Incremental value of live/real time three-dimensional transesophageal echocardiography over the two-dimensional technique in the assessment of aortic aneurysm and dissection

We compared findings from intraoperative live/real time three-dimensional transesophageal echocardiography (3DTEE) and two-dimensional transesophageal echocardiography (2DTEE) with surgery in 67 patients having aortic aneurysm and/or aortic dissection. Of these, 20 patients had aortic aneurysm without dissection, 21 aortic aneurysm and dissection, and 26 aortic dissection without aneurysm. 3DTEE diagnosed the type and location of aneurysm correctly in all patients unlike 2DTEE, which missed an aneurysm in one case. There were four cases of aortic aneurysm rupture. Three of them were diagnosed by 3DTEE but only one by 2DTEE, and one missed by both techniques. The mouth of saccular aneurysm, site of aortic aneurysm rupture, and communication sites between perfusing and nonperfusing lumens of aortic dissection could be viewed en face only with 3DTEE, enabling comprehensive measurements of their area and dimensions as well as increasing the confidence level of their diagnosis. In all patients with aortic dissection, 3DTEE enabled a more confident diagnosis of dissection because the dissection flap when viewed en face presented as a sheet of tissue rather than a linear echo seen on 2DTEE which can be confused with an artifact. 2DTEE missed dissection in one patient. In six cases the dissection flap involved the right coronary artery orifice by 3DTEE and surgery. These were missed by 2DTEE. Aortic regurgitation severity was more comprehensively assessed by 3DTEE than 2DTEE. Aneurysm size by 3DTEE correlated well with 2DTEE and surgery/computed tomography scan. In conclusion, 3DTEE provides incremental information over 2DTEE in patients with aortic aneurysm and dissection.     

Unusual complication of aortic dissections: intimo–intimal intussusception

Angiography with a pre-diagnosis of acute coronary syndrome was performed in a 76-year-old female patient presenting to another hospital with symptoms of chest pain and syncope. Upon determination of type III aortic dissection, the patient was referred to our clinic. On CT angiography, the ascending aortic diameter was 57 mm and no dissection flap was observed. There was a filling defect suggestive of intimo–intimal intussusception at the level of the aortic arch, occlusion of the left arteria carotid communis, and a double-channel aorta extending from the left subclavian artery to the iliac artery. On transoesophageal echocardiography, the ascending aorta was seen to be larger than normal and no dissection flap was observed. There were findings suggestive of haematoma and intimo–intimal intussusception at the proximal part of the aortic arch. The dissection flap causing occlusion in the vascular structures was resected. Supracoronary graft replacement of the ascending aorta was performed. Transoesophageal echocardiography is an invasive investigative method with high sensitivity and specificity for the diagnosis of intimo–intimal intussusception.     

Comparison of diagnostic and therapeutic value of transesophageal echocardiography, intravascular ultrasonic imaging, and intraluminal phased-array imaging in aortic dissection with tear in the descending thoracic aorta (type B)

Transesophageal echocardiography (TEE) and conventional intravascular ultrasound (IVUS) have limited capabilities in type B aortic dissection. To evaluate its diagnostic value, intraluminal phased-array imaging (IPAI) was compared with IVUS and TEE. In 23 patients with type B aortic dissection, IPAI was tested with respect to its ability to depict true lumen (TL) and false lumen (FL), to localize which abdominal arteries originate from the TL and FL, and to identify all entries and reentries. After the completion of TEE, 2 additional examiners performed angiography and positioned an AcuNav catheter inside the TL. An IVUS catheter was then introduced into the TL by a fourth examiner. All examiners were blinded to one another. Four additional patients with type B aortic dissection developed peripheral malperfusion due to TL collapse. Transvenous IPAI was used to guide emergency fenestration of the intimal flap. TL and FL could be equally well identified by all diagnostic methods. IPAI detected more entries than IVUS (3.0 +/- 1.2 vs 0.8 +/- 0.5, p <0.001), and thoracic IPAI depicted more entries than TEE (1.8 +/- 1.0 vs 1.2 +/- 0.5, p <0.001). IPAI and IVUS showed >90% of the abdominal side branches. In all patients with peripheral malperfusion, successful emergency intimal flap fenestration was safely guided by IPAI. In conclusion, in the detailed diagnostic evaluation of type B aortic dissection, IPAI is superior to IVUS and TEE in detecting communications between the TL and FL. IPAI is also highly useful as a guiding tool for emergency intimal flap fenestration.     

