Detection of the intimal tear in aortic dissection and ulcer-like projection in intramural hematoma: usefulness of full-phase retrospective ECG-gated CT angiography

Biomechanical stress analysis of Type-A aortic dissection at pre-dissection, post-dissection, and post-repair states

Acute type A aortic dissection remains a deadly and elusive condition, with risk factors such as hypertension, bicuspid aortic valves, and genetic predispositions. As existing guidelines for surgical intervention based solely on aneurysm diameter face scrutiny, there is a growing need to consider other predictors and parameters, including wall stress, in assessing dissection risk. Through our research, we aim to elucidate the biomechanical underpinnings of aortic dissection and provide valuable insights into its prediction and prevention. We applied finite element analysis (FEA) to assess stress distribution on a rare dataset comprising computed tomography (CT) images obtained from eight patients at three stages of aortic dissection: pre-dissection (preD), post-dissection (postD), and post-repair (postR). Our findings reveal significant increases in both mean and peak aortic wall stresses during the transition from the preD state to the postD state, reflecting the mechanical impact of dissection. Surgical repair effectively restores aortic wall diameter to pre-dissection levels, documenting its effectiveness in mitigating further complications. Furthermore, we identified stress concentration regions within the aortic wall that closely correlated with observed dissection borders, offering insights into high-risk areas. This study demonstrates the importance of considering biomechanical factors when assessing aortic dissection risk. Despite some limitations, such as uniform wall thickness assumptions and the absence of dynamic blood flow considerations, our patient-specific FEA approach provides valuable mechanistic insights into aortic dissection. These findings hold promise for improving predictive models and informing clinical decisions to enhance patient care.

Tailored treatment modality in acute type A intramural hematoma

OBJECTIVES

Intramural hematoma may be generated by a minimal intimal tear. Most surgeries for acute type A intramural hematoma are performed on the proximal aorta alone regardless of the intimal tear site. Under the assumption that major adverse aortic events (MAAEs) would be related to the location of primary intimal tear, we reviewed preoperative computed tomography scan findings.

METHODS

Sixty patients with acute type A intramural hematoma who underwent surgery from January 2008 to December 2019 were retrospectively analyzed. The maximal diameter, maximal thickness of the intramural hematoma, and hematoma thickness ratio of the ascending and descending aortae were measured. MAAEs were defined as newly developed aortic dissection, rupture, newly developed penetrating aortic ulcer (PAU), enlargement of the PAU, and aortic death.

RESULTS

The number of patients with PAU in the descending aorta (dPAU) was significantly higher in the MAAE (+) group. The MAAE (+) group showed lower measurements of the ascending aorta and higher measurements of the descending aorta than the MAAE (-) group. In the univariate analysis, dPAU, hematoma thickness ratio of the ascending and descending aortae, and descending aorta hematoma thickness >8.58 mm were risk factors of MAAE. Intimal tear noted intraoperatively and ascending aorta hematoma thickness >10.25 mm were protective factors of MAAE.

CONCLUSIONS

Aortopathies (ie, PAU, ulcer-like projections, and the hematoma thickness ratio) are important clues to determine the location of intimal tear. Occurrence of MAAEs seems to be highly related to the pathology of the descending aorta. The modalities of treatment for stable acute type A intramural hematoma that do not meet the existing guidelines should be tailored to the location of the intimal tear.

Fast Approximate Quantification of Endovascular Stent Graft Displacement Forces in the Bovine Aortic Arch Variant

PURPOSE

Displacement forces (DFs) identify hostile landing zones for stent graft deployment in thoracic endovascular aortic repair (TEVAR). However, their use in TEVAR planning is hampered by the need for time-expensive computational fluid dynamics (CFD). We propose a novel fast-approximate computation of DFs merely exploiting aortic arch anatomy, as derived from the computed tomography (CT) and a measure of central aortic pressure.

