Computed Tomography Imaging Features in Acute Uncomplicated Stanford Type-B Aortic Dissection Predict Late Adverse Events

Abstract

Background: Medical treatment of initially uncomplicated acute Stanford type-B aortic dissection is associated with a high rate of late adverse events. Identification of individuals who potentially benefit from preventive endografting is highly desirable.

Methods and results: The association of computed tomography imaging features with late adverse events was retrospectively assessed in 83 patients with acute uncomplicated Stanford type-B aortic dissection, followed over a median of 850 (interquartile range 247-1824) days. Adverse events were defined as fatal or nonfatal aortic rupture, rapid aortic growth (>10 mm/y), aneurysm formation (≥6 cm), organ or limb ischemia, or new uncontrollable hypertension or pain. Five significant predictors were identified using multivariable Cox regression analysis: connective tissue disease (hazard ratio [HR] 2.94, 95% confidence interval [CI]: 1.29-6.72; P=0.01), circumferential extent of false lumen in angular degrees (HR 1.03 per degree, 95% CI: 1.01-1.04, P=0.003), maximum aortic diameter (HR 1.10 per mm, 95% CI: 1.02-1.18, P=0.015), false lumen outflow (HR 0.999 per mL/min, 95% CI: 0.998-1.000; P=0.055), and number of intercostal arteries (HR 0.89 per n, 95% CI: 0.80-0.98; P=0.024). A prediction model was constructed to calculate patient specific risk at 1, 2, and 5 years and to stratify patients into high-, intermediate-, and low-risk groups. The model was internally validated by bootstrapping and showed good discriminatory ability with an optimism-corrected C statistic of 70.1%.

Conclusions: Computed tomography imaging-based morphological features combined into a prediction model may be able to identify patients at high risk for late adverse events after an initially uncomplicated type-B aortic dissection.

Keywords: aneurysm; angiography; aorta; aortic rupture; computed; hypertension; regression analysis; tomography.

Figure 1. Three-dimensional assessment of maximum aortic diameter and circumferential extent false lumen

After generation of an aortic centerline (green line) from the proximal aortic arch to the aortic bifurcation the aorta is straightened along its centerline in a patient with uncomplicated type B aortic dissection. Blue line indicates the distal ostium of the left subclavian artery. The red line indicates the location of the maximum diameter of the aorta. The aortic cross-section (insert) is oriented orthogonal to the aortic centerline. Insert illustrates a false lumen circumferential extent of 258° (360°–102°) at this location.

Figure 2. Measurement of the false lumen (FL) circumferential extent of detachment in aortic dissection

Panels A–C demonstrate a mobile dissection membrane separating the false lumen (FL) from the true lumen (TL) in different positions on three contiguous images of the abdominal aorta in a patient with aortic dissection. Note the double contours of the dissection membrane in panel A, the smaller diameter (D1) in panel B, and the largest diameter (D2) of the false lumen in panel C. The schematic in panel D shows that the 190° circumferential extent of the false lumen in angular degrees remains constant over the cardiac cycle, despite the variable location of the dissection flap (dotted lines) and thus diameter measurements.

Figure 3. Hazard ratios of the 5 significant predictors selected by backward stepwise elimination

Shades of blue indicating the 90%, 95% and 99% Confidence Intervals.

Figure 4. Calibration plot of the model obtained via resampling at 2 years follow up

The number of bootstraps that were used was 1000. The optimism-corrected calibration line lies close to the line of perfect calibration. It shows a slight underestimation of risk for patients of relatively low risk of adverse events.

Figure 5. Kaplan-Meier curves of event-free survival stratified by tertile of the score on the linear predictor

A score can be calculated using the internally validated model from table 2 as: 0.841*(connective tissue disease) + 0.021*(false lumen circumferential extent) + 0.071*(maximum aortic diameter) − 0.001*(False lumen outflow volume) − 0.094*(number of intercostals). Note, that the time-to-event data for each risk tertile are based on the same events used to create the model.