A 55-year-old man with dilated cardiomyopathy (DCM) presented for open reduction and internal fixation of a tibial fracture. He had been in a motor vehicle accident. Past medical history included alcohol abuse, orthopnea, dyspnea on exertion, and several episodes of pulmonary edema. The patient’s medications included digoxin, furosemide, and captopril. Physical examination revealed bibasilar rales and S 3 gallop. A gated blood pool scan showed a left ventricular ejection fraction of 15%. Cardiac catheterization indicated a left ventricular end-diastolic pressure of 25 mm Hg, a cardiac index of 1.8 L/min/m 2 , 2 + mitral regurgitation, and no coronary artery disease.
Name possible etiologies for dilated cardiomyopathy.
DCM can be genetically derived or acquired and can exist in both inflammatory and noninflammatory forms. The genetic form comprises 20%–35% of DCM and is usually inherited in an autosomal dominant pattern, although there are also X-linked recessive and mitochondrial patterns of inheritance. DCM is a common cause of heart failure with a prevalence of 36 per 100,000 people. DCM is characterized by ventricular chamber enlargement and systolic dysfunction with normal left ventricular wall thickness.
The inflammatory variety, or myocarditis, is usually the result of infection or parasitic infestation. Myocarditis manifests with a clinical picture of fatigue, dyspnea, and palpitations that usually occur in the first weeks of infection. Palpitations progress to overt congestive heart failure (CHF) with cardiac dilation, tachycardia, pulsus alternans (i.e., regular alternation of pressure pulse amplitude with a regular rhythm), and pulmonary edema. Complete recovery from infectious myocarditis is usually the case, but there are exceptions, such as myocarditis associated with diphtheria or Chagas disease. Diphtheria can produce either right or left bundle-branch block. The combination of diphtheria and bundle-branch block has a mortality rate of approximately 50%. If complete heart block ensues, the mortality rate is 80%–100%. Chagas disease can lead to right bundle-branch block and other arrhythmias in 80% of patients. Viral infections, mycotic infections, and helminthic myocardial involvement have varying clinical profiles that include arrhythmias, CHF, pericarditis, or valvular or vessel obstruction. The noninflammatory variety of DCM also manifests with the clinical picture of myocardial failure but in this case secondary to toxic, degenerative, or infiltrative processes in the myocardium. In some cases, the exact etiology is unknown (idiopathic DCM).
Alcoholic cardiomyopathy is a typical hypokinetic, noninflammatory cardiomyopathy associated with tachycardia and premature ventricular contractions that progresses to left ventricular failure with incompetent mitral and tricuspid valves. This cardiomyopathy is probably due to direct toxic effects of ethanol or its metabolite, acetaldehyde, which releases and depletes cardiac norepinephrine. In chronic alcoholics, acute ingestion of ethanol produces decreases in contractility, elevations in ventricular end-diastolic pressure, and increases in systemic vascular resistance. Alcoholic cardiomyopathy is classified into three hemodynamic stages ( Table 3-1 ).
|Stage||Cardiac Output||Ventricular Pressures||LVEDV||Ejection Fraction|
Doxorubicin (Adriamycin) is an antibiotic medication with chemotherapeutic effects. It can disrupt myocardial mitochondrial calcium homeostasis and can produce a dose-dependent DCM. Amyloidosis can also cause DCM by myocardial infiltration, although it is also associated with restrictive and obstructive forms of cardiomyopathy, valvular lesions, conduction abnormalities, and infiltration of amyloid in the coronary arteries causing obstruction.
Explain the pathophysiology of dilated cardiomyopathy.
DCM is characterized by elevated filling pressures, failure of myocardial contractile strength, and a marked inverse relationship between arterial impedance and stroke volume. DCM manifests with a clinical picture very similar to CHF produced by severe coronary artery disease (CAD).
Pathophysiologically, as ventricular muscle weakens, the ventricle dilates to take advantage of the increased force of contraction that results from increased myocardial fiber length. However, as the ventricular radius increases, there is elevation of ventricular wall tension, increasing both oxygen consumption of the myocardium and total internal work of the muscle. As the myocardium deteriorates further, cardiac output decreases, and compensatory increase in sympathetic activity occurs to maintain cardiac output and organ perfusion.
One feature of the failing myocardium is inability to maintain stroke volume against elevated arterial impedance to ejection. As left ventricular dysfunction worsens, stroke volume becomes more dependent on arterial impedance (afterload). In the failing ventricle, stroke volume decreases almost linearly with increases in afterload. The increased sympathetic outflow that accompanies left ventricular failure initiates a vicious cycle of increased resistance to forward flow, decreased stroke volume, reduced cardiac output, and further sympathetic stimulation in an effort to maintain circulatory homeostasis ( Figure 3-1 ).