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730 PA R T I V / Pathophysiology and Management of Heart Disease
Hypertrophic Cardiomyopathy Medical Management
Treatment strategies in HCM are directed toward prevention of
Hypertrophic cardiomyopathy (HCM) is a familial cardiac disor- sudden cardiac death and symptom relief. 67 An ICD and amio-
der characterized by left and/or right ventricular hypertrophy, darone are used to prevent sudden cardiac death in patients at
which is usually asymmetric and involves the interventricular high risk. 66 Risk factors for sudden cardiac death include sudden
41
septum. The manifestations of HCM are complex and may in- cardiac death in first-degree family members, unexplained syn-
clude dynamic left ventricular outflow tract obstruction cope, abnormal blood pressure response to exercise, resting left
(LVOTO), mitral regurgitation, diastolic dysfunction, myocar- ventricular outflow gradient greater than 30 mm Hg, ventricular
dial ischemia, and cardiac arrhythmias. Many individuals with ectopy, and massive LVH. 68,69 Pharmacological therapy is de-
HCM have a life expectancy similar to the general adult popula- signed to increase diastolic filling and decrease LVOTO and gra-
tion, although there are subsets of patients that annual mortality dient. Catecholamines exacerbate the LVOTO and increase the
rates up to 6%. 62 HCM is the single most common cause of ath- heart rate, reducing filling time, so they are the target of therapy.
lete deaths in the United States, responsible for about one-third The medications used are -blockers or calcium channel blockers,
of the cases. 63 66
and the antiarrhythmic disopyramide.
The goal of surgical intervention is to reduce permanently the
Etiology
Familial disease with an autosomal dominant inheritance pre- LVOTO and gradient, thereby decreasing symptoms and improv-
dominates. This disorder affects 1:500 of the population. 46 Mu- ing quality of life. The size of the ventricular septum, and there-
tations in sarcomeric contractile protein genes cause disease. 41,64 fore the LVOTO, can be reduced through surgical myectomy or
66
Mechanisms thought to lead to septal hypertrophy include re- alcohol ablation. Successful surgical myectomy results in
duced contractile dysfunction leading to compensatory hypertro- marked improvement of symptoms. Percutaneous alcohol septal
phy of cardiac myocytes, insufficient levels of muscle ATP result- ablation was first reported in 1995, and involves the introduction
ing in deranged sarcomere function, and the induction of growth of alcohol into a target septal perforator branch of the left anterior
factors that stimulate hypertrophy and fibrosis. 65 descending coronary artery to induce an MI within the proximal
ventricular septum. This treatment results in a decrease in septal
Pathophysiology thickness. Improvement after septal ablation can occur immedi-
In HCM, the left ventricular volume is typically normal or re- ately in the catheterization laboratory, or over hours or several
62
duced, and systolic gradients are common. LVOTO is present in months. Patients are at risk for conduction problems so a tem-
30% to 50% of patients. LVOTO causes an increase in left ven- porary pacemaker is placed prior to the ablation. Some patients
70
tricular systolic pressure, which leads to prolonged ventricular re- may require a permanent pacemaker. There are no randomized
laxation, increased left ventricular diastolic pressure, myocardial clinical trials comparing surgery to ablation, therefore long-term
70,71
ischemia, and decreased cardiac output. The obstruction can be outcomes for these strategies are unknown.
dependent on changes in preload, afterload, and contractility, so Dual-chamber pacemaker therapy may be helpful to reduce
anything that influences these factors can affect the LVOTO. 64 symptoms in half of HCM patients. Patients with atrial fibrilla-
Mitral valve regurgitation is due to systolic anterior motion of the tion are aggressively treated to achieve a normal sinus rhythm. If
mitral valve. 66 Typical morphological changes include myocyte atrial fibrillation is chronic, the ventricular rate is controlled with
hypertrophy and disarray surrounding areas of increased loose -blockers, verapamil, or digoxin. Anticoagulation is also neces-
62
connective tissue. sary.
If the patient with HCM is hospitalized for deterioration, ad-
Assessment Findings equate volume and decreasing myocardial oxygen demands are
HCM is diagnosed by echocardiography in the presence of left important. 65 Positive inotropes and chronotropes should be
ventricular hypertrophy in the absence of other mechanical, meta- avoided as they worsen LVOTO. Nitrates decrease preload so
8
bolic, or genetic causes. 8,64 MRI can also aid in diagnosis. Pres- must be used with caution as that will also worsen LVOTO.
sure gradients between the aorta and left ventricle greater than 30 -Blockers are indicated. If hypotension is present, it should be
mm Hg signify severe LVOTO. The preferred method of eliciting managed with a purely -adrenergic agonist medication such as
presence of latent gradients during and/or immediately following phenylephrine. 64
exercise is treadmill or bicycle exercise testing along with Doppler In the past, patients with HCM and LVOTO at rest were con-
echocardiography. Knowledge of a latent gradient is very impor- sidered at risk for bacterial endocarditis and were prescribed ap-
tant to guide key management decisions. 8 propriate antibiotic prophylaxis for dental and surgical proce-
Classic findings in HCM include a systolic ejection murmur dures. 62,66,67,72 The new American Heart Association guidelines
that becomes increasing loud during maneuvers that decrease pre- for infective endocarditis (IE) now recommend prophylaxis for a
load, such as standing from a squatting position. 64 A mitral re- select group of patients. 97
gurgitation murmur can be heard because the mitral leaflet is Because of the genetic nature of HCM, annually clinical
open as it is pulled into the left ventricular outflow tract during screening of adolescent relatives aged 12 to 18 years, consisting of
systole. 65 a history and physical examination, 12-lead ECG, and two-di-
The majority of patients are asymptomatic throughout life. mensional echocardiography is indicated. Because some individu-
However, some will present with severe symptoms of dyspnea, als do not manifest HCM until adulthood, screening beyond ado-
64
8
angina, and syncope. The ECG will display signs of left ventric- lescence is recommended every 5 years. Patients are advised to
ular hypertrophy. Ventricular arrhythmias and premature sudden avoid athletic competition and extremes of physical exertion. 67
death are common and appear to be genetically linked. 41,64 Atrial Genetic testing may also be completed, but this testing is cur-
fibrillation is also commonly seen and thought to be due to atrial rently done in research laboratories, is very time-consuming and
enlargement. 66 expensive, and not routinely available. 68,72