Novel surface biochemical modifications of urinary catheters to prevent catheter-associated urinary tract infections.

More than 70% of hospital-acquired urinary tract infections are related to urinary catheters, which are commonly used for the treatment of about 20% of hospitalized patients. Urinary catheters are used to drain the bladder if there is an obstruction in the tube that carries urine out of the bladder (urethra). During catheter-associated urinary tract infections, microorganisms rise up in the urinary tract and reach the bladder, and cause infections. Various materials are used to fabricate urinary catheters such as silicone, polyurethane, and latex. These materials allow bacteria and fungi to develop colonies on their inner and outer surfaces, leading to bacteriuria or other infections. Urinary catheters could be modified to exert antibacterial and antifungal effects. Although so many research have been conducted over the past years on the fabrication of antibacterial and antifouling catheters, an ideal catheter needs to be developed for long-term catheterization of more than a month. In this review, we are going to introduce the recent advances in fabricating antibacterial materials to prevent catheter-associated urinary tract infections, such as nanoparticles, antibiotics, chemical compounds, antimicrobial peptides, bacteriophages, and plant extracts.

Comparison of voltage maps using OCTARAY catheter and PENTARAY catheter.

BACKGROUND: Recently, a new OCTARAY® mapping catheter was commercially launched. The catheter is designed to enable high-density mapping and precise signal recording via 48 small electrodes arranged on eight radiating splines. The purpose of this study was to compare bipolar voltage and low-voltage-area size, and mapping efficacy between the OCTARAY catheter and the PENTARAY® catheter METHODS: Twelve consecutive patients who underwent initial and second ablations for persistent atrial fibrillation within 2 years were considered for enrollment. Voltage mapping was performed twice, first during the initial ablation using the PENTARY catheter and second during the second ablation using the OCTARAY Long 3-3-3-3-3 (L3) catheter. RESULTS: Mean voltage with the OCTARAY-L3 catheter (1.64 ± 0.57 mV) was 32.3% greater than that with the PENTARAY catheter (1.24 ± 0.46 mV, p < .0001) in total left atrium. Low-voltage-area (<0.50 mV) size with the OCTARAY-L3 catheter was smaller than that with the PENTARAY catheter (6.9 ± 9.7 vs. 11.4 ± 13.0 cm2 , p < .0001). The OCTARAY-L3 catheter demonstrated greater efficacy than the PENTARAY catheter in terms of shorter mapping time (606 ± 99 vs. 782 ± 211 s, p = .008) and more mapping points (3,026 ± 838 vs. 781 ± 342 points, p < .0001). CONCLUSION: The OCTARAY catheter demonstrated higher voltage recordings, narrower low-voltage areas, and a more efficacious mapping procedure than the PENTARAY catheter.

The effect of rose oil aromatherapy and hand-holding on pain due to peripheral intravenous catheter insertion.

INTRODUCTION: The study aimed to evaluate the effectiveness of rose oil (Rosa Damascene Mill.) aromatherapy and hand-holding in reducing pain associated with peripheral intravenous catheter insertion. METHODS: A comparative mixed-method design. A total of 126 patients were included in the study. For the study's quantitative data, sociodemographic characteristics of the patients and the Patient Interview Form for the qualitative data of the Numeric Rating Scale were used. In all patients included in the study, PIVC insertion was performed a single time by the same nurse using a standard procedure. Chi-square and Bonferroni tests were used for comparative statistics. RESULTS: No statistically significant difference between the groups regarding age, gender, marital status, BMI, and education level (p>0.05). Pain scores: it was 2.40±1.78 in the rose oil group, 3.53±1.98 in the hand-holding group, and 4.88±1.56 in the control group. The difference between the groups regarding pain scores is statistically significant (p=0.001). CONCLUSIONS: The study determined that rose oil aromatherapy and hand-holding interventions reduce pain during PIVC. However, rose oil aromatherapy was more effective on pain than the hand-holding intervention. (Clinical Trial ID: NCT05425849).

Longer length peripheral catheters in sickle cell treatment: a more efficient and cost-effective care pathway.

Patients with sickle cell disease require frequent venous access for red blood cell exchange transfusions to manage their condition. Such frequent access can lead to scar tissue formation, increased pain on insertion, and difficult vascular access for the patients. Previous attempts at achieving successful venous access for patients with difficult venous access has been made with central venous lines, usually femoral lines, which required a large amount of nursing input and resulted in anxiety and pain on insertion for patients. In this article, the author reports on a new pathway with a longer-length peripheral intravenous catheter that reduces the nursing time burden during line insertion, requires less equipment and, crucially, results in a less painful procedure for patients. The increased efficiency of the pathway resulted in a cost saving of £149 per insertion, and patient feedback revealed that the longer-length catheter was preferred over femoral lines.

