7th March 2024

Dilated Cardiomyopathy

Background

Cardiomyopathies are heart muscle disorders with abnormalities of either systolic or diastolic function in which there is a primary abnormality of the heart muscle itself i.e., in the absence of coronary artery disease, hypertension, valvular heart disease or congenital heart disease. These disorders can be due to changes in the nature of the underlying intracellular make-up, deposition of pathological material in the intercellular space or abnormal function of cardiac muscle. 

The subclassification of cardiomyopathies remains an evolving field as we understand more about their pathologies, but a standard classification would include:

• Dilated Cardiomyopathy (DCM)
• Hypertrophic cardiomyopathy (HCM)
• Restrictive Cardiomyopathy (RCM)
• Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
• Unclassified – including Takotsubo cardiomyopathy and Left Ventricular non-compaction

Once classified as above, the cardiomyopathies can be subclassified as familial/genetic vs non-familial/non-genetic/acquired.

There is still ongoing discussion about these terms, particularly as some hypertrophic conditions can lead to restrictive physiology, which can lead to confusion regarding nomenclature. 

Symptomatology is largely related to the effect that the underlying pathology has on cardiac function. Conditions in which the underlying pathology is acquired as part of a multi-system disorder (such as HCM in the context of Friedrich’s ataxia) are likely to display a much wider range of symptoms, whilst those with intrinsic cardiac disease will show signs and symptoms purely of cardiac dysfunction related to the exact effect that the pathology has on the function heart.

All patients with a suspected cardiomyopathy should initially be investigated with:

• A full and thorough history with a focus on family history to elucidate any potentially inherited conditions. Specific questions should be asked about any history of sudden death or epilepsy in the family – often a misdiagnosis in the context of cardiogenic syncope
• Basic observations including temperature, heart rate, blood pressure, respiratory rate and oxygen saturation
• Blood tests including full blood count, renal function, liver function tests, NT pro-BNP, troponin, bone profile, cholesterol and HbA1C
• 12-lead ECG – at least 2 if the symptoms are acute to help rule out dynamic ECG changes
• Echocardiogram

Natriuretic peptides (BNP and NT-pro BNP) will be elevated almost without fail in cases with overt heart failure, as the release of these biomarkers is caused by elevations of intraventricular pressure.

There are some additional investigations pertinent to the individual classes of cardiomyopathy which will be discussed in the relevant sections.

Treatment will be related to either amelioration of the underlying disease process, treatment of impaired cardiac function, or aimed at prevention of further deleterious sequelae caused by the disease such as arrhythmia causing haemodynamic instability or sudden cardiac death.

Pathology

Dilated cardiomyopathy (DCM) is likely the most common of the cardiomyopathies. It is characterised by an enlarged and globally poorly contractile left ventricle. As with many of the following cardiomyopathies, it can be both acquired or inherited.

The genetic subtypes are numerous and include mutations in cytoskeletal or sarcomeric protein and nuclear membrane abnormalities. The acquired subtypes can include myocarditis, thiamine deficiency, alcohol and tachycardia induced cardiomyopathies. Peripartum cardiomyopathy is a form of DCM, in which the DCM occurs in the peripartum period, most typically in the post-partum period.

Signs and symptoms

DCM typically manifests signs and symptoms related to chamber enlargement and systolic dysfunction and thus will lead to typical signs and symptoms of heart failure. 

Symptoms

• Shortness of breath
• Orthopnoea
• Paroxysmal Nocturnal Dyspnoea
• Peripheral oedema

Signs

• Elevated JVP
• 3rd heart sound – gallop heart rhythm
• Displaced apex laterally towards the axilla
• Crepitations on auscultation

In the context of specific disorders leading to a DCM, such as alcohol abuse or thiamine deficiency, you will also see signs and symptoms of the specific disease, such as chronic liver disease and malnutrition, respectively.

Investigations 

The diagnosis of DCM requires imaging demonstrating cardiac dilation, typically with a left ventricular ejection fraction <45% and an LV end-diastolic diameter >117% of the predicted value, with other causes of myocardial disease excluded.

This is most commonly diagnosed on echocardiography, given the greater availability of the modality, but it can be seen or confirmed via other modalities such as cardiac MRI. Cardiac MRI can also provide useful information regarding the quality of the myocardial tissue including myocardial fibrosis, a greater extent of which is a poor prognostic marker. Both will often show an element of functional valvular regurgitation i.e., valvular disease due to dilation of the valve annulus not due to an intrinsic defect in the valve itself.

Reductions in global longitudinal strain and strain rate can also be seen prior to dilation and reductions in ejection fraction.

ECG can be relatively nonspecific, showing ST or T wave changes, sinus tachycardia or a bundle branch block due to the increased distance that the electrical impulses have to travel in the enlarged heart.

Given that genetic links are not uncommon, it is standard to perform a detailed family tree and offer genetic counselling if a link is suggested. This can involve inviting other family members in for genetic testing to identify the nature of the putative mutation.

Treatment

Dilated cardiomyopathies are typically treated as per standard medical therapy for heart failure. If there is a clear precipitant, then this should be treated if possible, otherwise there are conservative, medical and interventional treatments according to a range of parameters, including left ventricular ejection fraction as per standard heart failure guidelines.

All patients with symptoms of fluid overload should be considered for a diuretic, typically a loop diuretic in the first instance. For patients with reduced left ventricular ejection fraction, medications that they should be offered include: 

• ACE inhibitor/ Angiotensin receptor blocker/ Angiotensin receptor blocker + Neprolysin inhibitor (ARNI)
• Beta blockade 
• Mineralocorticoid receptor antagonist
• Sodium Glucose Transporter Type 2 Inhibitors

Interventional options include:

• Ablation for ventricular tachycardias
• Implantable cardiac defibrillator for those with DCM and a confirmed disease-causing mutation at high risk for sudden cardiac death
• Cardiac resynchronisation therapy +/- defibrillator – dependent upon ejection fraction, NYHA classification and QRS duration
• Left ventricular assist device – either as bridging to transplant or as destination therapy
• Cardiac transplant

References

• Classification of the cardiomyopathies: a position statement from the European society of cardiology working group on myocardial and pericardial diseases. Available at https://academic.oup.com/eurheartj/article/29/2/270/433902
• https://www.ahajournals.org/doi/full/10.1161/CIRCRESAHA.116.309396
• https://patient.info/doctor/dilated-cardiomyopathies
• https://www.nice.org.uk/guidance/ta314/documents/arrythmias-icds-heart-failure-cardiac-resynchronisation-fad-document2