Hypertrophic cardiomyopathy is a disease of the left and/or right ventricle characterized by the development of myocardial hypertrophy predominant at the interventricular septum. There is no direct cause, such as volume or pressure overload. In most instances, the disease is genetically transmitted in an autosomal dominant manner.
Ventricular hypertrophy is often asymmetrical and its localization and severity influence clinical manifestations. In the majority of cases, ventricular hypertrophy is mild to moderate with no obstruction. These patients often present with no symptoms or minimal symptoms, especially during exercise, and can be treated medically with beta-blockers. The obstructive form of the disease is characterized by a variable and dynamic obstruction of the left ventricular outflow tract that results in the manifestation of clinical symptoms with eventual progression to congestive heart failure. Following surgical myotomy, introduced in the early 1960s, surgical myomectomy, developed by Morrow in 1968, became the conventional surgical treatment and is still in use today. More recently, two interventional cardiology techniques have been added as alternatives to reduce outflow tract obstruction. The first is the use of a dual pacemaker, the efficacy of which is still controversial. The second is percutaneous transluminal septal myocardial ablation using ethanol injection into septal branches of the left anterior descending artery. This latter procedure is used more and more frequently as an alternative to the surgical septal myomectomy, which remains the most currently used treatment. However, patients with more severe forms of hypertrophic obstructive cardiomyopathy with mitral valve involvement may require a more complex reconstructive operation, as described later in this chapter.
ANATOMY AND PATHOPHYSIOLOGY
In hypertrophic obstructive cardiomyopathy, the left ventricular cavity is small and the hypertrophy is asymmetrical, predominant at the anterolateral wall ( Fig. 31-1 ). The septum is extremely hypertrophic with maximal thickening at the level of the free edge of the anterior leaflet in diastolic position (a) .
Although the principal cause of obstruction is the bulging of the interventricular septum, systolic anterior motion (SAM) of the mitral valve is another feature that results in obstruction (b) . Echocardiography has been a key imaging study for elucidating the characteristic features of hypertrophic obstructive cardiomyopathy and the mechanism of obstruction.
The characteristic features ( Table 31-1 ) include the anterior position of the papillary muscles contributing to the anterior displacement of the line of coaptation toward the left ventricular outflow tract. Additional features are narrow aorto-mitral angle, excess tissue of the posterior leaflet, and abnormal morphology of the anterior leaflet, which is elongated to such an extent that it mimics a “ langue de bœuf” *
* See Glossary .
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The mechanism of obstruction is illustrated in Figure 31-2 . As a result of the septal bulging, and the narrow aorto-mitral angle, the blood flow normally directed towards the apex is now directed towards the septum and the inflow chamber (a) . The posterior leaflet closes first and limits the full development of the anterior leaflet, which is pushed towards the left outflow tract during midsystole, causing a dynamic obstruction (b) and late mitral regurgitation (c) .
CLINICAL PRESENTATION
Clinical manifestations of hypertrophic obstructive cardiomyopathy include angina, fatigue, dyspnea on exertion, and syncope. Most patients present with a variety of symptoms that may appear at any age during the evolution of the disease. There is no direct correlation between the severity of symptoms and the severity of obstruction of the left ventricular outflow gradient. Supraventricular and ventricular arrhythmia may also occur and potentially result in sudden death.
Left ventricular diastolic dysfunction is a common finding in patients with hypertrophic obstructive cardiomyopathy. This results from an impairment of ventricular relaxation and leads to increased diastolic filling pressures. Systolic function is preserved during the early phase of the disease. Impaired ventricular contractility may, however, appear at the late stage because of the development of myocardial fibrosis, explaining the symptoms of severe congestive heart failure.
Echocardiography is the key element in the diagnosis of hypertrophic obstructive cardiomyopathy. It allows analysis of the location and severity of ventricular and septal hypertrophy and the degree of obstruction of the left ventricular outflow tract. The thickness of the septum ranges between 15 and 25 mm. Echocardiography also detects structural abnormalities such as anterior position of the papillary muscles or abnormal morphology of the mitral valve, as well as the presence of SAM that may be associated with mitral regurgitation ( Fig. 31-3 ). Echocardiography is also used to evaluate systolic and diastolic ventricular function.
Cardiac catheterization shows commonly an elevated left ventricular end-diastolic pressure and a left ventricle/aortic peak gradient greater than 50 mm Hg in severe obstructive forms. However, this is a dynamic parameter and left ventricular outflow gradients may change over time. The three main factors that influence this variable are ventricular contractility, preload and afterload. Increased ventricular contractility and decreased preload and/or afterload lead to increased outflow gradients. Finally, pulmonary artery pressures may also be elevated in patients with long-lasting disease and in those with SAM associated with mitral regurgitation.
SURGICAL MANAGEMENT
Indications
Surgical intervention is mostly indicated in symptomatic patients with left ventricular outflow tract obstruction at rest or during exercise that is refractory to medical therapy or repeated interventional cardiology procedures. We also recommend an early surgical intervention in patients with mild symptoms whenever SAM is associated with moderate to severe mitral regurgitation, provided that the patient can benefit from reconstructive surgery.
Techniques
Historically, initial surgical attempts consisted of performing a myotomy, as proposed in the mid-1960s by Brock, Cleland, and Bigelow. The goal of the myotomy was to disrupt the contractile function of the sphincterlike muscular ring surrounding the outflow tract, thus relieving obstruction. However, this procedure was associated with a high incidence of residual gradient and abandoned. Later, Morrow introduced the concept of septal myomectomy to increase the diameter of the left ventricular outflow tract and subsequently minimize the obstruction ( Fig. 31-4 ). The only limitation of this technique is that it may leave residual septal bulging (inset) because of the difficulty of achieving optimal orientation of the knife.