Localization of aortic dissection intimal flap by intraoperative two-dimensional echocardiography

Ascending (type I) aortic dissection carries a high morbidity and mortality. Proper identification of the proximal origin of the dissection and determination of concomitant aortic valve involvement significantly facilitate surgical repair, which may improve survival. In this case, intraoperative two-dimensional echocardiography with contrast injections was used to image the heart and great vessels before and after cardiopulmonary bypass. The proximal origin of the intimal flap of a type I dissection was identified, and primary aortic valve disease was excluded. Postprocedure intraoperative echocardiography demonstrated that the site of repair was imaged and that aortic regurgitation was absent. Intraoperative contrast two-dimensional echocardiography may be a valuable new tool to provide information otherwise unavailable by routine techniques.     

Echocardiographic Findings Mimicking Type A Aortic Dissection

BACKGROUND: Type A aortic dissection is a rare, but life-threatening disease. The prognosis is determined by an accurate and immediate diagnosis. CASE STUDY: A patient with suspected type A dissection based on outward transesophageal echocardiography (TEE) findings is reported. Renewed TEE showed dilation of the ascending aorta with pronounced wall thickness. A membrane-like structure was found in the ascending aorta. M-mode technique revealed movement of the suspected membrane that was partially in parallel to the aortic wall. Thus, there were severe doubts on the presence of type A dissection. By contrast, typical intimal rupture was found in the descending aorta. Computed tomography (CT) and angiography showed aortic dilation and an extended wall hematoma deriving from the entry at the descending part. There was no evidence of type A dissection. CONCLUSION: TEE is a noninvasive diagnostic tool to assess aortic dissection of type A with a sensitivity of 90-98% that is equal to CT or magnetic resonance imaging (MRI) solely. Complementary use of CT or MRI could improve the diagnostic accuracy. False-positive findings could result from echocardiographic artifacts concealing an intimal flap in the ascending aorta. Echo reverberations in dilated or calcified aortas had been judged to account for this phenomenon. In the present case, it could be assumed that the extended wall hematoma in accordance with vessel dilation mimicked the membrane-like structure. Oscillation or flutter of the suspicious intimal flap independently of aortal wall movement seem to be mandatory to avoid false-positive diagnoses. Ancillary findings such as flow signals, intimal fenestration or thrombosis are helpful to enhance the diagnostic specificity of TEE.     

Accuracy of biplane and multiplane transesophageal echocardiography in diagnosis of typical acute aortic dissection and intramural hematoma

Objectives. The purpose of this study was to evaluate the diagnostic accuracy of biplane and multiplane transesophageal echocardiography in patients with suspected aortic dissection, including intramural hematoma.Background. Transesophageal echocardiography is a useful technique for rapid bedside evaluation of patients with suspected acute aortic dissection. The sensitivity of transesophageal echocardiography is high, but the diagnostic accuracy of biplane and multiplane transesophageal echocardiography for dissection and intramural hematoma is less well defined.Methods. We studied 112 consecutive patients at a major referral center who had undergone biplane or multiplane transesophageal echocardiography to identify aortic dissection. The presence, absence and type of aortic dissection (type A or B, typical dissection or intramural hematoma) were confirmed by operation or autopsy in 60 patients and by other imaging techniques in all. The accuracy of transesophageal echocardiography for ancillary findings of aortic dissection (intimal flap, fenestration and thrombosis) was assessed in the 60 patients with available surgical data.Results. Of the 112 patients, aortic dissection was present in 49 (44%); 10 of these had intramural hematom (5 with and 5 without involvement of the ascending aorta). Of the remaining 63 patients without dissection, 33 (29%) had aortic aneurysm and 30 (27%) had neither dissection nor aneurysm. The overall sensitivity and specificity of transesophageal echocardiography for the presence of dissection were 98% and 95%, respectively. The specificity for type A and type B dissection was 97% and 99%, respectively. The sensitivity and specificity for intramural hematoma was 90% and 99%, respectively. The accuracy of transesophageal echocardiography for diagnosis of acute significant aortic regurgitation and pericardial tamponade was 100%.Conclusions. Biplane and multiplane transesophageal echocardiography are highly accurate for prospective identification of the presence and site of aortic dissection, its ancillary findings and major complications in a large series of patients with varied aortic pathology, Intramural hematoma carries a high complication rate and should be treated identically with aortic dissection.     

