Eur J Vasc Endovasc Surg (2015) 49, 246e247
INVITED COMMENTARY
Commentary on ‘Finite Element Analysis in Asymptomatic, Symptomatic, and Ruptured Abdominal Aortic Aneurysms e In Search of New Rupture Risk Predictors’ N. Chakfe a b
a,*
, F. Heim b, Y. Georg
a
Department of Vascular Surgery and Kidney Transplantation, University Hospital of Strasbourg, Strasbourg, France Laboratoire de Physique et Mécanique Textile, ENSISA, Université de Haute Alsace, Mulhouse, France
In their paper, Erhart et al.1 have evaluated finite element analysis (FEA) as a predictive abdominal aortic aneurysm (AAA) rupture risk model. In a single centre retrospective analysis they showed that retrospective FEA revealed biomechanical differences between asymptomatic, symptomatic, and ruptured AAA. Moreover, the results show that, to differentiate between subgroups, Peak Wall Rupture Risk Index (PWRI) can be considered a more reliable parameter than Peak Wall Stress (PWS). Their preliminary results suggest that AAA patients with PWRI values greater than 1.0 may be at imminent risk of becoming symptomatic or even rupturing.These results correlate with the standard approach used in mechanical engineering to predict the mechanical failure of any material. Actually, the amount of stress applied to a material is relevant only if compared with the strength of that same material. Failure occurs only if the applied load value reaches that strength limit. Unfortunately, the strength of the aortic wall varies from one location to another with weaker zones, more prone to aneurysm degradation. Therefore, working with PWRI rather than PWS makes sense, as the index takes the local strength into consideration. It is a very interesting topic that could help vascular surgeons moving closer to the Holy Grail of knowing which patients are at risk of AAA rupture. However, some points should be discussed in the paper. The first is the case selection. The authors performed a retrospective study in a well known high volume department of vascular surgery and selected 30 asymptomatic, 15 symptomatic, and 15 ruptured AAA over a 3 year period. Complex vessel morphology or contrast extravasation meant that two asymptomatic, three symptomatic, and nine ruptured AAA had to be excluded from the study. Consecutively performed CTA were used for FEA until study population size was reached. Consequently, it appears that FEA was DOI of original article: http://dx.doi.org/10.1016/j.ejvs.2014.11.010 * Corresponding author. N. Chakfe, Department of Vascular Surgery, Les Hôpitaux Universitaires de Strasbourg, B.P. 426, 67091 Strasbourg Cedex, France. E-mail address: [email protected] (N. Chakfe). 1078-5884/Ó 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejvs.2014.12.018
not feasible in about 25% of the primarily selected cases. Future studies based on a larger number of cases are required to improve the statistics and confirm the observed trends. Only then will it be possible to safely apply this investigation technique to predict AAA in the overall population. Moreover, if the definition of asymptomatic and ruptured AAA is not debatable, it is different for symptomatic AAA in which a strong link between symptoms such as pain and impending rupture is not always obvious. Finally, the last potential selection bias is that all patients were male. A previous paper co-signed by one of the authors2 reported a first analysis of stress and strength of the AAA wall with a gender perspective and showed that PWS did not differ, but that PWRR was slightly higher in women, suggesting that differences in biomechanical properties could be a contributing explanation for the higher rupture risk reported with female patients. The second point is the role of arterial blood pressure in the model. In their protocol, the authors considered a blood pressure ranging between 130 and 80 mmHg for asymptomatic and symptomatic AAA and actual recorded blood pressure in ruptured AAA. However, this choice could be responsible for biases. First, the ruptured AAA were probably characterized by significantly higher blood pressure at the time of the rupture onset, which could result in underestimation of the actual stresses at rupture. On the other hand, it would have been interesting to study the role of blood pressure in symptomatic and asymptomatic AAA. This would show if arterial blood pressure increase could have led to increased rupture risk in symptomatic versus asymptomatic AAA. Fillinger et al.3 calculated PWS in a cohort of 103 AAA patients followed for at least 6 months. They concluded that individual AAA PWS was a better predictor of complications and rupture than maximum transverse diameter (MTD). They showed no difference between PWS and MTD for small AAA, but a significant difference when PWS was calculated for a maximum arterial blood pressure. In conclusion, this paper is actually a significant contribution to the slow evolution from overall assessment of the risk of AAA rupture in the general population based on the simple measure of the MTD, to an accurate evaluation of the individual risk of rupture in a specific patient.
