Coordinated dispersal and pre-isthmian assembly of the Central American ichthyofauna

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo clínico randomizado e duplo cego comparando dois métodos de escleroterapia para veias reticulares e telangiectasias em membros inferiores

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Morphological Alterations in Newly Born Dentate Gyrus Granule Cells That Emerge after Status Epilepticus Contribute to Make Them Less Excitable

Computer simulations of external current stimulations of dentate gyrus granule cells of rats with Status Epilepticus induced by pilocarpine and control rats were used to evaluate whether morphological differences alone between these cells have an impact on their electrophysiological behavior. The cell models were constructed using morphological information from tridimensional reconstructions with Neurolucida software. To evaluate the effect of morphology differences alone, ion channel conductances, densities and distributions over the dendritic trees of dentate gyrus granule cells were the same for all models. External simulated currents were injected in randomly chosen dendrites belonging to one of three different areas of dentate gyrus granule cell molecular layer: inner molecular layer, medial molecular layer and outer molecular layer. Somatic membrane potentials were recorded to determine firing frequencies and inter-spike intervals. The results show that morphologically altered granule cells from pilocarpine-induced epileptic rats are less excitable than control cells, especially when they are stimulated in the inner molecular layer, which is the target area for mossy fibers that sprout after pilocarpine-induced cell degeneration. This suggests that morphological alterations may act as a protective mechanism to allow dentate gyrus granule cells to cope with the increase of stimulation caused by mossy fiber sprouting.

Biomeccanica del servizio e del diritto nel tennis: confronto fra atleti di livello di gioco differente

Il tennis è uno sport molto diffuso che negli ultimi trent’anni ha subito molti cambiamenti. Con l’avvento di nuovi materiali più leggeri e maneggevoli la velocità della palla è aumentata notevolmente, rendendo così necessario una modifica a livello tecnico dei colpi fondamentali. Dalla ricerca bibliografica sono emerse interessanti indicazioni su angoli e posizioni corporee ideali da mantenere durante le varie fasi dei colpi, confrontando i giocatori di altissimo livello. Non vi sono invece indicazioni per i maestri di tennis su quali siano i parametri più importanti da allenare a seconda del livello di gioco del proprio atleta. Lo scopo di questa tesi è quello di individuare quali siano le variabili tecniche che influenzano i colpi del diritto e del servizio confrontando atleti di genere differente, giocatori di livello di gioco diverso (esperti, intermedi, principianti) e dopo un anno di attività programmata. Confrontando giocatori adulti di genere diverso, è emerso che le principali differenze sono legate alle variabili di prestazione (velocità della palla e della racchetta) per entrambi i colpi. Questi dati sono simili a quelli riscontrati nel test del lancio della palla, un gesto non influenzato dalla tecnica del colpo. Le differenze tecniche di genere sono poco rilevanti ed attribuibili alla diversa interpretazione dei soggetti. Nel confronto di atleti di vario livello di gioco le variabili di prestazione presentano evidenti differenze, che possono essere messe in relazione con alcune differenze tecniche rilevate nei gesti specifici. Nel servizio i principianti tendono a direzionare l’arto superiore dominante verso la zona bersaglio, abducendo maggiormente la spalla ed avendo il centro della racchetta più a destra rispetto al polso. Inoltre, effettuano un caricamento minore degli arti inferiori, del tronco e del gomito. Per quanto riguarda il diritto si possono evidenziare queste differenze: l’arto superiore è sempre maggiormente esteso per il gruppo dei principianti; il tronco, nei giocatori più abili viene utilizzato in maniera più marcata, durante la fase di caricamento, in movimenti di torsione e di inclinazione laterale. Gli altri due gruppi hanno maggior difficoltà nell’eseguire queste azioni preparatorie, in particolare gli atleti principianti. Dopo un anno di attività programmata sono stati evidenziati miglioramenti prestativi. Anche dal punto di vista tecnico sono state notate delle differenze che possono spiegare il miglioramento della performance nei colpi. Nel servizio l’arto superiore si estende maggiormente per colpire la palla più in alto possibile. Nel diritto sono da sottolineare soprattutto i miglioramenti dei movimenti del tronco in torsione ed in inclinazione laterale. Quindi l’atleta si avvicina progressivamente ad un’esecuzione tecnica corretta. In conclusione, dal punto di vista tecnico non sono state rilevate grosse differenze tra i due generi che possano spiegare le differenze di performance. Perciò questa è legata più ad un fattore di forza che dovrà essere allenata con un programma specifico. Nel confronto fra i vari livelli di gioco e gli effetti di un anno di pratica si possono individuare variabili tecniche che mostrano differenze significative tra i gruppi sperimentali. Gli evoluti utilizzano tutto il corpo per effettuare dei colpi più potenti, utilizzando in maniera tecnicamente più valida gli arti inferiori, il tronco e l’arto superiore. I principianti utilizzano prevalentemente l’arto superiore con contributi meno evidenti degli altri segmenti. Dopo un anno di attività i soggetti esaminati hanno dimostrato di saper utilizzare meglio il tronco e l’arto superiore e ciò può spiegare il miglioramento della performance. Si può ipotizzare che, per il corretto utilizzo degli arti inferiori, sia necessario un tempo più lungo di apprendimento oppure un allenamento più specifico.

