Recommendations
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these events also occur during CT or MRI. However, adequate sedation with strict blood pressure control is mandatory. When Figure 7 Algorithm of diagnostic strategy of acute aortic dissection depending on whether the first test was transthoracic echocardiography or computed tomography. *Depending on availability, complications, and examiner experience. **Definitive diagnosis of type A dissection by transthoracic echocardiography permits the patient to be sent directly to surgery provided intraoperative transoesophageal echocardiography is performed before surgery. Figure 8
Transoesophageal echocardiography. (A) ascending aorta dissection by long-axis view. Arrows show the intimal flap. (B) descending thoracic aorta dissection by transverse view. Two jets from true lumen to false lumen identified the pres- ence at secondary communications. Echocardiography in aortic diseases 653 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from therapeutic decision-making is definitive by other techniques, TOE should be performed in the operating theatre before surgery or when the patient is haemodynamically stable with no chest pain. Given its accuracy in the diagnosis of aortic dissection, intramural haematoma and aortic ulcers, TOE is a technique of choice in acute aortic syndrome diagnosis when an expert echocardiogra- pher is available. Recommendation Although TOE is the technique of choice in aortic dissection diag- nosis, TTE may be used as the initial imaging modality in the emer- gency setting. Contrast may improve its accuracy. If the diagnosis of type A dissection by TTE or contrast-TTE is definitive, surgical treatment could be directly indicated, provided intraoperative TOE is performed just prior to surgery to confirm the diagnosis. In suspected type B dissections, TOE or CT should be performed according to clinical presentation, complications, and examiner experience. When contrast-TTE fails to show abnormalities, another imaging technique must be applied for acute aortic syn- drome to be definitively ruled out. Diagnosis of morphological and haemodynamic findings in aortic dissection TOE permits assessment of the main anatomical and functional aspects of interest for the management of aortic dissection. Intimal tear location The intimal tear appears as a discontinuity of the intimal flap. TOE provides a direct image of the tear and permits its measurement. Erbel et al. 55 demonstrated a different evolutive pattern according to the presence and location of the tear. TOE permits identifi- cation of the tear in 78 – 100% of cases. 55 Colour Doppler can reveal the presence of multiple small communications between the two lumina, especially in descending aorta. Anatomical controls showed that most of these communications might correspond to the origin of intercostal or visceral arteries. By pulsed Doppler imaging, flow velocities through the intimal tear reflect the pressure gradient between the two lumina. It is important to differ- entiate these secondary communications from the main intimal tear which usually has a diameter over 5 mm and is frequently located in the proximal part of the ascending aorta in type A dis- sections and immediately below the origin of the left subclavian artery in type B dissections. On occasions, 2D echocardiography does not permit visualization of the intimal tear in the proximal part of the arch. In these cases, contrast echocardiography may help by showing how contrast flows in the false lumen from the more proximal part of the aortic arch dissection. 48 True lumen identification Identification of the true lumen is of special clinical interest. When the aortic arch is involved, the surgeon needs to know whether the supra-aortic vessels originate from the false lumen. Similarly, when the descending aorta dissection affects visceral arteries and ischae- mic complications arise, it may be important to identify the false lumen prior to surgery or endovascular treatment such as intima fenestration or stent-graft implantation. Echocardiographic signs for differentiating the true lumen from the false lumen are summar- ized in Table 3 . Diagnosis of complications Appropriate diagnosis of dissection complications during the initial study may affect therapeutic decisions in the acute phase. Figure 9
Transoesophageal echocardiography. (A) Crescentic intramural haematoma in ascending aorta (large arrow) adjacent to the left main coronary ostium (small arrow). (B) Intramural haematoma in descending aorta. Arrow shows intima calcification. (C ) Penetrating aortic ulcer deforming the adventitia (arrow). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 3 Differentiation between true and false lumina True lumen False lumen Size True , false Most often: false . true lumen
Pulsation Systolic expansion Systolic compression Flow direction Systolic antegrade flow
