Cardiovascular system

Diseases of the arterial system

The most common pathological abnormality of the arterial tree is thickening and hardening of the walls, known as atherosclerosis (see Ch. 8 ). Among the risk factors for atherosclerosis are hypertension and diabetes mellitus. In both cases, specific vascular changes may be recognised, often superimposed on the changes of atherosclerosis. Some of the important arterial wall changes associated with hypertension are illustrated in this chapter in Figs 11.1 and 11.2 and in relation to the kidney in Fig. 15.13 .

Aneurysms

Abnormal dilatations of the heart or blood vessels are known as aneurysms . In clinical practice, aneurysms are most often encountered in relation to the aorta, ventricular wall of the heart or vessels of the base of the brain. In respect of aortic aneurysms, most are due to atherosclerosis, where the aortic wall is excessively thinned as a consequence of destruction of the tunica media. Table 11.1 lists the types of aneurysm, their aetiology and their most common sites of involvement. The main complications of an aneurysm are rupture, leading to haemorrhage, and thrombus formation, leading to occlusive or embolic phenomena (see Ch.9 ).

Inflammation of vessels (vasculitis)

Inflammation of the walls of blood vessels may occur in arteries (arteritis) , capillaries (capillaritis) or veins ( phlebitis , venulitis ); the collective term is vasculitis . The classification of this group of disorders reflects an increasing understanding of the underlying pathogenic mechanisms.

• ▪

  Direct infection: Some cases of vasculitis arise from direct infection of the blood vessel wall, for example syphilitic aortitis (see Fig. 5.11) and Aspergillus infection.

• ▪

  Damage to vessels: Vascular injury and resulting inflammation may be caused by direct damage to vessels, such as mechanical trauma and radiation injury.

• ▪

  Immunological: The most common types of vasculitis are caused by a variety of immunological mechanisms, including:

  • ▪

    The deposition of circulating immune complexes in the walls of blood vessels, as in Henoch – Schönlein purpura and post-infectious glomerulonephritis .

  • ▪

    Direct damage to vessel walls by antibodies that react with endothelial cells ( Kawasaki’s syndrome , systemic lupus erythematosus ) or glomerular basement membrane (Goodpasture’s syndrome) .

  • ▪

    Vasculitides associated with antineutrophil cytoplasmic antibody (ANCA) such as granulomatosis with polyangiitis (previously known as Wegener’s granulomatosis) and microscopic polyarteritis ( Fig. 11.7 ).

    
    
    
    

• ▪

  Idiopathic: In some cases, the pathogenesis is unknown. In giant cell arteritis ( Fig. 11.5 ) and Takayasu’s arteritis the underlying process may be an abnormality of cell-mediated immunity. Another major type of vasculitis, polyarteritis nodosa ( Fig. 11.6 ), probably belongs to the immunological group, but its aetiology remains unclear.

Malformations and tumours of blood vessels

There are a variety of malformations and tumours that arise from vascular channels. The commonest among these are haemangiomas ( E-Fig. 11.2 G ), often regarded as hamartomas or developmental abnormalities ( Fig. 11.8 ). Clinically, benign vascular malformations in the brain are of importance as there is a risk of spontaneous intracerebral haemorrhage. Often, such malformations are composed of both arterial and venous channels and are termed arteriovenous malformations ( Fig. 11.9 ).

True neoplasms arising from blood vessels are rare and range from the benign glomus tumour ( glomangioma ; Fig. 11.10 ) to malignant tumours such as Kaposi’s sarcoma ( Fig. 11.11 ) and angiosarcoma ( Fig. 11.12 ). Kaposi’s sarcoma is associated with human herpesvirus 8 (HHV-8) infections and can be seen in patients with immunosuppression, e.g. secondary to HIV infection.

Diseases of the heart

Rheumatic fever

Rheumatic fever is a systemic inflammatory disease that, in susceptible individuals, follows several weeks after a group A β-haemolytic streptococcal throat infection. The systemic manifestations represent a disordered immunological response resulting in inflammation of connective tissues. All parts of the body may be involved, for example the joints and skin, with painful short-term consequences. Involvement of the heart is of great clinical importance because of potentially fatal acute myocarditis and endocarditis and the long-term consequences of chronic scarring of the heart valves ( E-Fig. 11.6 G ).

Valvulitis (endocarditis of valves)

The heart valves may become subject to a variety of vegetative lesions that have traditionally been described as forms of endocarditis . The primary phenomenon underlying all these conditions is the formation of thrombus on the valve leaflets or cusps.

As in the arterial system, roughening of the endocardial surface predisposes to thrombus formation ( Ch. 9 ). This may occur when valve leaflets or cusps have been previously damaged by rheumatic fever or are congenitally abnormal. Thrombus formation may also follow autoimmune valve damage in systemic lupus erythematosus (Libman–Sacks endocarditis) and in the acute phase of rheumatic fever ( Fig. 11.16 ). The most frequent type of valve thrombus, however, occurs in so-called marantic endocarditis ( Fig. 11.17 ), in which warty, thrombotic vegetations develop on mitral and aortic valves. This phenomenon occurs in seriously ill patients, often those with widely disseminated malignancy, and is usually associated with a hypercoagulable state. Despite use of the term endocarditis in these conditions, inflammation is usually not a feature of the valve at the time of thrombus formation.

True valvular inflammation may arise, however, if these thrombotic vegetations on valves then become infected with bacteria, fungi or other organisms, conditions collectively referred to as infective endocarditis . Bacterial endocarditis tends to be divided into two clinicopathological patterns. In the first, traditionally known as subacute bacterial endocarditis , the thrombotic vegetations develop on previously damaged valves, which then become colonised by bacteria of low virulence such as Streptococcus viridans . Such organisms tend to reach the valves via a transient bacteraemia, for example following dental extraction. The major clinical consequences are those resulting from detachment of small thrombotic emboli, often infected, into the systemic circulation.

In the second type of bacterial endocarditis, known traditionally as acute bacterial endocarditis ( Fig. 11.18 and E-Fig. 11.8 G ), thrombi form on previously normal valves and become infected by virulent organisms such as Staphylococcus aureus . In this case, the patient is usually already severely debilitated and septicaemic, for example from an infected urinary catheter, and the infecting organism is responsible for the septicaemia. In contrast with the subacute pattern, in the acute form the fulminating infection extends into the substance of the valve, causing tissue necrosis. Rapid destruction of the valve leaflet leads to valvular incompetence, with acute cardiac failure as the usual clinical outcome.

Fungal endocarditis, formerly rare, is now appearing more commonly as a complication of immunosuppressive therapy, intravenous drug abuse or AIDS. Candida albicans (Fig. 5.15) is the most common organism.

Primary tumours of the heart

Whilst metastases to the pericardium and heart are not infrequent in the late stages of systemic malignancies, primary tumours of the heart are rare, the vast majority being benign. Of these, myxomas are the most common primary cardiac tumours occurring in adults ( Fig. 11.19 ). In contrast, in children, the commonest primary tumours encountered are rhabdomyomas , which are often multiple, present in infancy and have a strong association with tuberous sclerosis . Other tumours that may arise in the heart include lipomas, fibromas and angiosarcomas.

Questions