FEA in Asymptomatic, Symptomatic, and Ruptured AAAs
REFERENCES 1 Erhart P, Hyhlik-Dürr A, Geisbüsch P, Kotelis D, MüllerEschner M, Gasser TC, et al. Finite element analysis in asymptomatic, symptomatic and ruptured abdominal aortic aneurysms e in search of new rupture risk predictor. Eur J Vasc Endovasc Surg 2015;49:239e45.
247 2 Larsson E, Labruto F, Gasser TC, Swedenborg J, Hultgren R. Analysis of aortic wall stress and rupture risk in patients with abdominal aortic aneurysm with a gender perspective. J Vasc Surg 2011;54:295e9. 3 Fillinger MF, Marra SP, Raghavan ML, Kennedy FE. Prediction of rupture risk in abdominal aortic aneurysm during observation: wall stress versus diameter. J Vasc Surg 2003;37:724e32.
Eur J Vasc Endovasc Surg (2015) 49, 247
COUP D’OEIL
Giant Symptomatic Aneurysm of the Inferior Vena Cava V. Makaloski *, J. Schmidli Division of Vascular Surgery, Swiss Cardiovascular Center, University Hospital Bern, CH-3010 Bern, Switzerland
This 16-year old girl presented with acute abdominal pain and nausea after a syncope. The emergency computed tomography scan showed a large mass in the right abdomen, as well as perfusion defects in kidneys, spleen, and lungs. No history of blunt abdominal trauma was registered. Emergency surgery reconfirmed the suspected vena cava aneurysm (13 3 11 3 7 cm), which was partially filled with thrombus. After aneurysm resection and reconstruction with a patch-plasty, open pulmonary embolectomy and closure of the patent foramen ovale was performed to prevent further paradoxical embolisation. Histological findings pointed towards a potential congenital vascular malformation.
* Corresponding author. E-mail address: [email protected] (V. Makaloski). 1078-5884/Ó 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejvs.2014.09.002
INVITED COMMENTARY
Commentary on ‘Finite Element Analysis in Asymptomatic, Symptomatic, and Ruptured Abdominal Aortic Aneurysms e In Search of New Rupture Risk Predictors’ N. Chakfe a b
a,*
, F. Heim b, Y. Georg
a
Department of Vascular Surgery and Kidney Transplantation, University Hospital of Strasbourg, Strasbourg, France Laboratoire de Physique et Mécanique Textile, ENSISA, Université de Haute Alsace, Mulhouse, France
In their paper, Erhart et al.1 have evaluated finite element analysis (FEA) as a predictive abdominal aortic aneurysm (AAA) rupture risk model. In a single centre retrospective analysis they showed that retrospective FEA revealed biomechanical differences between asymptomatic, symptomatic, and ruptured AAA. Moreover, the results show that, to differentiate between subgroups, Peak Wall Rupture Risk Index (PWRI) can be considered a more reliable parameter than Peak Wall Stress (PWS). Their preliminary results suggest that AAA patients with PWRI values greater than 1.0 may be at imminent risk of becoming symptomatic or even rupturing.These results correlate with the standard approach used in mechanical engineering to predict the mechanical failure of any material. Actually, the amount of stress applied to a material is relevant only if compared with the strength of that same material. Failure occurs only if the applied load value reaches that strength limit. Unfortunately, the strength of the aortic wall varies from one location to another with weaker zones, more prone to aneurysm degradation. Therefore, working with PWRI rather than PWS makes sense, as the index takes the local strength into consideration. It is a very interesting topic that could help vascular surgeons moving closer to the Holy Grail of knowing which patients are at risk of AAA rupture. However, some points should be discussed in the paper. The first is the case selection. The authors performed a retrospective study in a well known high volume department of vascular surgery and selected 30 asymptomatic, 15 symptomatic, and 15 ruptured AAA over a 3 year period. Complex vessel morphology or contrast extravasation meant that two asymptomatic, three symptomatic, and nine ruptured AAA had to be excluded from the study. Consecutively performed CTA were used for FEA until study population size was reached. Consequently, it appears that FEA was DOI of original article: http://dx.doi.org/10.1016/j.ejvs.2014.11.010 * Corresponding author. N. Chakfe, Department of Vascular Surgery, Les Hôpitaux Universitaires de Strasbourg, B.P. 426, 67091 Strasbourg Cedex, France. E-mail address: [email protected] (N. Chakfe). 1078-5884/Ó 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejvs.2014.12.018
