Commentary on 'distinction between acute and chronic type B aortic dissection: is there a subacute phase?'.

The classification of aortic dissection has traditionally been based on anatomical factors (the DeBakey and Stanford classifications) and duration of symptoms prior to presentation. The definition of acute (presentation within 14 days of the onset of symptoms) and chronic has always been somewhat arbitrary, though supported by observed differences in outcomes from both conservative management and intervention. The advent of endovascular approaches, especially for Type B dissection, has led to renewed interest in the condition and in particular to the long term outcomes relating to progression of disease and the degree of aortic remodelling. The current series published by Steuer et al. describes a cohort of patients, undergoing treatment between 15-38 days of initial presentation. 1 The outcomes from intervention were significantly better than in the acute group, treated within 14 days of presentation, with no early deaths or neurological complications. The authors suggest that this represents a sub-acute phase in the transition from acute to chronic and question the current definition based on a 14 day cut-off. The Virtue Study also subdivided a cohort of 100 patients with Type B Dissection undergoing thoracic endografting into 3 subgroups, incorporating a sub-acute group with intervention from 14-28 days. 2 There was a significant reduction in peri-operative mortality and morbidity associated with intervention in the sub-acute period, with results similar to those in the chronic group. The 3 year follow up data will soon be presented which are likely to demonstrate degrees of aortic remodelling very similar to acute dissection with low reintervention rates. This raises a number of important issues with regard to the classification and management of acute type B dissection. Firstly, is it safer to intervene in the sub-acute period? It is feasible that hypothesise that waiting 14 days may allow stabilisation of the intimal tear, enabling the safer delivery of endografts into an otherwise very fragile aorta. However, the acute and sub-acute groups are non-comparable. In the current series, they are significantly younger, and a large proportion present with rapid aortic dilatation rather than impending or actual aortic rupture or malperfusion. Secondly, if it is safer to intervene in the sub-acute phase, would this influence a more aggressive policy of reintervention in the uncomplicated patients? The INSTEAD trial randomised patients with uncomplicated type B dissection to best medical therapy or early thoracic endografting and failed to demonstrate and advantage for early intervention. 3 However, long term follow up data have been presented demonstrating a significant number of patients in the best medical arm with sudden aortic death. Clearly further work is required to establish a subgroup of patients who may be most likely to benefit from early endografting. Thirdly, do sub-acute dissections behave in the long term in a similar manner to acute dissections? A number of studies have demonstrated significantly greater degrees of favourable aortic remodelling in the acute dissection compared to chronic, with diminution of the false lumen and re-expansion of the acute lumen. 4 This should ultimately lead to improved long term outcomes in terms or reintervention and aortic expansion. Longer term data are clearly required to further guide clinical practice. In the meantime, the current data do suggest a review of the definitions of acute and chronic dissection, both in terms of rationale for intervention, and presentation of long term outcomes.