Chinese Medical Journal 2008;121(21):2139-2143
Value of intravascular ultrasound imaging in following up patients with replacement of the ascending aorta for acute type A aortic dissection
HU Wei, François Schiele, Nicolas Meneveau, Marie-France Seronde, Pierre Legalery, Fiona Caulfield, Jean-François Bonneville, Sidney Chocron, Jean-Pierre Bassand
HU Wei (Department of Cardiology, Min Hang Central Hospital, Shanghai 201100, China)
François Schiele (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)
Nicolas Meneveau (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)
Marie-France Seronde (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)
Pierre Legalery (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)
Fiona Caulfield (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)
Jean-François Bonneville (Department of Radiology, Jean Minjoz Hospital, Besançon 25000, France)
Sidney Chocron (Department of Cardiac Surgery, Jean Minjoz Hospital, Besançon 25000, France)
Jean-Pierre Bassand (Department of Cardiology, Jean Minjoz Hospital, Besançon 25000, France)Correspondence to:HU Wei,Department of Cardiology, Min Hang Central Hospital, Shanghai 201100, China (Tel: 86-13501912045. Fax:86-21-64923400 ext 5154. E-mail:email@example.com)
Background The value of intravascular ultrasound (IVUS) imaging in patients with replacement of the ascending aorta for acute type A aortic dissection (AD) is unknown. The purpose of this study was to assess the potential use of IVUS imaging in this setting.
Methods From September 2002 to July 2005, IVUS imaging with a 9 MHz probe was performed in a series of 16 consecutive patients with suspected or established AD. This study focused on 5 of them with replacement of the ascending aorta for acute type A AD. Among these 5 patients, other imaging modalities including aortography, spiral computed tomography, magnetic resonance imaging and transesophageal echocardiography were performed in 5, 3, 3 and 1 patients, respectively.
Results There were no complications related to IVUS imaging. For the replaced graft, as other imaging modalities, IVUS could identify all 5 grafts, the proximal and the distal anastomoses, and the ostia of the reimplanted coronary arteries. In 2 cases, IVUS detected 2 peri-graft pseudo-aneurysms (1 per case), which were also detected by magnetic resonance imaging but omitted by aortography. For the residual dissection, IVUS had similar findings as other imaging modalities in detecting the patency (5/5), the longitudinal and the circumferential extent, the thrombus (4/5), the recurrent dissection (1/5) and an aneurysm distal to the graft (5 in 4 patients). However, it detected more intimal tears and side branch involvements than other imaging modalities (15 vs 10 and 3 vs 1, respectively).
Conclusions In following-up patients with replacement of the ascending aorta for acute type A AD, IVUS imaging can provide complete information of the replaced graft and the residual dissection. So, IVUS imaging may be considered when the four current frequently used imaging modalities can not supply sufficient information or there are some discrepancies between them.
Acute type A aortic dissection (AD) has a high mortality and requires urgent operative treatment.1,2 Depending on the condition of the aortic root and aortic valve, the ascending aorta is replaced either by a single or a composite graft.3,4 Recently, early diagnosis, advances of surgical techniques and intensive postoperative surveillance have substantially improved the survival rate, however, the late complications caused by the replaced graft or the residual dissection are not uncommon. The two most frequent ones are an aneurysm distal to the graft and the peri-graft pseudo-aneurysm.3,5-7 Currently, it is generally accepted that such patients warrant a long-term regular imaging follow-up. Computed tomography (CT) and magnetic resonance imaging (MRI) are the two most frequently used non-invasive imaging modalities. Semi-invasive transesophageal echocardiography (TEE) and invasive aortography are often additional tools. However, all of them have their own limitations.8-14
Intravascular ultrasound (IVUS) has been demonstrated to supply additional information to arterial angiography in patients with coronary heart disease.15 However, until now, only a few authors have evaluated the value of IVUS imaging in patients with AD, and most of them used a 20 MHz probe that has limitations in a dilated aorta.16-19 Compared with the four current frequently used imaging modalities, IVUS imaging has a higher spatial resolution, which permits us to detect small graft leakages and residual intimal tears resulting in two frequently occurring post-operative complications. However, no previous studies have assessed the potential use of IVUS imaging in patients with replacement of the ascending aorta for acute type A AD. For a conventionally used 20 MHz probe, the maximal ultrasonic penetrating depth is about 70 mm, in fact, according to the published data, it could not provide a good aortic image if the vessel >45 mm. For the currently available 9 MHz probe, the maximal ultrasonic penetrating depth is approximately 100 mm, but the experience with its use in the aorta is very scant.16-18 From September 2002 to July 2005, we performed imaging with this new system in a consecutive series of 16 patients with suspected or established AD, and this study focused on 5 of them with replacement of the ascending aorta for acute type A AD.
