Pathophysiology
Summary
Dilated cardiomyopathy primarily leads to systolic heart failure due to contractile dysfunction. It is most commonly idiopathic, but can be precipitated from various factors. Viral myocarditis and Chagas disease (T. Cruzi) are notable infectious triggers. Hereditary dilated cardiomyopathy, most commonly occurs due to autosomal dominant mutations in cytoskeletal proteins, and is the second most prevalent cause. Duchenne & Becker muscular dystrophy, X-linked conditions, can also induce dilated cardiomyopathy due to mutations in dystrophin, essential for connecting the myocyte cytoskeleton to the extracellular matrix. Alcohol abuse, can lead to this cardiomyopathy in two ways: directly, through cardiotoxicity from EtOH & acetaldehyde, as well as indirectly through wet beriberi. Some drugs, like the anthracycline chemotherapeutic agent doxorubicin, can cause free radical damage that can lead to cardiotoxicity. Unique conditions like pregnancy can sometimes lead to dilated cardiomyopathy, termed peripartum cardiomyopathy, while disorders like hemochromatosis can cause it through iron deposition in cardiomyocytes.
Clinically, patients often exhibit an S3 heart sound. Mural thrombi are also associated with dilated cardiomyopathy, which can lead thromboembolism or embolic stroke. Diagnosis is made using an ultrasound, which reveals an enlarged heart with dilation of all four chambers.
On the other hand, restrictive cardiomyopathy is characterized by diastolic heart failure due to reduced ventricular compliance. This condition can present with an S4 heart sound and jugular vein distension (JVD). Various causes like amyloidosis, hemochromatosis, and lysosomal storage diseases may lead to this form of cardiomyopathy. Endomyocardial biopsy is a diagnostic tool that may show amorphous and acellular pink material in the myocardium in cardiac amyloidosis, which further demonstrates apple-green birefringence under polarized light microscopy with Congo red stain. Other causes include myocardial fibrosis due to factors like chest irradiation or diseases prevalent in specific geographies like endomyocardial fibrosis and endomyocardial fibroelastosis.
Lesson Outline
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FAQs
Dilated cardiomyopathy involves the pathological enlargement and weakening of the myocardium, resulting in compromised systolic function and reduced cardiac output. While the majority of cases are idiopathic some well-recognized etiologies include viral myocarditis—often due to Coxsackievirus B—Chagas disease (T. cruzi), and genetic factors, particularly autosomal dominant mutations. Additionally, conditions such as Duchenne and Becker muscular dystrophy are known to predispose individuals to this form of cardiomyopathy due to a mutation in the protein dystrophin, which connects myocyte cytoskeleton to the extracellular matrix.
Dilated cardiomyopathy frequently precedes systolic heart failure. In this condition, the enlargement and weakening of the myocardium impair its contractile function. Consequently, the heart's capacity to effectively eject blood during systole, the contraction phase of the cardiac cycle, is reduced, culminating in systolic heart failure.
Several conditions and lifestyle factors are associated with an increased risk of developing dilated cardiomyopathy. Medical conditions such as peripartum cardiomyopathy and hemochromatosis, which results in iron deposition in cardiomyocytes, are notable examples. Lifestyle-related factors include alcohol abuse, which can cause cardiotoxicity (due to EtOH & acetaldehyde build-up) and wet beriberi (thiamine deficiency), both of which can cause dilated cardiomyopathy.
Restrictive cardiomyopathy manifests as a decrease in ventricular compliance, owing to stiffened ventricular walls that impair the heart's ability to fill adequately during diastole. This dysfunction commonly results in diastolic heart failure. The etiology varies, with infiltrative diseases like amyloidosis and sarcoidosis, as well as fibrotic processes like hemochromatosis and scleroderma, frequently implicated. Other contributory factors include lysosomal storage diseases and the sequelae of chest radiation therapy.
While both types of cardiomyopathies present with symptoms of heart failure, they can be distinguished by the type of heart failure and certain physical signs. Dilated cardiomyopathy often leads to systolic heart failure and can present with an S3 heart sound and possible mural thrombi. On the other hand, restrictive cardiomyopathy leads to diastolic heart failure and commonly presents with an S4 heart sound, jugular vein distension, or Kussmaul sign. Additionally, restrictive cardiomyopathy may manifest in a prominent Y descent in the jugular venous pressure waveform.
