Endocarditis: definitions, causes, diagnosis, echocardiography & treatment

Endocarditis

Endocarditis implies that a bacterial infection engages the heart valves and this is a serious condition. The focus of infection on the flap is called vegetation. As a rule, some kind of damage to native (own) valves is required to become vulnerable and contaminated by bacteria . Infections are difficult to heal because the heart valves are not vascularized and therefore it is difficult for the immune system to reach the bacteria.

Endocarditis can lead to the destruction of the valvular apparatus, as well as to embolization in the systemic circulation. The complications can be fatal. Approximately 500 Swedes are affected annually by endocarditis and the median age of 70 years at the onset of the disease. Approximately 12% die within 30 days, compared to the 30-day mortality of STEMI (ST segment elevation infarction) , which is about 6%.

Previously, alpha-streptococcus was the most common agent. These streptococci most often originate from the oral cavity and affect heart valves that have some kind of damage, change or degeneration. Endocarditis with alpha-streptococcus is most often subacute and can develop gradually over several days to weeks. More acute endocarditis is often caused by staphylococcus auerus. This usually affects drug users (intravenous addiction), elderly patients with altered valves, patients with valve prostheses or other cardiac devices (pacemaker, CRT, ICD). In addition to staphylococcus aureus , hemolytic streptococci and pneumococci cause acute endocarditis. Other microorganisms, generally, cause subacute endocarditis.

Endocarditis can affect native (own) valves and valve prostheses. As always, foreign materials pose a high risk of infection. Approximately 20% of all endocarditis affect people with valve prostheses and among other cases 18% show significant valvular disease.

Table 1. Etiologies in acute endocarditis.

Table 2. Etiologies in subacute endocarditis.

Echocardiography in endocarditis

In 1973, it was the first time to describe how echocardiography (M-mode) can be used to diagnose endocarditis. With 2D and later 3D ultrasound, the technology has been greatly refined. Similarly, the development of transesophageal echocardiography (TEE) has been extremely valuable. Echocardiography is used to assess the morphology of valves, the presence of vegetations, hemodynamic status, and the extent of endocarditis.

Endocarditis gives three typical findings on echocardiography:

1. Vegetations.
2. Abscesses.
3. Prosthetic detachment.

These three findings constitute the main criteria for diagnosing endocarditis. Traditionally, it has been considered that endocarditis can be diagnosed if at least two criteria exist.

Figure 1. Flow chart for the investigation of suspected endocarditis.

Vegetations

Vegetations are ecotate masses made up of the foci of infection. Vegetations can be found on the flaps and appear as moving masses. Mural vegetations are attached to the endocardium and, accordingly, less mobile.

Echocardiography is the first place method for detecting vegetation in case of suspicion of endocarditis. Transthoracic echocardiography (TTE) has a sensitivity of about 50% among them (this implies that 50% of all people with endocarditis will be diagnosed with TTE and, accordingly, 50% will be missed).

The sensitivity and specificity of echocardiography depend on several factors, such as image quality, vegetation localization, echogenicity and size, presence of valve prostheses, and the habit of the investigator. As with the clinical labor test (working ECG) , the value of echocardiographic examination depends on the *pre-test probability,*which is the probability that the patient actually has endocarditis (this the probability should be estimated before echocardiography is performed). Among patients with a very high probability of endocarditis, the sensitivity and specificity of the examination will increase, and vice versa.

In case of suspicion of endocarditis, transthoracic echocardiography (TTE) is initially done. If the images are of good quality and there are no signs of endocarditis, differential diagnoses should be considered first. If TTE is negative but clinical suspicion persists, transesophageal echocardiography (TEE) should be performed. TEE should always be performed if the patient has valve prostheses, as well as in difficult to assess cases and when the image quality with TTE is unsatisfactory. TEE should also be used if perivalvular complications are suspected, or if the infection is caused by highly virulent agents (e. g. beta-streptococci or staphylococcus auerus).

Native valve endocarditis

Transthoracic echocardiography (TTE) has low resolution and therefore low sensitivity to small vegetation compared to transesophageal echocardiography (TEE). TTE's sensitivity is approximately 25% for vegetation <5 mm; 70% on vegetation 6-10 mm. Of course, sensitivity is affected by other changes in the body, such as myxomatous thickening or calcification.

TEE provides better resolution and increases the sensitivity and specificity of vegetation. In studies comparing the sensitivity to vegetation, TTE has a sensitivity of about 50% while TEE has sensitivity between 90-100%.

The negative predictive value (NPV) for TEE is between 86% and 97%. This implies that the absence of vegetation on the TEE implies that it is 86— 97% likely that the patient does not have vegetation. Among patients with native valves, this implies that endocarditis is very unlikely. However, it should be mentioned that if TEE is done early in the course, the TEE may also be negative, despite the fact that the patient has endocarditis (Sochowski et al ) . TEE should be made if the TTE is inconclusive or negative and suspicion persists.