This is a single-center, prospective and observational study that obeyed the Declaration of Helsinki and was approved by the local ethics committee. A written consent form from all participants was obtained before the procedure. From September 2002 to July 2005, 102 patients suspected as acute AD were screened and IVUS imaging was performed in 16 of them; 8 with classic AD, 6 with intramural hematoma, 1 with penetrating atherosclerotic ulcer and 1 with ascending aortic aneurysm. This study focused on 5 patients with replacement of the ascending aorta for acute type A AD. The 5 replaced grafts consisted of 3 single supracoronary Dacron tube grafts, and 2 composite grafts (one adopted classic Bentall technique and another adopted Cabrol modified Bentall technique). All procedures used an included technique, Teflon reinforcement and gelatin-resorcin-formol glue. The indications of IVUS imaging have been published elsewhere.20,21 It has to be noted that not all IVUS imaging procedures were performed after aortography, which is applied as an additional tool for non-invasive imaging modalities.
IVUS imaging was performed using a Hewlett-Packard sonos intravascular imaging system (Hewlett-Packard, Andover, MA, USA) with a 9 MHz catheter-based ultrasound probe (Ultra ICETM intracardiac Echo catheter, Boston Scientific, USA). This kind of probe has an in-plane resolution of 0.25 mm × 0.60 mm and a penetrating depth of 100 mm, whereas a frequently used 20 MHz probe has an in-plane resolution of 0.2 mm × 0.3 mm and a penetrating depth of 70 mm. This 9 MHz probe was contained within a 9F (110 cm long) polyethylene catheter, and is rotated by an external motor at 600 r/min. The ultrasound beam was emitted from a 10° forward-angling tip of the single-crystal focused element. The probe produced circular images with the catheter in the center at the frame rate up to 30 f/s. The technical details of IVUS imaging have been published elsewhere.20,21 Briefly, the IVUS probe was introduced to the aortic root with the help of a 0.889 mm (0.035 inch) guide wire and a 110 cm sheath under fluoroscopy via the right femoral artery. After obtaining an optimal cross-sectional aortic image, it was manually pulled back and IVUS images were simultaneously recorded on the videotape for subsequent analysis. The scan order of IVUS imaging was aortic root, ascending aorta, aortic arch, descending aorta, thoracic aorta, abdominal aorta and the right iliac artery. The fluoroscopy and fluorography were used to localise the position of the IVUS probe.
IVUS images analyses
Two cardiologists (HW & FS), who were blinded to the findings of other imaging modalities, performed the IVUS image analyses using the same definitions, and a third observer (NM) was invited to settle the discrepancies. Echoplaque software (INDEC systems) was used to reconstruct a 2-dimensional IVUS image and to perform quantitative analyses if necessary. Two criteria were used to distinguish the replaced graft and the normal aorta: (1) the replaced graft often had a higher echo reflection than the normal aorta; (2) the replaced graft appeared as a thin single-layer structure for the whole circumference, whereas the normal aorta often has three layers. The proximal and the distal anastomoses were judged by the suture lines (appeared as saw-shaped structures). The peri-graft pseudo-aneurysm was deemed to be presented if blood flow was detected in peri-graft space. The reimplanted ostia of coronary arteries were also recorded. We adopted Weintraub’s method to interpret the residual or recurrent dissection (defined as the reopening of a thrombosed false lumen). Briefly, an intimal flap was defined as a moving curvilinear structure separating the aorta into a true and a false lumen; aortic dissection was diagnosed if an intimal flap presented; intimal tear was defined as an uncontinuous site of an intimal flap; thrombus was defined as a piece of fixed substance with a soft granular echo signal that often located in the false lumen; the distal aneurysm was diagnosed when the diameter of a non-replaced aorta was more than 1.5 times that of a normal aorta. The relation between the aortic side branches and the true or the false lumen or the intimal flap were also recorded.
Other imaging techniques and analysis
Spiral CT (with 4 detectors, Somatom Plus 4, Volumezoom, Siemens, Forchheim, Germany), TEE (with a 5 MHz multi-plane probe, Toshiba PEF-510MB 270A and 140A imaging systems, Japan), MRI (with 1.5 Tesla, Siemens MAGNETOM Sonata 1.5T High Field MRI, Germany) were performed using standard methods. The protocol of CT scan has been published elsewhere. Other experts interpreted these images by adopting standard definitions.
All five patients were male, and the mean age was (67.0±8.6) years old (ranged from 53 to 74). All except one were asymptomatic. Aortography, spiral CT, MRI, and TEE were performed in 5, 3, 3 and 1 patient, respectively (Table 1). The mean interval time between the initial operation and IVUS imaging was (98.6±108.7) months (ranged from 20 to 252). All interval time between IVUS imaging and other imaging techniques was less than 7 days.