Reversible Pulsed Electrical Fields as an In Vivo Tool to Study Cardiac Electrophysiology: The Advent of Pulsed Field Mapping.

BACKGROUND: During electrophysiological mapping of tachycardias, putative target sites are often only truly confirmed to be vital after observing the effect of ablation. This lack of mapping specificity potentiates inadvertent ablation of innocent cardiac tissue not relevant to the arrhythmia. But if myocardial excitability could be transiently suppressed at critical regions, their suitability as targets could be conclusively determined before delivering tissue-destructive ablation lesions. We studied whether reversible pulsed electric fields (PFREV) could transiently suppress electrical conduction, thereby providing a means to dissect tachycardia circuits in vivo. METHODS: PFREV energy was delivered from a 9-mm lattice-tip catheter to the atria of 12 swine and 9 patients, followed by serial electrogram assessments. The effects on electrical conduction were explored in 5 additional animals by applying PFREV to the atrioventricular node: 17 low-dose (PFREV-LOW) and 10 high-dose (PFREV-HIGH) applications. Finally, in 3 patients manifesting spontaneous tachycardias, PFREV was applied at putative critical sites. RESULTS: In animals, the immediate post-PFREV electrogram amplitudes diminished by 74%, followed by 78% recovery by 5 minutes. Similarly, in patients, a 69.9% amplitude reduction was followed by 84% recovery by 3 minutes. Histology revealed only minimal to no focal, superficial fibrosis. PFREV-LOW at the atrioventricular node resulted in transient PR prolongation and transient AV block in 59% and 6%, while PFREV-HIGH caused transient PR prolongation and transient AV block in 30% and 50%, respectively. The 3 tachycardia patients had atypical atrial flutters (n=2) and atrioventricular nodal reentrant tachycardia. PFREV at putative critical sites reproducibly terminated the tachycardias; ablation rendered the tachycardias noninducible and without recurrence during 1-year follow-up. CONCLUSIONS: Reversible electroporation pulses can be applied to myocardial tissue to transiently block electrical conduction. This technique of pulsed field mapping may represent a novel electrophysiological tool to help identify the critical isthmus of tachycardia circuits.

Predictors of early catheter replacement after HoLEP. Results from a high-volume laser center.

INTRODUCTION: The aim of the study was to investigate clinical and surgical factors associated with early catheter replacement in patients treated with Holmium Laser Enucleation of the Prostate (HoLEP). MATERIALS AND METHODS: Data of patients treated with HoLEP at our Institution by a single surgeon from March 2017 to January 2021 were collected. Preoperative variables, including non-invasive uroflowmetry and abdominal ultrasonography (US), were recorded. Bladder wall modifications (BWM) at preoperative US were defined as the presence of single or multiple bladder diverticula or bladder wall thickening 5 mm. Clinical symptoms were assessed using validated questionnaires. Only events occurred within the first week after catheter removal were considered. RESULTS: Overall, 305 patients were included, of which 46 (15.1%) experienced early catheter replacement. Maintenance of anticoagulants/antiplatelets (AC/AP) therapy at surgery (p=0.001), indwelling urinary catheter (p=0.02) and the presence of BWM (p=0.001) were more frequently reported in patients needing postoperative re-catheterization. Intraoperative complications (p=0.02) and median lasing time (p=0.02) were significantly higher in this group. At univariate analysis, indwelling urinary catheter (p=0.02), BWM (p=0.01), ongoing AC/AP therapy (p=0.01) and intraoperative complications (p=0.01) were significantly associated with early catheter replacement. At multivariate analysis, indwelling urinary catheter (OR: 1.28; p=0.02), BWM (OR: 2.87; p=0.001), and AC/AP therapy (OR: 2.21; p=0.01) were confirmed as independent predictors of catheter replacement. CONCLUSIONS: In our experience the presence of indwelling urinary catheter before surgery, BWM and the maintenance of AC/AP therapy were shown to be independent predictors of early catheter replacement after HoLEP.

Comparison of holmium laser, bipolar and conventional monopolar transurethral resection of bladder tumour in primary non-muscle invasive bladder cancer.