Transesophageal Doppler echocardiography in the diagnosis of dissecting aortic aneurysm

Transesophageal Doppler echocardiography (TEDE) was performed in three patients with proven or suspected DeBakey type I and type III aortic dissection. Case 1: A 66-year-old woman, with DeBakey type I aortic dissection. Clear images of a widened dissected aorta and an intimal flap were obtained in both the ascending and descending aorta, including the aortic arch. The site of an entry into the false lumen was identified by the defect of the intimal flap and the pulsatile entry flow through it. The reentry into the true lumen was also identified near the orifice of the celiac trunk. In this case, the observation was performed using this technique during the operation; i.e., replacement of the ascending aorta with an artificial graft. Case 2: A 77-year-old man, DeBakey type III aortic dissection. The study was performed after surgery which consisted of replacement of the descending aorta with an artificial graft. TEDE provided clear images of the artificial graft, the aorta, and their boundaries. The remaining intimal flap was clearly confirmed. Case 3: An 80-year-old man, DeBakey type III aortic dissection. In this case, though abdominal echography suggested aortic dissection, angiography and X-ray CT failed to facilitate the diagnosis. Only TEDE confirmed the diagnosis. The abnormal flow via the entry directing toward the false lumen was clearly demonstrated on the color Doppler images. We therefore conclude that TEDE is a useful and reliable means of diagnosing dissecting aortic aneurysm.     

Role of echocardiography in the diagnosis of aortic dissection

We evaluated sensitivity, specificity and predictive values of echocardiography in detecting aortic dissection. We studied in the same period of time two groups of consecutive patients with good quality echocardiographic examination. Group I, with high prevalence of the disease (76%), was composed of 25 patients; 19 patients with aortic dissection (11 of the type A and 8 of the type B) and 6 patients with clinical and echocardiographic suggestion of aortic dissection which was not confirmed by angiography. Group II, with lower prevalence of the disease (4%), was composed of 382 adult patients who underwent aortic angiography for different reasons. In this second group there were 16 out of the 19 patients of the first group, with aortic dissection, who underwent aortic angiography and the 6 patients with suspicion of aortic dissection which was not confirmed by angiography. Type A dissection: The finding of intimal flap on echocardiography was highly specific (98%) but relatively insensitive (45%); its positive predictive value was low (50% in the first and 34% in the second group). The specificity of increased thickness of aortic wall was lower (89%) and the sensitivity higher (81%); its positive predictive value was satisfactory in the first group (81%) and very low in the second (13%). Aortic root dilatation was fairly specific (76%); the sensitivity of this finding was high (87%) but its positive predictive value was still low (66% in the first and 7% in the second group). To conclude: the positive predictive value of the 3 echocardiographic signs of aortic dissection varied, in relation to the different prevalence of the disease, from 50, 81 and 66% in the first group to 34, 13 and 7% in the second group; the diagnostic utility of the echocardiographic examination appeared limited, in these patients, by the low values of sensitivity and positive predictive values; aortography is still the most valuable technique in the diagnosis of aortic dissection; echocardiography was useful in the early evaluation of some emergency cases (chest pain, shock, collapse...) suggesting sometimes the correct diagnostic hypothesis of aortic dissection; in the presence of a typical clinical picture, the contemporary presence of the 3 echocardiographic signs, though having the lowest sensitivity (36%), was highly predictive of the type A dissection. Type B dissection: In these patients the clinical picture, in contrast with type A dissection, Type A, was not indicating careful and complete echocardiographic aortic scan. Then the echocardiographic examination was even more disappointing: sensitivity 25%.     

Missed diagnosis of limited ascending aortic dissection by multiple imaging modalities leading to fatal cardiac tamponade and aortic rupture

Modern diagnostic imaging modalities for ascending aortic dissection include transesophageal echocardiography (TEE), computed tomography angiography (CTA), and magnetic imaging resonance (MRI). All have extremely high sensitivity and specificity for detection of an intimal flap to diagnose ascending aortic dissection. We present a case of fatal cardiac tamponade caused by a limited aortic dissection not detected by multiple imaging modalities. This may represent a class of aortic dissection variant that cannot be detected by conventional testing. A high index of suspicion should be maintained in the appropriate clinical setting and should prompt serial imaging and even consideration for preemptive surgical exploration.     

