Heart valve emergencies

Epidemiology

The incidence of infective endocarditis is 3 to 10 episodes/100,000 person-years, of which prosthetic valve endocarditis (PVE) accounts for 20% to 30%. The male-to-female ratio is ≥2:1, and it is more common in the fifth and sixth decades of life.

In the developing countries, rheumatic heart disease is the commonest risk factor for infective endocarditis. Despite a fall in the incidence of rheumatic fever in developed countries, the prevalence of infective endocarditis has not fallen. In the developed world, the risk factors include the following:

• Host-related factors

  • Poor oral hygiene

  • Intravenous drug use (IVDU)

  • Severe renal disease, on haemodialysis

  • Diabetes mellitus

  • Mitral valve prolapse—particularly in the presence of valve incompetence or thickening of the valve leaflets

  • Degenerative valve sclerosis associated with age (mitral valve most common, then aortic, tricuspid and pulmonary valves, respectively)

• Procedure-related factors

  • Infected intravascular device

  • Post–genitourinary procedure

  • Post–gastrointestinal procedure

  • Surgical wound infection

Pathology and pathogenesis

In infective endocarditis, the interactions between host and organism are complex. Platelet-fibrin deposits form at sites of endothelial damage; this is known as non-bacterial thrombotic endocarditis. Invasion and multiplication by a virulent microbe lead to enlargement of these vegetations, which become infected. The consequences of this are the basis of the clinical complications of infective endocarditis. The vegetations can fragment and embolize, leading to distal foci of infection, called septic emboli. Obstruction of vessels by these fragments can also result in tissue ischaemia and infarction. Seeding from these fragments perpetuates the bacteraemia. Local destruction of the valve may produce intracardiac complications, such as rupture of the chordae tendineae, abscess of the valve annulus and conduction problems.

Staphylococcus aureus , entering through a breach in the skin, has surpassed Streptococcus viridans as the commonest bacterial pathogen in both native valve endocarditis (NVE) and PVE. This change reflects better dental care and an increased incidence of nosocomial infections, although significant geographical variation exists. In proven S. aureus bacteraemia, the incidence of infective endocarditis is 13% to 25%. Overall, three major pathogens account for more than 80% of cases: S. aureus , Streptococcus species and Enterococcus species.

Nosocomial infective endocarditis is defined as endocarditis occurring after 72 hours of hospital admission or within 4 to 8 weeks of an invasive procedure performed in a hospital. Organisms responsible for nosocomial endocarditis are Staphylococcus species (>75%, mainly S. aureus ) and Enterococcus species in genitourinary and gastrointestinal tract procedures. Organisms associated with particular host categories are shown in Table 5.7.1 .

Fungal infections account for less than 10% of cases and are most common in IVDU, the immunocompromised and those with prosthetic valves. The gram negative HACEK group ( Haemophilus species, Actinobacillus actinomycetemcomitans , Cardiobacterium hominis , Eikenella corrodens , Kingella kingae ) are growing in importance and lead to large vegetations that may result in large vessel embolization or cardiac failure. Endocarditis caused by the HACEK group is often culture-negative, as these bacteria are fastidious.

Prevention

The decision to administer a procedural prophylactic antibiotic to at-risk patients depends on the assessment of the risk of endocarditis in the abnormal valve coupled with the risk of bacteraemia of the procedure being undertaken. High-risk valve lesions are prosthetic valves, mitral valve prolapse with significant incompetence and acquired dysfunctional valves in indigenous patients (because of the high incidence of rheumatic heart disease). The indications for antibiotic prophylaxis have been significantly reduced in major infective endocarditis prophylaxis guidelines, and many now recommend against prophylaxis for gastrointestinal or genitourinary tract procedures. Prophylaxis for dental procedures that involve manipulation of either gingival tissue or the periapical region of teeth or perforation of the oral mucosa is reasonable for those with the highest risk of adverse outcomes from endocarditis ( Box 5.7.1 ). These changes are due to the changes in the risk-benefit ratio of prophylactic treatment. It is believed that infective endocarditis is much more likely to result from frequent exposure to random bacteraemias associated with daily activities than from those listed procedures.

When indicated, a single-dose antibiotic 30 to 60 minutes before the procedure is now recommended. Current recommendations from the European Society of Cardiology (ESC) suggest

• KH amoxicillin or ampicillin 2 g orally or intravenously for adults (50 mg/kg for children) or

• clindamycin 600 mg orally or intravenously if patient is allergic to penicillins

Clinical features

Infective endocarditis should be considered a multisystem disease. The symptoms and signs are non-specific, compounding the difficulty of diagnosis. Symptoms usually occur within 2 months of the event responsible for the initiation of bacteraemia, although this may be difficult to identify in retrospect. It is important to suspect infective endocarditis in patients with an unexplained fever and a predisposing factor.

The two most frequent systemic features are fever and malaise. Fever is present in 80% to 85% of cases; usually above 38°C but rarely above 39.4°C. It can be absent in the severely debilitated, the elderly and those with cardiac failure, chronic renal failure, liver failure, recent antibiotic use and if the infection is by a low-virulence organism.

