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Ashley EA, Niebauer J. Cardiology Explained. London: Remedica; 2004.

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Cardiology Explained.

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Chapter 11Cardiomyopathy

Hypertrophic cardiomyopathy

With a prevalence of only 0.2%, hypertrophic cardiomyopathy (HCM) is rarely encountered by generalists. Most cases are identified by screening family members of known sufferers – 50% of cases are familial.

Background

HCM is a primary, usually familial disorder of cardiac muscle with complex pathophysiology, significant heterogeneity in its expression, and a diverse clinical course. It is defined as cardiac hypertrophy that cannot be explained by pressure or volume overload, and is probably the most common genetically transmitted heart disease. The clinical course is highly variable; some patients remain asymptomatic throughout life, whereas others die prematurely – either suddenly or from progressive heart failure. HCM is characterized by mutations in the DNA encoding cardiac contractile or energy-related proteins, predominantly the β-myosin heavy chain, α-tropomyosin, and cardiac troponin T (see Figure 1 and Table 1).

Figure 1. Contractile proteins in the cardiac sarcomere.

Figure 1

Contractile proteins in the cardiac sarcomere. The top chain represents actin; the bottom chain represents myosin. Contraction occurs when calcium binds the troponin complex, allowing myosin to bind to actin with the production of force: "Myosin rows (more...)

Table 1. Mutations known to cause hypertrophic cardiomyopathy.

Table 1

Mutations known to cause hypertrophic cardiomyopathy.

Despite dramatic improvements in the knowledge and understanding of HCM, challenges and controversies still exist regarding its diagnosis, etiology, natural history, and management. For example, many HCM patients do not, in fact, have left ventricular hypertrophy (LVH). The shifting understanding of this complex disease can make terminology difficult. However, "hypertrophic cardiomyopathy" is the preferred expression for this condition. This nomenclature avoids the term "idiopathic subaortic stenosis" or inclusion of the word "obstructive", which imply left ventricular outflow tract obstruction (present in only 25% of cases). It also excludes secondary causes of LVH.

The classic features of HCM are asymmetrical LVH with a normal or small left ventricular cavity. However, wall thickness varies considerably. The majority of clearly identified patients have an unmistakably abnormal left ventricular mass. This averages at a septal thickness of 20–22 mm, but can be up to 60 mm (see Figure 2). This leaves a significant minority of patients in whom there will be diagnostic ambiguity with respect to cardiac morphology. In fact, the hallmark of the disease is myocardial fiber disarray. Clearly, this cannot be a useful diagnostic marker during life, and increasing attention is being given to molecular genetic diagnostic tools.

Figure 2. Left ventricular (LV) mass in a normal (N) individual and in a patient with hypertrophic cardiomyopathy (HCM).

Figure 2

Left ventricular (LV) mass in a normal (N) individual and in a patient with hypertrophic cardiomyopathy (HCM).

Regardless of the electrocardiogram (ECG) presentation, the prognosis for HCM patients can be unpredictable. Some with severe hypertrophy remain asymptomatic, while others with apparently less severe hypertrophy develop arrhythmias, increased ventricular stiffness, heart failure, or sudden death. Indeed, there can be considerable variation in phenotype within families (see Figure 2).

Clinical examination

HCM has classic clinical signs, most of which relate to outflow obstruction (hence their presence is not required for diagnosis). They are as follows:

  • jerky pulse
  • prominent "a" wave in jugular venous pressure (JVP)
  • double apex beat
  • S3
  • S4
  • late ejection quality systolic murmur over the aortic area that is increased by standing and decreased by squatting
  • a pansystolic murmur at the apex (indicating mitral regurgitation [MR])

The ECG may show LVH and T-wave inversion. With progressive left ventricular disease, left bundle branch block (LBBB) may appear.

Echo is the test of choice. Left ventricular wall thickness is measured from M-mode traces (see Chapter 4, Understanding the echocardiogram). Left ventricular outflow tract velocities can be measured and pressure drop estimated by continuous-wave Doppler. Diastolic dysfunction is common in HCM.

Specialist management

Medical

The main aim of medical treatment is to limit the effects of outflow tract obstruction. Beta-blockers and/or rate limiting calcium-channel blockers, such as verapamil, can improve diastolic filling (by reducing heart rate), reduce exercise-related outflow obstruction, and reduce the possibility of arrhythmia. Amiodarone and sotalol can prevent supraventricular and ventricular arrhythmia, but should only be used in patients with a previous episode.

