Congenital and acquired cardiomyopathies are an uncommon but potentially serious and occasionally unrecognized comorbidity in pediatric patients presenting for surgery. Care of these children requires a thorough understanding of the pathophysiology of the particular disease state and consultation with a pediatric cardiologist.
Keywordsanesthesia, cardiac arrest, cardiomyopathy, pediatric
A 3-year-old boy presents for inguinal hernia repair. His past medical history is unremarkable except for an upper respiratory infection 3 weeks ago that was characterized by a low-grade fever, thin rhinorrhea, and a mild cough that resolved last week. His physical examination and vital signs are normal. On anesthetic induction with nitrous oxide, oxygen, and sevoflurane his heart rate increases to 180 beats per minute, the electrocardiogram (ECG) QRS complex is noted to be wide, the pulse oximeter plethysmograph flattens, and no femoral pulse can be palpated. Full cardiopulmonary resuscitation is performed but proves unsuccessful. Autopsy reveals a dilated left ventricle and evidence of myocardial inflammation consistent with viral myocarditis.
The World Health Organization defines cardiomyopathies (CMs) as myocardial diseases associated with cardiac dysfunction. Primary CMs are classified by the dominant pathophysiology:
Dilated cardiomyopathy (DCM)
Hypertrophic cardiomyopathy (HCM)
Restrictive cardiomyopathy (RCM)
Arrythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/CM)
Left ventricular hypertrabeculation/noncompaction (LVHT/NC)
Secondary CM may result from a number of different etiologies:
Certain neuromuscular disorders
Unfortunately, many children with CM are asymptomatic or have mild symptoms of heart failure, making recognition of their condition very difficult in the preoperative period. There may be a history of decreased exercise tolerance, cough, breathlessness, syncope, chest pain, or poor feeding. A child with these symptoms or a condition known to be associated with CM should prompt a careful examination looking for signs of heart failure, an ECG, and possibly consultation with a pediatric cardiologist. An echocardiogram will usually establish a definitive diagnosis of which pathophysiologic category of CM is present. A family history of sudden cardiac death (SCD) may be the only indicator of potential CM in an otherwise healthy-appearing child or adolescent.
Dilated cardiomyopathy (DCM) is characterized by left ventricular chamber dilation and impaired systolic function involving the left ventricle (LV), right ventricle (RV), or both. DCM may be due to inflammatory (viral or immunologic), idiopathic, or genetic processes. A familial form of CM has been associated with SCD. DCM can result from toxin exposure or, in young children, be associated with a treatable congenital heart disease such as anomalous left coronary artery or critical aortic coarctation. In children diagnosed with CM the 5-year mortality rate has been reported to be 35% to 70%. Echocardiography usually demonstrates dilated, poorly contractile ventricles, biatrial enlargement, and atrioventricular (AV) valve regurgitation.
Hypertrophic cardiomyopathy (HCM) may involve the LV, RV, or both and is often asymmetric. Ventricular volume may be normal or reduced and is characterized by diastolic dysfunction, with preserved systolic function. The ECG may be normal or show ventricular hypertrophy, and echocardiography is diagnostic. HCM is most commonly a genetic or idiopathic disease but may also be associated with malformation syndromes, various neuromuscular disorders, and inborn errors of metabolism (e.g., glycogen storage disease type II or Pompe syndrome). Patients with idiopathic HCM may be asymptomatic or present with exertional dyspnea, chest pain, and syncope. The ECG shows a progressive pattern, from septal hypertrophy to generalized left ventricular hypertrophy. Typically these patients develop dynamic LV outflow tract obstruction, which may be the cause of some of the symptomatology. However, there is a subset of patients with focal hypertrophy that encases a coronary artery (i.e., myocardial bridge) who are subject to exertional myocardial ischemia and ventricular arrhythmias. This makes HCM the most common cause of SCD in children and young athletes.
Restrictive cardiomyopathy (RCM) is a rare form of CM characterized by restricted left or right (or both) ventricular filling due to reduced ventricular diastolic compliance. RCM may be idiopathic, or it can be associated with endomyocardial fibrosis or the hypereosinophilic syndrome. There may be normal or near-normal systolic function in the early stages of the disease that deteriorates over time. Elevated LV end-diastolic pressure leads to an insidious, relentless increase in pulmonary vascular resistance followed by cor pulmonale and death. The echocardiogram is characterized by small ventricular volumes with large, dilated atria.
Arrhythmogenic right ventricular cardiomyopathy (ARVCM) is characterized by fibrofatty replacement of right or left ventricular (or both) myocardium. ARVCM is a genetic cardiac disease with autosomal dominant inheritance and incomplete penetrance. Patients with ARVCM often present with dyspnea, fatigue, hepatomegaly, and ascites, but SCD may be the initial manifestation of the disease in an otherwise asymptomatic patient. Fifty percent of these patients have abnormal ECGs that may show impaired AV conduction. A definitive diagnosis is made with myocardial biopsy, but ARVCM is suggested by the combination of ventricular arrhythmias (most often sustained ventricular tachycardia) with a left bundle branch block configuration. Wall motion abnormalities in the free wall of the RV are seen on echocardiography. The echocardiogram may also show atrial dilation associated with near-normal ventricular dimensions and AV valve regurgitation.
Left ventricular hypertrabeculation/noncompaction (LVHT/NC) is a rare disorder often associated with neuromuscular diseases including muscular dystrophies, myopathies, mitochondrial diseases, and others. These patients often present with signs of heart failure, arrhythmias, and ECG abnormalities. There is decreased LV function on echocardiography, but the diagnosis may require magnetic resonance imaging. The natural course of disease is dictated by any underlying neuromuscular disorder, as well as the severity of myocardial dysfunction.
DCM is the most common form of CM in children and it has an equal prevalence in males and females. HCM usually does not present before adolescence, but morbidity and mortality are greatest in patients diagnosed at younger ages. Premature death is commonly due to ventricular fibrillation. RCM is uncommon in children but, when present, is often an end-stage finding after myocarditis or with an infiltrative myocardial disease. ARVCM is uncommon but accounts for a high percentage of sudden cardiac deaths in children and adolescents. The prevalence in females is threefold greater than in males. LVHT/NC should be considered in the following neuromuscular disorders: Duchenne and Becker muscular dystrophy, myotonic dystrophy, Charco-Marie-Tooth disease, Friedreich ataxia, Barth syndrome, mitochondriopathy, dystrobrevinopathy, glycogenosis, myoadenylate-deaminase deficiency, and zaspopathy.
In DCM, cardiac output is maintained by sympathetically mediated tachycardia and ventricular chamber dilation with increased stroke volume. However, this leads to increased myocardial wall tension and oxygen utilization. In HCM, there is ventricular inflow obstruction secondary to diastolic dysfunction. Approximately 25% of patients also have dynamic obstruction of the left ventricular outflow tract. The systolic volume of the LV, the force of left ventricular contraction, and the transmural pressure gradient distending the outflow tract determine the severity of the obstruction. With RCM, the ejection fraction is maintained early in the process. However, as ventricular fibrosis progresses, left ventricular end-diastolic pressure increases, resulting in pulmonary hypertension and decreased stroke volume and cardiac output. With ARVCM, contractility is normal initially, but the onset of ventricular arrhythmias coincides with a slow deterioration of right ventricular function. Eventually, ventricular tachyarrhythmias (ventricular tachycardia or fibrillation) become resistant to antiarrhythmic therapy. LVHT/NC presents with variable degrees of myocardial dysfunction and has been associated with ventricular chamber thrombus formation. Underlying neuromuscular disorders can further complicate the anesthetic management of these patients.