Recommendations
Yüklə 455,25 Kb. Pdf görüntüsü
|
|
iosum; and the descending aorta that extends from the ligamentum arteriosum to the level of the diaphragm. PA, right pulmonary artery. Modified from Diseases of the aorta. In: Feigenbaum H, Armstrong WF, Ryan T, eds. Feigenbaum’s Echocardiography. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005. p673; Ascending aorta values from Erbel et al. 46 Echocardiography in aortic diseases 649 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from (systolic/diastolic pressures) to relative change in diameter] 17 – 19 which is less affected by arterial pressure changes and is easily measured using echo-tracking devices. 17 In Marfan patients, aortic stiffness proved to have an important value in predicting progressive aortic dilatation. 20 ,
Also, indices of aortic stiffness are used in clinical studies for the assessment of the efficacy of different therapeutic regimens in these patients. 22 Abnormal aortic elastic properties were demonstrated also in patients with bicuspid aortic valve with no or mild aortic valve impairment. 23 Pulsed-wave velocity Pulsed-wave velocity (PWV) is defined as the travel speed through- out the aorta of the pulse wave. With increased aortic stiffness, PWV increases. PWV is expressed as the ratio of the distance between the two sites at which the onset of the wave is being recorded to the time of travel of the wave from the proximal to the distal sites. Accordingly, carotid – femoral PWV is considered the gold standard measurement of arterial stiffness and is the most widely used index. 16 PWV can be assessed by echocardiogra- phy, measuring the time from the QRS to the onset of the pulsed- wave Doppler envelope in proximal (carotid artery, ascending aorta) and distal (femoral artery, descending aorta) sites (the difference between them is the transit time), and the pulsed wave- length between the two points where the Doppler tracings were recorded. 17 ,
Normal PWV values increase from 4 – 5 m/s in the ascending aorta to 5 – 6 m/s in the abdominal aorta. 24 The indepen- dent prognostic value of PWV, as an index of aortic stiffness, for all-cause and cardiovascular mortality has been demonstrated in different populations including hypertensive, diabetic, or renal patients, the elderly, and the general population. 16 ,
– 27 Reflected waves When the stiffness of the aorta and the large arteries is increased, PWV is increased and the backward waves from the periphery return early to the ascending aorta, thereby increasing central systo- lic and decreasing central diastolic blood pressure. 17 The point where the incident wave merges with the reflected one can be identified in the central waveform and thus the augmented pressure, the difference between the merging point (shoulder of the wave- form) and the peak systolic pressure, is computed. 17 Augmentation index, calculated as the ratio between the augmentation pressure and the pulse pressure and expressed as a percentage, is an index used for the evaluation of the reflected wave function. Echo-tracking systems implemented in echocardiographic machines are able to measure this index at carotid level. 17 As with PWV, wave reflection indices have been demonstrated to be independent predictors of cardiovascular events in several diseases. Recommendation Aortic and arterial biophysical properties can be easily and reliably assessed by echocardiography and provide important pathophysio- logical and prognostic information that may have clinical impli- cations both in disease states and in the general population. Aortic atherosclerosis The presence of detectable atherosclerotic plaques in the aorta indicates the presence of atherosclerotic disease and is a possible source of embolism. 28 Aortic atheromas are characterized by irre- gular intimal thickening of at least 2 mm, with increased echogeni- city. They often have superimposed mobile components, mainly thrombi. The morphology of atheromatous plaques is dynamic, with frequent formation and resolution of mobile components. 29 TOE is the imaging modality of choice for diagnosing aortic ather- omas. It provides higher-resolution images than TTE and has good interobserver reproducibility. 30 However, suprasternal harmonic imaging by TTE also permits the visualization of protruding arch atheromas in many cases 2 and may be helpful in the routine assess- ment of the source of embolism. The prevalence of aortic athero- mas on TOE varies depending on the population studied. In a community-based TOE study, aortic atheromas were present in 51% of the population over 45 years, being complex in 7.6%. 31 Atheroma prevalence increased with age, smoking, and pulse pressure. TOE characterizes the plaque by assessing plaque thick- ness, ulceration, calcification and superimposed mobile thrombi, thereby determining the embolic potential of each plaque. The advantages of TOE over other non-invasive modalities include its ability to assess the mobility of plaque in real time. Another echo- cardiographic modality is intraoperative epiaortic ultrasound which facilitates the selection of a suitable aortic clamping site by avoiding calcifications with an increased risk of embolization. The French Aortic Plaque in Stroke group showed that increas- ing plaque thickness of ≥4 mm is associated with a significantly increased embolic risk. 32 The presence of mobile lesions (thrombi) superimposed on aortic atheromas has been recognized to imply a high embolic risk. Other characteristics of the lesions seen on TOE, such as ulceration ≥2 mm in aortic plaques and non- calcified plaques, were also associated with a higher risk of stroke.
