Causes of dilated cardiomyopathy (continued)
Valvular heart disease, especially aortic regurgitation and mitral regurgitation, cause dilated cardiomyopathy. Indeed, the gradual enlargement of the cardiac chambers is an important sign that the time may be right for valve replacement or repair.Nutritional abnormalities – especially a deficiency in vitamin B1 – can cause cardiomyopathy. This form of cardiomyopathy is mostly seen in third world countries, and in alcoholics.
Cardiomyopathy sometimes develops in women within a month of delivering a baby. This so-called peripartum cardiomyopathy is the result of a myocarditis that occurs for unknown reasons, associated with childbirth. While many of the affected women recover completely, others develop a rapid and severe dilated cardiomyopathy.
There are also genetic forms of dilated cardiomyopathy. This is why some families are clearly affected by an extremely high incidence of dilated cardiomyopathy.
Cardiac “overwork” is another cause of dilated cardiomyopathy. Any condition that causes the heart muscle to work at high loads for prolonged periods of time (weeks or months) can eventually cause cardiac dilation and weakening of the heart muscle. Such conditions include prolonged severe anemia, abnormal sustained tachycardias, chronic hyperthyroidism, and the overwork produced by leaky (regurgitant) heart valves.
In many cases, specific causes of dilated cardiomyopathy cannot be identified. In these cases, the dilated cardiomyopathy is said to be “idiopathic.”
What are the symptoms of dilated cardiomyopathy?
The symptoms of cardiomyopathy are those of heart failure. These include shortness of breath and/or fatigue with exertion or when lying down, waking up at night gasping for air, and swelling in the lower legs. As the disease progresses, so do the symptoms. Patients with dilated cardiomyopathy also have a greatly increased incidence of life-threatening arrhythmias, namely ventricular tachycardia and ventricular fibrillation. In these patients, an episode of syncope (fainting) should be regarded as a harbinger of sudden death.How is cardiomyopathy diagnosed?
Diagnosing dilated cardiomyopathy depends on demonstrating enlargement of the cardiac chambers, especially the ventricular chambers. Such enlargement can be seen on chest X-ray, but can be more accurately assessed using an echocardiogram or a MUGA scan.Once dilated cardiomyopathy is found, every effort should be made to identify a potentially reversible cause. Coronary artery disease and valvular heart disease need to be ruled out. Anemia, abnormal tachycardias, nutritional deficiencies, alcoholism, and thyroid disease also need to be ruled out. Sometimes, a cardiac biopsy is performed to rule out active myocarditis.
What are the clinical pattern and prognosis of dilated cardiomyopathy?
Since it is generally causes no symptoms until actual heart failure sets in, by the time cardiomyopathy is diagnosed, heart disease is usually already fairly advanced. Classically the clinical pattern of a patient with dilated cardiomyopathy is characterized by episodes of severe heart failure that lead to hospitalization, followed by relatively long periods of “baseline” symptoms. During this baseline period, patients often have symptoms only with exertion. As time goes by, the episodes of severe heart failure come more and more frequently, and the “baseline” periods are characterized by a gradually worsening level of symptoms. In the year or so prior to death, frequent hospitalizations are common, and it is usually apparent to both patient and doctor that a steady, unrelenting deterioration is under way.The left ventricular ejection fraction (LVEF, the proportion of its blood volume the left ventricle ejects with each contraction) is a good reflection of the amount of damage the left ventricle has sustained, and to some degree is a reflection of the prognosis in patients with dilated cardiomyopathy. Most people with dilated cardiomyopathy do not begin to experience significant symptoms until the LVEF is less than 40% (normal is 50% or greater). When first diagnosed, most patients with dilated cardiomyopathy have LVEFs in a wide range, anywhere between 10% and 40%. In general, the lower the LVEF, the worse the prognosis.
In just the past few years, new therapies (particularly the use of beta blockers and ACE inhibitors) have significantly improved the clinical course of many patients with cardiomyopathy. The second part of this series describes the treatment of cardiomyopathy and heart failure.