MATERIALS AND METHODS

We tested the fast-approximate approach against CFD gold-standard in 34 subjects with the "bovine" aortic arch variant. For each dataset, a 3-dimensional (3D) model of the aortic arch lumen was reconstructed from computed tomography angiography and CFD then employed to compute DFs within the aortic proximal landing zones. To quantify fast-approximate DFs, the wall shear stress contribution to the DF was neglected and blood pressure space-distribution was averaged on the entire aortic wall to reliably approximate the patient-specific central blood pressure. Also, DF values were normalized on the corresponding proximal landing zone area to obtain the equivalent surface traction (EST).

RESULTS

Fast-approximate approach consistently reflected (r2=0.99, p<0.0001) the DF pattern obtained by CFD, with a -1.1% and 0.7° bias in DFs magnitude and orientation, respectively. The normalized EST progressively increased (p<0.0001) from zone 0 to zone 3 regardless of the type of arch, with proximal landing zone 3 showing significantly greater forces than zone 2 (p<0.0001). Upon DF normalization to the corresponding aortic surface, fast-approximate EST was decoupled in blood pressure and a dimensionless shape vector (S) reflecting aortic arch morphology. S showed a zone-specific pattern of orientation and proved a valid biomechanical blueprint of DF impact on the thoracic aortic wall.

CONCLUSION

Requiring only a few seconds and quantifying clinically relevant biomechanical parameters of proximal landing zones for arch TEVAR, our method suits the real preoperative decision-making process. It paves the way toward analyzing large population of patients and hence to define threshold values for a future patient-specific preoperative TEVAR planning.

A Comparison of Retrospective ECG-Gated CT and Surgical or Angiographical Findings in Acute Aortic Syndrome

The best cardiac phases in retrospective ECG-gated CT for detecting an intimal tear (IT) in aortic dissection (AD) and an ulcer-like projection (ULP) in an intramural hematoma (IMH) have not been established. This study aimed to compare the detection accuracy of diastolic-phase and systolic-phase ECG-gated CT for IT in AD and ULP in IMH, with subsequent surgical or angiographical confirmation as the reference standard.In total, 81 patients (67.6 ± 11.8 years; 41 men) who underwent emergency ECG-gated CT and subsequent open surgery or thoracic endovascular aortic repair for AD (n = 52) or IMH (n = 29) were included. The accuracies of detecting IT and ULP were compared among only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase methods of retrospective ECG-gated CT; surgical or angiographical findings were used as the reference standard. The detection accuracy for IT and ULP using only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase methods of ECG-gated CT was 93% [95% CI: 87-97], 94% [95% CI: 88-97], and 95% [95% CI: 90-97], respectively. There were no significant differences in detection accuracy among the 3 acquisition methods (P = 0.55). Similarly, there were no significant differences in the accuracy of detecting IT in AD (P = 0.55) and ULP in IMH (P > 0.99) among only diastolic-phase, only systolic-phase, and both diastolic- and systolic-phase ECG-gated CT.Retrospective ECG-gated CT for detecting IT in AD and ULP in IMH yields highly accurate findings. There were no significant differences seen among only diastolic-phase, only systolic-phase, and both diastolic-phase and systolic-phase ECG-gated CT.

False lumen being larger than true lumen is associated with late aortic events in uncomplicated type B aortic dissection

OBJECTIVES

In uncomplicated type B aortic dissection, a large false lumen (FL) is reportedly a risk factor for late aortic events. However, it is unclear how the relationship between the false and true lumen (TL) diameters affects the dissected aorta. This study aimed to evaluate the impact on clinical outcomes of the FL being larger than the TL.

METHODS

We retrospectively reviewed 111 consecutive patients with uncomplicated acute type B aortic dissection between 2004 and 2018. We divided the patients into group A (FL > TL; n = 51) and group B (FL ≤ TL; n = 60), and compared the outcomes. The endpoints were aortic events, including surgery for aortic dissection and indication for surgery, and mortality.

RESULTS

The 5-year incidence rates of aortic events were 68.4% in Group A and 33.6% in Group B (P = 0.002). The 5-year all-cause mortality rates were 5.3% in Group A and 21.9% in Group B (P = 0.003). The multivariable analyses revealed that FL > TL was an independent factor associated with aortic events (adjusted hazard ratio 2.482, 95% confidence interval 1.467-4.198, P < 0.001), but had low mortality (adjusted hazard ratio 0.209, 95% confidence interval 0.073-0.597, P = 0.003).