33 Thus, atherosclerotic plaques are defined as complex in the presence of protruding atheromas of .4 mm in thickness, mobile debris, or the presence of plaque ulceration, and defined as simple if the plaques lack these morphological features. Two recent community-based studies found no association between aortic atheromas and future stroke. 31 , 34 An alternative explanation is that atheromatous plaque is merely a marker for diffuse athero- sclerosis that predisposes patients to systemic embolism by other cardiovascular mechanisms. The embolic potential of atherosclerotic aortic lesions during invasive procedures or during open-heart surgery is well estab- lished.
35 , 36 Some studies have shown the risk of stroke or periph- eral embolism after cardiac catheterization or intra-aortic balloon pump placement in patients with severe aortic atherosclerosis diagnosed by TOE. 35 A strong association between aortic stenosis and aortic atherosclerosis has recently been established. 37 The presence of plaques in the aorta of patients with aortic stenosis has important implications since these patients often undergo inva- sive diagnostic and therapeutic procedures that can dislodge par- ticularly thick plaques and the attached thrombotic material. Large mobile aortic thrombi are possible causes of systemic emboli and appear to be a complication of atherosclerosis. TOE is the best technique for diagnosing and monitoring the evolution of these large thrombi. 38 The optimal management of these com- plications remains to be defined. Anticoagulation therapy appears to be a logical approach, although surgical removal has been indi- cated in cases with recurrent embolic events. 39 A. Evangelista et al. 650 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from Recommendation TOE is the imaging modality of choice for diagnosing aortic atheromas. Advantages of TOE over other non-invasive modalities [computed tomography (CT) and magnetic resonance imaging (MRI)] include the accurate measurement of size and mobility of the plaque in real time. When atherosclerosis is present, the severity and location of the most severe atheromas should be reported. The suprasternal window may be useful for the diagnosis of plaques in the aortic arch by TTE when the acoustic window is optimal. Aortic aneurysm TTE is an excellent modality for imaging aortic root dilata- tion,
10 , 13 , 14 which is important for patients with annuloaortic ectasia, Marfan syndrome, or bicuspid aortic valve. Since the pre- dominant sites of dilatation are in the proximal aorta, TTE often suffices for screening (Figure 5 ). In ascending aorta dilatation, some echocardiographic features play an important role in the assessment of the mechanisms of functional aortic regurgitation. Functional classification of aortic root abnormalities responsible for aortic insufficiency has been suggested. 40 –
This classification is based on assessment of leaflet function and aortic root size and provides important information for surgical management strategies. Tethering of the leaflets is the feature most closely associated with functional aortic regurgitation. This tethering depends on the sino- tubular junction/annulus mismatch. This information is useful for targeting the optimal time and strategy for aortic valve-sparing surgery in the setting of ascending aorta aneurysms (Table 2 ).
progressive impact of sinotubular junction dilatation on valve func- tion in patients with ascending thoracic aorta aneurysm for valve- sparing surgery to be indicated before leaflet damage occurs. TTE suffices in the assessment of proximal ascending aorta when the acoustic window is adequate. However, TOE is clearly superior to TTE for assessing aneurysms located in the aortic arch and descending thoracic aorta. However, TOE is limited in tortuous aortas, since in these cases, the aorta may be separated from the oesophagus, resulting in inability to image these aorta segments. Thus, the modalities of choice are MRI and CT. Although TTE transducers are not optimal for assessing the abdominal aorta, the segment of the aorta between the coeliac trunk and renal arteries is frequently well visualized. The presence of abdominal aorta aneurysms in patients with atherosclerosis or aortic diseases is not uncommon and assessment of the abdominal aorta may be useful.
