Influence of pseudoxanthoma elasticum on the lipid profile and prognostic implications.

Background: Pseudoxanthoma elasticum (PXE) is a rare, inherited disease characterised by specific skin lesions, progressive loss of vision and early onset atherosclerosis. Atherosclerosis in PXE leads to an increased rate of vascular occlusion and severe intermittent claudication. Although genetically determined, the individual course of PXE is highly variable. Up to now, there is no sufficient parameter to identify individuals at risk of rapid disease progression. This present study focused the lipid profile of patients with PXE and its possible influence on the clinical severity of peripheral artery disease (PAD). Patients and methods: 112 patients with PXE were retrospectively screened. Patients without a complete lipid profile consisting of total cholesterol (TC), triglycerides (TGC), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and Lipoprotein(a) (Lp[a]) where excluded as well as patients with already initiated lipid-lowering therapy. 52 patients met the inclusion criteria. An age-adjusted ordinal regression model was applied to determine the association of each lipid fraction with the severity of PAD assessed as Fontaine classification. Results: The lipid profile of patients with PXE was unremarkable (TGC: 135.8±105.8 mg/dl; TC: 172.5±44.4 mg/dl; HDL: 63.0±18.2 mg/dl; Lp[a]: 64.7±93.5 nmol/l). Ordinal regression showed a significant association of Lp(a) with the severity of PAD with an odds ratio of 1.01 (1.00-1.02; p = 0.004), whereas the other fractions of the lipid profile had no significant influence. Conclusions: This study provides the largest evaluation of blood lipids up to now and the first characterization of Lp(a) levels in patients with PXE. We were able to provide first evidence of a correlation between elevated levels of Lp(a) and the severity of PAD. The present results suggest that determination of Lp(a) in early stages of PXE could help to identify patients at risk of rapid disease progression and with the need of intensified walking exercise training.

A RAND/UCLA-Modified VAS Study on Telemedicine, Telehealth, and Virtual Care in Daily Clinical Practice of Vascular Medicine.

Background: Telemedicine is increasingly used in several fields of healthcare, including vascular medicine. This study aimed to investigate the views of experts and propose clinical practice recommendations on the possible applications of telemedicine in vascular medicine. Methods: A clinical guidance group proposed a set of 67 clinical practice recommendations based on the synthesis of current evidence and expert opinion. The Telemedicine Vascular Medicine Working Group included 32 experts from Europe evaluating the appropriateness of each clinical practice recommendation based on published RAND/UCLA methodology in two rounds. Results: In the first round, 60.9% of clinical practice recommendations were rated as appropriate, 35.9% as uncertain, and 3.1% as inappropriate. The strongest agreement (a median value of 10) was reached on statements regarding the usefulness of telemedicine during the 2019 coronavirus disease (COVID-19) pandemic, its usefulness for geographical areas that are difficult to access, and the superiority of video calls compared to phone calls only. The lowest degree of agreement (a median value of 2) was reported on statements regarding the utility of telemedicine being limited to the COVID-19 pandemic and regarding the applicability of teleconsultation in the diagnosis and management of abdominal aortic aneurysm. In the second round, 11 statements were re-evaluated to reduce variability. Conclusions: This study highlights the levels of agreement and the points that raise concern on the use of telemedicine in vascular medicine. It emphasizes the need for further clarification on various issues, including infrastructure, logistics, and legislation.

Carotid Artery Stenosis as a Predictor for Stroke Following Transcatheter Aortic Valve Implantation.

Stroke remains a clinical risk in the long-term follow-up of patients after transcatheter aortic valve implantation (TAVI). We aimed to investigate the association between existing carotid artery stenosis (CS) and the risk of stroke after TAVI. The study participants were consecutive patients who underwent TAVI between 2008 and 2020 and were screened for CS at baseline and at the 30-day follow-up. Hemodynamically relevant CS was defined as a reduction of the carotid artery caliber by >50% in relation to the distal segment. The primary endpoint of this study was ischemic stroke or transient ischemic attack (TIA) within 30 days of TAVI. Stroke-related death was also assessed. Of the 1,537 patients included, 220 (14.3%) patients had CS ≥50%. Within 30 days following TAVI, 41 patients (2.7%) experienced an ischemic stroke or TIA, and seven had stroke-related death. The median time from TAVI to stroke/TIA was 3.0 days. Patients with CS ≥50% had a 2.56-fold increased risk of stroke/TIA after TAVI (95%CI: 1.29-5.10, P = .006). The association was consistent in the multivariable model after adjusting for sex, atrial fibrillation, and estimated glomerular filtration rate. Investigations are needed to mitigate the risk of stroke in patients with CS ≥50%.

