Christos V. Ioannou

The Role of Geometric Parameters in the Prediction of Abdominal Aortic Aneurysm Wall Stress

OBJECTIVE To study the correlation between peak wall stress (PWS) and abdominal aorta aneurysm (AAA) geometric parameters in the presence of intraluminal thrombus (ILT). DESIGN Computational study using finite element analysis. MATERIAL AAA models were created by three-dimensional (3D) reconstruction of in vivo acquired computed tomography (CT) images from 19 patients. METHODS PWS was evaluated in the presence and absence of ILT. DeltaPWS% represents the percentage change in PWS in the presence of ILT. The 3D lumen centrelines were extracted, and the values of torsion, tortuosity and mean curvature were estimated. RESULTS A positive correlation was observed between DeltaPWS% and relative ILT volume (P=0.03). PWS in the presence of ILT significantly correlated only with the degree of centerline tortuosity (P=0.003) and maximum diameter (P<0.0001). The optimal predictive model for PWS in the presence of ILT was estimated to contain both maximum diameter and centreline tortuosity. CONCLUSIONS Specific geometric parameters in AAA models in the presence of ILT could serve as potential predictors of elevated PWS. PWS correlated significantly with the maximum diameter and the degree of centreline tortuosity. Centreline tortuosity may become a useful addition to maximum diameter in the decision-making process of AAA treatment.

Computational Evaluation of Aortic Aneurysm Rupture Risk: What Have We Learned So Far?

In current clinical practice, aneurysm diameter is one of the primary criteria used to decide when to treat a patient with an abdominal aortic aneurysm (AAA). It has been shown that simple association of aneurysm diameter with the probability of rupture is not sufficient, and other parameters may also play a role in causing or predisposing to AAA rupture. Peak wall stress (PWS), intraluminal thrombus (ILT), and AAA wall mechanics are the factors most implicated with rupture risk and have been studied by computational risk evaluation techniques. The objective of this review is to examine these factors that have been found to influence AAA rupture. The prediction rate of rupture among computational models depends on the level of model complexity and the predictive value of the biomechanical parameters used to assess risk, such as PWS, distribution of ILT, wall strength, and the site of rupture. There is a need for simpler geometric analogues, including geometric parameters (e.g., lumen tortuosity and neck length and angulation) that correlate well with PWS, conjugated with clinical risk factors for constructing rupture risk predictive models. Such models should be supported by novel imaging techniques to provide the required patient-specific data and validated through large, prospective clinical trials.

Chronic venous disease progression and modification of predisposing factors

AIM This study evaluated long-term characteristics of chronic venous disease (CVD) progression and its correlation with the modification of specific risk factors. METHODS The contralateral limb of 73 patients (95% women; mean age, 48 +/- 12 years) undergoing varicose vein surgery was prospectively evaluated using physical and color duplex examination and classified by CEAP. After 5 years of follow-up, development of new sites of reflux among the contralateral, preoperatively asymptomatic limbs and modification of predisposing factors, including prolonged orthostatism, obesity, estrogen therapy (ET), multiparity, and elastic stockings use (ESU), were assessed. Data were analyzed with Pearson chi(2), t test, binary logistic regression, and Spearman rho. RESULTS Forty-eight new sites of reflux (superficial system, 37; perforators, 5; deep veins, 6) were revealed in 38 limbs (52%). CEAP scores significantly deteriorated: clinical, 2.2 +/- 0.5 from 0.1 +/- 0.03 (P < .01); anatomic, 3.8 +/- 1.2 from 2.6 +/- 2.5 (P < .05); disability, 1.9 +/- 0.7 from 0 (P < .01); and severity, 7.9 +/- 2.4 from 2.7 +/- 2.2 (P < .01). Patient compliance to predisposing factor modification was low; no change was observed during follow-up (orthostatism, P = .9; obesity, P = 0.7; ET, P = .9; multiparity, P = .4; ESU, P = .3). CVD progression was significantly lower in patients who controlled orthostatism vs those who maintained orthostatism or initiated it (P < .001) and in patients who controlled preoperative obesity vs those who became obese or maintained obesity (P < .001). Non-ESU patients had a significantly higher incidence of CVD progression vs those who started ESU or continued during the study (P < .001). By binary logistic regression analysis, orthostatism (P = .002; B coefficient value [BCV] = 1.745), obesity (P = .009; BCV = 1.602), and ESU (P = .037; BCV = 0.947) were independent predictive factors for CVD progression, whereas multiparity (P = .174) and ET (P = .429) were not. CONCLUSIONS In about half of patients with unilateral varicosities, CVD developed in the contralateral initially asymptomatic limb in 5 years. CVD progression consisted of reflux development and clinical deterioration of the affected limbs. Obesity, orthostatism, and noncompliance with ESU were independent risk factors for CVD progression, but ET and multiparity were not. Maintenance of a normal body weight, limitation of prolonged orthostatism, and systematic ESU may be recommended in patients with CVD to limit future disease progression.

