Electric-field-enhanced selective separation of products of an enzymatic reaction in a membrane micro-contactor.

Processes employed in separations of products of enzyme reactions are often driven by diffusion, and their efficiency can be limited. Here, we exploit the effect of a direct current (DC) electric field that intensifies mass transfer through a semipermeable membrane for fast, continuous, and selective separation of electrically charged molecules. Specifically, we separate low-molecular-weight reaction products (phenylacetic acid, 6-aminopenicillanic acid) from the original reaction mixture containing a free enzyme (penicillin acylase). The developed microfluidic dialysis-membrane contactor allows a stable counter-current arrangement of the retentate and permeates liquid streams on which DC electric field is perpendicularly applied. The applied electric field significantly accelerates the transport of electrically charged products through the semipermeable membrane yielding high separation efficiencies at short residence times. The residence time of 5 min is sufficient to reach 100% separation yield in the electric field. The same residence time provides only a 50% yield in the diffusion-controlled experiments. We experimentally demonstrated that a combined microreactor-microextractor with a recycle of the soluble penicillin acylase can continuously produce both the reaction products at high concentrations. The developed membrane-contactor is a versatile platform allowing to tune its characteristics, such as selectivity given by the membrane, or the type of the retentate phase, for a specific application.

Optimization of aqueous two-phase systems for the production of 6-aminopenicillanic acid in integrated microfluidic reactors-separators.

Aqueous two-phase systems (ATPSs) were screened for the production of 6-aminopenicillanic acid (6-APA) catalyzed by penicillin acylase, followed by the extractive separation of 6-APA from the reaction mixture. The key point of this study was to find an ATPS exhibiting a large difference in the partition coefficients of the biocatalyst and reaction products. Several ATPSs based on polyethylene glycol (PEG)/phosphate, PEG/citrate, and PEG/dextran were tested. We found that an ATPS consisting of 15 wt% of PEG 4000, 10 wt% of phosphates, 75 wt% of water (pH value 8.0 after dissolution) provided optimal separation of 6-APA from the enzyme. While the 6-APA was mainly found in the top PEG phase, the free enzyme favored the bottom salt-rich phase. This ATPS also fulfils other important requirements: (i) high buffering capacity, reducing an undesirable pH decrease due to the dissociation of phenylacetic acid (the side product of the reaction), (ii) a relatively low cost of the ATPS components, (iii) the possibility of electrophoretic transport of fine droplets as well as the reaction products for both the acceleration of phase separation and the enhancement of 6-APA concentration in the product stream. Extraction experiments in microcapillary and batch systems showed that the transport of 6-APA formed in the salt-rich phase to the corresponding PEG phase could occur within 30 s. The experimental results described form a base of knowledge for the development of continuously operating integrated microfluidic reactors-separators driven by an electric field for the efficient production of 6-APA.

Renal denervation--hypes and hopes.

Catheter-based renal denervation (RDN) is a novel invasive approach in the treatment of resistant hypertension. It is considered a minimally invasive and safe procedure which, as shown by initial experimental and clinical trials, is able not only to reduce blood pressure but also to modify its risk factors by modulation of autonomic nervous system. Recently published results of a randomized Symplicity HTN-3 trial, which failed to demonstrate RDN-induced reduction of blood pressure at six months, decreased the initial enthusiasm regarding RDN and raised a question about real efficacy of this procedure. Nevertheless, still there are some other conditions characterized by increased sympathetic tone such as heart failure, atrial fibrillation, or ventricular arrhythmias that may benefit from RDN. Furthermore, novel therapeutical approach toward RDN using adapted electrophysiological or new specially designed electrodes may improve effectiveness of RDN procedure.

Ganglionated plexus ablation vs linear ablation in patients undergoing pulmonary vein isolation for persistent/long-standing persistent atrial fibrillation: a randomized comparison.