Impact of interstitial lung disease on left ventricular myocardial function.

BACKGROUND: Interstitial lung disease (ILD) comprises a wide variety of pulmonary parenchymal disorders within which progressive fibrosing ILD (PF-ILD) constitutes a phenotypic subset. By use of speckle tracking-based strain analysis we aimed to evaluate the degree of left ventricular (LV) dysfunction in progressive vs. non-progressive fibrosing ILD (non-PF-ILD). METHODS: A total of 99 ILD patients (mean age 63.7 ± 13.5 years, 37.4% female), composed of 50 PF-ILD and 49 non-PF-ILD patients, and 33 controls were prospectively enrolled and underwent conventional and speckle tracking echocardiography. Additional laboratory and pulmonary function testing, as well as six-minute walk test were performed. RESULTS: As compared to the non-PF-ILD cohort, PF-ILD patients exhibited a significantly impaired forced vital capacity (2.4 ± 1.0l vs. 3.1 ± 0.9l, p = 0.002), diffusion capacity for carbon monoxide (DLCO, 25.6 ± 16.3% predicted vs. 43.6 ± 16.67% predicted, p <0.001) and exercise capacity response as measured by the six-minute walk test distance (268.1 ± 178.2m vs. 432.6 ± 94.2m, p <0.001). Contrary to conventional echocardiographic LV parameters, both regional and global longitudinal LV strain measurements were significantly altered in ILD patients as compared to controls. No differences in LV strain were found between both patient groups. Significant correlations were observed between global longitudinal strain, on the one hand, and systemic inflammation markers, total lung capacity (TLC) and DLCO, on the other hand (high-sensitivity C-reactive protein: Pearson´s r = -0.30, p< 0.001; interleukin-6: Pearson´s r = -0.26, p = 0.007; TLC % predicted: Pearson´s r = 0.22, p = 0.02; DLCO % predicted: Pearson´s r = 0.21, p = 0.02). CONCLUSIONS: ILD is accompanied by LV dysfunction. LV functionality inversely correlates with the severity of the restrictive ventilatory defect and inflammation marker levels. These observations support the assumption of persistent low-grade systemic inflammation that may link systemic cardiovascular function to ILD status.

Carotid Stiffness After Transcatheter Aortic Valve Replacement.

The present study aimed to analyze common carotid artery strain properties in patients (n = 59) with severe aortic valve stenosis who underwent transcatheter aortic valve replacement (TAVR). Arterial compliance of the common carotid artery was assessed by ultrasound speckle-tracking before and after TAVR. For sub-analysis the study cohort was divided according to aortic valve area <.75 cm2 (n = 30) vs ≥.75 cm2 (n = 29). Comparison of pre- and post-procedural strain variables showed an improvement in median radial velocity (P < .0001), radial displacement (P = .007), circumferential strain (P = .004), radial strain rate (P = .023), and circumferential strain rate (P < .0001), while the increase of radial strain showed a trend (P = .082). Analysis of aortic valve area revealed an inverse correlation between aortic valve area and the differences (post-procedural-pre-procedural values) for radial strain rate, and circumferential strain. Moreover, sub-analysis revealed that the increase of carotid strain variables before and after TAVR were more pronounced in the sub-group of aortic valve area .75 vs ≥.75 cm2. TAVR led to a reduction of arterial wall stiffness of the common carotid artery assessed by ultrasound speckle-tracking. The decrease of arterial wall stiffness after TAVR was more pronounced in more severe aortic valve stenosis.

Pseudoxanthoma elasticum is associated with cardiocirculatory inefficiency.

