The indications for CT Angiography and Cardiac CT in patients with suspected or diagnosed IE include:

1) Diagnosis of IE and cardiac complications. Cardiac CT is more accurate than transesophageal echocardiography for diagnosing perivalvular and periprosthetic complications of IE (abscesses, pseudoaneurysms, and fistulae) and is recommended in both native valve endocarditis and prosthetic valve endocarditis. In addition, cardiac CT can significantly influence subsequent surgical decision-making. Cardiac CT should be acquired according to the recommendations of cardiac CT guidelines to ensure high diagnostic accuracy, and can be performed alone or in combination with PET.

2) Detection of distant lesions and sources of bacteraemia. Whole-body and brain CT are useful for assessing IE systemic complications, including septic emboli. The detection of distant lesions adds a minor diagnostic criterion leading to a more conclusive diagnosis of definite or rejected IE, and can be relevant for decision-making. CT angiography can detect mycotic arterial aneurysms complicating IE in almost any site of the vascular tree, including the central nervous system (CNS).

3) Pre-operative assessment. Cardiac CT is a valuable alternative for non-invasive assessment of coronary artery disease (CAD) before cardiac surgery in patients with IE.

4) Alternative diagnosis. In patients in whom IE is ruled out, or even in doubtful patients with possible IE, an alternative diagnosis can be reached by whole-body CT, as it can help to detect alternative infectious foci.

In the past year we have gathered around 40 cases of infective endocarditis diagnosed by angiotomography and cardiac CT. We noticed that angiotomography had a better diagnostic capacity for evaluating right-sided endocarditis compared to both transthoracic and transesophageal echocardiography, mainly due to their greater difficulty in evaluating the pulmonary valve.

We've listed 8 clinical cases below, with multiplanar and three-dimensional reconstructions of complications related to infective endocarditis, as well as detailed our institution's angiotomography protocol for IE.

Vegetation: Oscillating or non-oscillating intracardiac mass (hypoattenuating filling defects) on valve or other endocardial structures, or on implanted intracardiac material.

Fig 1: Cardiac Computed Tomography Angiography (CCTA) in the sagittal (A) and coronal (C) planes, showing three hypoateanuating lobulated formations adhered to a biological pulmonary prosthesis (white arrow). Dynamic Cine-CT Angiography (B) and cine-CT with 3D volume rendering technique demonstrating the mobility of the lesions during the cardiac cycle. The patient has undergone valve replacements in both the pulmonary and mitral positions and presented with symptoms of fever and drowsiness. Subsequent blood cultures yielded positive results for Enterococcus faecalis. Both transthoracic and transesophageal echocardiography had no window for adequate assessment of the pulmonary valve prosthesis. The angiotomographic findings are compatible with vegetations, confirming the presence of major diagnostic criteria for infective endocarditis. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023. Key abbreviations: LA (left atrium), LV (left ventricle), RV (right ventricle).

Pseudoaneurysm of the mitral-aortic fibrosa or intervalvular fibrosa: Cavity in the mitral-aortic junction communicating with the left ventricular outflow tract.

Fig 2: CCTA with reconstructions in the three-chamber view (A) and in the oblique sagittal plane centred on the aortic root (B) presenting dissection of the mitral-aortic fibrosis (*), resulting in the formation of a pseudoaneurysm around the aortic root (*), observed in a 33-year-old patient with a prosthetic biological aortic valve with the with the diagnosis of infective endocarditis. (C,D) 3D volume rendering technique demonstrating the sacculations generated by the formation of pseudoaneurysms. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023. Key abbreviations: Ao (Aorta), LA (left atrium), LV (left ventricle).

Pseudoaneurysm: Abnormal outpouchings or dilatation which are bounded only by the tunica adventitia, the outermost layer of the arterial wall.

Fig 3: Cardiac Computed Tomography Angiography (CCTA) in the coronal (A) and axial (B) planes, along with 3D volume rendering technique (C) collectively reveal an elongated outpouching (indicated by the arrow), which is consistent with a pseudoaneurysm located in the ascending aorta. The diagnosis of infective endocarditis involving a mechanical prosthetic aortic valve was subsequently confirmed. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Perforation: Interruption of endocardial tissue continuity.

Fig 4: CCTA-3D volume rendering technique with endoluminal reconstruction (A), short axis (B) and three-chamber view (C) in sistolic phase (with a closed mitral valve) reveal a pathological unnatural communication (pink arrows), consistent with perforation of the mitral valve, secondary to infective endocarditis caused by Staphylococcus epidermidis. (D) Doppler echocardiography confirming the presence of significant mitral valve regurgitation through this defect (D). © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Abscess: Collection of fluid attenuation around the aortic valve surrounded by inflammatory tissue with peripheral contrast enhancement.

Fig 5: Cardiac Computed Tomography Angiography (CCTA) in the axial plane and three-chamber view with angiographic window (A,C) and mediastinal window (B,D), showing an elongated, hypodense formation (*) with peripheral contrast enhancement (arrow), and densification of the surrounding fat, indicative of a periprosthetic aortic abscess in a patient diagnosed with infective endocarditis (Staphylococcus lugdunensis) of a biological aortic prosthesis. In the long-axis three-chamber view of the left ventricle (C and D), we can see accurately that the abscess clearly extends from the aortic root to the ascending aorta. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Septic embolism: Vascular obstruction caused by embolisation of an infected thrombus that may lead to infarction and possible abscess formation.

