the other cardiomyopathies. It is commonly the result of infiltrative diseases where there is a deposition of substance in the myocardium such as amyloid, iron or granulomas. As such, classic causes include amyloidosis, haemochromatosis (iron overload) and sarcoidosis. It can also occur due to inheritance of an abnormal sarcomere gene, storage diseases or tropical diseases (e.g. endomyocardial fibrosis).

Infiltration of the heart reduces compliance and this leads to inadequate ventricular filling in diastole. This causes increased pressures, dilated atria and the development of diastolic heart failure.

Clinical features

The clinical presentation is similar to heart failure with features of breathlessness, fatigue, peripheral oedema, paroxysmal nocturnal dyspnea, reduced exercise tolerance and/or palpitations. Patients may develop syncope due to conduction disease, especially with infiltrative diseases that may damage the sinoatrial node or atrioventricular node.

Diagnosis

The diagnosis of RCM is made on formal imaging such as echocardiography or cardiac MRI. This shows evidence of non-dilated, non-thickened ventricles with abnormal ventricular filling, features of diastolic dysfunction and usually atrial enlargement. However, it can be difficult to identify diastolic dysfunction.

Constrictive (chronic) pericarditis due to scarring of the pericardial sac can also cause impaired ventricular filling and diastolic heart failure. It may be difficult to differentiate between the two and lead to extensive investigation including endomyocardial biopsy.

Management

Treatment of RCM should be aimed at the underlying cause whilst optimising patients with heart failure, particularly fluid overload. However, many prognostic medications used in chronic heart failure are ineffective in patients with RCM.

ACM are a group of disorders characterised by frequent arrhythmias and ventricular dysfunction.

ACM is broadly defined as the clinical presentation of an arrhythmia alongside myocardial structural abnormalities. However, the condition really reflects a group of disorders that are characterised by frequent ventricular arrhythmias and dysfunction of one or both ventricles.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is the most well characterised ACM caused by a genetic mutation.

Aetiology & pathophysiology

ARVC is the most well characterised form of ACM that is due to a mutation in a desmosomal gene in 40-60% of cases. The right ventricular myocardium is replaced with fibrous and/or fatty tissue with abnormal function and predisposition to arrhythmias. Left ventricular involvement is also commonly seen in ARVC leading to the more global term ACM.

Other causes of ACM can include acquired causes such as Chagas disease, due to the protozoan Trypanosoma cruzi, and sarcoidosis. In these conditions, there is predominant conduction disease and arrhythmias alongside myocardial involvement.

Clinical features

Patients with ACM may be asymptomatic for many years. The presentation is highly variable and can include:

• Palpitations
• Syncope
• Chest pain
• Breathlessness
• Features of heart failure

The development of syncope or palpitations is usually a sign of dangerous ventricular arrhythmias and may lead to sudden cardiac death. Unfortunately, sudden cardiac death may be the first presentation of the disease.

Diagnosis

The diagnosis of ACM, particularly ARVC, may be challenging and involves a combination of typical ECG findings, echocardiography with/without cardiac MRI. A diagnostic criterion is available to aid the diagnosis.

Management

The key to management is the prevention of sudden cardiac death that usually requires anti-arrhythmias (e.g. beta-blockers) with or without the use of an implantable cardiac defibrillator (ICD). It is important to slow the rate of disease progression, particularly RV dysfunction in ARVC with the use of prognostic medications similar to chronic heart failure.

This predominantly refers to two specific cardiomyopathies known as left ventricular non-compaction and Takotsubo’s.

Left ventricular non-compaction

This condition is characterised by an abnormal left ventricular trabecular meshwork. There is continuity between the left ventricular cavity and deep trabecular recesses. It is thought to be due to intrauterine growth arrest of the normal compaction process of the trabecular meshwork. Several causative genes have been identified.

Takotsubo’s cardiomyopathy

Also known as ‘stress-induced cardiomyopathy’ or ‘broken-heart syndrome’. A stressful event can lead to characteristic apical ballooning with transient systolic dysfunction. The exact cause is unknown but thought to be related to catecholamine-induced spasm of the small vessels in the microvasculature. The condition preferentially affects postmenopausal women.