Echocardiography should be performed very liberally in the following groups of patients:

• Patients with bacteraemia with S. aureus.
• Patients with repeated bacteriaemia with the same agent without a clear focus.
• Patients with devices (pacemaker, ICD, CRT) with fever without clear focus.

Differential diagnoses in case of suspicion of endocarditis

Echocardiography can not distinguish infectious vegetations from aseptic vegetations. Several other conditions may give rise to aseptic vegetation, including:

1. Libman-Sack's endocarditis (affects patients with SLE).
2. Antiphospholipid syndrome.

Libman-Sack Endocarditis

Libman-Sack's endocarditis is similar to infective endocarditis on echocardiography. However, this type of endocarditis is aseptic and the vegetation consists of immune cells, hematoxil bodies, coagulation factors and platelets. Libman-Sack's endocarditis does not lead to the destruction of the valves, which is why the condition is less acute than bacterial endocarditis. This endocarditis most often has little hemodynamic influence, which is why most patients are asymptomatic. The absolute majority of patients have SLE (systemic lupus erythematosus).

Libman-Sack's endocarditis most often affects the mitral valve and/or the aortic valve. Echocardiographically, it is difficult to distinguish these vegetations from bacterial vegetations. In addition, the aseptic vegetation can become the site of bacteria, in which a bacterial endocarditis occurs. In Libman-Sack endocarditis, embolization is rare, but it occurs.

Antiphospholipid syndrome is also associated with Libman-Sack's endocarditis.

Prostethic valve endocarditis

Valvular prostheses complicate transthoracic diagnostics of endocarditis. Therefore, the TTE must be supplemented with TEE if the patient has valve prostheses. This applies to both mechanical and biological prostheses. The sensitivity of the TTE is 36 -69%, while the TEE has sensitivity of 86-94% and specificity 88 -100%.

Valve prostheses have several components that interfere with imaging, such as sewing collar, stent in percutane valve prostheses, discs in mechanical flaps, etc. These structures are ecotdense and give rise to artifacts that complicate the visualization of vegetation. In vegetations on the sewing collar, it appears thicker and more irregular. However, it is difficult to distinguish these changes from those seen in thrombosis and pannus formation.

Biological valve prostheses, like native valves, can be destroyed by endocarditis.

Right sided endocarditis

Right-sided endocarditis most often affects intravenous addicts, and vegetation, generally, is large. This means that TTE is usually enough to diagnose. Vegetations are found, generally, on the atrial side of the tricuspid valve. Studies show that TTE is as effective as TEE for endocarditis affecting tricuspidalis. However, for the pulmonary valve, TEE appears to have higher sensitivity and specificity.

Infected electrodes and devices

TEE has a higher specificity and sensitivity to endocarditis affecting electrodes and other devices. Sensitivity for TEE is 94% and for TTE 23%. Reverbations and other species factors make it difficult to detect endocarditis on electrodes with TTE.

Complications of endocarditis

Infected valves, generally, are insufficiency. This may be due to several causes, such as valve damage (native and biological valves), loosening of valve prostheses, or vegetation impairs coaptation (possibility for the cuss/discs to meet and close tightly).

Native and biological valves are permanently damaged by endocarditis. Damage varies from small perforations to total valve destruction. Perforation or destruction affects 50% of aortic endocarditis and 15% of mitral endocarditis.

If endocarditis engages chordae tendinae , the threads may detach from the valve, resulting in prolapse.

The infection can spread from the valves to surrounding tissues, which is associated with a worse prognosis. This can result in infections, abscesses, fistulas of the myocardium and perivalvular structures.

Perivalvular abscesses can affect all types of valves but are most common in valve prostheses. Abscesses have low echo density, which implies they are seen as darker, well-delimited areas on the 2D image. TTE has sensitivity and specificity of 28% and 99%, respectively, for abscesses. The corresponding figures for TEE are 87% and 95%.

Other investigation of endocarditis

• Blood cultures are fundamental for diagnostics and treatment. Three pairs of bottles of 10 ml in each bottle are taken from 3 points. In about 10% of diagnosed cases, the cultures are negative.
• Blood tests: blood, electrolyte status. CRP. SR. Glucose. CRP is often only slightly moderately elevated (20-50 mg/l) with endocarditis lenta. Troponin.
• Echocardiography. See above.
• regular temperature controls;
• Lung and heart auscultation daily
• resting ECGThe
  • new appearance of AV blockade indicates an abscess.
  • Arrhythmias are common; telemetry should be linked.
• Chest X-ray/DT thorax with a problem of heart failure, septic embolism.
• DT brain at focal neurological symptoms.