Utility of two-dimensional echocardiography in suspected ascending aortic dissection

The value of 2-dimensional echocardiography (2-D echo) in patients with suspected ascending aortic dissection was assessed. During a 5.5-year period, 56 consecutive patients underwent bedside 2-D echo for unexplained chest pain possibly due to ascending aortic dissection. Patients with obvious aortic dissection who proceeded directly to aortography were excluded and in all 56 study cases, 2-D echo was the initial diagnostic test. Using standard criteria, 2-D echo correctly identified all 13 patients with ascending aortic dissection. There were 5 false-positive study results and 38 true-negative results, yielding a sensitivity of 100%, specificity of 88% and overall diagnostic accuracy of 91%. In the group of 13 patients with confirmed ascending aortic dissection, 2-D echo identified 4 with pericardial fluid, and 3 of these patients (75%) died within 24 hours. In comparison, 7 patients in the group of 43 without confirmed dissection had pericardial fluid by 2-D echo and only 1 died (p less than 0.001). Finally, in the group of 38 patients with true-negative results, 2-D echo provided useful information in 16 (42%) that assisted or was essential in establishing an alternative diagnosis. However, 5 patients in this group had type III dissection and in none was it identified by 2-D echo. Thus, our data indicate that 2-D echo represents a reliable noninvasive method for rapidly diagnosing ascending aortic dissection at the bedside; offers important prognostic information which is directly related to the presence of pericardial fluid, and provides useful additional information which assists or establishes an alternative diagnosis when ascending aortic dissection is absent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diagnosis of acute aortic dissection by echocardiography

Until recently, the diagnosis of aortic dissection rested on aortography. The purpose of this study was to evaluate the diagnostic value of echocardiography in that disease and its ability to inform on the extent of the dissection and on the presence of associated lesions. Twenty-six patients (mean age 64 +/- 10 years) admitted for suspected aortic dissection were explored by echocardiography and the results were compared with those of angiography and/or anatomical findings. Echocardiography provided the diagnosis in 14 of the 16 patients with aortic dissection and excluded it in the remaining 10 patients. The sensitivity and specificity of the method were 87.5 p. 100 and 100 p. 100 respectively. The type of dissection was correctly determined in 90 p. 100 of the patients whose aorta had been totally explored by echocardiography. Aortic regurgitation and pericardial effusion were detected in 81 p. 100 and 50 p. 100 respectively of patients with aortic dissection. These results confirm the diagnostic value of echocardiography in dissection of the aorta. The extent of the lesion can only be evaluated when the whole of the aorta is visualized. The echocardiographic diagnosis is easier when the ascending aorta is involved (type I), while in type III aortic dissection there is a risk of missing a retrograde lesion of the aorta and confusing this type with type I. In this study two kinds of intimal flap motion were observed: in the first one the motion was independent of that of the aorta, while the second one resembled a division of the aortic, wall the motion of which is parallel to that of the aorta.     

主动脉夹层CTA的诊断及介入治疗

目的对主动脉夹层CTA的诊断及介入治疗进行探讨与分析。方法本研究共纳入研究对象60例,均为2012年6月到2014年1月我院收治的主动脉夹层患者,所有患者均经DSA抑或MR T1-FS确诊。对患者的内膜瓣、管壁增厚、夹层动脉瘤和双腔征等影像学征象进行回顾性分析。结果 60例患者中出现主动脉夹层病变的70处,其中30例前循环,40例后循环。在70处主动脉夹层病变当中,有27处内膜瓣,7处双腔征,36处血管狭窄。相比DSA诊断,通过CTA可以把23处内膜瓣显示出来,占85.2%(23/27),可把5处双腔征显示出来,占71.4%(5/7),可把34处血管狭窄显示出来,占94.4%(34/36)。而在显示主动脉夹层脉瘤和血管闭塞上差异不显著。CTA比MR T1-FS更容易把血管内膜增厚给显示出来。结论通过CTA诊断主动脉夹层,能够把多种影像学征象给清晰显示出来,包括管壁和血管腔在内的主动脉夹层,是一种有效的影像学方式,对临床上运用适当的介入治疗有着重要的指导作用。     

Aortic dissection occurring during coronary angioplasty: Angiographic and transesophageal echocardiographic findings

A localized acute aortic dissection was produced in 2 patients, complicating coronary angioplasty. In both cases a coronary dissection provided the entry door, with subsequent retrograde progression of the dissection into the aortic root. After sealing the entry door, both patients could be managed conservatively using transesophageal echocardiography to accurately define the location of the intimal flap and to rule out dissection progression. Cathet. Cardiovasc. Diagn. 42:412–415, 1997. © 1997 Wiley-Liss, Inc.     

