Most studies on patient populations with acute aortic dissection (AAD) are based on data from large tertiary referral centers, such as the International Registry of Acute Aortic Dissection (IRAD), which reports considerably high hospital mortality rates for type A and type B AAD, at 22% and 14% respectively. However, many patients do not reach these tertiary centers (those performing aortic surgery or TEVAR procedures) due to acute complications, deaths, or a conservative treatment approach. Consequently, there is an unknown number of aortic dissection cases that may never be registered in large international registries, making it difficult to accurately assess the real prognosis of this disease. To address this issue, this group used the Danish national civil personal data registry as a source, which allows the inclusion of all registered AAD cases that had hospital contact (even in non-tertiary centers) across the population, allowing a more complete long-term follow-up and view of all patients with AAD. The goal of this study was to evaluate the short and long-term characteristics and outcomes of these patients.

Data from patients diagnosed with AAD for the first time between 2006 and 2015 were analyzed. Initially, 2671 were cataloged as some type of aortic dissection; after reviewing cases including their imaging tests, 280 patients were excluded for having had a previous aortic dissection, 213 for not having AAD, and 465 patients for having an unspecific diagnosis of dissection. Finally, of the 1713 patients included in the study, 68% had type A dissection and 32% had type B, with median ages of 66 years (range 57-74 years) and 70 years (range 61-79 years), respectively. 64% were men. The average follow-up was 8.9 years (range 6.8-11.5 years). In type A dissection, 74% were surgically treated, while in type B, 22% received surgery or endovascular treatment. Hospital mortality was 27% in type A (18% with surgery, 52% without surgery) and 16% in type B (13% with surgery/endovascular therapy, 17% with conservative treatment; p<0.001). Patients with type A dissection who were discharged had a better survival than those with type B (p<0.001). The unadjusted 1- and 3-year survival for patients with type A dissection who were discharged was 96% and 91% with surgery, and 88% and 78% without it, respectively. In type B, it was 89% and 83% with endovascular/surgical management, and 89% and 77% with conservative management, respectively.

The authors conclude that hospital mortality in both types of aortic dissection was higher than reported in referral center registries. Type A presented higher mortality in the acute phase, while, in patients discharged, mortality was higher in type B.

COMMENTARY:

The conclusions derived from the results obtained in this study are particularly significant. This is because it is based on an extensive national registry, which has a distinctive feature compared to previous similar research. In this study, AAD patients were included, both those admitted to referral hospitals, where there is the possibility of surgical intervention, and those diagnosed with AAD at any type of hospital.

In this study conducted by Pedersen M. et al., several key findings are highlighted:

1. The hospital mortality rate in AAD type A and type B cases exceeds that of other international referral registry rates.
2. A lower proportion of patients underwent surgery in the case of AAD type A compared to similar international registries.
3. The average age of patients with AAD type B is higher than that of those with AAD type A.
4. The hospital mortality of AAD type A is significantly higher than that of AAD type B.
5. The long-term mortality, age-adjusted, also shows an upward trend in the case of AAD type A.
6. As for the long-term survival of discharged patients, a better prognosis is recorded in the group of patients with AAD type A.

Once again, this study clearly highlights that AAD continues to be a condition with an extremely high hospital mortality rate. However, compared with previous studies based on tertiary referral center registries, some differences worthy of analysis are revealed.

Regarding AAD type A in this study, it is observed that hospital mortality follows the common pattern of being higher in patients who did not undergo intervention (52%) compared to those who underwent surgery (18%). However, it is important to highlight that overall hospital mortality is higher in this study compared to data reported in the IRAD (27% versus 20%-21%).

Recent reports from the IRAD have recorded an increase in the proportion of patients undergoing surgical treatment, reaching 90%. However, in the context of this study, only 75% of AAD type A cases underwent surgery. This discrepancy could be explained because international registries, like the IRAD, are based exclusively on data from large tertiary referral centers. This, in turn, may underestimate the real prognosis of AAD, as some patients might die before reaching a tertiary referral center due to the high mortality in the first hours of this disease or rejection in transfer given their comorbid condition, serious irreversible sequelae derived from the dissection and/or the predicted surgical risk being unassumable. In fact, in this particular study, it was identified that 10% of patients did not manage to access a tertiary referral center, and within this group, the hospital mortality rate was doubled, as evidenced in the subgroup analysis.

Regarding the hospital mortality rate of AAD type B in this study, a figure higher than that reported by the IRAD is also observed (16% compared to 11%). This discrepancy could be attributed to a possible selection bias in the IRAD, given that patients with AAD type B in that registry presented an average age six years younger than the patients included in this study.

When analyzing mortality during the follow-up in this study, it was observed that patients who survived until hospital discharge after a DA type A exhibited long-term survival rates higher compared to patients with DA type B, which is consistent with previous findings in the field. Additionally, during the follow-up, it was identified that mortality in both categories of diseases in this study was mainly attributable to non-cardiovascular causes. Something we already intuited from the results of the IRAD, where the hospital parameters that accurately predicted hospital mortality in aortic dissection type A did not seem to influence mortality during the follow-up.

The most significant limitation of this study, undoubtedly, lies in that 465 patients were not included due to a diagnosis of unspecified AAD, despite having employed a reclassification process that involved evaluating computed tomographies and combining diagnoses with surgical procedure codes. Although not explained in full clarity, it is inferred that these patients with unspecified AAD could have had some type of acute aortic syndrome different from dissection or it was not possible to distinguish if it was a type A or B AAD. It is regrettable not to have information on the evolution of this group of patients, as this would have contributed to adding value to the overall analysis of these results. Secondly, it is important to consider that, as suggested by population studies, a substantial number of patients with AAD die before reaching the hospital for evaluation. With the design of this study, also excluded are the patients not admitted, and within those admitted, there is the risk that some patients die shortly after their arrival at the emergency department, where the DA is not registered or even not recognized as the cause of death. Therefore, the presence of a certain degree of selection bias cannot be dismissed. Thirdly, this study lacked information on the time elapsed between the onset of symptoms and hospital admission. This type of data would have been particularly valuable, given the high probability of serious complications during the acute phase, especially in the case of AAD type A.

As previously mentioned, evidence from population-based registries should ideally encompass the entire spectrum of AAD, which includes those unfortunate patients who die or are selected for conservative treatment and never reach a tertiary referral center. This study based on a national registry partly contributes to the inclusion of this group of patients. This approach provides valuable data on the essential aspects of early detection, decision-making, and timely referral, all of which are of vital importance to improve survival rates in patients with AAD.

Therefore, it would be highly advisable for current large-scale international AAD registries to broaden their scope to also include centers that are not tertiary referral centers. This would allow for a more complete and representative view of the disease and its outcomes, for the benefit of patient care and prognosis.

REFERENCE:

Pedersen MW, Kragholm K, Oksjoki R, Møller JE, Gundlund A, et al. Characteristics and Outcomes in Patients with Acute Aortic Dissection: A Nationwide Registry Study. Ann Thorac Surg. 2023 Dec;116(6):1177-1184. doi: 10.1016/j.athoracsur.2023.06.019.