Andersons pediatric cardiology 1649

FIG 61.1 Histopathologic slide of hypertrophic cardiomyopathy showing myocyte disarray and interstitial fibrosis Pathophysiology Left Ventricular Outflow Tract Obstruction LVH and resultant subaortic outflow tract obstruction formed the early basis for identifying the disease process.10 The early hemodynamic studies also identified the potential for inducible dynamic obstruction with pharmacologic stimulation.212,213 Outflow tract obstruction may be multifactorial but is driven by septal hypertrophy and systolic anterior motion of the mitral valve The numerous abnormalities of the mitral valve and mitral valve apparatus associated with HCM may play a role in some patients.199–202 Left ventricular obstruction is also modifiable via physiologic nonpharmacologic manipulation Obstruction (and the accompanying murmur) is typically variable and may be augmented by decreases in ventricular volume or blood pressure as well as increases in contractility (e.g., Valsalva, exercise) Interventions that increase volume load or blood pressure or decrease contractility typically reduce the murmur accordingly (e.g., squatting, handgrip exercise) Diastolic Dysfunction Diastolic dysfunction is common in both children and adults with HCM and may contribute to symptoms.214–219 Impaired relaxation leads to impairment of the rapid, early filling phase in diastole and raises the importance of atrial systole in ventricular filling Chronic changes in diastolic filling (with worsening ventricular compliance) lead to left atrial dilation, and this remodeling places patients at risk for cardiovascular death, atrial fibrillation, and thromboemobolism.220–222 Indeed, left atrial diameter is one of the important components of the ESC sudden cardiac death calculator.223 Diastolic dysfunction is thought to contribute to symptoms in patients with nonobstructive HCM who develop significant activity intolerance and heart failure.224 Atrial Fibrillation Atrial fibrillation is the most common chronic arrhythmia in HCM Although it is uncommon in children, the lifetime prevalence of atrial fibrillation in HCM is 20% to 30%, with increasing prevalence with patient age, worsening diastolic dysfunction, and left atrial dilation.42,220,221,225 The consensus guidelines currently recommend systemic anticoagulation in patients with HCM and atrial fibrillation This is independent of a patient's CHA2DS2-VASc score, given the ineffectiveness of the score in predicting embolic risk.221 Ventricular Arrhythmia The pathologic features of myocardial fibrosis, coronary disease, microvascular disease, and outflow tract obstruction create the substrate for life-threatening ventricular arrhythmia and sudden death.45,226–228 Early reports from tertiary referral centers pointed to annual sudden death rates of 3% to 6%/year in children with HCM.49,229,230 More recent data suggest that the rate of sudden cardiac death is approximately 0.5%/year with current management strategies as well as adjustment for the selection bias inherent to early studies from tertiary referral centers.34–36,231,232 Isolated ventricular ectopy is relatively common in children with HCM (up to two-thirds of patients), but nonsustained and sustained ventricular tachycardia are relatively rare.36,233 Although aborted sudden cardiac death is relatively rare among pediatric patients, those with this history are at high risk for subsequent events.34,36,234 Systolic Dysfunction Progression to ventricular dilation and systolic dysfunction is rare in both children234 and adults with HCM.38 When present, however, it is a significant risk factor for death or indicates the need for heart transplantation.35,37,38 The presence of systolic dysfunction should also raise the possibility for nonsarcomeric causes of HCM.235 Clinical Features Symptoms The majority of patients with HCM are asymptomatic at presentation.34–36 Diagnosis is commonly made after detection of a murmur or screening due to familial disease or syndromic disease in infants.34,35,234 Patients with mixed phenotypic disease, syndromic disease, and those who present as infants are significantly more likely to present with symptoms, notably heart failure.34,37 Infants who are symptomatic typically present with tachypnea, feeding intolerance, sweating with feeds, and failure to thrive Older children and teenagers may present with fatigue, exercise intolerance, palpitations, angina, syncope, or near syncope The symptoms may occur independent of the degree of obstruction and may be suggest diastolic dysfunction and microvascular disease Physical Examination The general physical examination may provide important diagnostic clues to the diagnosis of HCM as well as the possible underlying cause (see Box 61.1) From a prognostic and treatment perspective (e.g., for possible enzyme replacement), it is important to identify the cause of hypertrophy The cardiac examination is variable and related to the degree of hypertrophy and obstruction and the patient's physiologic state A prominent and laterally displaced apical impulse may be palpable A double apical impulse may be present, reflecting atrial contraction Patients with outflow tract obstruction may have a double-peaked pulse with a rapid upstroke and a midsystolic decrease (bisferiens pulse) The auscultatory findings are variable based on the degree of outflow tract obstruction Patients with outflow tract obstruction typically have a systolic ... ventricular tachycardia are relatively rare.36,233 Although aborted sudden cardiac death is relatively rare among pediatric patients, those with this history are at high risk for subsequent events.34,36,234 Systolic Dysfunction