SAMIR S. SHAH
HISTORY OF PRESENT ILLNESS
A 14-year-old boy was brought to the emergency department after collapsing at school. He was at basketball practice when he collapsed to the ground. The paramedics were called and brought him to the emergency department. He awoke within a few minutes of the fall. There was no seizure activity reported. He did not complain of shortness of breath, palpitations, or chest pain. He denied fever, cough, and rhinorrhea. He has no complaints at present. He denied having taken any illicit drugs.
The boy has been healthy with no significant medical history. There was no family history of early cardiac deaths in children or young adults. He takes no medications and all his immunizations are up-to-date.
T 37.0°C; HR 112 bpm; RR 20/min; BP 124/78 mmHg
Weight 90th percentile and Height 75th percentile
On examination he was awake and in no acute distress. His mucous membranes were moist. His lungs were clear to auscultation. His cardiac examination revealed a regular rate and rhythm with a normal S1 and S2 and an S3 gallop rhythm. No murmur could be detected. His abdomen was soft without any hepatosplenomegaly. His extremities were warm and well perfused with strong peripheral pulses. His neurologic examination was normal.
Because of the syncopal episode, he had a bedside glucose level checked which returned at 108 mg/dL. Electrolytes and a complete blood count were normal. The chest radiograph revealed a top-normal sized cardiothymic silhouette.
COURSE OF ILLNESS
An ECG (Figure 18-3) suggested the diagnosis.
FIGURE 18-3. ECG.
DISCUSSION CASE 18-3
This case of syncope is probably caused by a cardiac etiology due to the abnormal physical examination findings as well as the ECG and chest radiography abnormalities. Of all the abnormalities present, the left ventricular hypertrophy seen on the ECG is the most concerning (Figure 18-3). Etiologies to consider include systemic hypertension, aortic valvular stenosis, and hypertrophic cardiomyopathy. Metabolic disorders such as glycogen storage disease, type II may also cause left ventricular hypertrophy.
Echocardiography revealed a large intraventricular septum and a top-normal sized left ventricular end-diastolic dimension. There was no left ventricular outflow obstruction detected. Exercise stress testing did not reveal any arrhythmias; however, there was a 3-mm ST segment depression during maximal exercise. The diagnosis is hypertrophic cardiomyopathy. He was started on a beta-blocker to reduce the pressure gradient across the left ventricular outflow tract. He was also counseled to avoid strenuous competitive athletic activity and strenuous physical exertion. An implantable cardioverter defibrillator (ICD) was considered to prevent sudden arrhythmic death.
INCIDENCE AND EPIDEMIOLOGY
Hypertrophic cardiomyopathy (HCM), a relatively common genetic disease, is the leading cause of sudden cardiac death in preadolescent and adolescent children. There is autosomal dominant inheritance with variable penetrance; approximately 50% of cases are familial. There is a considerable heterogeneity of clinical expression and prognosis even in familial cases. The prevalence of HCM is not well defined. It is detected in 0.5% of outpatients referred for echocardiography. However, population-based studies report a much lower incidence of 1 in 500 or 0.2% of the general adult population. Furthermore, a substantial proportion of patients in the general population probably have a mutant gene for HCM, yet are undetected due to lack of clinical due to lack of clinical symptoms.
HCM is frequently suspected because of a heart murmur, positive family history, new clinical symptoms (e.g., syncope), or an abnormal ECG. The physical examination of patients with HCM is often normal because most (>75%) affected patients do not have outflow tract obstruction; abnormal findings on physical examination are usually related to left ventricular outflow tract obstruction. If an outflow tract obstruction is present, a murmur can be heard. The murmur is louder with increasing outflow obstruction such as valsalva maneuvers and softer with relief of the obstruction such as can be seen with squatting.
Complications of HCM include congestive heart failure, ventricular and supraventricular arrhythmias, atrial fibrillation with mural thrombus, and sudden death. The overall rate of sudden cardiac death is approximately 1% per year. ICDs prolong life by effectively terminating life-threatening ventricular arrhythmias. In contrast, pharmacologic therapy does not appear to protect against sudden cardiac death.
The American College of Cardiology Foundation and the American Heart Association have published practice guidelines to assist healthcare providers in clinical decision-making.
Echocardiogram. HCM is defined as left ventricular hypertrophy (maximal wall thickness ≥15 mm) without left ventricular dilatation and without cardiac or systemic conditions that can explain the extent of hypertrophy. Transthoracic echocardiography should be performed in the initial evaluation of all patients with suspected HCM. Transthoracic echocardiography should also be repeated if any change in clinical status occurs, including new cardiovascular events.
Electrocardiogram. An ECG can be of benefit in the diagnosis of HCM. It is abnormal in 75% or more of patients and has a wide range of patterns. Twenty-four-hour ambulatory (Holter) ECG monitoring should be repeated every 1-2 years in patients with HCM who have no previous evidence of ventricular tachycardia to identify patients who may be candidates for implantable cardioverter defibrillator therapy.
Clinical screening. Clinical screening, including ECG and echocardiography, is recommended for all first-degree relatives of patients with HCM.
Genetic screening. Evaluation of familiar inheritance and genetic counseling is recommended as part of the assessment of patients with HCM. Genetic testing is reasonable in the index patient to facilitate identification of first-degree family members at risk for developing HCM. For those with pathogenic mutations who do not express the HCM phenotype, serial ECGs, transthoracic echocardiograms and clinical assessment is required every 12-18 months for children and every 5 years for adults. However, ongoing screening is not indicated in genotype-negative relatives in families with HCM.
Myocardial biopsy. Biopsy specimens of HCM hearts reveal cellular disarray patterns in sections of the heart that are affected by the disease.
The treatment for patients with HCM is as variable as their presentation. Patients with HCM should not participate in intense competitive sports (e.g., basketball, soccer, football), whether or not they have left ventricular outflow tract obstruction. The main goal of pharmacologic therapy is to alleviate symptoms of exertional dyspnea, palpitations, and chest discomfort. Beta-blockers are the main pharmacologic therapy because of their negative inotropic effects and their ability to attenuate adrenergic-induced tachycardia. Patients unresponsive to or unable to tolerate beta-blockers may receive calcium channel blockers for symptomatic relief. ICDs prevent sudden cardiac death. Patients with HCM and at sufficient risk of sudden cardiac death should be offered ICD placement. Septal reduction therapy should be considered in patients with severe, drug-refractory symptoms and a resting or provoked left ventricular outflow tract gradient of 50 mmHg or greater. Surgical septal myectomy is preferred over alcohol septal ablation.
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