The American Heart Association (AHA) released a scientific statement about imaging and surveillance of chronic aortic dissection that was published in Circulation: Cardiovascular Imaging.
Acute aortic dissection has received much scientific and public attention. Due to advancements in treatment strategies, an increasing number of patients survive the acute phase of disease and progress to live with chronic aortic dissection. However, as chronic aortic dissection has received little attention, the AHA released a scientific statement which evaluated the current state and challenges of delivering optimum care.
The contemporary definition of aortic dissection is subdivided into the hyperacute (first 24 hours), acute (>24 hours-14 days), subacute (15-90 days), and chronic (>90 days) phases. Patients who survive to the chronic stage of disease require life-long monitoring for any remaining aortic false lumen which will ultimately degenerate, causing aneurysmal dilation.
The prevalence of chronic aortic dissection is approximately 4 to 6 per 100,000 per year and the majority of these patients (approximately 60%) have surgically corrected ascending Stanford type A dissection with persistent false lumen distal to the surgical repair. Patients with type A dissection have a long-term survival of 65%to 89% at 5 years and 45%to 65% at 10 years.
The typical management strategy for chronic aortic dissection includes antihypertensive therapy (eg, anti-impulse therapy with b-blockers with afterload reducing drugs), life-long imaging surveillance, and timely surgical intervention of aneurysmal progression. Together this approach has been termed “watchful waiting” which was designed to balance the risks of surgical repair with the expected morbidity and mortality of the disease.
Current guideline recommendations, published in 2010 to 2017, have not reached consensus about imaging surveillance schedules. However, a generalization is that after surgical repair, patients should be assessed at 6 and 12 months and yearly thereafter. Patients who have a stable, moderate-sized aneurysm may be evaluated at intervals of 1.5 to 3 years.
Computed tomography angiography (CTA) is the most common imaging surveillance tool for chronic aortic dissection. The typical protocol comprises an optional noncontrast scan to identify the surgical graft and high-attenuation foci to mimic pseudoaneurysm. Finally, a 50- to 150-mL contrast medium-enhanced angiographic image with a 5 to 20 second exposure should be acquired.
Acceptable alternative imaging approaches include magnetic resonance imaging (MRI), transthoracic echocardiography (TTE), and transesophageal echocardiogram (TEE). These approaches may be a better choice for younger patients or those with Marfan syndrome due to the lack of exposure to ionizing radiation; however, there is concern about lower spatial resolution or that not all aortic segments can be interrogated.
Risk for aortic rupture is evaluated by measuring aortic caliber and adjacent segments. Despite regular patient screening, there remains few specifications about how to perform and compare feature measurements.
Aortic diameters should be measured perpendicular to the long axis of the aorta using double-oblique images or multiplanar reformations (MPRs). The MPRs can be obtained manually or by using semiautomated approaches. The statement authors cautioned that, although axial images are useful for obtaining a first impression of a patient’s aortic status, these images should not be used to measure maximum aortic diameter.
In order to provide the best surveillance care, serial measurements should always be obtained in the same anatomic location and identical orientation along the aorta with direct side-by-side comparisons. The authors acknowledged this can be a time-consuming process; however, comparing independent measurements without validating the congruence of the images can lead to spurious conclusions.
For patients with disease progression, current guidelines recommend for aneurysmal intervention to occur at diameters of less than 6.0 cm. Other indications for surgical intervention are a rapid aneurysm growth rate or, for patients with connective tissue disease, an aneurysm diameter of 5.0 to 5.5 cm. The standard surgical intervention is open repair because of the limited benefit or durability of thoracic endovascular aortic repair. In general, there is no consensus for the optimal operation strategy.
Future Developments and Research
The most recent development for chronic aortic dissection is leveraging the large amount of imaging data by using machine learning approaches to predict patient outcomes. Despite the promise of such approaches, the current state of these algorithms is not sufficient for clinical-grade applications.
In addition to machine learning-based approaches, there remains a need for ongoing research into that pathophysiology, management, and prediction of clinical trajectories of patients with chronic aortic dissection. To accomplish therapeutic advances, the research effort will require interdisciplinary collaborations across large research and clinical networks due to the inherent difficulties of studying this disease, such as the long follow-up time and modest-sized patient population.
“Chronic aortic dissection is an underrecognized cardiovascular disease and growing health care burden,” the statement authors wrote. “Imaging and image processing will continue to play a pivotal role in surveillance and clinical decision-making in these patients, as long as accurate and standardized measurements of aortic dimensions over time are provided.”
Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.
Fleischmann D, Afifi RO, Casanegra AI, et al. Imaging and surveillance of chronic aortic dissection: A scientific statement from the American Heart Association. Circ Cardiovasc Imaging. Published online February 17, 2022. doi:10.1161/HCI.0000000000000075