Systolic antegrade flow reduced or absent, or retrograde flow Communication flow From true to false lumen in systole Contrast echo flow Early and fast Delayed and slow A. Evangelista et al. 654 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from Pericardial effusion and periaortic bleeding Pericardial effusion is not always due to extravasation of blood from the aorta and may be secondary to irritation of the adventitia produced by the aortic haematoma or small effusion from the wall. In any event, the presence of pericardial effusion in an ascending aorta dissection is an indicator of poor prognosis and suggests rupture of the false lumen in the pericardium. Echocardiography is the best diagnostic technique for estimating the presence and severity of tamponade. Periaortic haematoma and pleural effusion are best diagnosed by CT. The presence of periaortic haematoma has been related to an increase in mortality. 47 , 55 Aortic regurgitation Aortic regurgitation is a frequent complication, occurring in 40 –
76% of patients. The diagnosis and quantification of aortic regurgi- tation severity can be correctly made with Doppler echocardiogra- phy, both TTE and TOE. Furthermore, TOE provides information on possible mechanisms that influence aortic regurgitation, which may greatly aid the surgeon in deciding whether to replace the aortic valve 58 (Table
4 ). Arterial vessel involvement Diagnosis of involvement of the main arterial vessels of the aorta is important as it may explain some of the symptoms or visceral com- plications that accompany the dissection and permit selection of an appropriate therapeutic strategy. Involvement of coronary arteries in dissection has been considered to be 10 – 15%, with the right coronary artery being most frequently affected. Detection of seg- mental wall motion abnormalities of the left ventricle by TTE may help to identify this complication. In any event, left ventricular func- tion assessment should be included in the TTE exam when acute aortic syndrome is suspected since some patients have previous left ventricular dysfunction secondary to hypertensive heart disease or other conditions. On the other hand, TOE shows the most proximal segment of the coronary arteries; thus, it can be verified whether the coronary ostium originates in the false lumen or whether coronary dissection is present. TOE is not a good technique for assessing supra-aortic branch involvement. However, in a recent work, sensitivity, specificity, and accuracy in the diagnosis of supra-aortic trunks were 60, 85, and 78%, respectively. 7 The origin of the left subclavian artery is easily observed. However, the origin of innominate or brachiocephalic trunk and left carotid arteries remains inconsistently detected. In these cases, the TTE suprasternal view appears very useful. TOE permitted the diagnosis of coeliac trunk involvement, dissection, or compression in most cases. Visceral or peripheral malperfusion syndrome is a complication with high morbidity and mortality. However, CT provides far more precise information and is irre- placeable for diagnosing renal and iliac artery disease. TOE, like CT, can diagnose two types of circulation disorders of arterial branches: dissection or dynamic obstruction of the intimal dissection at the ostium of the arterial branches leaving the aorta. Differentiating the two mechanisms has important thera- peutic implications. 8 Recommendation TOE should define the entry tear location, mechanisms and sever- ity of aortic regurgitation, and true lumen compression. Pericardial effusion/tamponade and left ventricular function (global and seg- mental) may be assessed by TTE. In some specific complications, such as periaortic haematoma or involvement of the abdominal arterial trunks, additional information by CT or MRI is advisable. Diagnosis of traumatic and iatrogenic aortic lesions Blunt chest trauma may cause aortic rupture, dissection, or intra- mural haematoma. Rupture is due to a complete transection of the aorta where all three vascular layers are disrupted circumfer- entially. However, the adventitia may remain intact, or adjacent structures may contain the haemorrhage. A pseudoaneurysm then results, defined as disruption of at least one layer of the vessel wall and containment of rupture by the remaining layers and/or surrounding tissues. TOE has several advantages over other imaging methods in the evaluation of critically ill patients with trauma. 59 It can be performed quickly, at the bedside, without interrupting therapeutic measures. Nevertheless, it cannot be performed in patients with cervical spine fractures, which represent 5 – 25% of trauma victims. Iatrogenic dissection of the aorta rarely occurs during heart catheterization. It is not infrequently seen following angioplasty of an aortic coarctation but can also be observed after cross- clamping of the aorta and after intra-aortic balloon pumping. Most catheter-induced dissections are retrograde dissections. Pro- gression of the coronary dissection into the aortic root may be observed. Iatrogenic aortic trauma from vascular manipulation may cause dislodgement of debris from protruding or mobile atheromas. TOE may be the technique of choice for visualizing such lesions and assessing their embolic potential. Recommendation TOE should be considered a technique of choice when aortic com- plications are suspected after thoracic trauma since it is accurate, rapid, and can be performed at the bedside. Similarly, TOE is highly useful to rule out iatrogenic complications due to intravas- cular procedures. Acute aortic syndrome prognosis and follow-up Age, signs and/or symptoms of organ malperfusion and clinical instability, fluid extravasation into the pericardium, and periaortic Table 4
