Myocardial disease that is not due to a specific heart muscle disorder or a known infiltrative, metabolic/toxic or neuromuscular disorder may be caused by:
• An acute or chronic inflammatory pathology (myocarditis)
• Idiopathic myocardial disease (cardiomyopathy)
Myocarditis, whether idiopathic or infective, is the most common form of inflammatory endomyocardial disease. A definitive aetiology with isolation of viruses or bacteria is uncommon. Causative factors include: VIRUSEs, particularly Coxsackie, influenza, rubella, polio, adenovirus and echovirus.
PROTOZOA, e.g. Trypanosoma cruzi, which causes Chagas’ disease and is endemic in central and South America, and Toxoplasma gondii-a common cause of myocarditis in the newborn or in immunologically compromised adults.
RADIATION, CHEMICALS AND DRUGS, e.g. lead poisoning, emetine and chloroquine,
BACTERIAL INFECTION, e.g. diphtheria, which is due to an exotoxin produced by Corynebacterium, Rickettsia, Chlamydia, Coxiella (the causative agent of Q fever).
Patients present with an acute illness, often characterized by fever and cardiac failure. There may be a history of previous respiratory or febrile illness. Physical examination reveals soft heart sounds, a prominent third sound and tachycardia (gallop rhythm). Often a pericardial friction rub may be heard.
CHEST X-RAY may show some cardiac enlargement, depending on the stage and virulence of the disease. THE ECG demonstrates ST and T wave abnormalities and arrhythmias. Diphtheritic myocarditis may induce heart block, and Chagas’ disease produces both heart block and ventricular tachyarrhythmias.
CARDIAC ENZYMES are elevated.
CARDIAC BIOPSY shows acute inflammation.
VIRAL ANTIBODY TITRES may be increased.
General management includes bed rest and the eradication of any acute infection. Therapy is directed towards the management of cardiac failure and the treatment of cardiac arrhythmias. Depending on the aetiology, the prognosis is usually good, although a chronic cardiomyopathy may occasionally ensue.
These idiopathic conditions are classified according to their clinical presentation as:
1 Dilated cardiomyopathy-ventricular dilatation
2 Hypertrophic cardiomyopathy-myocardial hypertrophy
3 Restrictive cardiomyopathy-impaired ventricular filling
Dilated cardiomyopathy (oeM)
DCM is characterized by dilatation and impaired systolic function of the left ventricle and/or right ventricle. The aetiology of idiopathic DCM is unknown. The frequency of the ACE DD genotype is higher than matched controls suggesting that ACE gene variants may contribute to the pathogenesis. There is also an association with viral (Coxsackie) infection and an immunemediated pathogenesis is likely. Many cases of systemic heart muscle disease present with clinical features of DCM and they include:
CARDIOVASCULAR DISEASE (ischaemic, rheumatic, congenital, systemic hypertension)
GENERALIZED DISEASE, e.g. haemochromatosis, sarcoidosis
CONNECTIVE TISSUE DISORDERS, e.g. systemic lupus erythematosus, systemic sclerosis
NEUROMUSCULAR DISEASE, e.g. muscular dystrophy, Friedreich’s ataxia
GLYCOGEN STORAGE DISEASE, e.g. Pornpe’s disease
PRIMARY HEART MUSCLE DISEASE, e.g. amyloidosis
CYTOTOXIC DRUG THERAPY, e.g. doxorubicin, cyclophosphamide
Symptoms depend on the relative degree of right and left heart failure and the incidence of cardiac arrhythmias and emboli.
Physical signs reflect heart failure, i.e. cardiomegaly, tachycardia, jugular venous pressure elevation, third or fourth heart sounds and basal crackles. Ventricular dilatation leads to functional mitral or tricuspid valvular regurgitation.
CHEST X-RAY demonstrates generalized cardiac enlargement THE ECG shows diffuse non-specific ST segment and T wave changes. Conduction disturbances, sinus tachycardia and arrhythmias (such as atrial fibrillation, ventricular premature contractions or ventricular tachycardia) may also be seen.
THE ECHOCARDIOGRAM reveals dilatation of the left ventricle and/or right ventricle with poor global contraction.
CARDIAC BIOPSY shows variable fibrosis and nonspecific leucocyte infiltration. Infiltrative disorders (e.g. amyloid) may be detected in specific cases.