Dual-chamber pacing

Patients who remain symptomatic despite drug therapy can have a DDD pacemaker inserted (see Chapter 8, Arrhythmia), set to a short atrioventricular (AV) delay. The effect of this is to pace the right ventricle each beat and induce an LBBB-type activation of the left ventricle, which reduces outflow obstruction by desynchronizing contraction of the septum and the posterior wall. Patients can be treadmill-tested to confirm that the AV delay is sufficiently short to maintain right ventricle capture at higher heart rates.

Nonsurgical septal reduction

A recent technique involving cardiac catheterization has been proposed as an alternative for outflow tract pressure gradient reduction and symptom improvement. This technique came to light following observations, in the early eighties, that upon balloon inflation in the left anterior descending (LAD) coronary artery there is a reduction of outflow tract velocities and gradients. The procedure involves balloon inflation in the proximal segment of the first septal perforator of the LAD and assessment of outflow tract gradient. If the gradient drops significantly, a small quantity of alcohol (3–5 mL) is injected down the cannulated artery, distal to the balloon, in an attempt to induce a localized proximal septal infarction. The velocities are then measured.

The stress-induced outflow tract gradient after dobutamine injection is also assessed, both before and after the procedure. If the results are not satisfactory, these steps are repeated while cannulating the second perforator of the LAD. Procedural success is always associated with significant myocardial enzyme rise and a fall in outflow tract velocities, development of significant conduction disturbance, and septal incoordinate relaxation. Mid- and long-term follow-up after nonsurgical septal reduction have proved promising in terms of a decrease in symptoms and maintained low outflow tract gradient.

Surgery

Until the last decade, the major nonmedical option for treating HCM with persistent symptoms was surgical myotomy/myectomy. In this procedure, which is also called the "Morrow procedure", a small portion of the proximal septal myocardium is resected to widen the outflow tract. Mortality from this technique is now <2% and there is a subjective symptomatic improvement in 70% of patients. However, complications are common and for the majority of patients it results in complete LBBB or they require a permanent pacemaker for complete heart block. As a consequence, surgeons have explored other possibilities, such as mitral valve replacement and anterior leaflet extension, to reduce MR, reduce outflow obstruction, and stiffen the anterior leaflet.

Preparticipation screening for sport

HCM is occasionally discovered during preparticipation screening for sport, and should be considered when a young athlete presents with voltage criteria LVH. In this situation, the question as to when to refer for echocardiography arises. The most common voltage criterion is that of Sokolow–Lyon (SV1 + RV5 >3.5 mV) (see Chapter 3, Conquering the ECG). Although the vast majority of young athletes in this category will have a normal heart, most cardiologists would recommend that any young, normotensive patient who meets these voltage criteria should be referred for an echo.

The ECG and echo are the key diagnostic tools. However, the overall prevalence of relevant conditions (0.2%) makes these cost-ineffective. Approximately 200 screenings are required to detect one abnormality, while 200,000 are needed to prevent one death. Thus, it is important to maximize the information available from history and examination (see Table 2).

Table 2. Key points in history and examination for preparticipation screening in athletes.

Table 2

Key points in history and examination for preparticipation screening in athletes.

There is consensus that history and physical examination are the only cost-effective screening tools for sudden cardiac death in athletes. However, these are very poor at identifying the primary causes of sudden death:

  • HCM in its nonobstructive form (~35%) produces no murmur (see Figure 3)
  • coronary artery abnormalities (~20%) are not detectable by simple clinical examination

Figure 3. Hypertrophic nonobstructive cardiomyopathy.

Figure 3

Hypertrophic nonobstructive cardiomyopathy. Note the grossly hypertrophied interventricular septum.

ECG patterns are distinctly abnormal (LVH, inverted T waves, deep Q waves, axis deviation, or LBBB) in about 15% of athletes, and mildly abnormal (borderline LVH, flat T wave, long PR interval, right bundle branch block) in another 25%. Early repolarization may account for another 15%. Bradycardia <60 bpm is found in more than a third. Abnormalities are most common in males younger than 20 years who are involved in endurance sports such as cycling, rowing, and cross-country skiing. In one series, 5% of over 1,000 consecutively examined athletes had structural abnormalities such as HCM or dilated cardiomyopathy (DCM).