Objectives: To compare the efficiency and safety profile of conventional monopolar, bipolar plasmakinetic and holmium laser techniques for transurethral resection of bladder tumour. Method: The prospective comparative study was conducted from July 2019 to May 2021 after approval from the ethicsreview committee of Kafrelsheikh University, Egypt, and comprised patients of either gender with primary non muscle invasive bladder cancer who qualified for transurethral resection of bladder tumour. The patients were stratified into low-risk group A, intermediate risk group B and high-risk group C in accordance with the guidelines of the European Association of Urology. Comprehensive cystoscopy and panendoscopy were done in all cases. Once panendoscopy was done, tumour resection was performed with monopolar resectoscope in group A, plasmakinetic resectoscope in group B and holmium laser in group C). Data was collected at preoperative, peroperative, postoperative and follow-up stages. Data was analysed using SPSS 21. RESULTS: Of the 84 patients, 67(79.76%) were males and 17(20.23%) were females. There were 27(32.14%) patients in group A; 21(77.8%) males and 6(22.2%) females withy mean age 60.63±11.76 years. Group B had 32(38%) patients; 26(81.2%) males and 6(18.8%) females with mean age 65.34±7.55 years. Group C had 25(29.76%) patients; 20(80%) males and 5(20%) females with mean age 59.48±12.6 years. The mean follow-up period was 12.97±2.70 months in group A, 12.81±2.75 monthsin group B and 13.48±3.3 monthsin group C. Visualised complete resection was done in 23(85.8%) group A patients, 29(90.6%) group B patients and 24(96%) group C patients(p=0.018). Visualised complete resection, tumour multiplicity, tumour size, catheter duration, and hospital stay were significant predictors (p<0.05). Survival analysis showed 26(96.3%), 30(93.75%) and 25(100%) cases in groups A, B and C, respectively. CONCLUSIONS: Bipolar plasmakinetic and holmium laser techniques were found to be more effective and safer than the conventional monopolar technique for transurethral resection of bladder tumour in patients with primary non-muscle invasive bladder cancer.

Mapping Atrial Fibrillation After Surgical Therapy to Guide Endocardial Ablation.

BACKGROUND: Surgical ablation for atrial fibrillation (AF) can be effective, yet has mixed results. It is unclear which endocardial lesions delivered as part of hybrid therapy' will best augment surgical lesion sets in individual patients. We addressed this question by systematically mapping AF endocardially after surgical ablation and relating findings to early recurrence, then performing tailored endocardial ablation as part of hybrid therapy. METHODS: We studied 81 consecutive patients undergoing epicardial surgical ablation (stage 1 hybrid), of whom 64 proceeded to endocardial catheter mapping and ablation (stage 2). Stage 2 comprised high-density mapping of pulmonary vein (PV) or posterior wall (PW) reconnections, low-voltage zones (LVZs), and potential localized AF drivers. We related findings to postsurgical recurrence of AF. RESULTS: Mapping at stage 2 revealed PW isolation reconnection in 59.4%, PV isolation reconnection in 28.1%, and LVZ in 42.2% of patients. Postsurgical recurrence of AF occurred in 36 patients (56.3%), particularly those with long-standing persistent AF (P=0.017), but had no relationship to reconnection of PVs (P=0.53) or PW isolation (P=0.75) when compared with those without postsurgical recurrence of AF. LVZs were more common in patients with postsurgical recurrence of AF (P=0.002), long-standing persistent AF (P=0.002), advanced age (P=0.03), and elevated CHA2DS2-VASc (P=0.046). AF mapping revealed 4.4±2.7 localized focal/rotational sites near and also remote from PV or PW reconnection. After ablation at patient-specific targets, arrhythmia freedom at 1 year was 81.0% including and 73.0% excluding previously ineffective antiarrhythmic medications. CONCLUSIONS: After surgical ablation, AF may recur by several modes particularly related to localized mechanisms near low voltage zones, recovery of posterior wall or pulmonary vein isolation, or other sustaining mechanisms. LVZs are more common in patients at high clinical risk for recurrence. Patient-specific targeting of these mechanisms yields excellent long-term outcomes from hybrid ablation.

Dual-chambered venous access port as alternative access for extracorporeal apheresis therapy.