Malaise is reported in up to 95% of cases. Other symptoms are variable and non-specific and may include headache, confusion, cough, chest pain (more common in IVDU), dyspnoea, abdominal pain, anorexia, weight loss and myalgia.

Other clinical features include immunological phenomena as well as those related to the lesion itself and systemic embolization. Immunological phenomena include glomerulonephritis, Osler nodes, Roth spots and an elevated rheumatoid factor.

A new or changed incompetent murmur may be found on clinical examination of the heart. However, in 70% to 95% of cases, a murmur is already present; hence the discovery of an acute murmur is an uncommon but highly significant finding. The absence of a murmur does not exclude the diagnosis of infective endocarditis. A new murmur or a change of murmur is more likely in patients with a prosthetic valve or congestive cardiac failure.

Petechiae are commonly found in the palpebral conjunctivae and are also present in the mucosal membranes. Splinter haemorrhages under the fingernails, Osler nodes (painful tender swellings of the fingertips or toe pads), Janeway lesions (small haemorrhages with a slightly nodular character on the palms and soles) and Roth spots (oval retinal haemorrhages with a clear pale centre) are uncommon.

Complications

Congestive cardiac failure may occur and is usually a result of infection-induced valvular damage. Involvement of the aortic valve is more likely to cause congestive cardiac failure than mitral valve damage. The other cause is extension of the infective process beyond the valvular annulus. Involvement of the septum produces atrioventricular, fascicular and bundle-branch blocks. Cardiac rupture and tamponade have been reported but are rare. Pericarditis can result from extension into the sinus of Valsalva. Myocardial infarction can also occur as a result of infective embolism to the coronary arteries but is rare.

Neurological manifestations, the result of embolic events from left-sided lesions, are present in approximately 15% of patients and are more likely if the pathogen is S. aureus . These include meningoencephalitis, focal deficits, transient ischaemic attacks and stroke. Embolic stroke is the most frequent event, but intracranial haemorrhage may occur as a result of rupture or leak of a mycotic aneurysm, septic arteritis or bleeding into an infarct. The mortality is high.

Systemic embolization occurs in 40% of cases and gives rise to the peripheral manifestations of infective endocarditis. The embolization usually precedes the diagnosis. Its incidence falls with the administration of appropriate antibiotics. Embolization may involve any organ but skin; splenic, hepatic and renal emboli are most common. Notably, systemic emboli are absent in infective endocarditis of the tricuspid valve, but multiple pulmonary abscesses are characteristically present.

Renal dysfunction may be due to altered renal haemodynamics, immune complex–mediated glomerulonephritis or nephrotoxicity from medications. Splenomegaly is present in 30% of cases. This is due to splenic abscesses arising from direct seeding from the bacteraemia or from an infective embolus. It leads to persistent fever, abdominal pain and diaphragmatic irritation. Tender hepatomegaly may also be present. Anaemia is common.

Complications are summarized in Table 5.7.2 .

Diagnosis

The diagnosis of infective endocarditis requires a high degree of suspicion along with integration of data from various sources. This is due to the non-specific nature of the clinical manifestations. The Duke criteria for infective endocarditis are a useful diagnostic tool that has good specificity and a negative predictive value above 92%. These combine patient risk factors, isolates from blood cultures, the persistence of bacteraemia, echocardiographic findings and other clinical and laboratory data. It has been regularly updated and the version in the latest 2015 European Society of Cardiology guidelines is shown in Boxes 5.7.2 and 5.7.3 .

Severely ill patients with obvious sepsis should be treated without delay according to the ‘Surviving Sepsis’ guidelines. However, infective endocarditis commonly presents in a more insidious way. When fever is persistent and unexplained, infective endocarditis must be considered, particularly in situations such as the following:

• Patients with acquired or congenital valvular heart disease, a pre-existing prosthetic valve, hypertrophic cardiomyopathy, congenital heart disease (patent ductus arteriosus [PDA], ventricular septal defect [VSD], coarctation of the aorta), intracardiac pacemakers, central venous lines or intra-arterial lines or a new or changed cardiac murmur

• Patients with known bacteraemia. In S. aureus bacteraemia, the risk of infective endocarditis is higher if it is community acquired, there is no primary focus of infection, there is a metastatic complication and, in the context of an intravascular catheter being a possible focus of infection, if fever or bacteraemia is present for greater than 3 days despite removal of the catheter

• Cases with features of an embolic event, especially if recurrent

• Young patients with unexpected stroke or subarachnoid haemorrhage

• Patients with a history of IVDU, especially if there are pulmonary features, such as cough and pleuritic chest pain

• Cases of persistent bacteraemia or fever despite treatment, congestive cardiac failure or new ECG features of atrioventricular heart block, fascicular block and bundle branch block

Clinical investigations

Treatment

Management involves the use of antibiotics to eradicate the pathogen and other interventions to deal with the intracardiac and distal complications of the infections. Cardiac surgery may be required, the timing of which is difficult to judge. Early specialist referral is critical, particularly if signs and symptoms of congestive heart failure are present.