Dilated Cardiomyopathy (DCM): Definition, Types, Diagnostics & Treatment
Dilated cardiomyopathy (DCM)
Dilated cardiomyopathy (DCM) is defined as dilation of one or both ventricles. Dilation of the left ventricle is virtually always accompanied by impaired left ventricular systolic function. It should be noted that several types of cardiomyopathies (e.g ischemic cardiomyopathy, tachycardia-induced cardiomyopathy, diabetic cardiomyopathy, etc.) may ultimately lead to ventricular dilation. However, the term dilated cardiomyopathy (DCM) refers to idiopathic or genetic dilation of the left ventricle. Patients with DCM typically develop heart failure early in life and a family history of heart failure, ventricular arrhythmias or sudden cardiac arrest is common.
The following cardiomyopathies lead to dilation of the ventricle:
- Dilated cardiomyopathy (DCM) – Idiopathic or genetic.
- Ischemic cardiomyopathy
- Alcoholic cardiomyopathy
- Diabetic cardiomyopathy
- Takotsubo cardiomyopathy
- Tachycardia-induced cardiomyopathy
- Non-compaction cardiomyopathy
- Peripartum cardiomyopathy
- Cardiomyopathy secondary to valvular heart disease
Long-term prognosis varies markedly across these conditions. The prognosis in idiopathic dilated cardiomyopathy may be poorer than the prognosis for most cancers, whereas tachycardia-induced cardiomyopathy can be cured completely by restoring sinus rhythm. Dilated cardiomyopathy is currently the most common indication for heart transplantation.
Echocardiography can not distinguish different types of dilated cardiomyopathy. Other causes of ventricular dilation (e.g ischemic cardiomyopathy) must be excluded before establishing a diagnosis of DCM. Patient characteristics, clinical features, family history and genetic testing are important clues in the investigation. Additional examinations (e.g coronary angiography, cardiac MRI) are frequently necessary.
Left ventricular dilation entails a markedly elevated risk of ventricular tachycardia and cardiac arrest, regardless of the underlying cause of the dilation. The only exception to this rule is ventricular dilation secondary to non-compaction cardiomyopathy, which confers only slightly elevated risk of ventricular arrhythmias (Almeida et al).
Genes and DCM
Approximately 40% of all cases of DCM are genetic. Thus, a family history with early onset of heart failure is common among these individuals. The majority of the mutations are inherited in an autosomal dominant manner with variable penetrance and expressivity. Autosomal recessive, X-linked recessive, and mitochondrial forms occur, albeit less frequently (McNally et al).
Screening of family members is justified, including a 12-lead ECG, echocardiography, clinical examination and a pedigree. Studies show that approximately 30% of family members will exhibit signs of dilated cardiomyopathy (Burkett et al).
More than 100 genes have been implicated in dilated cardiomyopathy. The majority of these encode proteins in the sarcomere, Z disk or the cytoskeleton (Herschberger et al). De novo mutations are less common than inherited mutations. Clearly, not all DCM genes have been discovered.
Genetic testing for DCM
Genetic testing of patients with confirmed or likely dilated cardiomyopathy can be recommended. There are several commercially available gene panels, which enables testing of over 100 genes.
Absence of known mutations defines the condition as idiopathic dilated cardiomyopathy.
Echocardiography in dilated cardiomyopathy (DCM)
- In dilated cardiomyopathy (DCM), both ventricles are dilated and left ventricular systolic function is impaired (i.e ejection fraction is reduced).
- Left ventricular diastolic function may be normal or exhibit a restrictive pattern (increased E/A ratio and rapid deceleration time; see Diastolic function).
- Left ventricular wall thickness may be normal, but since the ventricle is enlarged, the ventricular mass is always increased.
- Myocardial contractile function is globally impaired (i.e general hypokinesia exists). Regional wall motion abnormality can be seen in the septum in the setting of left bundle branch block.
- Although the ejection fraction is reduced in DCM, stroke volume may be normal due to the large ventricular volume. Symptoms may, therefore, not manifest until advanced stages of cardiomyopathy, when stroke volume is declining.
- Ventricular dilation leads to dilation of the mitral annulus and tricuspid annulus, resulting in mitral regurgitation and tricuspid regurgitation.