Mechanisms of significant aortic regurgitation in aortic dissection Dilatation of the aortic annulus secondary to dilatation of the ascending aorta Rupture of the annular support and tear in the implantation of one of the valvular leaflets Asymmetrical dissections, the haematoma itself may displace a sigmoid below coaptation level Prolapse of the intima in the outward tract of the left ventricle through the valvular orifice Previous aortic valve disease Echocardiography in aortic diseases 655 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from haematoma have poor prognosis in the acute phase. 55 Imaging techniques play an important role in identifying predictors of com- plications during follow-up. 60 The maximum aortic diameter in the subacute phase was a significant predictor of progressive dilatation. Other variables have been considered to have poor prognosis, such as compression of the true lumen 61 or partial false lumen thrombosis. 62 In contrast, a completely thrombosed false lumen showed a protective role. 55 , 62 Prognostic and therapeutic impli- cations of TOE in aortic dissection are well established. Antegrade or retrograde false lumen flow, false lumen thrombosis, and the presence of communications have prognostic implications and are easily detected by TOE. 55 TOE has an important role in the follow-up of patients with aortic dissection as it shows the struc- ture of the dissection, surgical repair, healing of the dissection and obliteration of the false lumen, or blood flow dynamics in true and false lumina. However, TOE is less useful than CT or MRI in the follow-up of aortic diameter dilatation, which is one of the predictors of worse prognosis. The intramural haematoma can heal or evolve to aneurysm for- mation or even dissection. 63 In addition to maximal aortic diam- eter, some TOE information such as echolucent areas has been related to dissection and enlargement evolution. 61 The natural history of PAU is unknown. Like intramural haematomas, several evolutive possibilities have been proposed. As in other acute aortic syndromes, ascending aorta involvement carries a higher risk of severe complications than type B involvement. Both in intra- mural haematoma and aortic ulcer, CT and MRI with a larger field of view have some advantages in the follow-up of complications of these diseases. Recommendation Although TOE provides prognostic information on acute aortic syndrome evolution, particularly in aortic dissection, CT or MRI is more useful in the follow-up of arch and descending aorta diameters. Intraoperative and post-operative echo Echocardiography plays a crucial role in the pre-operative, intrao- perative, and post-operative assessment of aortic diseases. Repla- cement by a composite graft (synthetic graft, valve mechanical prosthesis, and reimplantation of coronary arteries) has been con- sidered the conventional treatment for patients with significant aortic incompetence caused by aortic root dilatation. Wall wrap- ping with stent-graft implantation has also been used as a treat- ment option. However, when the root is dilated but the leaflets are normal, valve-sparing root resection yields excellent results without the need to implant a prosthetic aortic valve. Knowledge of aortic root dimensions, aortic regurgitation severity and its mechanisms would enable pre-operative selection of the best sur- gical strategy and preparation of an adequately sized graft tube, repair or replacement of aortic valve, and shorten surgical ischae- mia time. Previous studies have demonstrated that pre-operative measurement of aortic annular diameter by TTE and multiplane TOE is accurate and clinically feasible. The important role of echocardiography in aortic valve repair lies in the recognition of the exact lesions that may be responsible for the insufficiency, and the selection of adequate operative manoeuvres to correct these abnormalities. TOE provides a highly accurate anatomical assessment of all types of aortic regur- gitation lesions. In addition, the functional anatomy of aortic regur- gitation defined by TOE is strongly and independently predictive of valve reparability and post-operative outcome. 41 The combination of functional evaluation by TOE and anatomical inspection at surgery is therefore paramount when assessing the suitability of the conditions for repair. By echocardiography, the tethering indices might have the potential to guide the planning of aortic valve-sparing surgery (see aortic aneurysm section). Accurate echocardiographic measurements of aortic root diameters are also essential in other types of surgery such as the Ross procedure, homograft aortic valves 64 or in percutaneous aortic valve implantation. 