not feasible in about 25% of the primarily selected cases. Future studies based on a larger number of cases are required to improve the statistics and confirm the observed trends. Only then will it be possible to safely apply this investigation technique to predict AAA in the overall population. Moreover, if the definition of asymptomatic and ruptured AAA is not debatable, it is different for symptomatic AAA in which a strong link between symptoms such as pain and impending rupture is not always obvious. Finally, the last potential selection bias is that all patients were male. A previous paper co-signed by one of the authors2 reported a first analysis of stress and strength of the AAA wall with a gender perspective and showed that PWS did not differ, but that PWRR was slightly higher in women, suggesting that differences in biomechanical properties could be a contributing explanation for the higher rupture risk reported with female patients. The second point is the role of arterial blood pressure in the model. In their protocol, the authors considered a blood pressure ranging between 130 and 80 mmHg for asymptomatic and symptomatic AAA and actual recorded blood pressure in ruptured AAA. However, this choice could be responsible for biases. First, the ruptured AAA were probably characterized by significantly higher blood pressure at the time of the rupture onset, which could result in underestimation of the actual stresses at rupture. On the other hand, it would have been interesting to study the role of blood pressure in symptomatic and asymptomatic AAA. This would show if arterial blood pressure increase could have led to increased rupture risk in symptomatic versus asymptomatic AAA. Fillinger et al.3 calculated PWS in a cohort of 103 AAA patients followed for at least 6 months. They concluded that individual AAA PWS was a better predictor of complications and rupture than maximum transverse diameter (MTD). They showed no difference between PWS and MTD for small AAA, but a significant difference when PWS was calculated for a maximum arterial blood pressure. In conclusion, this paper is actually a significant contribution to the slow evolution from overall assessment of the risk of AAA rupture in the general population based on the simple measure of the MTD, to an accurate evaluation of the individual risk of rupture in a specific patient.
FEA in Asymptomatic, Symptomatic, and Ruptured AAAs
REFERENCES 1 Erhart P, Hyhlik-Dürr A, Geisbüsch P, Kotelis D, MüllerEschner M, Gasser TC, et al. Finite element analysis in asymptomatic, symptomatic and ruptured abdominal aortic aneurysms e in search of new rupture risk predictor. Eur J Vasc Endovasc Surg 2015;49:239e45.
247 2 Larsson E, Labruto F, Gasser TC, Swedenborg J, Hultgren R. Analysis of aortic wall stress and rupture risk in patients with abdominal aortic aneurysm with a gender perspective. J Vasc Surg 2011;54:295e9. 3 Fillinger MF, Marra SP, Raghavan ML, Kennedy FE. Prediction of rupture risk in abdominal aortic aneurysm during observation: wall stress versus diameter. J Vasc Surg 2003;37:724e32.
Eur J Vasc Endovasc Surg (2015) 49, 247
COUP D’OEIL
Giant Symptomatic Aneurysm of the Inferior Vena Cava V. Makaloski *, J. Schmidli Division of Vascular Surgery, Swiss Cardiovascular Center, University Hospital Bern, CH-3010 Bern, Switzerland
This 16-year old girl presented with acute abdominal pain and nausea after a syncope. The emergency computed tomography scan showed a large mass in the right abdomen, as well as perfusion defects in kidneys, spleen, and lungs. No history of blunt abdominal trauma was registered. Emergency surgery reconfirmed the suspected vena cava aneurysm (13 3 11 3 7 cm), which was partially filled with thrombus. After aneurysm resection and reconstruction with a patch-plasty, open pulmonary embolectomy and closure of the patent foramen ovale was performed to prevent further paradoxical embolisation. Histological findings pointed towards a potential congenital vascular malformation.
* Corresponding author. E-mail address: [email protected] (V. Makaloski). 1078-5884/Ó 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejvs.2014.09.002