Mobility of the Intimal Flap and Thrombus Formation in Aortic Dissection: A Transesophageal Echocardiographic Study

The mechanisms of the motion of the intimal flap and of thrombus formation in acute or chronic aortic dissection are not definitively elucidated. Transesophageal echocardiography seems to be a technique of choice to analyze the flow in the true and false lumina. Twenty-one consecutive patients were studied in order to define the mobility of the intimal flap, the color Doppler flow patterns, the presence of spontaneous echocardiographic contrast, and thrombus formation at different levels of the aorta. The results suggest that clotted false lumen is more often seen in chronic aortic dissection at the level of the descending thoracic aorta. However, thrombosed false lumen in the aortic arch is suggestive of a retrograde aortic dissection. In cases of complete obliteration of the false lumen, the differentiation between aortic dissection and aortic ectasia with mural thrombus may be extremely difficult.     

Atypical Aortic Dissection Diagnosed by Transesophageal Echocardiography

This case report describes a patient in whom a thin dissection of the proximal aorta was diagnosed by transesophageal echocardiography. Dissection was not firmly diagnosed in our patient with computed tomography, angiography, or magnetic resonance imaging. A definitive diagnosis was made prospectively using intraoperative transesophageal echocardiography by demonstrating the presence of a thin immobile dissection flap located very close to the anterior aortic wall. Color Doppler examination showed absence of flow signals in the small false lumen, suggesting that it may be clotted. At surgery the presence of dissection involving the ascending aorta, as well as a clotted false lumen were confirmed. This finding demonstrates the utility of transeophageal echocardiography in the diagnosis of aortic dissection and the ability of this test to differentiate a thin dissection from intimal thickening. (ECHOCARDIOGRAPHY, Volume 11, May 1994)     

Prolapse of aortic intimal flap into the left ventricle: a rare cause of global myocardial ischemia in acute type A aortic dissection.

A 62-year-old woman experienced an acute type A aortic dissection complicated with profound shock caused by acute myocardial ischemia. Intraoperative transesophageal echocardiography (TEE) identified a circumferentially dissected intimal flap at 5.5 cm above the aortic valve, prolapsing into the left ventricle through the aortic valve during diastole and obstructing both coronary ostia. Acute aortic dissection must be kept in mind when presented with myocardial ischemia and TEE is the most useful method for detecting a prolapsing cylindrical intimal flap.     

Diagnostic goals in aortic dissection. Value of transthoracic and transesophageal echocardiography]

The combination of different ultrasound techniques like transthoracic, suprasternal, subcostal and transesophageal echocardiography have a high sensitivity and specificity in the diagnosis of aortic dissection. The limitation of this combined ultrasound technique is related to the visualization of the ascending part of the aortic arch which, cause of the interposition of the trachea, can not be visualized completely. The beginning or the end of a dissection in this part of the aorta may be misinterpreted. False negative results are rare. False positive results due to artefacts resulting from reverberations in an ectatic ascending aorta have to be taken into account. The most important diagnostic aims in acute or chronic aortic dissection can be described: 1. confirmation of the diagnosis by visualization of the intima membrane, 2. the differentiation of the true and false lumen depending on visualization of spontaneous echocardiographic contrast thrombus formation, slow or reduced reversed flow, systolic diameter reduction and signs of entry jet into the false lumen, 3. detection of intimal tear, demonstrating communication by two-dimensional or color Doppler echocardiography, 4. determination of the extent of the dissection with classification according to DeBakey type I, II and III or Stanford A and B with differentiation to communicating or non-communicating dissection, antegrade or retrograde dissection limited to the descending aorta or expanding to the ascending aorta, 5. detection of wall motion abnormalities as a sign of preexisting coronary artery disease or myocardial ischemia due to ostium occlusion by an intimal flap, coronary artery rupture or collapse of the true lumen during diastole, 6. detection and grading of aortic insufficiency, 7. detection of side branch involvement by suprasternal, subcostal and abdominal sonography, which will gain the information which side can be chosen for cannulation or catheterization at the femoral artery, 8. detection of pericardial pleural effusion and mediastinal hematoma as a sign of emergency as rupture can occur within minutes. Without surgical intervention have be performed. Based on these informations, surgery can be performed in all acute situations in type A dissection without further investigations. This decision is particularly important in patients with signs of emergency like pericardial or pleural effusion or mediastinal hematoma.     

