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J Thorac Cardiovasc Surg 2007;133:127-135
© 2007 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
a Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, New York, NY
b Department of Anesthesiology, Mount Sinai School of Medicine, New York, NY.
Read at the Eighty-fifth Annual Meeting of The American Association for Thoracic Surgery, San Francisco, Calif, April 10-13, 2005.
Received for publication April 12, 2005; revisions received June 15, 2006; accepted for publication June 17, 2006. * Address for reprints: James C. Halstead, MA (Cantab), MB, BChir, MRCS (Eng), Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029. (Email: jameschalstead{at}yahoo.co.uk).
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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METHODS: One hundred seventy-nine consecutive patients (70% male; mean age, 60 years) with acute type A dissection underwent aggressive resection of the intimal tear and open distal anastomosis (1986-2003). Hospital mortality was 13.4%. Survivors had serial computed tomographic scans: digitization yielded distal segmental dimensions. Segment-specific average rates of enlargement and factors influencing faster growth were analyzed. Distal reoperations and patient survival were examined.
RESULTS: Eighty-nine (57%) patients had imaging data sufficient for growth rate calculations. The median diameters after repair were as follows: aortic arch, 3.6 cm; descending aorta, 3.7 cm; and abdominal aorta, 3.2 cm. Subsequent growth rates were 0.8, 1.0, and 0.8 mm/y, respectively. Initial size of greater than 4 cm (P = .005) and initial diameter of less than 4 cm with a patent false lumen (P = .004) predicted greater growth in the descending aorta, and male sex (P = .05) significantly affected growth in the abdominal aorta. No significant factors were found for the aortic arch. There were 25 distal aortic reoperations (16 patients), and risk of reoperation was 16% at 10 years. Risk factors reducing long-term survival after repair of acute type A dissection included age (P < .0001), new neurological deficit at presentation (P = .04), absence of preoperative thrombus in the false lumen of the ascending aorta (P = .03), and a patent distal false lumen postoperatively (P = .06) but not distal reoperation.
CONCLUSIONS: Growth of the distal aorta after repair of acute type A dissection is typically slow and linear. Distal reoperation is uncommon, and late risk of death is approximately twice that of a healthy population.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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The extent of operation was determined by each of several surgeons. However, composite graft replacement was used almost exclusively when the coronary sinuses were dissected. This aggressive strategy of resection rather than repair of the dissected aortic root resulted in a high proportion of composite graft replacements.1
When conservative repair was undertaken, the aorta was transected at the sinotubular junction and reinforced with an externally placed circumferential piece of Teflon felt (DuPont, Parkersburg, WV) and an internal gusset of felt or autologous pericardium, so as to realign the commissural geometry. Tissue glues were not used. Occasionally, separate valve replacement was undertaken in cases of bicuspid, stenotic, or residually regurgitant valves.
For the composite graft replacements, a manufactured conduit with a mechanical valve was used in most patients. In a minority of patients, a biologic valve was sutured to an appropriately sized tubular woven graft. Coronary reconstruction was usually undertaken by using buttons on the outside of the graft (the button-Bentall technique).
After the proximal repair, during a single period of hypothermic circulatory arrest, the arch was inspected, and an open distal anastomosis was undertaken. The presence and site of the intimal tear or fragile tissues in the arch determined the extent of distal resection (Table 2). The dissected layers were reapproximated with supporting external Teflon felt. The distal end of the graft was sewn within this construct, and the arch or arch graft was carefully deaired. Antegrade reperfusion was instituted through an arterial cannula inserted into the ascending graft in cases in which cardiopulmonary bypass had been initiated through the femoral artery; otherwise, perfusion was resumed through the right axillary artery.
Follow-up
Surviving patients were invited for annual clinical review and CT scanning of the entire aorta. Clinical data were compiled from these office visits, telephone contact with patients, and input from primary care physicians. It included, but was not limited to, information concerning aortic reoperations or ruptures, thromboembolic events, hemorrhagic complications, cardiac pathology (eg, episodes of endocarditis), and patient survival. Cause of death, where available, was also recorded. The median patient follow-up time after hospital discharge was 61 months (range, 0-218 months).
Growth Rates
A process of CT digitization, previously described in detail,2 was used to assess the whole of the residual aorta after surgical intervention. Segmental expansion rates were calculated by using dimensions derived from multiple CT scans. For inclusion into analysis of expansion rates, at least 2 CT scans had to have been taken postoperatively at least 6 months apart. Once an aortic segment had been subject to reoperative surgical intervention, its dimensions were no longer considered part of the growth rate calculations. CT scans were also analyzed for evidence of a patent false lumen.