PURPOSE: To evaluate the use of a dual-chambered venous access port for extracorporeal apheresis therapy. METHODS: This was a single-center retrospective analysis of all patients who received a dual-chambered venous access port for apheresis therapy over a 36-month period. Clinical success was defined as successful completion of at least one round of apheresis via the venous access port. Major complications were defined as any event requiring elevation of patient care and/or venous access port removal or repositioning. Minor complications were defined as venous access port issues resolved with clinical intervention. RESULTS: Forty-four patients had a venous access port placed at the time of this study. Patients underwent red cell exchange (n = 33), therapeutic plasma exchange (n = 6) or extracorporeal photopheresis (n = 5). Forty (90%) patients had autoimmune diseases and four (10%) had neoplastic processes. Clinical success was achieved in 42 (95.5%) patients. Average venous access port dwell time was 632 days (range = 42-1191 days). All therapies through the venous access ports were well tolerated and no patients reported pain or discomfort. Major complications were seen in nine (20.5%) patients-the majority (n = 7) of which were due to venous access port malfunction-and resolved with catheter revision. One (2.27%) major complication involved an infected venous access port, and one involved a large hematoma at the venous access port site. Minor complications were seen in eight (18.2%) patients, where simple flushing of the catheter with saline or tissue plasminogen activator resolved the issue. CONCLUSION: The dual-chambered venous access port was successfully used for sustained blood flow in apheresis therapy with a moderate, yet correctable complication rate.

Optical Mapping-Validated Machine Learning Improves Atrial Fibrillation Driver Detection by Multi-Electrode Mapping.

BACKGROUND: Atrial fibrillation (AF) can be maintained by localized intramural reentrant drivers. However, AF driver detection by clinical surface-only multielectrode mapping (MEM) has relied on subjective interpretation of activation maps. We hypothesized that application of machine learning to electrogram frequency spectra may accurately automate driver detection by MEM and add some objectivity to the interpretation of MEM findings. METHODS: Temporally and spatially stable single AF drivers were mapped simultaneously in explanted human atria (n=11) by subsurface near-infrared optical mapping (NIOM; 0.3 mm2 resolution) and 64-electrode MEM (higher density or lower density with 3 and 9 mm2 resolution, respectively). Unipolar MEM and NIOM recordings were processed by Fourier transform analysis into 28 407 total Fourier spectra. Thirty-five features for machine learning were extracted from each Fourier spectrum. RESULTS: Targeted driver ablation and NIOM activation maps efficiently defined the center and periphery of AF driver preferential tracks and provided validated annotations for driver versus nondriver electrodes in MEM arrays. Compared with analysis of single electrogram frequency features, averaging the features from each of the 8 neighboring electrodes, significantly improved classification of AF driver electrograms. The classification metrics increased when less strict annotation, including driver periphery electrodes, were added to driver center annotation. Notably, f1-score for the binary classification of higher-density catheter data set was significantly higher than that of lower-density catheter (0.81±0.02 versus 0.66±0.04, P<0.05). The trained algorithm correctly highlighted 86% of driver regions with higher density but only 80% with lower-density MEM arrays (81% for lower-density+higher-density arrays together). CONCLUSIONS: The machine learning model pretrained on Fourier spectrum features allows efficient classification of electrograms recordings as AF driver or nondriver compared with the NIOM gold-standard. Future application of NIOM-validated machine learning approach may improve the accuracy of AF driver detection for targeted ablation treatment in patients.

Focal Pulsed Field Ablation for Pulmonary Vein Isolation and Linear Atrial Lesions: A Preclinical Assessment of Safety and Durability.

BACKGROUND: A novel ablation and mapping system can toggle between delivering biphasic pulsed field (PF) and radiofrequency energy from a 9-mm lattice-tip catheter. We assessed the preclinical feasibility and safety of (1) focal PF-based thoracic vein isolation and linear ablation, (2) combined PF and radiofrequency focal ablation, and (3) PF delivered directly atop the esophagus. METHODS: Two cohorts of 6 swine were treated with pulsed fields at low dose (PFLD) and high dose (PFHD) and followed for 4 and 2 weeks, respectively, to isolate 25 thoracic veins and create 5 right atrial (PFLD), 6 mitral (PFHD), and 6 roof lines (radiofrequency+PFHD). Baseline and follow-up voltage mapping, venous potentials, ostial diameters, and phrenic nerve viability were assessed. PFHD and radiofrequency lesions were delivered in 4 and 1 swine from the inferior vena cava onto a forcefully deviated esophagus. All tissues were submitted for histopathology. RESULTS: Hundred percent of thoracic veins (25 of 25) were successfully isolated with 12.4±3.6 applications/vein with mean PF times of <90 seconds/vein. Durable isolation improved from 61.5% PFLD to 100% with PFHD (P=0.04), and all linear lesions were successfully completed without incurring venous stenoses or phrenic injury. PFHD sections had higher transmurality rates than PFLD (98.3% versus 88.1%; P=0.03) despite greater mean thickness (2.5 versus 1.3 mm; P<0.001). PF lesions demonstrated homogenous fibrosis without epicardial fat, nerve, or vessel involvement. In comparison, radiofrequency+PFHD sections revealed similar transmurality but expectedly more necrosis, inflammation, and epicardial fat, nerve, and vessel involvement. Significant ablation-related esophageal necrosis, inflammation, and fibrosis were seen in all radiofrequency sections, as compared with no PF sections. CONCLUSIONS: The lattice-tip catheter can deliver focal PF to durably isolate veins and create linear lesions with excellent transmurality and without complications. The PF lesions did not damage the phrenic nerve, vessels, and the esophagus.

