Hendrik von Tengg-Kobligk

Hybrid procedures for thoracoabdominal aortic aneurysms and chronic aortic dissections – A single center experience in 28 patients

OBJECTIVE We report our 6-year experience with the visceral hybrid procedure for high-risk patients with thoracoabdominal aortic aneurysms (TAAA) and chronic expanding aortic dissections (CEAD). METHODS Hybrid procedure includes debranching of the visceral and renal arteries followed by endovascular exclusion of the aneurysm. A series of 28 patients (20 male, mean age 66 years) were treated between January 2001 and July 2007. Sixteen patients had TAAAs type I-III, one type IV, four thoracoabdominal placque ruptures, and seven patients CEAD. Patients were treated for asymptomatic, symptomatic, and ruptured aortic pathologies in 20, and 4 patients, respectively. Two patients had Marfans syndrome; 61% had previous infrarenal aortic surgery. The infrarenal aorta was the distal landing zone in 70%. In elective cases, simultaneous approach (n = 9, group I) and staged approach (n = 11, group II) were performed. Mean follow-up is 22 months (range 0.1-78). RESULTS Primary technical success was achieved in 89%. All stent grafts were implanted in the entire thoracoabdominal aorta. Additionally, three patients had previous complete arch vessel revascularization. Left subclavian artery was intentionally covered in three patients (11%). Thirty-day mortality rate was 14.3% (4/28). One patient had a rupture before the staged endovascular procedure and died. Overall survival rate at 3 years was 70%, in group I 80%, and in group II 60% (P = .234). Type I endoleak rate was 8%. Permanent paraplegia rate was 11%. Three patients required long-term dialysis (11%). Peripheral graft occlusion rate was 11% at 30 days. Gut infarction with consecutive bowel resection occurred in two patients. There was no significant difference between group I and II regarding paraplegia and complications. CONCLUSIONS Early results of visceral hybrid repair for high-risk patients with complex and extended TAAAs and CEADs are encouraging in a selected group of high risk patients in whom open repair is hazardous and branched endografts are not yet optional.

Influence of human serum albumin on longitudinal and transverse relaxation rates (r1 and r2) of magnetic resonance contrast agents.

Objectives:Exogenous magnetic resonance (MR) contrast media (CM) are used to improve detection and delineation of physiological and pathologic structures. Temporary binding between CM and proteins such as human serum albumin (HSA) may alter the relaxation-enhancing properties of specific contrast agents. In this study, the presence and strength of HSA interaction with different CM was investigated. Material and Methods:Three contrast agents were chosen: Gd-DTPA, Gd-BT-DO3A, and Gd-BOPTA, each of which is known to have a different protein interaction. Samples were prepared using 7 different HSA concentrations, all at a constant CM concentration of 0.5 mmol/L. The relaxation rates, R1 and R2, of each sample were measured at 1.5 T. Virtual docking studies were performed to estimate the number of high affinity-binding sites of Gd-BOPTA and the surface of the HSA dimer. Results:Gd-BOPTA caused the greatest increase in R1 and R2, which followed an exponential dependency with increasing HSA concentration. Between the range of 0 and 7 g/dL of HSA, Gd-DTPA and Gd-BT-DO3A showed a relative change in both relaxation rates of approximately 13% and 22% for R1 and 26% and 30% for R2, respectively. In contrast, Gd-BOPTA demonstrated a relative increase of approximately 108% and 363% for R1 and R2, respectively. Changes of HSA concentration within physiological range (3.5–5.5 g/dL) resulted in an increase of R1 and R2 of approximately 40% when using Gd-BOPTA. The docking study revealed that approximately 10 small hydrophobic pockets exist on the HSA surface where the aromatic tail of Gd-BOPTA can fit in and a stronger noncovalent binding can occur compared with Gd-DTPA and Gd-BT-DO3A. Conclusion:Relaxation rates of Gd-BOPTA showed a strong dependency on HSA. In contrast, Gd-DTPA and Gd-BT-DO3A demonstrated little or no relevant dependency. On the basis of these results, the influence of serum protein concentration should be considered in both research studies and in clinical use.