Recommendation In aortic root aneurysms, the accurate measurement of diameters by TTE or TOE is crucial for surgical indication and surgical man- agement strategies. In the arch and descending aorta, other imaging modalities with better reproducibility and larger field of view, such as CT or MRI, may be more suitable. Acute aortic syndrome diagnosis Acute aortic syndrome has a high mortality rate and early medical and surgical treatment is crucial. Therefore, rapid and accurate diagnostic techniques, which can be applied in critically ill patients, are essential. The diagnosis of acute aortic syndrome can be made with similar accuracy using different imaging techniques such as TOE, CT, or MRI; 43 however, the decision to use a specific tech- nique depends on two major factors: availability of the techniques and experience of the imaging staff. Compared with other highly accurate diagnostic techniques (CT and MR), echocardiography has the advantage of being applicable in any hospital setting (emer- gency, intensive care, and operating theatre), without the need to transfer the patient who is often in an unstable haemodynamic situ- ation, monitored, and with intravenous drugs. However, in two large registries, the international registry of acute aortic dissec- tion 44
45 CT was the first most used imaging technique in the diagnosis of dis- section, (61 and 77%, respectively). A possible explanation for this fact is that patients with acute aortic syndrome are usually admitted to the emergency departments of community hospitals where TOE may not be available. Nevertheless, it should be emphasized that even in experienced centres, most patients with acute aortic syndrome undergo more than one imaging modality; this syndrome is much too critical to leave room for diagnostic doubts.
Echocardiographic diagnosis Aortic dissection and its variants, included in the ESC classification of aortic
dissection, 46 can be correctly diagnosed by Table 2 Determinants of functional aortic regurgitation with anatomically normal aortic valve and ascending aorta aneurysm by transoesophageal echocardiography Annulus, Valsalva sinuses, sinotubular junction, and tubular tract dimensions Coaptation leaflet height: maximum distance between protodiastolic coaptation of the leaflet tips and the annulus plane. Diastolic tenting of the leaflets .8 – 10 mm Sinotubular junction/annulus ratio .1.6 Figure 5 Parasternal long-axis view by transthoracic echocar- diography. (A) Annuloaortic ectasia with pyriform morphology. (B) Ascending aorta aneurysm located in the upper part of the sinotubular junction. Echocardiography in aortic diseases 651 by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from echocardiography. The diagnosis of classical aortic dissection is based on the demonstration of the presence of an intimal flap that divides the aorta into two, true and false, lumina. In most cases, false lumen flow is detectable by colour Doppler but may be absent in totally thrombosed and retrograde dissections. Intra- mural haematoma is characterized by circular or crescentic thickening of the aortic wall .5 mm and penetrating aortic ulcer (PAU) presents as an image of crater-like outpouching with jagged edges in the aortic wall, generally associated with extensive aortic atheromas. Transthoracic echocardiography Classically, TTE has been considered limited in the diagnosis of aortic dissection. In older series, sensitivity in the diagnosis of ascending aorta dissection was 78 – 90% but only 31 – 55% in des- cending aortic dissection. Specificity for type A aortic dissection was reported to range from 87 to 96% and for type B dissection 60 – 83%. 47 However, these data are derived from old studies when the current imaging technology, such as harmonic imaging, was not available. Recently, harmonic imaging (Figure 6 ) and the use of contrast enhancement have been shown to improve the sensitivity and specificity of TTE in the diagnosis of aortic dissec- tion. 48
of type A aortic dissection (sensitivity 93% and specificity 97%), although it is more limited in type B involvement (sensitivity 84% and specificity 94%), mainly in the presence of non-extended dis- section, intramural haematoma, and aortic ulcers. 48 However,
given its availability, rapidity, and additional information on cardiac status, TTE may be used as the initial imaging modality when aortic dissection is clinically suspected in the emergency room.
