Dilated Cardiomyopathy



Dilated Cardiomyopathy


Reema Hasan

Taylor Alexander Lebeis

Supriya Shore

Monica Mechele Colvin



INTRODUCTION

Cardiomyopathy is a disease of the heart muscle, which can include dilatation and impaired contraction of one or both ventricles as well as infiltrative diseases of the myocardium. Due to the dilatation and hypertrophy that develops after myocardial injury, patients may develop impaired systolic function, resulting in dilated cardiomyopathy (DCM).1 DCM has many causes and all of them affect ventricular function to a varying degree. While most patients with DCM have symptoms, some may be asymptomatic because of compensatory mechanisms. Continued enlargement of the ventricles leads to a decline in ventricular function followed by conduction system abnormalities, ventricular arrhythmias, thromboembolism, and heart failure.

The earlier patients are identified and treated, the better the prognosis.

Without medical therapy, DCM is progressive, leading to heart failure and death. Once end-stage heart failure develops, survival rates are poor without heart transplants. In this chapter, we discuss the various etiologies of DCM, its pathogenesis, diagnosis, and management.


Definition and Classifications

The classification of DCM has evolved over time with advances in genetics and disease recognition. Currently, DCM refers to a spectrum of heterogeneous myocardial disorders that are characterized by ventricular dilation and depressed myocardial performance in the absence of hypertension, valvular, congenital, or ischemic heart disease. In clinical practice, the etiology of heart failure (HF) has been categorized as ischemic or nonischemic cardiomyopathy, with the latter interchangeably used with DCM. However, this fails to recognize that nonischemic cardiomyopathy can include cardiomyopathies caused by volume or pressure overload (such as hypertension or valvular heart disease) that are not conventionally accepted under the definition of DCM.

Classification schemes, such as the one proposed by the American Heart Association (AHA), divide cardiomyopathies into two major groups based on predominant organ involvement: primary cardiomyopathies (ie, genetic, nongenetic, and acquired) are those solely or predominantly confined to heart muscle, whereas secondary cardiomyopathies have myocardial involvement as part of a generalized systemic (multiorgan) disorder (ie, amyloidosis, hemochromatosis, sarcoidosis, autoimmune/collagen vascular diseases, toxins, cancer therapy, and endocrine disorders such as diabetes mellitus).

The European Society of Cardiology (ESC) Working Group on Myocardial and Pericardial Diseases takes a different approach based on a clinically oriented classification in which heart muscle disorders are grouped into specific morphologic and functional phenotypes, including hypertrophic cardiomyopathies, DCM, arrhythmogenic right ventricular dysplasia, restrictive cardiomyopathies, and unclassified cardiomyopathies. Each phenotype is then subclassified into familial and nonfamilial forms.

Most recently, the MOGE(S) nosology system was developed, which incorporates the morphofunctional phenotype (M), organ(s) involvement (O), genetic inheritance pattern (G), etiologic annotation (E) including genetic defect or underlying disease/substrate, and the functional status (S) of the disease using both the American College of Cardiology (ACC)/AHA HF stages and New York Heart Association (NYHA) functional class. This nomenclature is endorsed by the World Heart Federation and is supported by an internet-assisted application. It also assists in the description of cardiomyopathy in symptomatic and asymptomatic patients, as well as family members in the context of genetic testing.


Epidemiology

The reported incidence and prevalence of dilated cardiomyopathies worldwide are affected by geographic differences, evolving diagnostic criteria, and socioeconomic factors. In the United States, the age-adjusted prevalence of DCM is reported to be approximately equal to 36 cases per 100,000 population or 1:2500 individuals.2 Approximately, 30% to 40% of patients diagnosed with DCM have a nonischemic origin.3 DCM is more commonly seen in men than women. While DCM typically occurs in the third or fourth decade of life, it can be seen in children and the elderly. Age is an independent risk factor for mortality in DCM.


PATHOGENESIS

Enlargement of the left ventricle (LV) or both the right and left ventricles occurs in DCM due to LV failure or a secondary myopathic process that is causing biventricular failure. Reduced systolic function is thought to be due to myocardial remodeling that causes an increase in both end-systolic and end-diastolic volumes (Figure 70.1). Dilatation of the ventricles can lead to
tricuspid or mitral insufficiency. Over time, this will lead to a reduced ejection fraction and increased ventricular wall stress. To compensate, heart rate and peripheral vascular tone increase, resulting in additional myocardial injury. Neurohormonal activation of the renin-angiotensin-aldosterone system and an increase in catecholamines are compensatory mechanisms that occur. Natriuretic peptides levels also increase. Ultimately, the compensatory mechanisms become injurious creating myocardial ischemia. Eventually, the heart becomes overwhelmed and fails. Histologic examination of the myocardium typically shows nonspecific changes of fibrosis and hypertrophy, although myocardial injury with an infiltrate of inflammatory cells is also seen.







CLINICAL PRESENTATION AND EVALUATION


History and Physical

DCM can be asymptomatic for many years. If untreated, most patients will develop the syndrome of HF. Symptoms of HF include paroxysmal nocturnal dyspnea, orthopnea, leg swelling, and shortness of breath with exertion or at rest. Nonspecific symptoms include fatigue, malaise, and weakness. More advanced cases can include thromboembolic complications, conduction disturbances, arrhythmias, or sudden cardiac death. Since symptoms can be nonspecific, it is not uncommon for the diagnosis to be missed or confused with asthma.

Physical exam findings include crackles in the lungs, elevated jugular venous pressures, peripheral edema, and a S3 gallop. The point of maximum impulse, or PMI, may be displaced laterally. Tricuspid or mitral regurgitation murmurs can be present because of ventricular enlargement and annular dilation. Neck examination can reveal jugular venous distention, large V-waves, brisk Y descent, and a positive hepatojugular reflux. The murmur of mitral regurgitation may not be holosystolic, and the usual inspiratory increase in the murmur of tricuspid regurgitation (Carvallo’s sign) is frequently absent.

The initial diagnostic approach should exclude all potentially reversible causes of LV dysfunction (Algorithm 70.1). Laboratory testing should include thyroid function tests, HIV serology, electrolytes, hemoglobin A1c, hematocrit, and iron studies. Urine toxicology screen and alcohol level can be checked when substance abuse is suspected. Excess alcohol consumption has been reported in up to 40% of patients with idiopathic DCM. A history of alcohol consumption is important since abstinence may result in a dramatic increase in ejection fraction. A recent viral illness, particularly one accompanied by myalgias or pericarditis, may suggest a role for myocarditis. Ischemic heart disease should be considered whenever coronary risk factors or chest pain on exertion is present. If a complete family history suggests a familial cardiomyopathy, echocardiography may need to be performed in close relatives to rule out asymptomatic abnormalities.

Hypothyroidism, hyperthyroidism, and anemia should be excluded before diagnosing DCM. A chest x-ray may show cardiomegaly and evidence of pulmonary effusions and venous
congestion. Electrocardiogram (ECG) may show nonspecific ST-segment and T-wave abnormalities or even atrial fibrillation. Oxygen consumption of less than 14 mL/kg/min on a metabolic stress test indicates a poor prognosis.







May 8, 2022 | Posted by in CARDIOLOGY | Comments Off on Dilated Cardiomyopathy
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