Effects of early detection of peritoneal catheter migration on clinical outcomes: 15-years experiences from a single centre.

AIM: Catheter migration is an important cause of catheter malfunction in peritoneal dialysis (PD). The purpose of this study was to investigate the effect of early detection of catheter migration on clinical outcomes. METHODS: A retrospective review of 135 consecutive patients initiating PD immediately following catheter insertion from 2002 to 2017 was undertaken. In order to detect catheter migration without malfunction early, serial abdominal-pelvic radiographic examinations were performed according to a predefined protocol. Conservative management with rigorous catharsis was undertaken to correct catheter migration. A Kaplan-Meier method was used to calculate survival rate. RESULTS: Mean follow-up period was 42.8 ± 34.9 months. Catheter migration occurred in 62.4%. Among them, 85.9% occurred within the first 2 weeks after catheter insertion. There were no significant associations between catheter migration and variables such as gender, obesity, DM and type of catheter. Success rate of conservative management with rigorous catharsis was 91.1%. Catheter survival at 1 and 5 years were 91.5% and 64.6% in the migration group and 81.2% and 69.9% in the non-migration group, respectively (Log-rank test, P = 0.915). Patient survival at 1 and 5 years were 96.8% and 85.8% in the migration group and 91.9% and 82.3% in the non-migration group, respectively (P = 0.792). CONCLUSION: Early detection of PD catheter migration allowed the migrated tip to be easily corrected with conservative management. Once the migrated catheter tip was restored, catheter migration itself did not affect catheter survival. These findings suggest that early detection and correction of catheter migration is important for improving clinical outcomes.

Prevenção da infeção associada ao cateter venoso central na pessoa em situação crítica: intervenção de enfermagem especializada / Prevention of central venous catheter-associated infection in critically ill people: specialized nursing intervention

O presente relatório pretende demonstrar, de modo crítico e reflexivo, as atividades realizadas, bem como o percurso de aquisição de competências que visam a atribuição do grau de mestre em Enfermagem na área de especialização Pessoa em Situação Crítica. Os crescentes avanços na área da emergência oncológica, aliados ao desenvolvimento científico-tecnológico verificado, acarretam inúmeros desafios para o enfermeiro, nomeadamente situações de grande complexidade que exigem respostas eficazes, de forma global e holística, às necessidades da pessoa em situação crítica e sua família. A pessoa com doença hemato-oncológica apresenta uma vulnerabilidade e instabilidade física e emocional acrescidas, decorrentes da doença, complexidade de tratamentos e procedimentos invasivos, porque estão mais suscetíveis a processos infeciosos e desenvolvimento de sépsis, ameaçando a integridade de um ou mais órgãos vitais, tornam-se por isso pessoa em situação crítica. O cateter venoso central apresenta-se como ferramenta essencial na prestação de cuidados a esta pessoa, quer pela possibilidade de monitorização hemodinâmica, quer pela capacidade de administração rápida de terapêutica de life saving. Todavia a sua utilização não está isenta de riscos, nomeadamente, a exposição do doente a infeções nosocomiais da corrente sanguínea. Pretende salientar-se a intervenção especializada do enfermeiro como uma estratégia eficaz para prevenir a infeção associada ao cateter venoso central, naquela pessoa, associando a perspetiva transformativa de ambiente e a sua influência no desenvolvimento da pessoa e família (Teoria Ambientalista de Florence Nightingale), com a ação de cuidar enquanto elemento facilitador do processo de transição vivenciado pela pessoa em situação crítica e família no momento de instabilidade (Teoria das Transições de Afaf Meleis).