A number of patients died before 2 postoperative studies at least 6 months apart could be completed, others declined further studies, and a few were lost to follow-up. Thus only 89 (57%) patients were included in the analyses for CT-derived rates of expansion. A number of factors were compared between patients who contributed CT scans and those who did not to determine whether the group who contributed scans was representative of the entire cohort of patients who survived the procedure. The factors examined were as follows: age; sex; presence of aortic dilatation, chronic obstructive pulmonary disease (COPD), diabetes, or Marfan syndrome; a history of hypertension or diabetes; the presence of thrombosis in the false lumen of the ascending aorta, hemodynamic compromise, or new neurological symptoms at presentation; use of a composite graft at the time of the operation; postoperative descending aortic dilatation; or the presence of an open false lumen.
Statistical Methods
Hospital death was defined as death within the same hospitalization. From a wide array of potentially important clinical and dissection-related variables, independent risk factors for hospital death were identified by means of logistic regression analysis. Similarly, the influence of these factors together with others reflecting the postoperative course, such as postoperative patency of aortic false lumina and reoperations, on late survival was examined with Cox proportional hazards regression. Late actuarial survival and risk factors for death were assessed among hospital survivors. For the purposes of comparison with other published data, overall actuarial survival from hospital admission is also given. Survival rates for a cohort matched for age and sex to the hospital survivors were derived from data from the 1990 Vital Statistics of the United States.
The growth rates of the serial CT scans of patients contributing 2 or more scans at least 6 months apart are described in 2 ways. First, the observed measurements of the serial scans were shown in "spaghetti plots" for each segment. Then the slopes of the rates of growth in each patient for each segment were estimated separately, and the medians of these estimated slopes are given. Finally, data from the serial CT scans were analyzed by using hierarchical linear models for repeated measures to study factors that influenced the growth rates.
Reoperations to resect segments of the residual native aorta were classified according to site: arch, descending aorta, thoracoabdominal aorta, abdominal aorta, or aortic root. Cumulative incidence functions3,4 were calculated to estimate the rates of reoperation distal to the prior resection at 1, 5, and 10 years.
Statistical analyses were performed with SAS software (Version 8; SAS Institute, Inc, Cary NC).
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Results |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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Two significant differences were found between the patients contributing scans and those who did not: a higher proportion of patients contributing scans had preoperative false luminal thrombosis in the ascending aorta (P = .03), and fewer had an initial postoperative diameter in the descending aorta of 4 cm or larger (P = .04). Because these differences might have led to an underestimation of the overall median growth rates from our sample, we show the data separately according to these factors in Table E1, which is a summary of segmental growth rates.
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Postoperative growth rates in the residual ascending aorta were not analyzed because only a few patients had residual ascending segments identified on the initial postoperative CT scan. We report instead a comparison of the diameter of the implanted graft, according to the manufacturer, with its diameter on the first postoperative CT scan. This analysis shows a median increase of 12.3% postoperatively in the diameter of the implanted graft.
The median maximal diameter of the aortic arch after repair was 3.6 cm, and the subsequent median growth rate was 0.8 mm/y. Male sex was predictive of slightly higher growth rates, but this did not reach statistical significance (P = .10).
For the descending aorta, the median maximal diameter was 3.7 cm, and the median growth rate was 1.0 mm/y. An initial dimension of 4 cm or larger (P = .005) predicted more rapid growth (median, 1.3 vs 0.9 mm/y). In patients with an initial diameter of less than 4 cm, a patent false lumen (P = .004) was associated with faster subsequent expansion (median, 1.2 vs 0.8 mm/y).
The results for the abdominal aorta showed a median initial diameter of 3.2 cm and a median growth rate of 0.8 mm/y. Male sex was predictive of more rapid aortic expansion (P = .05).
Analysis of spaghetti plots, which show the behavior of the individual patients’ aortic segments over time, illustrates that the growth rates in all segments are typically slow and linear. This can be seen for the aortic arch, the descending aorta, and the abdominal aorta in Figure 1.
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balancing this risk against an estimate of the operative risk for a given individual. If operative risk was deemed smaller than the likelihood of rupture within a year, surgical intervention was usually advised.