BACKGROUND: The optimal ablation technique for persistent and long-standing persistent atrial fibrillation (AF) is unclear. Both linear lesion (LL) and ganglionated plexus (GP) ablation have been used in addition to pulmonary vein isolation (PVI), but no direct comparison of the 2 methods exists. OBJECTIVE: The aim of this study is to assess the comparative safety and efficacy of 2 different ablation strategies-PVI+LL vs PVI+GP ablation -in patients with persistent or long-standing persistent AF. METHODS: Two hundred sixty-four consecutive patients with persistent/long-standing persistent AF were randomly assigned to 2 different ablation schemes: PVI+LL (n = 132) and PVI+GP (n = 132) ablation. Consistent sinus rhythm (SR) off antiarrhythmic drug was assessed after follow-up of at least 3 years with the use of an implanted monitoring device. RESULTS: All procedural end points were acutely achieved. At 12 months after a single procedure, 47% of the patients treated with PVI+LL were in SR compared to 54% of the patients treated with PVI+GP (P = .29). At 3 years, 34% of the patients with PVI+LL and 49% of the patients with PVI+GP maintained SR (P = .035). Atrial flutter was more frequent in the PVI+LL group than in PVI+GP group (18% vs 6%; P = .002). After a second procedure in 78 patients of the PVI+LL group and 55 patients of the PVI+GP group, the long-term overall success rate was 52% and 68%, respectively (P = .006). CONCLUSIONS: PVI+GP ablation confers superior clinical results with less ablation-related left atrial flutter and reduced AF recurrence compared to PVI+LL ablation at 3 years of follow-up.

Percutaneous epicardial ablation of ventricular tachycardia after failure of endocardial approach in the pediatric population with arrhythmogenic right ventricular dysplasia.

BACKGROUND: Despite the high efficacy of catheter ablation of ventricular tachycardia (VT) in patients with arrhythmogenic right ventricular dysplasia (ARVD), in some patients, conventional endocardial ablation is ineffective. These failures could be explained by the presence of epicardial arrhythmogenic substrate. In these cases, a percutaneous epicardial ablation may be required. OBJECTIVE: This study sought to report the feasibility and results of epicardial VT ablation in a pediatric population of ARVD patients in whom endocardial ablation was unsuccessful. METHODS: Seventeen ARVD pediatric patients (mean age 14 ± 4 years) in whom a percutaneous epicardial radiofrequency ablation of VT was attempted were included in this retrospective analysis. A total of 20 mappable, hemodynamically stable, monomorphic VTs were induced (2 macroreentrant and 18 focal). All patients underwent right ventricular epicardial VT ablation. RESULTS: At the end of the procedure, 16 (94.1%) of the 17 patients had no inducible VT. Pericardial effusion occurred in 4 patients (23.5%), with 1 (5.9%) patient having tamponade that required percutaneous pericardial drainage. During a mean follow-up of 26 ± 15 (range 6 to 42) months, 12 (70.6%) patients remained free of any episodes of VT. All patients with successful RF ablation were free from any antiarrhythmic drugs. There were no deaths during the follow-up period. Recurrences of VT were recorded in 5 (29.4%) patients. CONCLUSION: Percutaneous epicardial catheter ablation is feasible and relatively safe in pediatric ARVD patients with recurrent VT in whom conventional endocardial ablation failed.

Left atrial appendectomy after failed catheter ablation of a focal atrial tachycardia originating in the left atrial appendage.

This report describes a case of left atrial appendectomy after a failed endocardial catheter ablation of a continuous drug-refractory left atrial appendage (LAA) tachycardia in a 9-year-old boy. Electrophysiologic study showed atrial tachycardia (AT) originating in the LAA. Numerous radiofrequency applications with an irrigated-tip catheter were ineffective. During surgery, direct pressure on the apex of the LAA by forceps immediately terminated the AT and restored sinus rhythm. After a left atrial appendectomy, the patient remained free of any arrhythmias during a follow-up period of 18 months.