Cardiac changes following arteriovenous fistula creation in a mouse model

Arteriovenous Loops for Free Flaps to the Abdomen and Pelvis: Case Reports and Pearls

Arteriovenous (AV) loops formed from the greater saphenous vein and femoral artery can facilitate free tissue transfer to the abdomen or pelvis when adequate recipient vessels are not available. Here, we present the application of this technique in 3 cases where patients had significant abdominal or pelvic defects due to oncological resection or trauma. AV loops were successfully created using a saphenous vein turned up into the femoral artery at the level of the groin. These loops were then tunneled through the groin and cut back to form recipient vessels for anterolateral thigh (ALT) flaps in a single-stage procedure. In all 3 cases, AV loops constructed with this technique served as reliable conduits for free ALT flaps. Only 1 complication occurred. Following a drop in tissue oximetry, 1 patient was taken back to the operating room. A stitch was found to be compressing the pedicle. Following release, no further complications were observed and all patients achieved complete wound healing. In this article, we highlight key surgical techniques to maintain the orientation of the vein during AV loop anastomosis, which prevents kinking. We provide technical insights regarding tunneling the AV loop through the groin without compression, anchoring the pedicle appropriately, and positioning the ALT flap anastomosis. Our success with this technique underscores its potential in facilitating complex pelvic and abdominal reconstruction.

Hemodialysis Patients with High-Flow Arteriovenous Fistulas: An Evaluation of the Impact on Cardiac Function

Purpose

: Patients undergoing hemodialysis often experience changes in cardiac function when they have a high-flow arteriovenous fistula (AVF). This study aimed to assess the effect of high-flow AVFs on cardiac function in patients undergoing hemodialysis.

Materials and Methods

: A longitudinal study was conducted on hemodialysis patients with high-flow AVFs. Echocardiographic parameters, such as left ventricular ejection fraction (LVEF), left atrial diameter (LAD), left ventricular end-diastolic dimension (LVEDD), right ventricular end-diastolic dimension (RVEDD), inferior vena cava diameter (IVCD), systolic blood pressure, and diastolic blood pressure, were measured and compared before and after AVF creation.

Results

: One hundred hemodialysis patients with high-flow AVFs (mean age: 55.95±13.39 years, mean body mass index: 24.71±3.43 kg/m²) were studied. LVEF significantly decreased (51.10%±5.39% to 47.50%±5.79%), while LAD, LVEDD, and IVCD significantly increased after AVF creation (P<0.05). Systolic (132.49±16.42 mmHg to 146.60±17.43 mmHg) and diastolic (79.98±8.40 mmHg to 83.33±9.68 mmHg) blood pressure substantially rose post-fistularization (P<0.001). Notably, LVEF reduction was more significant in brachio-cephalic AVFs (46.29%±4.24%) compared to distal radio-cephalic or snuffbox AVFs (49.17%±7.15%) (P=0.014).

Conclusion

: High-flow AVFs can significantly affect echocardiographic parameters in hemodialysis patients, thereby increasing the risk of cardiac failure. Close cardiac monitoring may be necessary for early intervention. Distal AVFs may be preferable in patients with decreased cardiac function.

The rodent models of arteriovenous fistula

Arteriovenous fistulas (AVFs) have long been used as dialysis access in patients with end-stage renal disease; however, their maturation and long-term patency still fall short of clinical needs. Rodent models are irreplaceable to facilitate the study of mechanisms and provide reliable insights into clinical problems. The ideal rodent AVF model recapitulates the major features and pathology of human disease as closely as possible, and pre-induction of the uremic milieu is an important addition to AVF failure studies. Herein, we review different surgical methods used so far to create AVF in rodents, including surgical suturing, needle puncture, and the cuff technique. We also summarize commonly used evaluations after AVF placement. The aim was to provide recent advances and ideas for better selection and induction of rodent AVF models. At the same time, further improvements in the models and a deeper understanding of AVF failure mechanisms are expected.

Biomimetic cardiac tissue chip and murine arteriovenous fistula models for recapitulating clinically relevant cardiac remodeling under volume overload conditions

Cardiovascular events are the primary cause of death among dialysis patients. While arteriovenous fistulas (AVFs) are the access of choice for hemodialysis patients, AVF creation can lead to a volume overload (VO) state in the heart. We developed a three-dimensional (3D) cardiac tissue chip (CTC) with tunable pressure and stretch to model the acute hemodynamic changes associated with AVF creation to complement our murine AVF model of VO. In this study, we aimed to replicate the hemodynamics of murine AVF models in vitro and hypothesized that if 3D cardiac tissue constructs were subjected to "volume overload" conditions, they would display fibrosis and key gene expression changes seen in AVF mice. Mice underwent either an AVF or sham procedure and were sacrificed at 28 days. Cardiac tissue constructs composed of h9c2 rat cardiac myoblasts and normal adult human dermal fibroblasts in hydrogel were seeded into devices and exposed to 100 mg/10 mmHg pressure (0.4 s/0.6 s) at 1 Hz for 96 h. Controls were exposed to "normal" stretch and experimental group exposed to "volume overload". RT-PCR and histology were performed on the tissue constructs and mice left ventricles (LVs), and transcriptomics of mice LVs were also performed. Our tissue constructs and mice LV both demonstrated cardiac fibrosis as compared to control tissue constructs and sham-operated mice, respectively. Gene expression studies in our tissue constructs and mice LV demonstrated increased expression of genes associated with extracellular matrix production, oxidative stress, inflammation, and fibrosis in the VO conditions vs. control conditions. Our transcriptomics studies demonstrated activated upstream regulators related to fibrosis, inflammation, and oxidative stress such as collagen type 1 complex, TGFB1, CCR2, and VEGFA and inactivated regulators related to mitochondrial biogenesis in LV from mice AVF. In summary, our CTC model yields similar fibrosis-related histology and gene expression profiles as our murine AVF model. Thus, the CTC could potentially play a critical role in understanding cardiac pathobiology of VO states similar to what is present after AVF creation and may prove useful in evaluating therapies.