Left ventricular hypertrophy induced by reduced aortic compliance.

Aim: It was the aim of this study to investigate the long- term effects of reduced aortic compliance on cardiovascular hemodynamics and cardiac remodeling. Method: Sixteen swine, divided into 2 groups, a control and a banding group, were instrumented for pressure and flow measurement in the ascending aorta. Teflon prosthesis was wrapped around the aortic arch in order to limit wall compliance in the banding group. Hemodynamic parameters were recorded throughout a 60-day period. After sacrifice, the mean cell surface of the left ventricle was documented. Results: Banding decreased aortic compliance by 49 ± 9, 44 ± 16 and 42 ± 7% on the 2nd, 30th and 60th postoperative day, respectively (p < 0.05), while systolic pressure increased by 41 ± 11, 30 ± 11 and 35 ± 12% (p < 0.05), and pulse pressure by 86 ± 27, 76 ± 21 and 88 ± 23%, respectively (p < 0.01). Aortic characteristic impedance increased significantly in the banding group. Diastolic pressure, cardiac output and peripheral resistance remained unaltered. The mean left ventricular cell surface area increased significantly in the banding group. Conclusions: Acute reduction in aortic compliance results in a significant increase in characteristic and input impedance, a significant decrease in systemic arterial compliance and a subsequent increase in systolic and pulse pressures leading to left ventricular hypertrophy.

Treatment of abdominal aortic aneurysm with a new type of polymer-filled low profile device

PURPOSE OF THE STUDY To evaluate the mid-term safety and effectiveness of a novel stent graft for treatment of abdominal aortic aneurysm (AAA). METHODS Thirty-three patients with AAA (20 males and 13 females; mean age: 71.3 y) were treated with the Ovation™ Abdominal Stent Graft System (TriVascular, Inc., Santa Rosa, CA, USA). Indications for endovascular aneurysm repair: AAA ≥ 5.5 cm, neck ≥ 7 mm, angulation ≤ 60° and with an inner wall diameter of no less than 16 mm and no greater than 30 mm; the presence of neck calcification and thrombosis is not much of a problem in this device because aortic seal is achieved with 2 polymer-filled sealing rings and the fixation by means of a suprarenal stent with 8 pairs of anchors. Patients were followed through discharge and returned for follow-up visits. The follow-up protocol included a CT-A exam at 1 and 12 months after the intervention; the mid-term follow up was performed at 3 and 6 months with contrast-enhanced ultrasound (CEUS). Mean follow-up duration was 18.6 months (range: 3-25 months). MAIN FINDINGS Technical success was 100%. Mean implantation procedure time was 31.1 minutes, and median hospital stay was 4.6 days. None of the patients required conversion to open surgery, and no aneurysm enlargement, rupture, fracture, or migration were observed. No type I, III or IV endoleaks were observed. Hospitalization death rate was 0%. Death rate at 30 days was 0%. No major complications were observed. CONCLUSIONS The first results from this 3-center study with the Ovation stent graft are promising with high technical success and excellent safety and effectiveness.

Aneurysm sac shrinkage after endovascular treatment of the aorta: Beyond sac pressure and endoleaks

The isolation of the aneurysm sac from systemic pressure and its consequent shrinkage are considered criteria of success after endovascular repair (EVAR). However, the process of shrinkage does not solely depend on the intrasac pressure, the predictive role of which remains ambiguous. This brief review summarizes the additional pathophysiological mechanisms that regulate the biomechanical properties of the aneurysm wall and may interfere with the process of aneurysm sac shrinkage.