Management involves the conventional treatment of heart failure and arrhythmias. A history of embolization is an indication for anticoagulant treatment. Prolonged bed rest, corticosteroid therapy, the avoidance of alcohol, and nutritional supplements may be indicated in special cases. Metoprolol has been shown to improve haemodynamic and clinical function in some patients. Severe congestive cardiomyopathy in relatively young adults is treated with cardiac transplantation.
Hypertrophic cardiomyopathy (HeM)
Also known as hypertrophic obstructive cardiomyopathy (HOCM), this is characterized by marked hypertrophy of the left and/or right ventricle, particularly the interventricular septum in the absence of a cardiac or systemic cause. The hypertrophied muscle results in distorted left ventricular contraction and abnormal mitral valve movement during systole. Some degree of mitral regurgitation may develop. Apposition of the anterior cusp of the mitral valve to the hypertrophied septum may cause some obstruction to left ventricular emptying. About half of the cases of HCM are familial and due to a genetic disorder of cardiac f3-myosin heavy chain (f3MHC). In the families with a high instance of sudden death, there is an increased frequency of ACE gene polymorphism (DD) (see p. 110). It has been suggested that allele D, which is associated with increased plasma ACE levels, interacts with growth regulators, e.g. c-myc. Thus the high frequency of allele D and different f3MHC mutations may account for the variable clinical presentations of HCM. The aetiology is unknown in sporadic cases. The failure of hypertrophy to manifest before completion of the adolescent growth phase may make diagnosis difficult in children.
Patients with this condition may present with syncope or presyncope (typically exertional), angina, cardiac arrhythmias or sudden death. As with other cardiomyopathies, dyspnoea due to left ventricular failure is a common but late presentation. In this case left ventricular failure is not due to the failing contractile function of the myocardium; instead, it is due to the inability of the heart muscle to relax. Thus, left ventricular filling and therefore left ventricular emptying are impaired.
The classical physical findings are:
DOUBLE APICAL PULSATION (forceful atrial contraction produces a palpable fourth heart sound)
JERKY CAROTID PULSE because of rapid ejection and sudden obstruction to left ventricular outflow during asystole
EJECTION SYSTOLIC MURMUR because of left ventricular outflow obstruction late in systole that can be increased by physical manoeuvres, e.g. Valsalva, squatting
PAN-SYSTOLIC MURMUR due to mitral regurgitation
FOURTH HEART SOUND
CHEST X-RAY is usually unremarkable.
THE ECG demonstrates left ventricular hypertrophy and ST and T wave changes.
THE ECHOCARDIOGRAM is diagnostic because it shows septal hypertrophy (greater than the hypertrophy of the posterior wall), abnormal mitral valve movement and a very vigorously contracting ventricle.
Firstly, sudden death must be avoided by antiarrhythmic treatment. Long-term amiodarone treatment is effective. Syncope or chest pain may be treated with f3-blockade. Vasodilators should be avoided because they may aggravate left ventricular outflow obstruction owing to peripheral venous blood pooling. Occasionally, resection of septal my ocardium may be indicated.
Some cardiomyopathies do not present with muscular hypertrophy or ventricular dilatation. Instead, ventricular filling is restricted (as with constrictive pericarditis). Conditions associated with this form of cardiomyopathy are amyloidosis, sarcoidosis, Loeffler’s endocarditis and endomyocardial fibrosis; in the latter two conditions there is myocardial and endocardial fibrosis associated with eosinophilia. Thrombus formation is common in restrictive cardiomyopathy.
Dyspnoea, fatigue and embolic symptoms may be the presenting features. Restriction to ventricular filling also results in persistently elevated venous pressures and consequent hepatic enlargement, ascites and dependent oedema.
Physical signs are similar to those of constrictive pericarditis, i.e. a high jugular venous pressure with diastolic collapse (Friedreich’s sign) and elevation of the jugular venous pressure with inspiration (Kussmaul’s sign). Cardiac enlargement with a third or fourth heart sound is common.
CHEST X-RAY confirms the cardiac enlargement. THE ECG usually has low-voltage and ST segment and T wave abnormalities.
THE ECHOCARDIOGRAM shows symmetrical myocardial thickening and a normal systolic ejection fraction, but impaired ventricular filling.
TRANSVENOUS ENDOCARDIAL BIOPSY may be useful for more detailed diagnosis.
There is no specific treatment. Cardiac failure and embolic problems should be treated. Cardiac transplantation should be considered in some severe cases.