49 The low negative predictive value of TTE does not permit dissection to be ruled out, and further tests will be required if the TTE exam is negative. The value of TTE is also limited in patients with abnormal chest wall configuration, obesity, pulmon- ary emphysema, and in those on mechanical ventilation. These limitations may prevent adequate decision-making in some cases, but have been overcome by TOE. In patients with acute chest pain, special attention should be paid during the TTE exam to aortic root dilatation, aortic regurgitation, and/or pericardial effu- sion, since these findings should raise the suspicion of acute aortic syndrome. If a dissection cannot be directly visualized, other imaging techniques are mandatory (Figure 7 ). Transoesophageal echocardiography TOE has constituted a decisive advance in the diagnosis of aortic dissection. It can image the entire thoracic aorta except for a small portion of the distal ascending aorta near the proximal arch. The proximity of the oesophagus to the aorta, without inter- ference from the chest wall or lung, permits high-quality images to be obtained (Figure 8 ). Since the first multicentre European Cooperation study by Erbel et al.,
47 several studies have demonstrated the accuracy of TOE in the diagnosis of aortic dissection with sensitivity of 86 – 100%, specificity 90 – 100%, and a negative predictive value of 86 – 100%. 47
50 The low specificity of the technique described in some series 51 is explained by the fact that the majority of Figure 6 Aortic dissection diagnosis by transthoracic echocardiography. Intimal flap (arrows) and two lumina are visualized in: (A) aortic root, (B) aortic arch and distal ascending aorta, (C ) proximal descending aorta (arrowhead shows the entry tear), and (D) dissection of abdominal aorta. Colour Doppler helps to identify the true lumen (TL). Arrowheads signal secondary communications. A. Evangelista et al. 652
by guest on January 17, 2011 ejechocard.oxfordjournals.org Downloaded from
intraluminal images in the ascending aorta were considered diag- nostic of dissected intima. The analysis of larger studies 6 ,
, 50 , 51 showed that 3.5% of cases with clinically suspected dissection were erroneously diagnosed as having ascending aorta dissection. Altogether, the experience accumulated in recent years demon- strates that the presence of an intraluminal linear image in the ascending aorta alone should not be accepted as a dissection cri- terion. In the ascending aorta, particularly when dilated, linear reverberation images are very common, being observed in 44 – 55% of studies. 6 Artefacts in the aortic root are a reverberation from the anterior wall of the left atrium. In the middle third of the ascending aorta, they are due to reverberations from the pos- terior wall of the right pulmonary artery. The assessment of location and movement of these intraluminal images by M-mode echocardiography is the best way to differentiate between intimal flap and imaging reverberations. Typically, intraluminal reverberations in the aortic root are located twice as far from the transducer as the posterior aortic wall, and their movement is parallel to the posterior aortic wall but with double displacement amplitude. Intraluminal reverberations in ascending aorta are located at twice the distance from the right pulmonary artery pos- terior wall as from the posterior aortic wall. 6 TOE is clearly superior to TTE in the diagnosis of intramural haematoma and aortic ulcers. Echocardiographic findings of intra- mural haematoma are circular or crescentic thickening (.5 mm) of the aortic wall (Figure 9 A and B) and there should be no flow within. 52 – 54 Diagnosis is straightforward in typical cases, but the haematoma may sometimes be mistaken for an intraluminal thrombus or a dissection with thrombosed false lumen. Displace- ment of intimal calcification caused by accumulation of blood within the aortic media is useful for the differential diagnosis. Usually, the inner margin of intramural haematoma is smooth, and aortic thickening occurs beneath the bright echo-dense intima, whereas an irregular margin with dilated aorta is commonly observed in patients with aneurysmal dilatation and mural thrombi. In some cases, echolucent areas are present but no flow into these areas is detected. Intramural haematoma is quite easily differen- tiated from classical aortic dissection with flow in two lumina. However, the diagnosis can be difficult when the false lumen of dis- section is totally thrombosed. 55 , 56 Diagnosis of penetrating ulcers by echocardiography is based on the image of crater-like outpouching of the aortic wall, generally associated with extensive aortic atheroma 57 (Figure
9 C). Although both CT and MRI permit an easy diagnosis of these images because of their larger field of view, TOE may provide better infor- mation on the differential diagnosis of ulcerated plaques, penetrat- ing atherosclerotic ulcers or ulcer-like images secondary to focal intimal rupture in the evolution of intramural haematomas. Aortic wall thickening with inward displacement of intimal calcifica- tion was an indication of associated intramural haematoma. TOE is semi-invasive and requires sedation and may cause a rise in systemic pressure from retching and gagging. Although isolated cases of aortic rupture during the procedure have been reported, the incidence in prospective series is very low, being more related to the intrinsic risk of the disease than the procedure itself, as Yüklə 455,25 Kb. Dostları ilə paylaş:
|