This report aims at presenting, in a critical and reflective manner, the conducted activities and the path followed to acquire competencies, which lead to the attribution of the master's degree in Nursing with a specialization in Critical Patients. The increasing advances in the area of oncological emergency, combined with scientific and technological developments, create numerous challenges for the nurse. These include situations of great complexity that require effective responses, both globally and holistically, to the needs of the critically ill individual and his/her family. Patients who suffer from hemato-oncological diseases present a greater vulnerability, as well as an increased physical and emotional instability. This is a consequence of the experienced condition, coupled with the complexity of invasive treatments and procedures. These patients are more susceptible to infections and to the development of sepsis, which might threaten the integrity of one or more vital organs, leading to critical situations. While providing care to such individuals, the central venous catheter is an essential tool, due to the possibility of hemodynamic monitoring and of rapidly administrating life-saving therapeutics. However, its use poses some risks, namely the patient's exposure to nosocomial infections affecting the bloodstream. The present work intends to emphasize the nurse's specialized intervention as an effective strategy to prevent infections associated with central venous catheters in these individuals. To achieve this, it combines two points of view: 1) a transformative perspective regarding the environment and its influence on the development of individuals and families (Florence Nightingale's Environmental Theory); 2) the provision of care seen as a facilitator of the transition process experienced by the critically ill patient and his/her family, during the period of instability (Afaf Meleis' Transitions Theory).

Evaluation of pain and catheter-related bladder discomfort relative to balloon volumes of indwelling urinary catheters: A prospective study.

PURPOSE: To evaluate patients' tolerance to indwelling urinary catheters (IUCs) before and after reducing their balloon volumes. IUCs are a source of discomfort or pain. MATERIALS AND METHODS: All consecutive patients hospitalized in our department with IUCs were included during the study period with some exclusion. Each patient was his/her own control before and two hours after reduction of the balloon volume (RBV) by half using two types of assessments, a visual analog scale for pain and a catheter-related bladder discomfort (CRBD) symptom questionnaire. RESULTS: Forty-nine patients were included in our study that completed the assessments. The mean scores for pain before and after RBVs were 2.80 and 2.02, respectively. The difference was significant (p<0.05). The mean grades of the CRBD before and after RBVs were 1.02 and 0.75, respectively. The difference was significant (p<0.05). CONCLUSIONS: A 50% RBV has shown a significant amelioration in tolerating the catheter.

Controversies in the management of vesicovaginal fistula.

Achieving 100% closure and continence rate in the management of vesicovaginal fistulas remains a challenge. There is still debate about several aspects of the care including the following.

Characteristics of Scar-Related Ventricular Tachycardia Circuits Using Ultra-High-Density Mapping: A Multi-Center Study.

BACKGROUND: Ventricular tachycardia (VT) with structural heart disease is dependent on reentry within scar regions. We set out to assess the VT circuit in greater detail than has hitherto been possible, using ultra-high-density mapping. METHODS: All ultra-high-density mapping guided VT ablation cases from 6 high-volume European centers were assessed. Maps were analyzed offline to generate activation maps of tachycardia circuits. Topography, conduction velocity, and voltage of the VT circuit were analyzed in complete maps. RESULTS: Thirty-six tachycardias in 31 patients were identified, 29 male and 27 ischemic. VT circuits and isthmuses were complex, 11 were single loop and 25 double loop; 3 had 2 entrances, 5 had 2 exits, and 15 had dead ends of activation. Isthmuses were defined by barriers, which included anatomic obstacles, lines of complete block, and slow conduction (in 27/36 isthmuses). Median conduction velocity was 0.08 m/s in entrance zones, 0.29 m/s in isthmus regions ( P<0.001), and 0.11 m/s in exit regions ( P=0.002). Median local voltage in the isthmus was 0.12 mV during tachycardia and 0.06 mV in paced/sinus rhythm. Two circuits were identifiable in 5 patients. The median timing of activation was 16% of diastole in entrances, 47% in the mid isthmus, and 77% in exits. CONCLUSIONS: VT circuits identified were complex, some of them having multiple entrances, exits, and dead ends. The barriers to conduction in the isthmus seem to be partly functional in 75% of circuits. Conduction velocity in the VT isthmus slowed at isthmus entrances and exits when compared with the mid isthmus. Isthmus voltage is often higher in VT than in sinus or paced rhythms.