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J Am Coll Cardiol, 2000; 36:884-890 © 2000 by the American College of Cardiology Foundation |
a Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Boston, Massachusetts, USA
b Thoracic Aortic Center, Massachusetts General Hospital, Boston, Massachusetts, USA
Manuscript received June 21, 1999; revised manuscript received March 15, 2000, accepted April 14, 2000.
Reprint requests and correspondence: Dr. Eric M. Isselbacher, Massachusetts General Hospital, 15 Parkman St, ACC 469, Boston, Massachusetts 02114
isselbacher.eric{at}mgh.harvard.edu
| Abstract |
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The purpose of this study was to use transesophageal echocardiography (TEE) to define the mechanisms of aortic regurgitation (AR) in acute type A aortic dissection so as to assist the surgeon in identifying patients with mechanisms of AR suitable for valve preservation.
BACKGROUND
Significant AR frequently complicates acute type A aortic dissection necessitating either aortic valve repair or replacement at the time of aortic surgery. Although direct surgical inspection can identify intrinsically normal leaflets suitable for repair, it is preferable for the surgeon to correlate aortic valve function with the anatomy prior to thoracotomy.
METHODS
We studied 50 consecutive patients with acute type A aortic dissection in whom preoperative TEE findings were considered by the surgeons in planning aortic valve surgery. Six patients did not undergo surgery (noncandidacy or refusal) and one patient had had a prior aortic valve replacement and therefore was excluded from the analysis.
RESULTS
Twenty-seven patients had no or minimal AR and 22 had moderate or severe AR. In all, there were 16 with intrinsically normal leaflets who had AR due to one or more correctable aortic valve lesion: incomplete leaflet closure due to leaflet tethering in a dilated aortic root in 7; leaflet prolapse due to disrupted leaflet attachments in 8; and dissection flap prolapse through the aortic valve orifice in 5. Of these 16 patients, 15 had successful aortic valve repair whereas just 1 underwent aortic valve replacement after a complicated intraoperative course (unrelated to the aortic valve). Nine patients underwent aortic valve replacement for nonrepairable abnormalities, including Marfans syndrome in four, bicuspid aortic valve in four, and aortitis in one. In patients undergoing aortic valve repair, follow-up transthoracic echocardiography at a median of three months revealed no or minimal residual AR, and clinical follow-up at a median of 23 months showed that none required aortic valve replacement.
CONCLUSIONS
When significant AR complicates acute type A aortic dissection, TEE can define the severity and mechanisms of AR and can assist the surgeon in identifying patients in whom valve repair is likely to be successful.
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Previous echocardiographic studies of aortic dissection have documented the ability of TEE to detect aortic dissection accurately and to define its anatomic features, such as the extent of dissection, sites of intimal tear, presence of pericardial effusion, and presence and severity of AR (1723). To date and to our knowledge, however, no study has systematically addressed the role of TEE in defining the mechanisms of AR in acute aortic dissection. We hypothesized that TEE performed in patients with acute type A aortic dissection can, in addition to assessing the severity of AR, assist the surgeon in identifying those patients with mechanisms of AR suitable for aortic valve repair as opposed to those with fixed abnormalities (e.g., bicuspid aortic valve, aortic stenosis, marfanoid aortic root) requiring aortic valve replacement.
| Methods |
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Echocardiography.
All patients underwent preoperative or intraoperative TEE. The studies were performed with a standard two-dimensional and color-coded Doppler flow ultrasound system (Hewlett Packard Sonos 1500 / 2500 / 5500) equipped with a flexible 5-MHz multiplane transesophageal probe. The probe was passed after sedation and/or administration of anesthesia, and before the thoracic cavity was opened. The clinical purpose of the TEE examination was to confirm the diagnosis of aortic dissection, determine its location and extent and evaluate the severity and specific mechanisms of AR when present. Two echocardiographers interpreted the TEE findings, which were in turn considered by the surgeons in planning aortic valve surgery. The severity of AR was assessed by a semiquantitative method based on the ratio of the proximal jet height to annular diameter (<0.25 = trace; 0.25 to 0.46 = mild; 0.47 to 0.64 = moderate;
0.65 = severe) (24) measured in a long-axis view obtained at approximately 120° by multiplane TEE; this method has been validated in vitro and correlates well with angiographic grading (25). We defined five potential mechanisms of AR in this population, the first three of which were considered repairable without need for valve replacement: 1) incomplete closure of intrinsically normal leaflets due to leaflet tethering by a dilated sinotubular junction (Figs. 1 and 2); 2) leaflet prolapse due to disruption of leaflet attachments by a dissection flap that extends below the sinotubular junction and into the aortic root (Figs. 1 and 3); 3) prolapse of the dissection flap through intrinsically normal leaflets that disrupts leaflet coaptation (Figs. 1 and 4); 4) a bicuspid aortic valve with associated leaflet prolapse unrelated to the dissection process; and 5) degenerative leaflet thickening resulting in abnormal leaflet coaptation. Some patients had more than one mechanism of AR. Follow-up transthoracic echocardiogramsthe timing of which was based on clinical factorswere performed in all patients who underwent aortic valve repair.