The ovation abdominal stent graft for the treatment of abdominal aortic aneurysms: current evidence and future perspectives

ABSTRACT The Ovation Abdominal Stent Graft System is a trimodular endoprosthesis recently introduced for the endovascular repair of abdominal aortic aneurysm (AAA). It uncouples the stages of stent-graft fixation and sealing with the suprarenal fixation achieved with a long, rigid anchored stent while the sealing onto the neck is accomplished via a pair of polymer-filled inflatable rings that accommodate to each patient’s individual anatomy. Moreover, the lack of Nitinol support enables lower profiles of the endograft’s delivery system, thus facilitating the navigation through angulated and stenosed iliac vessels. Ovation’s novel design expands further the AAA eligibility to endovascular repair. This article discusses the clinical and hemodynamic consequences of the Ovation design and contributes to better understanding of current and future implications.

Peak Wall Stress Does Not Necessarily Predict the Location of Rupture in Abdominal Aortic Aneurysms

UNLABELLED Using finite element analysis, we evaluated if the site of an aortic bleb, known to be prone to rupture, coincides with the location of peak wall stress (PWS) in a patient-specific abdominal aortic aneurysm (AAA) model. REPORT PWS was not located at the bleb site, even when stress values were estimated for different bleb wall thicknesses (0.5-2.0 mm) while the rest of the AAA wall was considered constant (2 mm). DISCUSSION The sites of PWS in AAAs should not always be considered as the sites most prone to rupture since other factors, such as wall strength, may play a role in rupture-risk prediction, depicting the need for further investigation of these parameters.

The - Not So - Solid 5.5 cm Threshold for Abdominal Aortic Aneurysm Repair: Facts, Misinterpretations, and Future Directions.

Abdominal aortic aneurysms (AAAs) represent a focal dilation of the aorta exceeding 1.5 times its normal diameter. It is reported that 4–8% of men and 0.5–1% of women above 50 years of age bear an AAA. Rupture represents the most disastrous complication of aneurysmal disease that is accompanied by an overall mortality of 80%. Autopsy data have shown that nearly 13% of AAAs with a maximum diameter ≤5 cm were ruptured and 60% of the AAAs >5 cm in diameter never ruptured. It is therefore obvious that the “maximum diameter criterion,” as a single parameter that fits all patients, is obsolete. Investigators have begun a search for more reliable rupture risk markers for AAA expansion, such as the level and change of peak wall stress or AAA geometry. Furthermore, it is becoming more and more evident that intraluminal thrombus (ILT), which is present in 75% of all AAAs, affects AAA features and promotes their expansion. Though these hemodynamic properties of AAAs are significant and seem to better describe rupture risk, they are in need of specialized equipment and software and demand time for processing making them difficult in use and unattractive to clinicians in everyday practice. In the search for the addition of other risk factors or user-friendly tools, which may predict AAA expansion and rupture, the use of the asymmetrical ILT deposition index seems appealing since it has been reported to identify AAAs that may have an increased or decreased growth rate.

Endovascular vs Open Aneurysm Repair in the Young: Systematic Review and Meta-analysis.

Purpose: To examine the results of elective abdominal aortic aneurysm (AAA) repair in young patients (<70 years old) and compare the outcome of endovascular aneurysm repair (EVAR) and open surgical repair (OSR) techniques. Methods: The MEDLINE, CENTRAL, and OpenGray databases were searched from January 2000 to March 2015. Periprocedural (30-day mortality and morbidity, length of hospitalization) and long-term outcomes (long-term mortality, rate of secondary procedures) were compared between young patients undergoing EVAR and OSR. For the meta-analysis of comparative studies, the random effects model was used to calculate combined overall effect sizes of pooled data. One randomized control trial and 8 observational studies were included in the analysis. Data are presented as the odds ratio (OR) or mean difference (MD) with 95% confidence interval (CI). Results: EVAR was associated with a decreased risk of 30-day mortality (OR 0.25, 95% CI 0.14 to 0.42, p<0.001) and 30-day morbidity (OR 0.36, 95% CI 0.22 to 0.58, p<0.001) and shorter length of hospitalization (MD −4.28 days, 95% CI −4.86 to −3.70, p<0.001). Moreover, a potential long-term survival benefit did not reach statistical significance (OR 0.48, 95% CI 0.17 to 1.34, p=0.16), whereas the need for reintervention was similar between EVAR and OSR groups (OR 0.94, 95% CI 0.61 to 1.54, p=0.89). Conclusion: There are insufficient data for definite conclusions to be drawn regarding the relative effectiveness of EVAR and OSR in young subjects. Contemporary evidence suggests that EVAR should not be discouraged in this cohort of patients based solely on the age criterion.