CONCLUSIONS

Patients with uncomplicated type B aortic dissection with FL > TL at admission are at increased risk of aortic events but improve mortality compared to patients with FL ≤ TL.

CLINICAL TRIAL REGISTRATION

UMIN000036997.

Significance of systolic-phase imaging on full-phase ECG-gated CT angiography to detect intimal tears in aortic dissection

Purpose

For patients with aortic dissection (AD) and intramural hematoma (IMH), the optimal cardiac phase to detect intimal tears (IT) and ulcer-like projections (ULP) on retrospective electrocardiogram (ECG)-gated computed tomography angiography (CTA) remains unclear. The purpose of this study was to compare the accuracy of retrospective ECG-gated CTA for detecting IT in AD and ULP in IMH between each cardiac phase.

Materials and methods

A total of 75 consecutive patients with AD and IMH of the thoracic aorta were enrolled in this single-center retrospective study. The diagnostic performance to detect IT and ULP in the thoracic aortic regions (including the ascending aorta, aortic arch, and proximal and distal descending aorta) was compared in each cardiac phase on retrospective ECG-gated CTA.

Results

In the systolic phase (20%), the accuracy, sensitivity, and specificity to detect IT in AD was 64% (95% confidence interval [CI] 56–72%), 69% (95%CI 60–78%), and 25% (95%CI 3.3–45%), respectively. In the diastolic phase (70%), the accuracy, sensitivity, and specificity to detect IT in AD was 52% (95%CI 43–60%), 52% (95%CI 42–61%), and 50% (95%CI 25–75%), respectively. The accuracy to detect IT in AD on ECG-gated CTA was significantly higher in the systolic phase than that in the diastolic phase (P = 0.025). However, there were no differences in the accuracy (83%; 95%CI 78–89%), sensitivity (71%; 95%CI 62–80%), or specificity (100%; 95%CI 100%) to detect ULP in IMH between the cardiac cycle phases.

Conclusion

Although it is currently recommended for routine diagnosis of AD and IMH, single-diastolic-phase ECG-gated CTA has risk to miss some IT in AD that are detectable in the systolic phase on full-phase ECG-gated CTA. This information is critical for determining the optimal treatment strategy for AD.

Note the descending aorta: predictors of postoperative major adverse aortic event in pure acute type A intramural hematoma

Background

Intramural hematomas (IMHs) may originate from small intimal tears. Although most surgeries for acute type A IMH are conventionally performed solely at the proximal aorta, regardless of the primary intimal tear site, the remnant aortic remodeling stays important during the follow-up period after surgery.

Methods

Forty-seven patients with “pure” acute type A IMHs who underwent surgery from January 2008 to December 2019 were retrospectively analyzed. Acute type A IMH in the entire region without penetrating aortic ulcer (PAU) and aortic dissection (AD), which upon initial computed tomography (CT), can be considered as an intimal tear site, was defined as “pure” type. The maximal diameter of the aorta, maximal thickness of the IMH, and hematoma thickness ratio (HTR) of the ascending and descending aortae were measured from the preoperative computed tomographic scan. The hematoma thickness index was defined as the HTR of the descending aorta divided by that of the ascending aorta. Major adverse aortic events (MAAEs) were defined as AD, rupture, or newly developed PAU and aortic death. Predictors for postoperative MAAEs were analyzed using preoperative computed tomographic findings.

Results

The measurements of the descending aorta were larger and those of the ascending aorta were smaller in the MAAEs group, than in the corresponding other. The hematoma thickness index was significantly higher in the group with MAAEs, than in the group without; this variable was an independent predictor of MAAEs. During surgery, intimal tears were found in 16/47 (34%) patients. The hematoma thickness index was significantly smaller in the group with intimal tears than in the group without the tears. The aortic measurement appears to reflect the tear site.

Conclusions

Hematoma thickness index was an independent predictor of MAAE after acute type A IMH surgery. Long-term periodical follow-up with early reintervention may, therefore, be necessary to improve outcome in these patients. As the optimal treatment method is still controversial, inferring the location of the primary tear through the hematoma thickness index can be helpful in determining the treatment method.