Pseudoxanthoma elasticum (PXE) is a rare, genetic, metabolic disease characterized by dystrophic calcification of elastic fibres in the skin, retina and vascular wall. Data on cardiac involvement are inconsistent. Hence, we aimed to evaluate cardiorespiratory response to incremental cardiopulmonary exercise testing (CPET) in PXE. A total of 30 PXE patients (54.0 ± 11.2 years, 40.0% male) and 15 matched controls underwent symptom-limited incremental CPET. PXE patients presented an impaired peak work rate as compared to controls (84.2 ± 16.0% vs. 94.7 ± 10.4%, p = 0.03) that was accompanied by a lower peak oxygen uptake (in % predicted and mL/min/kg), reduced increments in oxygen uptake per increments of work rate (ΔV´O2/ΔWR, 8.4 ± 3.0 mL/min/W vs. 11.3 ± 4.9 mL/ min/W, p = 0.02), lower peak oxygen pulse (78.0 ± 12.3% vs. 90.6 ± 19.6%, p = 0.01) and reduced minute ventilation at peak exercise (V´E, 66.2 ± 16.8% vs. 82.9 ± 25.2%, p = 0.02). To summarize, we presently observed impairment in mainly cardiocirculatory parameters, whilst no substantial ventilatory limitation was detected. The potential implications of this finding for PXE management warrant further study.

Preclinical atherosclerotic burden in carotid and lower extremity arteries in adults with congenital heart disease.

Background: Over 90% of patients with congenital heart defects now reach adulthood, due to significant medical advances in recent decades. With advancing age, the risk of acquired cardiovascular diseases increases in addition to the already existing risk due to the congenital defect. The aim of this study was to evaluate the prevalence of atherosclerotic lesions in carotid and lower extremity arteries in adults with congenital heart disease (ACHD). Patients and methods: A total number of 108 ACHD patients (40.6±15.0 years, 50.0% male) and 22 healthy controls (39.3±16.6 years, 40.9% male) were included in this prospective study and underwent a comprehensive angiological examination that included vascular strain analysis on the common carotid artery. Results were stratified by the underlying ACHD lesion groups: shunt lesions (n=26), left-sided obstructive lesions (n=29), right-sided lesions (n=26) and complex lesions (n=27). Results: Colour-coded duplex sonography revealed atherosclerotic lesions in lower extremity arteries in 19 ACHD patients (17.6%). This prevalence did not significantly differ from the one assessed in controls (13.6%, p=0.77). All cases were asymptomatic and therefore classified as Fontaine stage I. 20.4% of ACHD patients presented atherosclerotic lesions in extracranial carotid arteries; amongst controls, the corresponding proportion was 18.4% (p=1.00). No significant differences were observed in atherosclerotic burden in extracranial carotid and lower limb arteries across the four ACHD patient groups (p=0.67 and p=0.89, respectively). Vascular strain analysis revealed no differences between patients and controls. Though circumferential strain varied over ACHD groups (p<0.05), comparison of strain measurements across all specific underlying defect subgroups revealed no significant difference for any of the studied strain parameters. Conclusions: ACHD patients present an atherosclerotic burden in extracranial carotid and lower limb arteries and a vascular stiffness that is comparable to healthy controls.

High prevalence of peripheral and carotid artery disease in patients with interstitial lung diseases.

Background: Interstitial lung diseases (ILD) are a heterogenous group of diseases, which have pulmonary fibrosis, restrictive lung disease, and decreased diffusion capacity as a common final path. Premature death frequently results not from ILD itself but from comorbidities. Peripheral artery disease (PAD) is a common comorbid disease in different chronic lung diseases. The focus of the present study is to clarify the prevalence of PAD in ILD. Patients and methods: A total of 97 patients with ILD and 30 controls were included in the study. Patients with ILD were subdivided into two groups according to the progression of pulmonary fibrosis: progressive fibrosing and non-progressive fibrosing ILD (PF-ILD and nPF-ILD, respectively). All participants underwent standard angiological and pneumological diagnostic procedures including six-minute walking test, measurement of ankle-brachial-index, and colour-coded duplex sonography. Results: We observed no relevant differences in the baseline characteristics except age. Both, PF-ILD and nPF-ILD patients, presented with a highly increased incidence of atherosclerotic lesions compared to the control group (p<0.001). PAD was present in all patients with PF-ILD and in 73% of patients with nPF-ILD. These results were confirmed by age-adjusted regression analyses. Conclusions: The present results indicate that ILD is an independent risk factor for atherosclerosis. Patients with PF-ILD are more severely affected than nPF-ILD patients with age as a confounding variable. Atherogenesis in ILD may be mediated by increased cardiovascular risk, systemic inflammation and chronic hypoxemia.