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In patients whose valves were preserved, the proximal aorta was completely transected at the sinotubular junction and blood clot was removed from the false lumen. Leaflet prolapse was corrected by suturing together a sandwich of the aortic layers immediately distal to the aortic valve commissures, thereby resuspending the aortic leaflets in the aortic root. Incomplete leaflet closure due to leaflet tethering by a dilated aorta was corrected by reducing the diameter of the sinotubular junction, thereby restoring normal aortic leaflet coaptation.
Under hypothermic arrest, the cross clamp was removed and the aorta was completely transected distally at the junction of the ascending aorta and arch. The ascending aorta, including the intimal tear (if evident), was resected, which corrected dissection flap prolapse when present. A collagen-impregnated Dacron graft, sized to match the diameter of the reconstituted sinotubular junction, was anastomosed to the distal ascending aorta. Bypass was reinstituted and the anastomosis of the graft to the proximal aorta was made while the patient was being rewarmed.
Composite aortic root replacement was performed in all patients with Marfans syndrome or a preexisting aortic root aneurysm in order to avoid retaining any portion of the diseased aortic sinuses that might be prone to subsequent dilatation and rupture. All patients with bicuspid aortic valves and significant AR due to leaflet prolapse (unrelated to the dissection process) underwent aortic valve replacement. A valve-graft composite prosthesis was sutured to the aortic valve annulus after valve excision, and the coronary arteries were implanted directly into the Dacron graft as previously described. The distal aorta was managed with circulatory arrest in the manner described above.
Statistical analysis. Statistical analysis was performed with software (SPSS 8.0; SPSS, Inc.). Normally distributed continuous variables were expressed as the mean ± 1 SD. Nonparametric continuous variables were expressed as the median and range.
| Results |
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Five of the 27 patients with no, trace or mild AR were treated medically: 2 refused surgery; 1 had cold agglutinins that were considered a contraindication to deep hypothermic arrest; 1 had a very localized catheter-induced dissection that remained stable; and 1 had several comorbid conditions and mesenteric ischemia and was therefore treated with percutaneous fenestration of the abdominal aortic intimal flap only. The remaining 22 patients underwent aortic surgery: 18 had isolated replacement of the ascending aorta with an interposition graft; 2 required aortic valve replacement with a composite graft because of either Marfans syndrome or a bicuspid aortic valve with significant stenosis; and 2 underwent aortic valve repair in addition to ascending aortic replacement with an interposition graft. These latter two cases had echocardiographic evidence of significant aortic leaflet prolapse that necessitated valve repair, but neither had more than mild AR due to prolapse of the intimal flap that occluded the valve orifice in diastole.
Twenty-two patients had moderate or severe AR. All but one patientwho had comorbid massive hemoptysis and mesenteric infarctionunderwent aortic surgery. Eight patients required a composite aortic graft with aortic valve replacement: three patients had Marfans syndrome; three had a bicuspid aortic valve and severe AR; one had active aortitis; and one underwent valve replacement at the surgeons discretion after a prolonged complicated intraoperative course (unrelated to the aortic valve disease). The remaining 13 patients underwent aortic valve repair and replacement of the ascending aorta with an interposition graft. Among those undergoing aortic valve repair, the following mechanisms of AR were identified by TEE, with some patients having more than one mechanism present: seven had incomplete aortic leaflet closure; six had aortic leaflet prolapse; three had prolapse of the intimal flap through the valve; and five had degenerative leaflet thickening. No patient undergoing aortic valve repair proceeded to aortic valve replacement for an inadequate repair.
In summary, of the 43 patients who underwent aortic surgery, 33 (77%) did not require aortic valve replacement. The severity of AR, mechanisms of AR and management strategies for all patients undergoing aortic valve procedures are presented in Table 4.
