To reverse or not to reverse the radial artery in coronary artery bypass graft surgery? Histopathologic concerns and media thickness

Background and aims

Radial artery (RA) is a popular coronary artery bypass grafting (CABG) conduit. The challenging issue is vasospasm. A few studies are available on histopathological differences between RA's proximal and distal ends. This study aims to compare histopathological features of the proximal and distal end of RA to find the best technique for anastomosis.

Methods

In this matched case-control study, 80 patients were included who underwent CABG and used RA as a graft. Ten subjects were excluded. RA was harvested by open technique, and a cocktail of Papaverine, Verapamil, and Nitroglycerine was frequently applied topically. One centimeter of proximal and distal ends of the RA was evaluated considering its Histopathology. Clinical signs of RA graft vasospasm were monitored from harvesting until the post-operative period. Intima, media, and intima-media thickness (IMT) index were compared between the two cohorts.

Results

Vasospasm occurred in 1.41% of patients. The mean intimal thickness in the proximal and distal ends were, respectively, 0.20 (standard deviation [SD] 0.17 mm) vs. 0.31 (SD 0.18 mm) (p < 0.001). The mean media thickness in the distal end was higher than the proximal end (0.98 [SD 0.36] vs. 1.09 [SD 0.37], p = 0.004). IMT index of the proximal and distal ends showed a statistically significant difference (0.22 [SD 0.17] vs. 0.31 [SD 0.19]) (p < 0.001).

Conclusion

The overall incidence rate of vasospasm in our study is comparable with other studies using the same cocktail. Proximal RA has a relatively lower medial thickness compared to the distal part, which may induce less vasospasm in CABG patients.

Effects of the Arteriovenous Fistula on Pulmonary Artery Pressure and Cardiac Output in Patients with Chronic Renal Failure

Introduction

Access to the vascular system is necessary in patients with chronic renal failure planned to undergo dialysis. One of the complications of end-stage renal disease patients is pulmonary hypertension (PHT). Temporary arterio-venous access closure and successful kidney transplantation causes a significant fall in cardiac output and pulmonary artery pressure (PAP), indicating the possibility that excessive pulmonary blood flow is involved in the pathogenesis of the disease. We attempted to study the relationship of PHT with arteriovenous fistula (AVF) creation, as well as to assess the relationship between AVF flow and fistula characteristics.

Methods

Fifty patients were included in the study. Echocardiography was used to evaluate systolic PAP, cardiac output (CO), and ejection fraction (EF) before creating the AVF. After a follow-up interval of at least 6 months, a second echocardiographic assessment and a Doppler sonographic assessment of their fistula flow were carried out. Complete data were available for 34 patients.

Results

Study data were collected from 34 patients, 28 males and 6 females with a mean age of 52 yrs ranging from 15–78 yrs. The data showed a statistically significant positive correlation between fistula flow and PAP2 and PAP changes (p<0.05). Mean fistula flow was 1322 ml/min in patients without PHt and 2750 ml/min in patients with PHT. this difference (1428 ml/ min) was statistically significant (p=0.03). We found a significant negative correlation between PAP1 and EF1 and PAP2 and EF2 (p<0.05). In addition, the mean EF2 in patients without PHT was 57% in contrast to 46% in patients with PHT. Mean fistula flow in radial fistulae (mean=422 ml/min, range: 370–474 ml/min) was significantly less than brachial fistulae (mean=1463 ml, range: 270–3300 ml/min) (p=0.03). Mean systolic PAP2 of 14.8 mmHg in transplanted patients was 5.9 mmHg less than those who were not transplanted (20.7 mmHg). Diabetes was the most common cause of renal failure and diabetics had a significant reduction in their EF (15.5%) compared with non-diabetic patients (1% reduction) (p=0.016).

Conclusion

Fistula flow, PAP and EF of all patients should be checked at least 6 months after fistula creation. Patients with higher fistula flow rates and patients with diabetes mellitus need to be more closely observed. In addition, elderly patients with significant cardiac and other comorbidities may be more prone to develop symptoms after AVF creation

Is severe electrolyte imbalance a contraindication for heart transplant?

Owing to the increasing numbers of patients with end-stage congestive heart failure awaiting heart transplant and the limited number of suitable donor organs, a decrease in stringency of donor criteria has become widely accepted over the last decade. Here, we present a case of a heart donor with severe electrolyte imbalance, specifically severe hypokalemia, and severe hypernatremia. Despite this, heart transplant was a success, and the recipient was discharged from the hospital in good general condition. We recommend further study of this issue with a larger sample size.