Ambulatory follow-up of aortic dissection by transesophageal two-dimensional and color-coded Doppler echocardiography

Follow-up of 18 patients with aortic dissection (five with type I, one with type II, 11 with type III dissection according to DeBakey) by transesophageal, two-dimensional and color-coded Doppler echocardiography showed a persistence of the false lumen in five of seven patients (71%) after surgery and in nine of 11 patients (82%) after medical therapy. In two patients treated with surgery, the dissected part of the aorta had been resected, whereas in two patients treated medically, a progressive and complete obliteration of the false lumen was observed. In the false lumen, thrombus formation was absent in four, localized in four, and progressive in six patients. Flow within the false lumen could be registered in 14 patients, and two distinct flow patterns were differentiated (laminar biphasic flow or slowly circulating flow). Persisting intimal tears were visualized by two-dimensional echocardiography in four patients, whereas color-coded Doppler showed an additional one to three intimal tears in the descending aorta in 10 patients. Flow across these intimal tears was biphasic in 75% of patients; that is, systolic flow was directed from the true to the false lumen with diastolic flow reversal. Unidirectional flow was detected in 25% of the communications, directed in 20% from the true to the false lumen, serving as an entry only and in one (5%) as reentry only. Additional information concerning complications like extension of the dissection (one of 18 patients), localized dilatation of the regurgitation (three of 18 patients) were detected by this method. Concerning the morphologic findings and the detection of flow characteristics, the transesophageal approach was superior to conventional echocardiography especially in the descending thoracic aorta. Thus, transesophageal two-dimensional and color-coded Doppler echocardiography seems to be an ideal method not only for the easy detection of aortic dissection but also for follow-up.     

食管超声心动图在重危心脏病人诊断治疗中的价值

目的　为评价食管超声心动图 (TEE)在重危心脏病人诊断治疗中的价值 ,对 3 7例收住监护病房的重症心血管病人进行了经胸超声心动图 (TTE)和TEE检查 ,其中男 2 5例 ,女 1 2例 ,平均年龄57( 1 9～ 85)岁。入选对象包括怀疑夹层动脉瘤 2 3例、心脏瓣膜功能异常 9例、感染性心内膜炎 3例 ,心内分流 2例。结果　所有病人均可耐受TEE检查 ,无并发症发生 ,TEE较TTE可提供更高的阳性诊断结果 ,阳性率分别为 65 0 %和 3 8 0 % ,在怀疑夹层动脉瘤者中 ,TEE检出夹层撕裂膜 1 4例 ;而TTE仅检出 7例 ,且图象欠清 ,检出部位有限。在 4例人工机械瓣膜功能异常者中 ,TEE发现瓣膜部位血栓形成 3例。结论　在对心脏大血管疾病的诊断中 ,TEE阳性诊断率高于TTE ,尤其在怀疑夹层动脉瘤及人工机械瓣膜病变时 ,应行TEE检查。即使在重危病人 ,TEE也是一种安全有效的诊断手段。     

Two-dimensional echocardiographic recognition of an aortic intimal flap prolapsing into the left ventricular outflow tract

A 59 year old man presented with dyspnea and a new murmur of aortic regurgitation. Two-dimensional echocardiography demonstrated a to and fro motion of the intimal flap as it prolapsed into the left ventricle and was thrust into the aorta during diastole and systole, respectively. At surgery, the echocardiographic and angiographic findings were confirmed and a proximal aortic dissection was identified. Prolapse of an intimal flap from the aorta into the left ventricular outflow tract represents a new two-dimensional echocardiographic sign of aortic dissection.