MR Enterography in Crohn's Disease: Comparison of Contrast Imaging with Diffusion-weighted Imaging and a special Form of Color Coding. / MR-Enterografie bei Morbus Crohn: Vergleich der Kontrastbildgebung mit diffusionsgewichteter Bildgebung und einer besonderen Form der Farbcodierung.

PURPOSE: We compared contrast-enhanced MR enterography with diffusion-weighted sequences to evaluate the validity of diffusion-weighted sequences for activity assessment in Crohn's disease compared to endoscopy. In addition, we investigated a new color-coded image post-processing technique in comparison with standard sequences and endoscopy. MATERIALS AND METHODS: Included were 197 MR enterographies (2015-2017) performed by using standardized examination protocols. The intestine was divided into 7 segments, which were compared separately. The accuracy of the MR examinations with regard to disease activity was validated using the Seo and MaRIA score and endoscopy findings. In addition, the image data were post-processed using a color-coded evaluation method (DCE tool on OsiriX). RESULTS: The comparison between contrast-enhanced and diffusion-weighted sequences showed a highly significant correlation for all bowel sections with a mean Spearman correlation coefficient of 0.876 (0.809-0.928). The color-coded image post-processing showed a sensitivity of 83.2 % and a specificity of 70.5 % in comparison with the MaRIA score. In comparison to endoscopy, a sensitivity of 81.3 % and a specificity of 70.5 %. In comparison with endoscopy, the MaRIA score showed a sensitivity of 80.2 % and a specificity of 84.0 % at a cut-off of 7. The visual score according to Seo showed a sensitivity of 85.7 % with a specificity of 77.0 % in the contrast-weighted examination and a sensitivity of 87.9 % and a specificity of 71.8 % for diffusion weighted images. CONCLUSION: Diffusion-weighted sequences are as good as contrast-weighted sequences for assessing inflammatory activity in Crohn's disease. Contrast is often helpful for assessing complications, but this was not the purpose of this study. Visual imaging using color-coded data sets was similarly good at detecting inflammation. KEY POINTS: · MR enterography is possible without contrast using diffusion-weighted imaging with comparable high informative value.. · Inflammatory activity in MR correlates sufficiently well with endoscopy. · The MaRIA and Seo scores are comparable in their validity.. · The colored representation of inflamed bowel sections is a promising technique.. CITATION FORMAT: · Jakob M, Backes M, Schaefer C et al. MR Enterography in Crohn's Disease: Comparison of Contrast Imaging with Diffusion-weighted Imaging and a special Form of Color Coding. Fortschr Röntgenstr 2022; 194: 1119 - 1131.

Skeletal Status in Patients Scheduled for Elective Lumbar Spine Surgery: Comparison of Discectomy, Decompression, Fusion, and Revision.

STUDY DESIGN: Retrospective Cohort Study. OBJECTIVES: To investigate and compare the prevalence of low bone mineral density (BMD) and abnormal laboratory bone metabolism parameters in patients undergoing elective primary discectomy, decompression, and fusion and to outline possible differences in these parameters between patients undergoing revision for skeletal vs non-skeletal complications. METHODS: We retrospectively evaluated BMD measurements by dual-energy x-ray absorptiometry (DXA) in 389 consecutive patients scheduled for elective lumbar spine surgery. Next to demographic characteristics, laboratory bone metabolism parameters were assessed. Group comparisons were performed between primary discectomy, decompression, and fusion. In patients scheduled for revision surgery after fusion, potential differences in the skeletal status between those with skeletal vs non-skeletal complications were analyzed. RESULTS: Osteoporosis by T-score was detected in 6.7%, 11.0% and 14.7% of the patients undergoing discectomy, decompression and fusion, respectively. While vitamin D deficiency (67.6%) and hyperparathyroidism (16.4%) were frequently detected, no differences in laboratory bone metabolism markers could be found between the groups. Female sex (P<.001), higher age (P=.01) and lower BMI (P<.001) were associated with lower BMD. In the cohort of patients undergoing revision surgery due to complications after fusion, those with skeletal complications did not differ in BMD or bone metabolism from those with non-skeletal complications. CONCLUSIONS: Osteoporosis represents a relevant comorbidity in patients scheduled for elective spine surgery, which is why DXA should be routinely performed in these patients. However, DXA may provide limited information in identifying patients at increased risk for skeletal complications after fusion.