Short and midterm results after left subclavian artery coverage during endovascular repair of the thoracic aorta

BACKGROUND To analyze the sequelae of the intentional left subclavian artery (LSA) coverage during thoracic endovascular aortic repair (TEVAR). METHODS Retrospective analysis of prospectively collected data in a single center. Between March 1997 and October 2008, 88 of 220 patients (40%) had thoracic aortic lesions that required LSA coverage during TEVAR. Thirty-four of our patients (39%) were treated under urgent or emergent conditions for acute pathologies. The proximal landing zone was zone 0 in 10 patients (11%), zone 1 in 24 patients (27%), and zone 2 in 54 patients (61%). Debranching procedures of the supra-aortic vessels were performed in patients who were to undergo zone 0 or zone 1 deployment. Primary LSA revascularization was performed in 22 of the 88 patients (25%) at a median of 6 days before TEVAR. Median follow-up was 26.4 months (1-98 months). RESULTS Technical success was achieved in 97%. Five primary (9%) and two secondary (4%) type Ia endoleaks in patients who underwent zone 2 deployment were observed and required further interventions. Fourteen (16%) primary type II endoleaks were observed; 10 of them fed by the LSA. Paraplegia rate was lower in patients with LSA coverage without revascularization than in other patients (1.5% vs 1.9%; odds ratio [OR], 0.774; 95% confidence interval [CI], 0.038-6.173; P = 1.000). Prior or concomitant infrarenal aortic replacement (P = .0019), renal insufficiency (glomerular filtration rate < 90 mL/min/1.73 m(2)) (P = .0024) and long segment aortic coverage (>200 mm) (P = .0157) were associated with significant higher risk of postoperative paraplegia. Stroke rate was lower in patients with LSA coverage without revascularization than in other patients (3% vs 3.9%; OR, 0.570; 95% CI, 0.118-2.761; P = .7269). Two patients (3%) developed left upper extremity symptoms and another two patients (3%) subclavian steal syndrome and required secondary LSA revascularization. The technical success rate for LSA revascularization was 94%. CONCLUSION By using a selective approach to the LSA revascularization, coverage of the LSA can be used to extend the proximal seal zone for TEVAR without increasing the risk of spinal cord ischemia or stroke. Indications for revascularization include long segment aortic coverage, prior or concomitant infrarenal aortic replacement, and renal insufficiency. In addition, a hypoplastic right vertebral artery, a patent left internal mammary artery graft, and a functioning dialysis fistula in the left arm would also be indications to perform revascularization.

Contrast‐enhanced MR angiography of the run‐off vasculature: Intraindividual comparison of gadobenate dimeglumine with gadopentetate dimeglumine

To compare intraindividually gadobenate dimeglumine (Gd‐BOPTA) with gadopentetate dimeglumine (Gd‐DTPA) for multi‐station MR Angiography of the run‐off vessels.

Computational fluid dynamics modelling in cardiovascular medicine

This paper reviews the methods, benefits and challenges associated with the adoption and translation of computational fluid dynamics (CFD) modelling within cardiovascular medicine. CFD, a specialist area of mathematics and a branch of fluid mechanics, is used routinely in a diverse range of safety-critical engineering systems, which increasingly is being applied to the cardiovascular system. By facilitating rapid, economical, low-risk prototyping, CFD modelling has already revolutionised research and development of devices such as stents, valve prostheses, and ventricular assist devices. Combined with cardiovascular imaging, CFD simulation enables detailed characterisation of complex physiological pressure and flow fields and the computation of metrics which cannot be directly measured, for example, wall shear stress. CFD models are now being translated into clinical tools for physicians to use across the spectrum of coronary, valvular, congenital, myocardial and peripheral vascular diseases. CFD modelling is apposite for minimally-invasive patient assessment. Patient-specific (incorporating data unique to the individual) and multi-scale (combining models of different length- and time-scales) modelling enables individualised risk prediction and virtual treatment planning. This represents a significant departure from traditional dependence upon registry-based, population-averaged data. Model integration is progressively moving towards ‘digital patient’ or ‘virtual physiological human’ representations. When combined with population-scale numerical models, these models have the potential to reduce the cost, time and risk associated with clinical trials. The adoption of CFD modelling signals a new era in cardiovascular medicine. While potentially highly beneficial, a number of academic and commercial groups are addressing the associated methodological, regulatory, education- and service-related challenges.

Contrast-enhanced magnetic resonance imaging of central nervous system tumors: agents, mechanisms, and applications.

Brain tumors are one of the most common neoplasms in young adults and are associated with a high mortality and disability rate. Magnetic resonance imaging (MRI) is widely accepted to be the most sensitive imaging modality in the assessment of cerebral neoplasms. Because the detection, characterization, and exact delineation of brain tumors require a high lesion contrast that depends on the signal of the lesion in relation to the surrounding tissue, contrast media is given routinely. Anatomical and functional, contrast agent-based MRI techniques allow for a better differential diagnosis, grading, and especially therapy decision, planing, and follow-up. In this article, the basics of contrast enhancement of brain tumors will be reviewed. The underlying pathology of a disrupted blood-brain barrier and drug influences will be discussed. An overview of the currently available contrast media and the influences of dosage, field strength, and application on the tumor tissue contrast will be given. Challenging, contrast-enhanced, functional imaging techniques, such as perfusion MRI and dynamic contrast-enhanced MRI, are presented both from the technical side and the clinical experience in the assessment of brain tumors. The advantages over conventional, anatomical MRI techniques will be discussed as well as possible pitfalls and drawbacks.