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Follow-up of aortic valve repair. Follow-up transthoracic echocardiography (TTE) was performed in all 15 patients who underwent aortic valve repair. The median time to follow-up TTE was three months (range, 4 days to 22 months). One patient had no residual AR, six had trace AR and six had mild AR. None had moderate or severe AR and none had required reoperation at a median of 23 months of clinical follow-up (range, 1 to 38 months).
| Discussion |
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TEE assessment of the mechanisms of AR. This study shows that TEE can define the mechanisms and severity of AR that complicate acute type A aortic dissection, and that these TEE findings may help the surgeon to distinguish valves with geometric distortion amenable to repair from those with fixed abnormalities that require replacement. Although the severity of AR is certainly a consideration, it is the mechanism responsible for the AR that weighs more heavily in the decision to repair versus replace the aortic valve in such patients. Although in many cases a potentially repairable aortic valve can be identified by direct intraoperative inspection, in the setting of acute aortic dissection complicated by significant AR, many surgeons opt for valve replacement rather than repair because of the emergent nature of the surgery and the instability of the patients. In such situations, employing TEE to identify those mechanisms of AR amenable to repair may make the surgeon more confident that an attempt at aortic valve repair is likely to be successful.
Five different mechanisms of AR were identified by TEE in this study population. Three of these mechanismsleaflet thickening, bicuspid aortic valve disease and incomplete leaflet closure in a dilated aortic rootmay also be observed in patients without aortic dissection. Multiple mechanisms of AR were present in some patients. When aortic valve repair was performed, the surgeons made certain to correct all reversible mechanisms of AR identified by TEE and direct surgical inspection: for incomplete aortic leaflet closure, valve repair involved narrowing the diameter of the dilated sinotubular junction to relieve tension on the aortic leaflets, thereby restoring normal leaflet coaptation; for aortic leaflet prolapse, repair involved resuspending the aortic leaflets by reapposing the aortic layers at the commissures; for prolapse of the dissection flap through the valve orifice, repair involved resecting the ascending aorta including the redundant dissection flap. Importantly, in this study, TEE also identified two patients in whom AR was only mild but repair was nevertheless indicated because of severe anatomic distortionsincomplete leaflet closure or leaflet prolapse with concomitant dissection flap prolapse. Finally, intraoperative TEE provided confirmation of successful valve repair prior to closing of the chest.
In this study, the aortic valve was spared in 77% of the 43 patients undergoing aortic surgery, which is consistent with prior series that have reported aortic valve preservation in 56% to 89% of patients (68,10,11,13,15). Of the 16 patients determined by TEE to have potentially repairable mechanisms of AR, 15 did, in fact, undergo successful aortic valve repair with no, trace or at most mild residual AR; none needed subsequent aortic valve surgery at a median follow-up of 23 months. Only one patient underwent aortic valve replacement, this being at the surgeons discretion following a prolonged intraoperative course with complications unrelated to the aortic valve disease.
Study limitations. Although AR volume may decline in sedated or hypotensive patients (due to decreased diastolic aortic pressure), in this study, the assessment of AR was based on proximal jet dimension, a method that is relatively independent of driving pressure for a given orifice size at clinically relevant flow rates (25,29). Moreover, for the purposes of analysis, we broadly grouped patients into those with minimal AR (no, trace or mild AR) and with significant AR (moderate or severe AR), thereby diminishing the potential for error in categorization.
In this study, the mechanisms of AR were determined by two-dimensional echocardiography with color-flow Doppler. This technique has inherent limitations, however, because using standard two-dimensional imaging, it may be difficult to appreciate the true three-dimensional anatomy of the aortic valve. In future studies, therefore, it may be worthwhile to utilize recently developed techniques in three-dimensional echocardiography to define in more detail the anatomic and geometric abnormalities of the aortic valve that result in AR in patients with aortic dissection.
Aortic valve repair was not attempted in patients with Marfans syndrome, preexisting aortic root aneurysm or bicuspid aortic valve with significant AR. While this conservative approach has support in the aortic dissection literature (4,6,10,11,16,30), it should be noted that there are a growing number of reports of successful valve-sparing operations among these patients groups (3134); however, to date these series have been limited to a few centers and have included few patients with acute type A aortic dissection. Nevertheless, the future dissemination of such valve-sparing operations should serve only to increase the potential value of TEE to identify repairable mechanisms of AR.
Finally, the follow-up period in this study was relatively short. Although echocardiographic follow-up was obtained at a median of only three months, clinical follow-up was obtained at a median of 23 months. More importantly, the clinical follow-up showed that patients who underwent aortic valve repair did not require reoperation for progressive AR.
Conclusions and clinical implications. In summary, when significant AR complicates acute type A aortic dissection, TEE can define the severity and mechanisms of AR. The TEE findings may help the surgeon to distinguish those mechanisms of AR suitable for repair from the chronic fixed abnormalities requiring aortic valve replacement. While the highly experienced surgeon may feel comfortable making such a determination by direct surgical inspection alone, other surgeons may well appreciate the ability of TEE to define the aortic abnormality preoperatively and/or to confirm their own intraoperative impressions. Based on the results of this study, TEE may play an increasingly important role in patients with acute type A aortic dissection as cardiologists and cardiac surgeons work together to determine the optimal management of any consequent AR.
| Footnotes |
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| References |
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