Cardiomyopathy

Cardiomyopathy is a disease of the heart muscle, but it does not describe one particular type of heart disease. The myocardium may become enlarged and weak, abnormally thick, stiff, or affected by scar and other tissue changes that interfere with its electrical activity. That is why two people with cardiomyopathy can present very differently.

One patient may come into hospital with breathlessness and pulmonary oedema because a dilated left ventricle is no longer contracting effectively. Another may have a thickened ventricle that still contracts strongly but cannot relax and fill normally. Someone else may first come to attention after palpitations or a syncopal episode caused by an arrhythmia.

The name of the cardiomyopathy describes the pattern seen in the heart, but assessment goes further than naming that pattern. The team also needs to understand what may have caused it, how it is affecting cardiac function and rhythm, and whether there may be implications for the patient's family.

When the ventricle becomes dilated and weak

In dilated cardiomyopathy, the left ventricle, or sometimes both ventricles, becomes enlarged and contracts less effectively. Imagine the ventricle at the end of systole. Instead of squeezing down and ejecting an effective volume of blood, more blood remains inside the chamber. When the next filling phase begins, new blood enters a ventricle that already contains a larger residual volume. Over time the chamber becomes stretched and its ability to pump effectively can deteriorate further.

The patient can then develop problems on both sides of the ventricle. Less blood is being moved forward into the systemic circulation, while pressure rises behind the failing left ventricle and is transmitted back towards the pulmonary veins. Breathlessness may first appear with exertion. As congestion increases, lying flat can become uncomfortable and the patient may wake during the night feeling short of breath. If right-sided pressures also rise, fluid can accumulate in the peripheral tissues and the patient may develop ankle oedema, abdominal swelling or increasing weight.

Dilatation can also affect the mitral valve even when the valve leaflets themselves are normal. As the ventricle and mitral annulus stretch, the leaflets may no longer meet properly during systole. Some of the stroke volume then moves backwards into the left atrium as functional mitral regurgitation, adding to the volume the left side of the heart has to manage.

There are several possible causes. Some dilated cardiomyopathies have a genetic basis. Myocarditis, alcohol and other cardiotoxic substances, pregnancy-associated cardiomyopathy and some cancer treatments can also lead to a dilated phenotype. In other patients, investigation does not identify a single cause.

Hypertrophic cardiomyopathy is a different filling problem

In hypertrophic cardiomyopathy, the myocardium is abnormally thick. The interventricular septum is often prominently affected, although the pattern of hypertrophy varies between patients. A thick ventricle may still squeeze very well. The difficulty often appears during diastole, when that thickened myocardium has to relax so that the ventricle can fill.

If the muscle is stiff and relaxes poorly, a higher pressure is needed to fill the ventricle. Pressure can then be transmitted backwards towards the left atrium and pulmonary circulation, contributing to breathlessness even when the ejection fraction is normal or high. Ejection fraction describes the proportion of blood ejected from the ventricle. It does not tell us by itself whether that ventricle relaxed and filled normally before it contracted.

Some people with hypertrophic cardiomyopathy also develop obstruction as blood leaves the left ventricle. A thickened septum narrows the left ventricular outflow tract, and during systole the mitral valve can move towards the septum and narrow it further. Unlike a fixed obstruction, the severity can change with ventricular filling, heart rate and contractility. A patient may therefore experience exertional breathlessness, chest pain, dizziness or syncope.

Arrhythmias are another part of hypertrophic cardiomyopathy. Abnormal myocardial architecture and fibrosis can disturb electrical conduction, while raised atrial pressure and enlargement can contribute to atrial fibrillation. Ventricular arrhythmias are less common but are important because selected patients have an increased risk of sudden cardiac death.

When stiffness or abnormal myocardial tissue is the main problem

Restrictive cardiomyopathy is characterised by impaired ventricular filling because the myocardium has become unusually stiff. The ventricles may not be markedly enlarged, and systolic function can initially appear relatively preserved, but the chambers cannot relax and accept blood normally during diastole. Filling pressures rise and the atria may enlarge as blood repeatedly meets resistance entering the ventricles.

Cardiac amyloidosis can produce this type of physiology because abnormal protein deposits infiltrate the myocardium and make it less compliant. Restrictive physiology can have other causes too, so identifying the underlying disease is an important part of assessment.

Arrhythmogenic cardiomyopathy affects the myocardium in another way. Areas of abnormal fibrous and fatty tissue can develop within the ventricular muscle. The right ventricle, left ventricle or both may be involved. These tissue changes can interfere with the normal spread of electrical activity through the myocardium, creating a substrate for ventricular arrhythmias. For some patients, palpitations, presyncope or syncope appear before there is severe pump failure.