Dilated cardiomyopathy

DCM is a primary disease of the cardiac muscle and can be defined as left or right ventricular dilatation and failure in the absence of coronary artery disease, hypertension, valve disease, or congenital heart abnormality. Patients usually present with shortness of breath and signs of congestion in an identical way to heart failure of any other cause. There are many causes of DCM:

  • alcohol
  • familial
  • myocarditis
  • postradiation or chemotherapy (eg, adriamycin/doxorubicin)
  • hemochromatosis
  • thyrotoxicosis
  • thiamine deficiency

Prognosis

The prognosis is variable according to the degree of ventricular damage. It is generally agreed that patients with resistant high filling pressures do badly. Those with biventricular dilatation and impairment of function do even worse.

Investigations

The ECG shows no specific signs: it may be normal or show conduction disturbances. Chest x-ray shows increased cardiothoracic ratio and pulmonary vascular congestion.

Echo is the test of choice and will show a grossly dilated ventricle with thin walls and globally impaired systolic function. Disease progression results in functional MR and the development of left atrial dilatation. In rare cases, the disease solely affects the right heart. Cardiac catheterization is used to exclude coronary artery disease and measure intracardiac pressures.

Management

Management is as described for chronic heart failure (see Chapter 7, Heart failure).

Restrictive cardiomyopathy

Restrictive cardiomyopathy is a disease of the heart muscle that results in myocardial stiffness and an incompliant ventricle. Patients present with predominantly right-sided failure (gross peripheral edema, raised JVP, hepatomegaly) and a normal-sized heart. Classic clinical signs are rapid x and y descent of the JVP, and loud S3 and S4.

The most common causes are:

  • hemochromatosis
  • sarcoidosis
  • amyloidosis
  • carcinoid syndrome
  • glycogen storage disease
  • scleroderma
  • endomyocardial fibrosis and eosinophilic heart disease

Investigations

The ECG can be a useful tool, as subendocardial fibrosis can result in conduction disturbances. In addition, amyloid heart disease presents with low voltages. However, echo enables diagnosis. Classic findings include:

  • absence of ventricular dilatation or hypertrophy (common but not invariable)
  • left ventricle and right ventricle systolic function are often normal
  • there may be biatrial dilatation
  • the myocardium may be speckled or echogenic
  • the Doppler ventricular in-flow pattern exhibits a high E:A ratio (see Chapter 4, Understanding the echocardiogram)

The key differential diagnosis is constrictive pericarditis. This is an important distinction to make as constrictive pericarditis can be treated surgically.

Management

There is no specific medical treatment for restrictive cardiomyopathy. The main aim is to control symptoms of cardiac failure. In patients with high filling pressures, angiotensin-converting enzyme inhibitors in particular have shown a significant beneficial effect in unloading the left ventricle and improving symptoms. Atrial fibrillation should be controlled with digoxin and a prophylactic anticoagulant is usually recommended.

Eosinophilic cardiomyopathy can be treated with steroids, cytotoxic drugs, and prophylactic anticoagulants for thromboembolism. Endomyocardial fibrosis that is not controlled by medical therapy may warrant surgical intervention for subendocardial decortication. Carcinoid syndrome may require tricuspid valve replacement (see Chapter 9, Valve disease).

Further reading

  1. Maron BJ, Moller JH, Seidman C. et al. Impact of laboratory molecular diagnosis on contemporary diagnostic criteria for genetically transmitted cardiovascular disease: hypertrophic cardiomyopathy, long-QT syndrome, and Marfan Syndrome. Circulation. 1998;98:1460–71. [PubMed: 9760303]
  2. Pelliccia A, Maron BJ, Culasso F. et al. Clinical significance of abnormal electrocardiographic patterns in trained athletes. Circulation. 2000;102:278–84. [PubMed: 10899089]
  3. Prior SG, Aliot E, Blomstrom-Lundqvist C. et al. Task force on sudden cardiac death of the European Society of Cardiology. Eur Heart J. 2001;22:1374–450. [PubMed: 11482917]
Copyright © 2004, Remedica.
Bookshelf ID: NBK2209

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