Fig 6: Cardiac Computed Tomography Angiography (CCTA) in the axial (A) and coronal (B) planes demonstrating hypoattenuating lobulated formations adhered to the tricuspid valve (the largest centred on the cross-hair), compatible with vegetations, confirming the diagnosis of right-sided infective endocarditis. (C) Cine-CCTA showing the mobility of the lesions during the cardiac cycle. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Fig 7: CCTA in the axial (A), sagittal (B) and coronal (C) planes showing a small hypoattenuating filamentous formation attached to one of the leaflets of the pulmonary valve, with extension to the subvalvar region, compatible with vegetation (yellow arrows). This is therefore a case of right-sided infective endocarditis affecting both the tricuspid and pulmonary valves. (D) Contrast-enhanced chest CT in the axial plane showing a abnormal fluid collection of low attenuation with thickened walls and peripheral contrast enhancement, compatible with perivalvular abscess (red arrow). © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Fig 8: Angiotomography of the chest in the axial (A) and coronal (B) planes, showing a segmental filling defect in the brachiocephalic vein, adjacent to the dialysis catheter, compatible with a thrombus, possibly infected. In the context of endocarditis, it is assumed that the catheter was contaminated. (C) CT pulmonary angiography showing filling defects in the pulmonary arterial branches of the left lower lobe, consistent with pulmonary thromboembolism (red arrows). © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Fig 9: Chest CT with a lung parenchyma window in the axial (A), sagittal (B) and coronal (C) planes, showing multiple peripheral nodules, many of them excavated, diffusely distributed, with a predominance in the left lung, compatible with septic pulmonary embolism (red arrows), secondary to right-sided infective endocarditis. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Mitral valve aneurysm: It is a rare and uncommon complication of infective endocarditis. The infectious process leads to inflammation and softening of the mitral valve tissue, leading to aneurysm formation. The most feared mitral valve aneurysm's complications are perforation and mitral regurgitation.

Fig 10: Cardiac Computed Tomography Angiography (CCTA) in three-chamber view (A,B), short axis (C) and two-chamber view (D), showing deformity and thickening of the anterior leaflet of the mitral valve with focal bulging of the A2 leaflet white arrow) towards the left atrium, measuring 1 x 0,5 cm. Mitral valve aneurysm in a patient with confirmed infective endocarditis. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

CT Angiography Endocarditis Protocol (InCor-HCFMUSP)

Retrospective electrocardiographic gating is necessary for imaging throughout the entire cardiac cycle. We employ approximately 110 mL of high iodine concentration contrast (350 - 400 mg of iodine per mL), which is adjusted based on the patient's body mass index. Scan triggering is accomplished through bolus tracking, utilizing a region of interest (ROI) placed on the descending aorta. The entire cardiac cycle is acquired, with a field of view (FOV) of the coronaries and heart. Following the initial acquisition, angiotomography of the thoracic and abdominal aorta is performed. Subsequently, a 70-second venous phase of thorax and abdomen acquisition is carried out. The primary goal of these later phases is to detect peripheral complications associated with endocarditis, such as mycotic aneurysms, renal and splenic infarctions.  We set up a table with an example of angiotomography acquisition for the endocarditis protocol and separated the respective images generated.

Fig 11: Cardiac Computed Tomography Angiography (CCTA) in four-chamber (A), two-chamber (B), short axis (C) and three-chamber views (D), with reconstruction at every 10-10% of the R-R interval to generate cine clips. Thoracic and abdominal aortic CT angiography (E). Chest and abdomen CT venous phase (F). Acquisition stages of the CT Angiography Endocarditis Protocol. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

We do not routinely perform cranial CT angiography in the endocarditis protocol. Only in the case of associated focal neurological deficit, found in the following complication of IE:

Mycotic aneurysms:  Aneurysms resulting from infection of the arterial wall, usually bacterial. This is a complication of the haematogenous dissemination of a bacterial infection, usually from the heart.

Fig 12: Non-contrast CT Brain in the axial (A) and coronal (B) planes showing corticosubcortical hypodensity with loss of grey-white matter differentiation in the topography of the left precentral gyrus (red circle). Maximum projection intensity reconstruction of brain CT angiography (C,D) showing minimal parietal irregularities of the vessels, some with the formation of small sacculations, the largest measuring 0.4 cm, compatible with mycotic aneurysms (red arrow). Young patient with ischaemic stroke and mycotic aneurysms secondary to infective endocarditis of mitral valve prosthesis. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.

Fig 13: Contrast-enhanced abdominal CT scan showing peripheral, wedge-shaped hypoenhancing areas with subcapsular retractions of the spleen, compatible with splenic infarcts (blue and red arrows). Parenchymal perfusion defect involving both cortex and medulla, extending to the capsular surface of the middle third of the left kidney, compatible with renal infarction (red circles). Young patient with ischaemic stroke, mycotic aneurysms, splenic and renal infarcts secondary to infective endocarditis of mitral valve prosthesis. © Department of Radiology, Instituto do Coração (InCor-HCFMUSP), São Paulo/ Brazil 2023.