This is one reason a normal ECG recorded after an episode of palpitations or syncope does not necessarily settle the question. The abnormal rhythm may have stopped before the ECG was taken. Ambulatory monitoring can record the heart over a longer period, while the history helps establish what the patient was doing, what they felt before losing consciousness and how quickly they recovered.

Working out what is happening in the myocardium

Echocardiography can show chamber size, wall thickness, ventricular contraction, filling patterns and valve function. In hypertrophic cardiomyopathy it can also assess whether there is obstruction in the left ventricular outflow tract. These findings begin to define the cardiomyopathy phenotype.

Cardiac magnetic resonance imaging gives a more detailed view of the myocardium and can identify patterns of scar, fibrosis or infiltration that are not fully characterised by echocardiography. The ECG and ambulatory rhythm monitoring add information about electrical activity, while exercise testing may show symptoms, blood pressure changes, arrhythmias or outflow obstruction that are not apparent at rest. The investigation is therefore not simply about confirming that cardiomyopathy exists. It is about understanding the type of myocardial disease and the risks associated with it. This phenotype-based approach is central to current European Society of Cardiology guidance.

Family history can change the investigation considerably. Cardiomyopathy in a parent or sibling, unexplained heart failure, sudden cardiac death at a young age or a close relative with an implanted cardioverter defibrillator may point towards inherited disease. Genetic counselling and testing can sometimes identify a disease-causing variant. When inherited cardiomyopathy is identified or strongly suspected, relatives may be offered clinical and sometimes genetic screening even if they have no symptoms.

Treatment depends on what the cardiomyopathy is doing

There is no single treatment pathway for cardiomyopathy because the underlying physiology and risks are different. Dilated cardiomyopathy with reduced left ventricular systolic function may be treated using established heart failure therapies, alongside treatment of congestion and any identifiable underlying cause. Bleepbook's Heart Failure: What Happens to the Circulation? looks more closely at reduced forward flow and rising filling pressures.

In hypertrophic cardiomyopathy, treatment depends on symptoms, rhythm and whether left ventricular outflow tract obstruction is present. Medicines may be used to slow the heart, improve filling and reduce symptoms. People with persistent symptomatic obstruction despite medical treatment may be considered for specialist therapies or septal reduction procedures.

Rhythm risk is assessed across the cardiomyopathies rather than assuming that everyone with the diagnosis has the same chance of a dangerous arrhythmia. An implantable cardioverter defibrillator may be recommended for selected patients at increased risk of sudden cardiac death. Ventricular function, previous arrhythmias, imaging findings, genotype and other disease-specific risk markers can all contribute to that decision.

Atrial fibrillation can be poorly tolerated when ventricular filling is already impaired. Organised atrial contraction normally contributes to ventricular filling. When that contraction is lost and the ventricular rate is fast, there is less time and less assistance available for a stiff ventricle to fill. Bleepbook's Atrial Fibrillation: The Irregular Rhythm looks at atrial fibrillation separately.

Exercise advice is also individual. The type of cardiomyopathy, symptoms, ventricular function, arrhythmia history, genetic findings and the intensity of the proposed activity can all affect recommendations. This is particularly relevant in arrhythmogenic cardiomyopathy, where high-intensity exercise may contribute to disease progression and arrhythmic risk in susceptible patients.

Following the patient, not just the scan

Cardiomyopathy can change gradually, so comparing the patient with their own usual level of function can reveal deterioration before the resting observations become abnormal. Someone who previously walked to the shops comfortably but now needs to stop because of breathlessness has experienced a meaningful change in functional capacity. Orthopnoea, waking breathless at night, increasing oedema or rapid weight gain may suggest worsening congestion.

Palpitations, dizziness, presyncope and syncope bring rhythm disturbances into the assessment. Exertional syncope is particularly concerning in some cardiomyopathy phenotypes and needs investigation. New chest pain also needs assessment on its own merits rather than being assumed to come from an established cardiac diagnosis.

For some patients, the diagnosis changes the conversation from their own heart to the health of their family. Learning that children, siblings or parents may need screening can be difficult to process alongside a new diagnosis. Genetic testing does not always produce a simple answer either. A result may identify a disease-causing variant, find no causative variant or identify a variant whose significance is uncertain. Clear explanations and access to specialist genetic counselling help patients and families understand what the findings do and do not mean.

References

Arbelo, E. et al. (2023) 2023 ESC Guidelines for the management of cardiomyopathies. European Heart Journal, 44(37), pp. 3503–3626.

European Society of Cardiology (2023) Pocket Guidelines on Cardiomyopathies.

NHS Cardiomyopathy.

Elliott, P.M. et al. (2008) Classification of the cardiomyopathies: a position statement from the European Society of Cardiology Working Group on Myocardial and Pericardial Diseases. European Heart Journal, 29(2), pp. 270–276.