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There was 1 (4%) perioperative death among these reoperations: it occurred in the only patient undergoing reoperation because of rupture (Table 3). The cumulative probability functions for distal reoperation at 1, 5, and 10 years are shown in Figure E1.
There were also 5 proximal reoperations in 5 patients for aortic regurgitation caused by the development of an aortic root aneurysm after repair.
Long-term Survival
Actuarial survival rates for hospital survivors at 1, 5, and 10 years were 90.7% ± 2.3%, 77.9% ± 3.6%, and 66.2% ± 5.1%, respectively (Figure 2, seen together with the survival figures of a matched US population cohort). Cox proportional hazards regression showed that age (hazard ratio [HR], 1.1/y; P < .0001), new neurological symptoms at presentation (HR, 2.3; P = .04), and absence of preoperative false lumen thrombosis in the ascending aorta (HR, 3.8; P = .03) were independent predictors of death after hospital discharge; the presence of a patent false lumen postoperatively came close to statistical significance (HR, 1.9; P = .06). Distal reoperation, entered into the model as a time-changing covariate, does not affect survival.
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Overall actuarial survival rates from hospital admission at 1, 5, and 10 years were 79.1% ± 3.1%, 67.4% ± 3.7%, and 57.1% ± 4.7%, respectively.
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Discussion |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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We identified COPD, diabetes, malperfusion, and hemodynamic compromise as key determinants of perioperative mortality, which is also in broad agreement with factors cited in previous reports of acute type A dissection: in particular, we and others have found no independent influence of age.16 Unfortunately, the factors determining hospital survival are generally not subject to modification. Thus these analyses are only useful in identifying particularly high-risk groups, in whom it can and has been argued that surgical intervention for acute type A dissection should perhaps not be undertaken.17
Segmental Aortic Growth Rates
We have shown that the median diameters of the aortic arch, descending thoracic aorta, and abdominal aorta are all mildly enlarged after type A dissection repair. The median expansion rates of these segments are typically low, approximately 1 mm/y. Unfortunately, this analysis is based on incomplete CT follow-up, which obviously limits the strength of the findings. We did compare the characteristics of the group whose scans permitted analysis of growth rates with those of the entire cohort and found they matched closely; perhaps this suggests that our analysis is relevant to patients with acute type A dissection as a whole, but of this we have no certainty. Moreover, the fact that the analyzed group included a significantly greater proportion of patients with a preoperatively thrombosed false lumen in the ascending aorta, which is associated with greater longevity but no difference in segmental growth rates, and with a significantly smaller initial postoperative diameter in the descending aorta, which does predict a slower expansion rate in that segment of the aorta, suggests that our growth rates are likely to be somewhat conservative.
The analysis of risk factors for more rapid expansion in each distal aortic segment after acute type A dissection repair has shown that male sex seems to be important in determining faster growth both in the aortic arch and abdominal aorta. In the descending aorta initial size and patency of the false lumen are the dominant factors accelerating aortic expansion: patency of the false lumen has a highly significant effect on growth rates in patients with a small initial postoperative aortic diameter.
The finding that there is an increase in diameter of the implanted graft postoperatively is not widely recognized but is consistent with our clinical impressions from the small number of patients who require reoperation in the proximal aorta.
The influence of male sex on expansion rates of the aorta is a new observation that is somewhat at variance with the evidence in a recent study by Sueyoshi and colleagues18 indicating that female sex is associated with a tendency toward more rapid expansion of the aorta after type B dissection. The faster growth of the infrarenal aorta in male subjects might be related to whatever factors cause a higher incidence of infrarenal aneurysms in male subjects without dissection.
In contrast, the influence of a patent false lumen in determining faster subsequent growth of a dissected aorta has been noted previously.18,19 Sueyoshi and colleagues18 assessed expansion rates after nonoperatively managed type B aortic dissection using CT scanning and found the presence of blood flow in the false lumen to be the only significant risk factor for faster growth. The mean initial segmental dimensions found were similar to those in the present study, as was the overall abdominal aortic expansion rate, but growth rates in the aortic arch and descending aorta were twice those seen in our study. In addition to methodological differences, the discrepancy in the growth rates found in these studies might be explicable on the basis of differing underlying pathology (type A vs type B dissection), sites of intimal tear, and (operative vs nonoperative) management.
