Role of Re-entry Tears on the Dynamics of Type B Dissection Flap

Abstract

Mortality during follow-up after acute Type B aortic dissection is substantial with aortic expansion observed in over 59% of the patients. Lumen pressure differential is considered a prime contributing factor for aortic dilation after propagation. The objective of the study was to evaluate the relationship between changes in vessel geometry with and without lumen pressure differential post propagation in an ex vivo porcine model with comparison with patient clinical data. A pulse duplicator system was utilized to propagate the dissection within descending thoracic porcine aortic vessels for set proximal (%circumference of the entry tear: 40%, axial length: 2 cm) and re-entry (50% of distal vessel circumference) tear geometry. Measurements of lumen pressure differential were made along with quantification of vessel geometry (n = 16). The magnitude of mean lumen pressure difference measured after propagation was low (~ 5 mmHg) with higher pressures measured in false lumen and as anticipated the pressure difference approached zero after the creation of distal re-entry tear. False lumen Dissection Ratio (FDR) defined as arc length of dissected wall divided by arc length of dissection flap, had mean value of 1.59 ± 0.01 at pressure of 120/80 mmHg post propagation with increasing values with increase in pulse pressure that was not rescued with the creation of distal re-entry tear (p < 0.01). An average FDR of 1.87 ± 0.27 was measured in patients with acute Type B dissection. Higher FDR value (FDR = 1 implies zero dissection) in the presence of distal re-entry tear demonstrates an acute change in vessel morphology in response to the dissection independent of local pressure changes challenges the re-apposition of the aortic wall.

Keywords: Acute aortic dissection; Clinical FDR; Dilation; Ex vivo model; Lumen pressure; Strain.

Figure 1

Experimental set-up showing the major components. PD-1100 is the pulsatile flow pump, and is attached to the compliance chamber 1 (CC1). The outlet from CC1 is connected to a saline tank that houses the inlet and outlet ports to mount the aorta. CC2 acts as a downstream capacitor and the flow loops back to the CC1. Integrated Statys PD software is used for data acquisition.

Figure 2

Cross sectional view of post propagated aorta vessel highlighting flap arc length and the false lumen (FL) arc length used to calculate the False lumen Dissection Ratio (FDR). (a) The flap curved towards the True lumen (TL) during systole phase while the flap was curved towards the False Lumen (FL) in porcine aorta as seen in (b). (c) Representative non-gated CT scanned image depicting human descending thoracic aorta with the two measurements for the circumference of the false lumen (63.9 mm) and the length of the dissection flap (36.8 mm).

Figure 3

Boxplot showing the spatial variation and mean values of lumen pressure difference between FL and TL after propagation with and without distal re-entry tear. Mean values are represented by diamond symbol within the boxplot.

Figure 4

Boxplots showing the distribution and mean %TL cross sectional area of TL at peak systole and diastole without and with the creation of re-entry tear. Mean values are represented by diamond symbol within the boxplot.

Figure 5

Distribution of False lumen Dissection Ratio (FDR), defined as the ratio of false lumen arc length to the arch length of the flap with %undissected wall circumference at the proximal end with increase in pulse pressure (40, 60, 80 mmHg). The diastole pressure was kept constant at 80 mmHg with increase in pulse pressure.

Figure 6

Changes in FDR values over the length of the dissection with increasing pulse pressure (40, 60, 80 mmHg). Higher values of FDR are associated with creation of the re-entry tear and distal end of the dissection. Mean values are represented by diamond symbol within the boxplot.

Figure 7

Changes in circumferential Green strain in the flap over the length of the dissected aorta with increasing pulse pressure (40, 60, 80 mmHg). Flap strain values are cycle averaged; lower values are associated with the creation of re-entry tear. Mean values are represented by diamond symbol within the boxplot.