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CTEPH


chronic disease, V/Q remains more sensitive.8


The findings on CTPA in


CTEPH differ widely from those in acute PE because the clot becomes fibrosed, remodelled and intra-mural. The main pulmonary arteries are usually large (>3cm) and often taper rapidly. Intra- mural clot, webs, pouches and acute cut-offs can often be seen, but may require coronal views and reconstruction of images. In the lung parenchyma, mosaic perfusion and areas of old lung infarct can be visualised, so careful interpretation is required to not mistake these abnormalities for ground glass opacities. There can also often be evidence of right heart strain, with an enlarged right ventricle, D-shaped septum and even pericardial effusion.10–12 Thus, CTA becomes an integral part of the work-up of CTEPH, to both suggest the diagnosis and to determine the extent and proximal location of the clot which becomes an important determinant of surgical resectability. The test requires great technical skill both to perform, and to interpret correctly.


Magnetic resonance PA can be a powerful tool to image the pulmonary vascular tree. It can help make the diagnosis of CTEPH, determine the amount of vascular obstruction as well as its proximal extent, which aids in the decision regarding surgical resectability. Many centres, however, do not perform this procedure, and again a high degree of technical expertise is required.12,13 Usually the last diagnostic test performed is left and right heart catheterisation with pulmonary


angiogram. Depending on the centre performing the evaluation, this might be reserved for the referral centre where the decision regarding surgical resectability will be made. During this evaluation, haemodynamics must be measured meticulously. A pulmonary artery wedge pressure and/or a left ventricular end diastolic pressure must be obtained to rule out occult left heart disease. Careful measurements of PAP and cardiac output must be performed. An accurate calculation of pulmonary vascular resistance is necessary to prognosticate and help guide decisions regarding surgical resectability. High PVRs with relatively small amount of resectable clot implies more small vessel arteriopathy and a significantly higher surgical risk. Conventional pulmonary angiography will usually be performed at the same time as the right heart catheterisation. Classic findings of CTEPH confirm the diagnosis. These include: cut-offs, webs, pouches and an overall assessment of the amount of vascularity.14


Depending on the centre’s


preference, coronary angiography may also be performed. If co-existing coronary artery disease is detected, it can be corrected surgically at the time of pulmonary endarterectomy.


Surgical selection


After the diagnosis of CTEPH is confirmed, the preferred therapy is pulmonary thromboendarterectomy (PEA). Not all patients, however, are good candidates for the surgery. There are no clear guidelines regarding which patient is a good candidate for surgery, and this


must be determined in a centre experienced in performing this procedure, often by a multi-disciplinary team. Some aspects that are considered when making the decision include the patient’s age and co-existing medical conditions. Although no degree of elevation in PVR alone makes the patient ineligible for surgery, an elevated PVR pre-operatively elevates the surgical risk. In general, if the amount of clot that the surgeon feels he will be able to remove is unlikely to decrease the PVR significantly, the less likely a patient is to be considered a surgical candidate. In those deemed inoperable, or in recurrent and resistant CTEPH, there is the option for medical therapy and that is discussed elsewhere.


Surgery


Surgery is the only definitive therapy for CTEPH, with PEA being the surgical procedure of choice.15,16


The surgical


technique of PEA has been well described elsewhere.17–20


In brief, a median


sternotomy is performed, and the patient is placed on cardiopulmonary bypass with periods of hypothermic circulatory arrest. This provides a bloodless field for the surgeon to perform the necessary dissection. An incision is made in the right main pulmonary artery, and a plane is found between the intima and media. Chronic thromboembolic material is dissected out along this plane from all branches of the right pulmonary artery. It is very important for the surgeon to obtain the right plane, and dissect out distal ‘tails’ of chronic thromboembolic material from the distal segmental and


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