Fattori and associates19 followed very closely a cohort of 70 patients after surgical intervention for acute type A dissection with serial magnetic resonance imaging. In accord with the present study, they found the yearly aortic growth rate to be maximal in the descending aortic segment and to be significantly higher in the absence of false luminal thrombosis. The median descending aortic growth rate in our study, however, is considerably less than what was found by Fattori and associates (1 vs 3.7 mm/y), but in the absence of false luminal patency, the growth rate of the descending aorta in Fattori and associates’ series was only 1.1 mm/y, which is very close to the rate observed in the current study. Although no details of operative technique are provided by Fattori and associates, their descriptions suggest a much greater prevalence of less-extensive aortic resections, with repairs generally limited to the ascending aorta. This makes it plausible that their higher overall growth rate reflects a higher proportion of patients with the residual false lumen open (78% vs only 43% in the current series).
Given the importance of residual false luminal patency in determining distal aortic expansion and patient survival, it seems evident that surgical strategy in the treatment of acute type A dissection should include measures not only to optimize hospital survival but also to reduce the likelihood of persistent patency of the distal false lumen. These include avoidance of aortic clamping or resection of the clamp site, use of open distal anastomosis, aggressive resection of the intimal tear and adjacent friable aorta, and use of perfusion strategies that direct flow preferentially into the true lumen.
Aortic Reoperations
We attribute the low rate of proximal reoperation seen in this series to the liberal use of composite aortic root replacement.20 It has been our philosophy to resect aortic root tissue rather than to try to reapproximate dissected tissue by using glue or other adjuncts (Table 2). We believe that use of a composite aortic root replacement is a technique that can increasingly safely be used for acute dissection, even in centers not specializing in aortic surgery.1,20 However, we also recognize that the most important goal of initial operation in acute type A dissection is to permit immediate survival, with long-term outcome a less-important consideration.
The pattern of distal reoperation that we observed is similar to what has been quoted by others.21 The likelihood of reoperation appears to be higher in the presence of Marfan syndrome (31% vs 8%), although the numbers were too small to enable formal analysis of risk factors. We speculate that our low incidence of distal reoperation might be a consequence of our determination to resect the intimal tear at the time of the acute dissection because others have correlated failure to resect the intimal tear with risk of late reoperation.13,22
Late Mortality
Overall survival and discharged patients’ actuarial survival curves are similar to those of contemporary series from major aortic surgical institutions.22 Clearly, patient age is a potent risk factor influencing long-term survival, and its dominance has previously been noted. That the presence of a patent false lumen postoperatively increases late mortality, which depends significantly on aortic pathology, is supported by our data and once more highlights the importance of directing surgical strategy toward closing the false lumen.
The influence of neurological events occurring at the time of the dissection on long-term survival has been described before; indeed, the present study echoes earlier findings that a stroke precipitated by the dissection determines late mortality but not hospital death.23 This interesting paradox is perhaps explained by the likelihood that the most severe neurological insults at the time of dissection are accompanied by other related devastating acute processes, such as shock and malperfusion, which then emerge as dominant in the risk factor analysis for hospital death. However, for hospital survivors, the effects of a less-catastrophic stroke might ultimately significantly impair longevity: such patients are likely to have an enhanced risk of bronchopneumonia and other complications associated with chronically impaired levels of physical activity and to be vulnerable to further cerebrovascular events.
The influence of preoperative thrombosis of the false lumen in the ascending aorta on long-term survival remains a matter for speculation. Among patients with a thrombosed false lumen, there seems to be a trend toward less-extensive dissections. This preoperative finding might therefore define a subgroup of patients who have less-aggressive acute type A dissections, perhaps associated with a milder underlying abnormality of the aorta, possibly part of a continuum that includes intramural hematoma, who consequently have a lower risk of subsequent significant distal aortic disease.
Despite our attempts to monitor patients closely after acute type A dissection, the sum of deaths caused by rupture, graft infection, and unknown causes represents 40% of late deaths, which agrees quite closely with the 2-fold increase in the death rate of this patient group compared with that seen in a healthy matched population. Given the prevalence of aorta-related causes among late deaths and the failure of distal reoperation to have an adverse effect on mortality, there is a strong argument for a continued emphasis on the importance of close surveillance of the distal aorta after acute type A dissection. Nevertheless, 10-year actuarial survival is 66% versus 79% for age- and sex-matched control subjects, suggesting that the outlook for patients with a successfully operated acute type A dissection might not be as bleak as previously assumed.
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Conclusions |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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References |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionConclusionsReferences |
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