A Case Of Prosthetic Valve Endocarditis

A 62-year-old male presented with fever and breathlessness four weeks after a prosthetic aortic valve
replacement for aortic stenosis. On examination he appeared pale and had a temperature of 38°C (100.4°F). Auscultation of the heart revealed a prosthetic second heart sound and a long early diastolic murmur. Auscultation of the lungs revealed inspiratory crackles at both lung bases.
Initial investigations are shown.

Hb 11 g/dl
WCC 15 109/l
Platelets 400 109/l
ESR 70 mm/h
Sodium 140 mmol/l
Potassium 4.2 mmol/l
Urea 8 mmol/l
Creatinine 130 mol/l
12-lead ECG Left bundle branch block (old)
Chest X-ray Cardiomegaly and pulmonary oedema

Q 1. Which two of the following investigations will provide the most diagnostic information?
a. C-reactive protein.
b. Renal ultrasound.
c. ASO titres.
d. Serial blood cultures.
e. Transthoracic echocardiography.
f. Urinalysis for blood.
g. Complement fixation tests for Coxiella burnetii.
h. Transoesophageal echocardiography.

Answer:
d. Serial blood cultures and h. Transoesophageal echocardiography.

Question 2. 
Which organism is most likely to be present in the blood culture?
a. Streptococcus viridans.
b. Staphylococcus aureus.
c. Staphylococcus epidermidis.
d. Organism from the HACEK group.
e. Enterococci.

Answer: c. Staphylococcus epidermidis.

Discussion: The patient has developed a fever and murmur of aortic regurgitation only four weeks after a prosthetic aortic valve replacement, indicating early prosthetic valve endocarditis. In early PVE, micro-organisms usually reach the prosthesis by direct contamination during the intraoperative
period or via haematogenous spread several days or weeks after surgery. The consequences of early
PVE are grave as the organisms have direct access to the prosthesis annulus-interface and to perivalvular tissue around the sutures lines since the valve is not endothelialized. Patients with early PVE commonly develop valve dehiscence and annular abscesses. The risk of embolic phenomena is also greater with PVE. The clinical features are similar to native valve endocarditis.

Diagnosis relies on culturing the organisms from the blood. Three sets of blood cultures should be taken at intervals of >1 hour within the first 24 hours if the diagnosis is highly likely in a sick patient. If the patient is not acutely ill or when the diagnosis is not obvious, six sets of blood cultures should be taken within the first 24 to 48 hours.

The commonest organisms cultured in early PVE are Staphylococcus epidermidis followed by Staphylococcus aureus and then fungi. In contrast, organisms cultured in late PVE are similar to those
causing infection on native valves.

Transoesophageal echocardiography is the investigation of choice and is advocated as the first-line
echocardiographic modality in the investigation of PVE. TOE is much more sensitive than transthoracic echocardiography at identifying vegetations on the prosthetic valve. It is also superior at identifying complications such as paravalvular abscesses and fistula formation.

The treatment comprises high-dose intravenous antibiotics for six weeks. The need for surgical intervention is much higher than with native valve endocarditis.

Indications for surgery in PVE and native valve endocarditis are :

Prosthetic valve endocarditis
• Early PVE in first 2 months or less after surgery
• Murmurs suggestive of valve dysfunction
• Moderate to severe heart failure
• Annular or aortic root abscess or new cardiac conduction abnormalities on ECG
• Persistent fever for 10 or more days despite appropriate antibiotic therapy
• Staphylococcus aureus or fungi cultured from the blood.

Native valve endocarditis
• Acute AR or MR with heart failure
• Annular or aortic root abscess
• Fungal endocarditis
• Evidence of persistent infection despite appropriate antibiotic therapy for 10 days (fever, leucocytosis and bacteraemia)