The limitations of fully threaded screws in isolated percutaneous transarticular screw fixation of C1/C2.

Demographic aging accompanied by increased falls inevitably leads to an increased incidence of atlantoaxial instabilities (AAI). Minimally invasive surgical procedures decrease the perioperative risk and regarding the treatment of AAI, percutaneous transarticular screw fixation of C1/C2 was more frequently considered in the past. This study aims to investigate the outcome of patients treated for AAI by isolated percutaneous transarticular screw fixation of C1/C2 (IPTSFC1/C2) using 3.5 mm fully threaded screws to identify its chances and limitations. In this retrospective study, data from patients who underwent IPTSFC1/C2 were analyzed. 23 patients (17 females and 6 males) with an average age of 73.1 years (y) were included. Mean VAS decreased significantly from preoperative 3.9 ± 1.8 to the last follow-up 2.6 ± 2.5 (p = 0.020) and neurological functions were preserved. In the radiological follow-up, we saw a single malposition of an inserted screw (2.27%) and one single bony fusion (4.54%). However, in 6 of 7 patients (85.71%), there was a loosening of the inserted screws due course. We demonstrated that the use of 3.5 mm fully threaded screws for IPTSFC1/C2 results in low rates of osseous fusions between C1 and C2. Therefore, their use in IPTSFC1/C2 is not suitable, especially for geriatric patients with impaired bone status.

Pulmonary affection of patients with Pseudoxanthoma elasticum: Long-term development and genotype-phenotype-correlation.

Pseudoxanthoma elasticum (PXE) is a rare, heritable disease caused by various, mainly recessively transmitted mutations in the ABCC6 gene. Due to calcification of soft connective tissue phenotypic hallmarks are progressive loss of vision, alternation of the skin and early onset atherosclerosis. Beside these main features patients also suffer from impaired alveolar diffusion. The present study focused on impaired lung functioning based on a large cohort of patients with PXE, its long-term development, and genotype-phenotype correlation. Retrospectively, 98 patients and 45 controls were enrolled. All patients underwent body plethysmography and carbon monoxide diffusion testing. Of 35 patients three or more body plethysmographic records were available for long-term analysis. For genotype-phenotype analysis ABCC6 genotypes were grouped as two missense, mixed, or two nonsense mutations. Patients with PXE showed significantly reduced vital capacity (p < 0.05), diffusion capacity (p < 0.01), and diffusion transfer coefficient (p < 0.05). Over a mean period of 38 months diffusion capacity (p < 0.05) and diffusion transfer coefficient (p < 0.01) dropped significantly whereas lung volumes remained unchanged. Genotype-phenotype correlation revealed no connection between gene variants and lung functioning. In conclusion, PXE is accompanied by progressive reduction of alveolar diffusion indicating progressive alterations of lung tissue. Genotype-phenotype correlation with genotypes sorted as missense and nonsense mutations do not explain impaired lung functioning.

Multiple instance learning detects peripheral arterial disease from high-resolution color fundus photography.

Peripheral arterial disease (PAD) is caused by atherosclerosis and is a common disease of the elderly leading to excess morbidity and mortality. Early PAD diagnosis is important, as the only available causal therapy is addressing risk factors like smoking, hypercholesterolemia or hypertension. However, current diagnostic techniques often do not detect early stages of PAD. We theorize that PAD's underlying cause atherosclerosis can be detected on color fundus photography (CFP) images with a convolutional neural network architecture, which might aid earlier PAD diagnosis and improve disease monitoring. In this explorative study a deep attention-based Multiple Instance Learning (MIL) architecture is used to capture retinal imaging biomarkers on CFP images of 135 examinations. To capture subtle variations in vascular structures, higher image resolution can be utilized by partitioning the CFP into patches. Our architecture converts each patch into a feature vector, and determines its relative importance via an automatically computed attention weight. Our best model achieves an ROC AUC score of 0.890. Visualizing these attention weights provides insights about the network's decision and suggests ocular involvement in PAD. Statistical analysis confirms that the optic disc and the temporal arcades are weighted significantly higher (p < 0.001) than retinal background. Our results support the feasibility of detecting the presence of PAD with a modern deep learning approach.