Safety and Efficacy of Preoperative Portal Vein Embolization with Polyvinyl Alcohol in 58 Patients with Liver Metastases

OBJECTIVE The objective of our study was to evaluate the safety and efficacy of transhepatic lobar portal vein embolization (PVE) using polyvinyl alcohol (PVA) particles to induce contralateral lobar hypertrophy in patients with liver-only metastases and normal underlying liver function. MATERIALS AND METHODS Fifty-eight consecutive patients with small predicted future liver remnants (FLRs) underwent PVE with PVA particles to induce hypertrophy of the contralateral hemi-liver before surgical resection of liver metastases. Total liver, right hemi-liver, and left hemi-liver volumes were calculated before and after embolization using a 3D workstation. RESULTS Eight patients underwent left PVE; 47, right PVE; and three, right and segment IV PVE. There were no major complications of the procedure. The mean increases in the ratio of the FLR to the total estimated liver volume after right, right and segment IV, and left PVE were 9%, 10%, and 3%, respectively; the corresponding mean hypertrophy ratios were 24.3%, 31.9%, and 1.5%, respectively. CONCLUSION Right PVE using PVA particles alone as the embolic agent is safe and effective in achieving left hemi-liver hypertrophy. In contrast, left PVE did not induce significant right hemi-liver hypertrophy in this patient population.

Motion characterization of aortic wall and intimal flap by ECG-gated CT in patients with chronic B-dissection

RATIONALE AND OBJECTIVES To evaluate whether dynamic computed tomography (CT)-imaging can provide functional vessel information in patients with chronic aortic dissection type Stanford-B (ADB). MATERIALS AND METHODS In 32 patients, ECG-gated CT-angiography images were obtained. Cross-sectional area change and wall distensibility were investigated by semiautomatic vessel area segmentation at the end of aortic arch. Significance of distensibility differences was tested with regard to the aortic diameter, and the oscillation of the intimal flap was analyzed. RESULTS The aorta could be segmented successfully in all patients. These were separated into three subgroups: (A) 6 patients with an aortic diameter <4 cm and without a visible intimal flap, (B) 9 patients with an aortic diameter <4 cm, and (C) 17 individuals with an aortic diameter > or = 4 cm; (B) and (C) having a visible intimal flap. Differences in distensibility between the subgroups were not significant. Overall mean distensibility was D(tot)=(1.3+/-0.6) x 10(-5) Pa(-1). Analysis of intimal flap oscillation showed a pulsatile short axis diameter decrease of the true lumen of up to 29%. CONCLUSION Dynamic, ECG-gated CT-angiography can demonstrate pulsatile changes in aortic area and a highly variable motion of the intimal flap. Aortic distensibility appears independent of diameter or presence of a intimal flap. Follow-up studies may show correlation with possible complications.

3-D Quantification of the Aortic Arch Morphology in 3-D CTA Data for Endovascular Aortic Repair

We introduce a new model-based approach for the segmentation and quantification of the aortic arch morphology in 3-D computed tomography angiography (CTA) data for thoracic endovascular aortic repair (TEVAR). The approach is based on a model-fitting scheme using a 3-D analytic intensity model for thick vessels in conjunction with a two-step refinement procedure, and allows us to accurately quantify the morphology of the aortic arch. Based on the fitting results, we additionally compute the (local) 3-D vessel curvature and torsion as well as the relevant lengths not only along the 3-D centerline, but particularly also along the inner and outer contour. These measurements are important for preoperative planning in TEVAR applications. We have validated our approach based on 3-D synthetic as well as 3-D MR phantom images. Moreover, we have successfully applied our approach using 3-D CTA datasets of the human thorax and have compared the results with ground truth obtained by a radiologist. We have also performed a quantitative comparison with a commercial vascular analysis software.

Longitudinal computational fluid dynamics study of aneurysmal dilatation in a chronic DeBakey type III aortic dissection

Computational fluid dynamics, which uses numeric methods and algorithms for the simulation of blood flow by solving the Navier-Stokes equations on computational meshes, is enhancing the understanding of disease progression in type III aortic dissections. To illustrate this, we examined the changes in patient-derived geometries of aortic dissections, which showed progressive false lumen aneurysmal dilatation (26% diameter increase) during follow-up. Total pressure was decreased by 29% during systole and by 34% during retrograde flow. At the site of the highest false lumen dilatation, the temporal average of total pressure decreased from 45 to 22 Pa, and maximal average wall shear stress decreased from 0.9 to 0.4 Pa. These first results in the study of disease progression of type III DeBakey aortic dissection with computational fluid dynamics are encouraging.