Nordic Multicenter Study of Risk Factors, Surgical Treatment and Outcomes in Acute Type A Aortic Dissection

Research project plan

NORCAAD - Nordic Consortium for acute type A aortic dissection Nordic multicenter study of risk factors, surgical treatment and outcomes in acute type A aortic dissection

Background Acute type A aortic dissection (ATAAD) is a major vascular disaster. The overall incidence is quoted at 2-3/100.000/year but probably higher due to undiagnosed cases, and certainly higher in specific age (60-65 years and up) and risk groups (eg. connective tissue disease such as Marfan syndrome). At around 70%, case-fatality rate is on par with for example ruptured abdominal aortic aneurysm. The inciting pathogenic event is a disruption of the ascending aortic endothelium, a so-called entry tear (when located in the arch or descending aorta, the dissection is generally referred to as type B, and this form will not be further discussed). From this entry tear, shear stress of the bloodstream dissects the aortic wall layers, producing intense pain, but also a lethal threat with risk of rupture and tamponade, malperfusion of vital aortic branches, and aortic valve dysfunction with regurgitation and heart failure. Little, however, is known about risk factors. Hypertension is common in this patient group. Some cardiovascular abnormalities such as bicuspid aortic valve, aortic arch anomalies, or aortic coarctation are thought to increase risk, as is a pre-existing ascending aortic aneurysm or known cases of aortic dissection or aneurysm among first-degree relatives. Based on the poor prognosis, there is general consensus that ATAAD is treated surgically, with repair (graft replacement) of the ascending aorta. Data supports that this treatment is given as soon as possible, as mortality increase by the hour in ATAAD. Even with surgical therapy, early (30-day or in-hospital) mortality approaches 20% and severe complications (stroke, renal and respiratory insufficiency, multisystem organ failure) remain at substantial 10-20% prevalence each. Long-term outcomes for early survivors are acceptable, albeit not normal. Specifically, need for reintervention and reoperation due either to local or remote aortic conditions, persists or occur even long after primary surgery, necessitating often life-long surveillance.

Overview: knowledge gaps Despite a vast literature on ATAAD, many aspects remain poorly understood and/or controversial, and there are very few issues characterized by broad consensus. In parallel, treatment modalities evolve and successful concepts from elective aortic surgery is implemented also in the management of ATAAD and their respective roles remain to be determined.

Risk factors and predisposing conditions As mentioned, bicuspid aortic valve (BAV) is regarded as over-represented in ATAAD patients; its prevalence is estimated at 1-2% in a general population and often 5-15% in ATAAD case series. However, very little detail is known about what subtypes (according to the Sievers classification) are more common and if the are associated with pre-ATAAD dilatation of the aortic root and/or ascending aorta or with a valve dysfunction (and if so, more commonly stenosis or regurgitation?). It has been shown that ascending aortic diameter by itself is not a good predictor of ATAAD. Therefore, other radiological findings are explored to predict ATAAD risk. Aortic arch branching anomalies are one such feature, where specific aortic arch branch patterns seem prevalent. Such risk markers could be important in the decision-making process for prophylactic aortic surgery in selected patients.