- Pronounced ventricular dilation and impaired contractility lead to slow blood flow in the ventricular cavity. This may result in spontaneous echo contrast and the appearance of thrombi in the ventricle.
Stroke volume is generally normal in early stages of DCM. Progressive impairment of contractility leads to gradually diminishing stroke volumes and progression of heart failure symptoms.
ECG in dilated cardiomyopathy (DCM)
The ECG may be completely normal in early stages of DCM. Patients presenting with abnormal ECG during the early stages of the disease may display the following changes:
- Signs of left ventricular hypertrophy (LVH)
- Nonspecific ST-T changes
- Left bundle branch block (LBBB)
- Nonspecific intraventricular conduction delay (IVCD)
Advanced stages of DCM may present with the following ECG changes:
- Low voltage (low R wave amplitudes), which indicates widespread myocardial fibrosis and hypokinesia.
- Pathological Q waves may be due to DCM, but is more likely to be caused by myocardial infarction (i.e ischemic cardiomyopathy).
AV blocks suggest genetic DCM or inflammatory systemic diseases (sarcoidosis, Lyme disease, giant cell myocarditis).
Arrhythmias in DCM
Life-threatening ventricular arrhythmias are common in patients with DCM. Some patients, notably those with LMNA mutations, exhibit a very high risk of ventricular arrhythmias. DCM presenting with syncope, nonsustained ventricular tachycardia, frequent premature ventricular contractions is referred to as arrhythmogenic DCM. The risk of sudden cardiac arrest and sustained ventricular tachycardia is high among these individuals, regardless of the severity of left ventricular dysfunction. Also, a family history of ventricular arrhythmias predicts a high risk of arrhythmogenic DCM.
Other specific forms of dilated cardiomyopathy
Alcohol cardiomyopathy (cardiomyopathy caused by alcohol)
Regular alcohol consumption >80 g/day for more than 5 years confers a high risk of developing dilated cardiomyopathy (Fauchier et al). High alcohol consumption is presumably a common cause of ventricular dilation. There are large individual variations regarding the amount of alcohol required to cause cardiomyopathy, but in most cases, several years of high consumption is required before overt cardiomyopathy develops.
Alcohol affects multiple mechanisms in the myocardial cell (e.g ATP production, electromechanical coupling, calcium sensitivity, membrane potential, etc.). Alcohol may also directly cause inflammation and apoptosis (Maisch et al).
Alcohol cardiomyopathy causes dilation of both the left and right ventricle, making it difficult to distinguish from dilated cardiomyopathy. As a rule, the ejection fraction is < 45%.
Cardiomyopathy caused by diabetes: Diabetic cardiomyopathy
In recent years, it has become increasingly clear that people with diabetes may develop heart failure in the absence of traditional risk factors for heart failure (hypertension, valvular heart disease, ischemic heart disease, myocardial infarction, etc.). People with type 1 diabetes have up to 10 times increased risk of heart failure (Rawshani et al; Lind et al). Among people with type 2 diabetes, the risk may be up to 5 times, as compared with people without diabetes (Lind et al).
However, the mechanisms causing heart failure in individuals with diabetes remain elusive. Most studies have focused on hyperglycemia and demonstrated strong associations between HbA1c and the risk of heart failure. Interested readers refer to Sattar et al.
Diabetic cardiomyopathy is characterized by myocardial fibrosis, remodeling and diastolic dysfunction. Diastolic dysfunction appears to be the hallmark of the diabetic heart. Approximately 50% of all cases of heart failure among individuals with diabetes consist of heart failure with preserved ejection fraction (HFPEF), and the majority of people with diabetes exhibit diastolic dysfunction. Left ventricular hypertrophy is also common in the early stages of diabetic cardiomyopathy (Jia et al). Systolic dysfunction (i.e reduced ejection fraction) usually develops later, as does ventricular dilation.
Diabetic cardiomyopathy with reduced ejection fraction is managed according to guidelines for heart failure with reduced ejection fraction (HFREF).
There are no evidence-based interventions for diabetic cardiomyopathy with preserved ejection fraction (HFPEF), although multiple clinical trials are underway.