10-44: Dilated Cardiomyopathy

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Heart failure definitions have changed over the years and patients with a dilated cardiomyopathy are generally placed into the category of heart failure with reduced EF where the LVEF is defined as less than or equal to 40%. In about half of the patients in this category, there is LV enlargement and it is this group that defines dilated cardiomyopathy. This is a large group of heterogeneous myocardial disorders characterized by reduced myocardial contractility in the absence of abnormal loading conditions such as with hypertension or valvular disease. The prevalence averages 36 cases/100,000 in the United States and accounts for approximately 10,000 deaths annually. Black patients are afflicted three times as often as White patients. The prognosis is poor with 50% mortality at 5 years once symptoms emerge.

The causes are multiple and diverse. Up to 20–35% have a familial etiology. It is common for hereditary causes to first present with conduction system disease prior to a reduced LVEF. A 2020 report of 2538 patients with a dilated cardiomyopathy in whom genetics were available suggested a clear association with at least 12 differing genes. Recent attention has focused particularly on the Lamin A/C genotype. While a large proportion of dilated cardiomyopathy causes are listed as idiopathic, it is likely that genetic variants may be responsible for many of these. Endocrine, inflammatory, and metabolic causes include obesity, diabetes, thyroid disease, celiac disease, SLE, acromegaly, and growth hormone deficiency. Toxic, drug-induced, and inflammatory causes are listed in the prior section. Nutritional diseases such as deficiency of thiamine, selenium, and carnitine have also been documented. Dilated cardiomyopathy may also be caused by prolonged tachycardia either from supraventricular arrhythmias, from very frequent PVCs (more than 15% of heart beats), or from frequent RV pacing. Dilated cardiomyopathy is also associated with HIV, Chagas disease, rheumatologic disorders, iron overload, sleep apnea, amyloidosis, sarcoidosis, chronic alcohol usage, ESKD, or cobalt exposure (“Quebec beer-drinkers, cardiomyopathy”). Peripartum cardiomyopathy and stress-induced disease (tako-tsubo) are discussed separately.

CLINICAL FINDINGS

A. Symptoms and Signs

In most patients, symptoms of heart failure develop gradually. It is important to seek out a history of familial dilated cardiomyopathy and to identify behaviors that might predispose patients to the disease. The physical examination reveals rales, an elevated JVP, cardiomegaly, S₃ gallop rhythm, often the murmurs of functional mitral or tricuspid regurgitation, peripheral edema, or ascites. In severe heart failure, Cheyne-Stokes breathing, pulsus alternans (eFigure 10–75), pallor, and cyanosis may be present.