Cardiomyopathy is the term for a group of diseases that affect the heart muscle itself. Unlike coronary artery disease, which damages the heart by blocking its blood supply, cardiomyopathy arises from intrinsic abnormalities in the heart muscle cells or structure. The heart wall may become thickened, thinned, stiffened, or scarred, in each case impairing the heart's ability to pump effectively.
Cardiomyopathy is not a single condition. There are five main types, each with different causes, mechanisms, populations affected, and treatment priorities. What they share is the potential to cause heart failure, dangerous arrhythmias, and in some types -- particularly hypertrophic cardiomyopathy and ARVC -- sudden cardiac death, including in young, apparently healthy people.
Understanding Ejection Fraction
Before exploring the types of cardiomyopathy, it is helpful to understand ejection fraction -- the single most important measurement in cardiomyopathy assessment. The ejection fraction (EF) is the percentage of blood in the left ventricle that is pumped out with each heartbeat. In a healthy heart, 55-70% of the blood in the ventricle is ejected with each contraction. The remainder acts as a reserve. In individuals with reduced EF, approximately 40% or below of blood is ejected.
Ejection fraction is measured primarily by echocardiography (cardiac ultrasound) and confirmed by cardiac MRI in complex cases. It is the key number that guides most major treatment decisions in cardiomyopathy -- and it is one of the first things your cardiologist will want to know.
Types of Cardiomyopathy
The classification of cardiomyopathy is based on the structural and functional changes in the heart muscle. Each type has a distinct pathological mechanism, and treatment is guided by the specific type.
Dilated Cardiomyopathy (DCM)
In dilated cardiomyopathy, the left ventricle -- and often the right ventricle -- becomes enlarged and weakened, losing the ability to contract forcefully. This is the most common form of cardiomyopathy and the leading cause of heart transplantation worldwide. DCM accounts for approximately 1 in 250 adults and affects men more often than women.
Hypertrophic Cardiomyopathy (HCM)
Hypertrophic cardiomyopathy involves unexplained thickening of the left heart muscle, usually the wall between the ventricles. It occurs without other causes such as high blood pressure or aortic valve narrowing. It is the most common inherited cardiac condition, affecting approximately 1 in 500 people and is the most common cause of sudden cardiac death in young athletes.
Restrictive Cardiomyopathy (RCM)
It causes the ventricular walls to become stiff, reducing the heart’s ability to fill properly between beats. The ventricles become unable to relax and fill adequately, leading to elevated filling pressures and heart failure with preserved ejection fraction. RCM is less common than DCM or HCM but carries a serious prognosis due to progressive diastolic dysfunction.
Other and Secondary Cardiomyopathies
Heart muscle disease can also occur due to other conditions. These include cardiomyopathy related to pregnancy, certain chemotherapy drugs, metabolic disorders, and long-term heavy alcohol use. These conditions can weaken the heart, reduce its pumping ability, and may improve with early treatment or removal of the underlying cause.
Symptoms: How Cardiomyopathy Presents
Many patients with cardiomyopathy, particularly early in the disease, have no symptoms at all. The condition is often discovered incidentally on an ECG or echocardiogram performed for another reason. When symptoms do develop, they typically reflect the downstream consequences of impaired cardiac function:
Symptoms of Heart Failure
- Breathlessness: Shortness of breath is the most common symptom. It may first occur during activity and later happen even at rest in more advanced disease. Breathlessness when lying flat or waking up at night short of breath may indicate increased pressure within the heart.
- Fatigue and reduced exercise tolerance: The heart cannot meet the increased demand of exercise, leading to early fatigue, muscle weakness, and inability to perform activities previously managed without difficulty.
- Peripheral oedema: Swelling of the ankles, lower legs, and in advanced cases the abdomen (ascites), caused by elevated venous pressure and fluid retention.
- Abdominal bloating and early satiety: From hepatic congestion and ascites.
- Reduced urine output during the day, with increased nocturia (passing urine at night).
Symptoms from arrhythmias
- Palpitations: Rapid, irregular, or pounding heartbeat.
- Syncope (fainting): Sudden loss of consciousness, often brief. Syncope during exercise in a young person is a red flag symptom requiring urgent cardiac assessment.
- Pre-syncope: Lightheadedness or near-fainting without full loss of consciousness.
- Exertional chest pain or pressure: In obstructive HCM, the thickened heart muscles impedes blood flow out of the left ventricle during exercise.
- Exertional breathlessness disproportionate to the degree of heart failure.
- Sudden cardiac arrest: HCM-related sudden death can be the first presentation in a proportion of patients.
Causes and Risk Factors
The causes of cardiomyopathy vary substantially by type. Cardiomyopathies are broadly categorised as primary (arising from the heart muscle itself, often genetic) or secondary (arising from an identifiable systemic cause).
- Genetic and inherited causes: Some cardiomyopathies are inherited due to gene changes that affect heart muscle function and increase the risk of weakness or abnormal heart rhythms.
- Acquired causes: Acquired cardiomyopathies can result from infections, high blood pressure, coronary artery disease, alcohol, certain medications, metabolic disorders, abnormal heart rhythms, or pregnancy-related changes. These conditions can damage the heart muscle and reduce its function.
Risk factors for cardiomyopathy
- Family history of cardiomyopathy, heart failure, or sudden cardiac death in a first-degree relative
- Prior myocardial infarction or known coronary artery disease
- Chronic heavy alcohol use
- Chronic hypertension, obesity, or metabolic syndrome
- Autoimmune conditions -- sarcoidosis, lupus, connective tissue disorders
How Cardiomyopathy is Diagnosed
- Echocardiogram: The primary test for diagnosing cardiomyopathy. It uses ultrasound to assess heart structure and function, identify the type and severity of disease, and monitor changes with treatment.
- Electrocardiogram (ECG): Detects electrical abnormalities that may suggest different types of cardiomyopathy, including changes in heart muscle thickness, rhythm problems, conduction defects, and QT or ST abnormalities. A normal ECG does not exclude cardiomyopathy.
- Cardiac MRI: A detailed scan used to assess heart muscle structure, scarring, and fibrosis. It helps identify different types of cardiomyopathy, accurately measures heart function.
- Blood Tests: Checks for heart strain, heart muscle injury, and underlying causes of cardiomyopathy, such as thyroid disorders, iron overload, amyloidosis, inflammation, and autoimmune disease.
- 24-Hour Holter Monitor: Continuously records the heart rhythm for 24–48 hours to detect abnormal rhythms missed by a standard ECG. Findings such as non-sustained ventricular tachycardia may influence the need for an ICD in certain cardiomyopathy patients.
- Exercise Stress Test: Measures exercise capacity, blood pressure response, ECG changes, and exercise-related abnormal rhythms. It helps assess risk in cardiomyopathy, and evaluates functional ability in heart failure and transplant assessment.
- Coronary Angiography: Checks for coronary artery disease as a cause of reduced heart function. It helps differentiate ischaemic from non-ischaemic cardiomyopathy, as they require different treatments.
- Nuclear Scan or Cardiac Biopsy: Imaging tests can identify conditions such as cardiac sarcoidosis and amyloidosis. A heart muscle biopsy is reserved for cases where other tests are inconclusive and a tissue diagnosis is required.