Table 1. Patient demographics
There were no complications related to IVUS imaging. IVUS could supply us with a good cross-sectional aortic image from the aortic root to the bifurcation of the iliac artery, and most of its side branches, even in a much dilated aorta (the biggest aortic diameter was 90 mm). The detection rate of three arch branches, the celiac trunk artery, the superior and the inferior mesenteric arteries and the renal arteries were 100% (Table 2).
Figure 1. A small false aneurysm omitted by aortography was detected by IVUS. The star represented a small false aneurysm that was caused by suture line dehiscence (indicated by an arrow; transverse sonogram).
Figure 2. A big peri-graft aneurysm omitted by aortography was documented by IVUS and demonstrated by MRI. A: IVUS detected a big peri-graft false aneurysm (represented by two stars) and their mouth (indicated by a double head arrow) at the distal anastomosis. The triangle represents the real lumen (transverse sonogram). B: The tube graft and the valve prosthesis (indicated by an arrow) were opacified, whereas the false aneurysm was not opacified (left anterior oblique angiogram). C: A transversal MRI image. The false aneurysm is represented by two stars and the real lumen is represented by a triangle. The arrow indicates the suture line dehiscence site.
For the residual dissection, IVUS had similar findings as other imaging modalities in detecting: the patency (5/5), the longitudinal and circumferential extent, the thrombus (4/5), the recurrent dissection (1/5), and the aneurysm (5 in 4 cases). However, it detected more intimal tears and side branch involvements than other imaging modalities (15 vs 10 and 3 vs 1, respectively).
Treatment and follow-up
All therapeutic decisions were made independent of IVUS imaging findings. Cases 1 and 5 were operated on for their descending aortic aneurysms and were medical therapy and had no adverse events. Case 2 maintained until time of publication. Case 4 received refused the proposed operation and died of aortic rupture. Case 3 underwent a new operation but died of low cardiac output.
IVUS imaging in coronary arteries has been proven to be a safe examination.15 According to previous studies, there were no complications reported related to IVUS imaging in the aorta and,in combination with our results, we believe that intra-aorta IVUS imaging is a safe procedure.16-20 In addition, our study showed that IVUS imaging with a 9 MHZ probe could overcome the limitations of a 20 MHZ probe in a very dilated aorta,16-18 which was often seen in previous studies. In our series, the biggest aortic diameter was 90 mm and the detecting rate of three arch branches: the celiac trunk artery, the superior and inferior mesenteric arteries, and the renal arteries were 100%.
We found that IVUS imaging could easily identify the replaced graft, the proximal and distal anastomoses and the ostia of the reimplanted coronary arteries. We also found that IVUS imaging was able to detect pathologic changes of the replaced graft, in this study two peri-graft false aneurysms were detected by IVUS imaging and confirmed by other imaging techniques. Moreover, this study also showed that IVUS imaging could easily localize these pathologic changes and ascertain their causes, which will be very helpful for the treatment strategy. However, considering that all our five patients had been operated on by adopting an included technique and using a Dacron tube graft, we can not draw any conclusion on IVUS imaging in patients with replacement of the ascending aorta by adopting an interposed technique and using other types of grafts.
Since the most frequent late complications were due to the aneurysmal dilatation of the false lumen in patients with replacement of the ascending aorta for acute type A AD, it is very important to acquire residual dissection information for an imaging technique.3,5 In fact, several authors have already demonstrated that IVUS imaging could provide complete information of AD.16,17 Our study showed that: by comparison with other imaging techniques, IVUS imaging provided similar information such as: the patency of the false lumen, the thrombus in the false lumen, the longitudinal and circumferential extent of the residual dissection, the recurrent dissection, and the aneurysm distal to the graft, but it was more sensitive in detecting the intimal tear and the involvement of a side branch vessel.
Compared with the currently used imaging techniques such as: aortography, CT, TEE and MRI, IVUS imaging may have several advantages in identifying the replaced graft and its pathologic changes. (1) It has a unique interior view that may avoid the reflection of the replaced graft. (2) It has no potential blind zones. (3) It can directly identify the replaced graft. (4) It does not need contrast. However, IVUS imaging also has some limitations. (1) It is an invasive procedure and has potential damage. (2) It is unable to judge the functional state of the aortic valve prosthesis, but that is not a big problem, because this information may be supplemented by a transthoracic echocardiography examination.
Therefore, we believe that as an invasive imaging technique, IVUS cannot be used as a regular examination in following up patients with replacement of ascending aorta for acute type A AD, and we agree with other authors that non-invasive MRI seems to the best choice.8-11 However, IVUS imaging may be considered when the four current frequently used imaging modalities can’t supply sufficient information or there are discrepancies between them.
In conclusion, in following patients with replacement of the ascending aorta for acute type A AD, IVUS imaging can provide complete information of the replaced graft and the residual dissection. So, IVUS imaging may be considered when the four current frequently used imaging modalities can’t supply sufficient information or there are some discrepancies between them.
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