28th July 2023

Cardiovascular Infections

Infections of the cardiovascular system are rare. The most commonly seen in medicine are endocarditis and septic thrombophlebitis.

Infective endocarditis

Endocarditis refers to any infection of the endocardial lining of the heart, i.e. the endocardium. It most commonly affects valvular tissues. It is associated with a high degree of morbidity and mortality rate. Endocardial infections lead to bacteraemia, and a hallmark is, therefore, positive blood culture.

Many organisms can cause infective endocarditis, with the commonest being Gram positive bacteria, such as Streptococci, Staphylococci (generally Staphylococcus aureus) and Enterococci species. The HACEK (Haemophilus, Aggretobacter, Coxiella, Eikenella, Kingella) group of Gram negative bacteria may also cause endocarditis.
Staphylococcus aureus endocarditis is often rapidly progressive and quickly fatal without prompt antibiotic treatment. Enterococcal endocarditis typically affects elderly men and takes a subacute course. The urinary tract system may be the initial source. Streptococcus viridans are commensals of the oropharynx and can translocate and cause endocarditis, especially in the context of poor dentition and an abnormal heart valve. Streptococcus bovis is part of the gut flora, and endocarditis with this organism has been associated with colorectal cancer – warranting further investigation.
Diagnosis of infective endocarditis relies on a combination of microbiological investigation and imaging (i.e. echocardiogram). The Duke’s modified criteria is used for diagnosis and is important to know for MRCP exams (see below). To diagnose endocarditis definitively, one of the following conditions must be fulfilled:

• 2 major and 1 minor criteria
• 1 major and 3 minor criteria
• 5 minor criteria

Table 1: Duke’s modified criteria for infective endocarditis

Empiric antibiotic treatment covers the main organisms until an organism is identified, which allows targeted treatment. Generally:

• Staphylococcus aureus – high dose flucloxacillin
• Streptococci species – benzylpenicillin
• Enterococci species – amoxicillin
• HACEK organisms – ceftriaxone.
• Gentamicin can be added to some regimens for Streptococci endocarditis to shorten the duration of treatment and is often used for synergistic effects to treat Enterococci.

The indications for surgery are nuanced but essentially comprise heart failure, uncontrolled infection, large vegetations, or aortic root abscess. A vegetation of > 3c m is an indication for surgery.

Septic thrombophlebitis

Septic thrombophlebitis is seen in intravenous drug users, where injection into the vein causes a deep vein thrombosis to form, which then becomes infected. This is commonly in the groin area.
The bacteria implicated in this area may comprise usual skin flora, anaerobes and Gram negative bacteria. Ultrasound helps to confirm the presence of thrombosis with positive blood cultures proving the infection. Broad spectrum antibiotics are often required due to the infection’s polymicrobial nature, and the treatment duration is usually around 6 weeks.