by Avril Lowry
Continuing professional development is essential for nurses and midwives practising in an ever-changing healthcare environment. With this in mind the WIN Continuing Education section 2007 is focusing on two clinical areas which impact on all areas of the Irish health service – cardiology and diabetes.
As comorbidity with these two conditions is common, the two modules inevitably overlap. Diabetes is one of the primary risk factors for the development of coronary heart disease.
The Cardiology Module to date has focused on: Cardiac risk and type 2 diabetes; Women and stroke; Cardiac rehabilitation; Blood pressure management; Sudden cardiac death; Lipid management; and ECG recording and interpreting.
This month’s module focuses on the treatment of infective endocarditis.
The choice and length of treatment are dictated by the pathogen isolated from cultures and require the close collaboration of microbiologist and physician.
Empirical antibiotic treatment is considered necessary until cultures are resulted on, but should be switched to the appropriate antibiotic as soon as sensitivity has been established. Recommendations for the treatment of most of the common pathogens have been published and the general consensus is that treatment is needed for four to six weeks post identification of pathogen.1 Short course antibiotic treatment (two weeks) has been investigated in patients with right-sided infective endocarditis and uncomplicated infective endocarditis secondary to Streptococcus viridans and found to be safe and efficacious without significant valvular complications.2
Selected patients may also be suitable for once-daily dosage allowing consideration for outpatient management. Treatment with oral linezolid may also be an option for some patients reducing the length of hospitalisation.
The incidence of prosthetic valve IE ranges from 0.1%-2.3% and accounts for almost 10%-15% of cases.3 Transoesophageal echocardiography is almost always needed for investigation, as vegetations are often small and imaging is made difficult by arte-facts related to previous surgery and ‘acoustic shadows’ cast by a metallic prosthesis.
Prosthetic valve endocarditis may be classified as early or late in onset according to the timing of symptoms in relation to the original valve surgery, and a distinct shift in the pattern of infecting organisms is seen one year after surgery.
Staphylococci predominate in early onset prosthetic valve endocarditis, whereas the microbiological spectrum in late onset prosthetic valve endocarditis mirrors that of native valve endocarditis.
Complications are common, and aortic root abscess is a particularly frequent finding when prosthetic valve endocarditis involves the aortic valve. Treatment is difficult, requiring prolonged use of antibiotics, and surgery, when needed, is technically demanding. Overall mortality remains worryingly high at 40%-50%, and specialist care is mandatory.
Intravenous drug abusers
The incidence of infective endocarditis in intravenous drug users is 1%-5% a year and seems to be rising steadily in the UK population. Infection occurs with equal frequency on right-sided and left-sided valves, and Staph. aureus is the most common pathogen.4
These patients present particular management difficulties because of their drug-seeking behaviour and poor compliance with treatment. They often struggle with prolonged hospital stays as a result.
Furthermore, the incidence of recurrent infective endocarditis is high because of repeated drug misuse after successful treatment. Cardiac surgeons may be reluctant to offer surgery in this setting and mortality is substantial.
Who needs cardiac surgery?
Surgery for infective endocarditis is potentially life saving. Morbidity and mortality associated with infective endocarditis are related to valvular regurgitation and abscess formation secondary to tissue destruction, heart failure, and embolic complications.
Rarely, vegetations may become sufficiently large to cause valve obstruction. Overall, surgery is needed in approximately 50% of patients who develop infective endocarditis, and careful timing is essential to ensure a good outcome. In most stable patients, surgery is best delayed until antibiotics are completed to reduce the risk of perioperative complications and early prosthetic valve endocarditis.
Unstable patients with haemodynamic or perivalvular complications have a poor prognosis and are best transferred to a centre at the earliest opportunity.
Indications for urgent valve surgery include:
Surgery is often difficult and associated with high risk, not least because patients are frequently extremely sick with multi-system disease. Furthermore, in the developing world scarce resources and limited access to surgical care may affect management decisions.
Overall surgical mortality in active infective endocarditis is 8%-16%, with actuarial survival rates of 75% at five years and 61% at 10 years.4 Surgery usually involves valve replacement with a metallic or biological prosthesis, but valve-sparing techniques with chordal preservation or partial leaflet resection are becoming more widespread.
Valve replacement with a homograft or use of the Ross procedure (aortic valve replacement using the patient’s own pulmonary valve combined with a pulmonary homograft) have particular attractions in patients with infective endocarditis affecting the aortic valve, especially when complicated by abscess formation. However, application of these techniques may be limited by difficulties with valve procurement or available surgical expertise.
Postoperative antibiotic treatment
A full course of antimicrobial treatment should be completed regardless of the duration of treatment prior to surgery, for at least seven to 15 days postoperatively. In patients with a positive intraoperative culture, myocardial abscess, or a positive gram stain for organisms on the prosthesis removed from a patient with prosthetic endocarditis, a full course of postoperative therapy four to six weeks is required.
Relapse of infective endocarditis usually occurs within two months of the discontinuation of antibiotic therapy, and is known to occur in 2%-20% of patients, the higher range affecting people infected with Staph. aureus.
Recent advances made in international collaboration on investigations and management of infective endocarditis is allowing the development of new diagnostic and treatment strategies. Several exciting developments offer the prospect of improved prevention and treatment of infective endocarditis.
Vaccines targeted at specific bacterial adhesions may inhibit valve colonisation, and newer antibacterial agents with novel effects may tone down the invasive properties of virulent organisms such as Staph. aureus. Modified materials currently in development may also reduce the risk of infective endocarditis in patients with artificial valves. However, despite these advances, the diagnosis and management of infective endocarditis remain a considerable challenge across the range of medical disciplines.
Avril Lowry is an educational facilitator at St James’s Hospital, Dublin