Ex vivo evaluation of insulin nanoparticles using chitosan and arabic gum

Polymeric delivery systems based on nanoparticles have emerged as a promising approach for peroral insulin delivery. The aim of the present study was to investigate the release of insulin nanoparticulate systems and ex vivo studies. The nanoparticles were prepared by the ion gelation method. Particle size distribution, zeta potential, and polydispersity index of the nanoparticles were determined. It was found that the nanoparticles carried positive charges and showed a size distribution in the range of 170–200 nm. The electrostatic interactions between the positively charged group of chitosan and negatively charged groups of Arabic gum play an important role in the association efficiency of insulin in nanoparticles. In vitro insulin release studies showed an initial burst followed by a slow release of insulin. The mucoadhesion of the nanosystem was evaluated using excised rat jejunum. Ex vivo studies have shown a significant increase in absorption of insulin in the presence of chitosan nanoparticles in comparison with free insulin.

Development of a Gas Empowered Drug Delivery system for peptide delivery in the small intestine

The aim of this investigation was to design a novel Gas Empowered Drug Delivery (GEDD) system for CO(2) forced transport of peptide drugs together with mucoadhesive polymers to the surface of the small intestine. The GEDD effect of the core tablet was achieved using CO(2) gas to push insulin together with the mucoadhesive excipients poly(ethyleneoxide) (PEO) and the permeation enhancer trimethyl chitosan (TMC) to the surface of the small intestine. The in-vitro insulin release showed that almost 100% of the insulin was released from enterically coated tablets within 30 min at pH 6.8. The designed GEDD system was shown to increase the insulin transport by approximately 7 times in comparison with the free insulin across sheep's intestine ex-vivo. Three different peroral formulations were administered to male rabbits: F1 containing no TMC or PEO, F2 containing PEO but no TMC and F3 containing both PEO and TMC. The administrations of insulin using the formulation F1 resulted in a low FR value of 0.2%+/-0.1%, while the formulations F2 and F3 resulted in a much higher FR values of 0.6+/-0.2% and 1.1%+/-0.4%, respectively. Hence, the insulin permeation achieved by the GEDD system is primarily due to the enhancing effect of TMC and the mucoadhesive properties of PEO both of which synergistically increase the bioavailability of insulin.

Permeation enhancer effect of chitosan and chitosan derivatives: comparison of formulations as soluble polymers and nanoparticulate systems on insulin absorption in Caco-2 cells

In this study four quaternized derivatives of chitosan: trimethyl chitosan (TMC), dimethylethyl chitosan (DMEC), diethylmethyl chitosan (DEMC) and triethyl chitosan (TEC) with degree of substitution of approximately 50+/-5% were synthesized and their effect on the permeability of insulin across intestinal Caco-2 monolayers was studied and compared with chitosan both in free-soluble form and in nanoparticulate systems. Transepithelial electrical resistance (TEER) studies revealed that all four chitosan derivatives in free-soluble forms were able to decrease the TEER value in the following order TMC>DMEC>DEMC=TEC>chitosan, indicating their abilities to open the tight junctions. Recovery studies on the TEER showed that the effect of the polymers on Caco-2 cell monolayer is reversible and proves the viability of cells after incubation with all polymers. A similar rank order was also observed when measuring the zeta-potentials of the various polymers in solution form. Transport studies of insulin together with the soluble polymers across Caco-2 cell layers showed the following ranking: TMC>DMEC>DEMC>TEC>chitosan which is in agreement with the strength of the cationic charge of the polymer. In comparison to the free-soluble polymers, the nanoparticles prepared by ionic gelation of the chitosan and its quaternized derivatives had much lower effect on decreasing the TEER by opening of the tight junctions. This can be explained by the reduced available amount of positive charge at the surface of the nanoparticles. In accordance with these results, the insulin loaded nanoparticles showed much less permeation across the Caco-2 cell monolayer in comparison to the free-soluble polymers. Mass balance transport studies revealed that a substantial amount of the nanoparticles has been entrapped into the Caco-2 monolayer or attached to the cell surface. It can thus be stated that while free-soluble polymers can reversibly open the tight junctions and increase the permeation of insulin, the nanoparticles had basically only a low effect on the opening of the tight junction and the paracellular transport of insulin across the Caco-2 cell monolayer. These data convincingly show that nanoparticles consisting of chitosan and its quaternary ammonium derivatives loaded with insulin are less effective in facilitating paracellular transport across Caco-2 cell monolayers than the corresponding free polymers.