65 , 66 Pre-operative or intraoperative TOE is essential for planning the surgical treatment of acute aortic syndrome and in deciding whether to replace the aortic valve 58 (see section on TOE) and can further be used to evaluate the placement of cannulae, assess perfusion in the different compartments of the aorta, and whether or not the true lumen has been perfused. 67 TOE may help to avoid early reoperations by showing the correct connec- tion of the distal part of the graft tube to the true lumen, arch and supra-aortic vessel involvement, and the severity of residual aortic regurgitation. Finally, intraoperative TOE may detect compli- cations such as pseudoaneurysm formation, most of which are sec- ondary to a leak in coronary artery reimplantation to the graft tube, communication of the distal part of the tube to the false lumen, significant aortic regurgitation, periaortic haemorrhage, or segmental abnormalities in left ventricular contraction. In cases where TOE cannot be performed intraoperatively, it should be attempted prior to extubation of the patient in the post- operative period for the early detection of complications. Recommendation Echocardiography is crucial in selecting and monitoring surgical treatment and detecting complications. Thus, intraoperative TOE should be considered mandatory. When intraoperative TOE has not been performed, the study should be made immediately after surgical treatment. Endovascular therapy monitoring by intraoperative transoesophageal echocardiography Intraoperative TOE is highly useful during endovascular therapy of the descending thoracic aorta, especially in type B aortic dissection, since it provides additional information to angiography/fluoroscopy for guiding correct stent-graft placement. For example, TOE is able to detect peri-stent leaks and/or small re-entry tears with much higher sensitivity than angiography. 68 – 72 In several publications, TOE provided decisive additional information to angiography/ fluoroscopy, leading to successful procedural changes in up to 40 – 50% of patients. 70 – 72 TOE is useful in the operating theatre both before and after stent-graft deployment. (1) Prior to stent-graft deployment in patients with type B aortic dissection, TOE is useful for guidewire repositioning (not poss- ible with fluoroscopy) from the false to the true lumen and for A. Evangelista et al. 656
by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from
correct guidewire entrance into elephant trunk prostheses in patients with previous aortic arch surgery. In atherosclerotic aneurysms, protruding aortic plaques at the proximal neck may impede tight adhesion between the stent-graft and aortic wall, leading to dangerous proximal leaks. These plaques are usually detected by TOE and not by angiogra- phy/fluoroscopy. Therefore, just prior to proximal stent-graft deployment, TOE is essential for selecting an aortic wall segment without protruding plaques and confirming selection of the stent-graft diameter. (2) After stent-graft deployment, colour-Doppler TOE is highly useful for detecting peri-stent leaks which can be promptly resolved by balloon dilatation or further stent-graft implan- tations. Most of these leaks are not usually visible on angiogra- phy. In aortic dissection, TOE is also useful for detecting small distal re-entry tears not visible on angiography; thoracic re-entry tears can subsequently be resolved by additional stent-graft deployment. TOE has some limitations: (i) TOE is not able to guide abdomi- nal endovascular procedures. In these treatments, conventional IVUS or intraluminal phased-array ultrasound imaging (IPAI) can be used. In a recent small study, IPAI proved to be superior to IVUS and to TOE in detecting communications between the true and false lumina of aortic dissection. 73 However, IVUS and IPAI are disposable and therefore more expensive than TOE; (ii) TOE is partially limited for visualizing the innominate and left carotid artery ostia, and this information may be crucial to proximal posi- tioning of the stent graft; and (iii) TOE is useful when a Dacron stent graft is used, whereas it is not useful with PTFE (gore-tex) prostheses since PTFE acts as a barrier to ultrasound. Recommendation Intraoperative TOE is highly useful during endovascular treatment, particularly in descending aortic dissections. It permits correct guidewire entrance by identifying the true lumen in aortic dissec- tions, provides additional information helpful to guide correct stent-graft positioning, and identifies suboptimal results and the presence of leaks and/or small re-entry tears, with much higher sensitivity than angiography. Conflict of interest: none declared. References 1. Evangelista A, Flachskampf F, Lancellotti P, Badano L, Aguilar R, Monaghan M et al. European Association of Echocardiography for standardization of performance, digital storage and reporting of echocardiographic studies. Eur J Echocardiogr 2008;9:438 – 48. 2. Schwammenthal E, Schwammenthal Y, Tanne D, Tenenbaum A, Garniek A, Yüklə 455,25 Kb. Dostları ilə paylaş:
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