Therapy of Pseudoxanthoma Elasticum: Current Knowledge and Future Perspectives.

Pseudoxanthoma elasticum (PXE) is a rare, genetic, metabolic disease with an estimated prevalence of between 1 per 25,000 and 56,000. Its main hallmarks are characteristic skin lesions, development of choroidal neovascularization, and early-onset arterial calcification accompanied by a severe reduction in quality-of-life. Underlying the pathology are recessively transmitted pathogenic variants of the ABCC6 gene, which results in a deficiency of ABCC6 protein. This results in reduced levels of peripheral pyrophosphate, a strong inhibitor of peripheral calcification, but also dysregulation of blood lipids. Although various treatment options have emerged during the last 20 years, many are either already outdated or not yet ready to be applied generally. Clinical physicians often are left stranded while patients suffer from the consequences of outdated therapies, or feel unrecognized by their attending doctors who may feel uncertain about using new therapeutic approaches or not even know about them. In this review, we summarize the broad spectrum of treatment options for PXE, focusing on currently available clinical options, the latest research and development, and future perspectives.

Retinal and choriocapillaris perfusion are associated with ankle-brachial-pressure-index and Fontaine stage in peripheral arterial disease.

The purpose of this prospective case-control study was to assess whether parameters of retinal and choriocapillaris perfusion are altered in patients with peripheral arterial disease (PAD). Patients with PAD and healthy controls were imaged with swept-source optical coherence tomography angiography (OCT-A). Macula centered 3 × 3 mm OCT-A scans were acquired, binarized and perfusion was evaluated for vessel density (VD) and choriocapillaris non-perfused area. Clinical examination and non-invasive assessment included Fontaine staging, ankle-brachial-pressure-index (ABI) and vascular color-coded Doppler sonography. Fifty-two patients with PAD and 23 healthy controls were included. Superficial retinal VD was reduced in patients compared to controls (difference = - 0.013, p = 0.02), decreased with higher Fontaine stage (p = 0.01) and correlated with ABI (r = 0.42, p < 0.0001, 95% confidence interval [CI] 0.23-0.58). Choriocapillaris non-perfused area was larger in patients compared to controls (difference = 3.64%, p = 0.002, 95% CI 1.38-5.90%) and significantly correlated with ABI (r = - 0.22, p = 0.03, 95% CI - 0.40- - 0.03). Multivariate multiple regression analysis revealed a significant association of all OCT-A parameters with ABI and of deep retinal vessel density and choriocapillaris non-perfused area with Fontaine stage. In this first study of retinal and choroidal perfusion in patients with PAD we found both retinal and choroidal perfusion to be significantly impaired. OCT-A parameters could aid as indirect imaging biomarkers for non-invasive PAD staging and monitoring.

Long-term incidence of upper extremity venous obstruction in implantable cardioverter defibrillator patients.

BACKGROUND: Very little is known about the long-term prevalence of severe venous obstruction and occlusion in patients with transvenous implantable cardioverter-defibrillator leads. The objective of the current investigation was to elucidate the incidence and prevalence and to identify predisposing conditions in an ICD cohort over a long follow-up period. METHODS: Based on a prospective database, we analyzed consecutive patients who received an ICD implantation in our hospital between 06/1988 and 2009 as well as all corresponding follow-up data until 02/2018. Cavographies were used for analysis, and all patients with at least one device replacement and one follow-up cavography were included. RESULTS: Over a mean follow-up period of 94 ± 50 months, severe venous obstruction was found in 147 (33%) of 448 patients. Kaplan-Meier analysis shows a severe obstruction or occlusion in 50% of patients after a period of 14.3 years. The total number of leads (p < .001, HR 2.01, CI 2.000-2.022), an advanced age (p = .004, HR 1.023 per year, CI 1.022-1.024) and the presence of dilated cardiomyopathy (p = .035, HR 1.49, CI 1.47-1.51) were predictive of venous obstruction whereas the presence of anticoagulation was not. CONCLUSION: Severe obstruction of the access veins after ICD implantation occurs frequently and its prevalence shows a nearly linear increase over long-time follow-up. Multiple leads, an advanced age and DCM as underlying disease are associated with an increased risk of venous obstruction while the role of anticoagulation to prevent venous obstruction in ICD patients is unclear.