Sistemi riconfigurabili a basso consumo per applicazioni di monitoraggio distribuito

The term Ambient Intelligence (AmI) refers to a vision on the future of the information society where smart, electronic environment are sensitive and responsive to the presence of people and their activities (Context awareness). In an ambient intelligence world, devices work in concert to support people in carrying out their everyday life activities, tasks and rituals in an easy, natural way using information and intelligence that is hidden in the network connecting these devices. This promotes the creation of pervasive environments improving the quality of life of the occupants and enhancing the human experience. AmI stems from the convergence of three key technologies: ubiquitous computing, ubiquitous communication and natural interfaces. Ambient intelligent systems are heterogeneous and require an excellent cooperation between several hardware/software technologies and disciplines, including signal processing, networking and protocols, embedded systems, information management, and distributed algorithms. Since a large amount of fixed and mobile sensors embedded is deployed into the environment, the Wireless Sensor Networks is one of the most relevant enabling technologies for AmI. WSN are complex systems made up of a number of sensor nodes which can be deployed in a target area to sense physical phenomena and communicate with other nodes and base stations. These simple devices typically embed a low power computational unit (microcontrollers, FPGAs etc.), a wireless communication unit, one or more sensors and a some form of energy supply (either batteries or energy scavenger modules). WNS promises of revolutionizing the interactions between the real physical worlds and human beings. Low-cost, low-computational power, low energy consumption and small size are characteristics that must be taken into consideration when designing and dealing with WSNs. To fully exploit the potential of distributed sensing approaches, a set of challengesmust be addressed. Sensor nodes are inherently resource-constrained systems with very low power consumption and small size requirements which enables than to reduce the interference on the physical phenomena sensed and to allow easy and low-cost deployment. They have limited processing speed,storage capacity and communication bandwidth that must be efficiently used to increase the degree of local ”understanding” of the observed phenomena. A particular case of sensor nodes are video sensors. This topic holds strong interest for a wide range of contexts such as military, security, robotics and most recently consumer applications. Vision sensors are extremely effective for medium to long-range sensing because vision provides rich information to human operators. However, image sensors generate a huge amount of data, whichmust be heavily processed before it is transmitted due to the scarce bandwidth capability of radio interfaces. In particular, in video-surveillance, it has been shown that source-side compression is mandatory due to limited bandwidth and delay constraints. Moreover, there is an ample opportunity for performing higher-level processing functions, such as object recognition that has the potential to drastically reduce the required bandwidth (e.g. by transmitting compressed images only when something ‘interesting‘ is detected). The energy cost of image processing must however be carefully minimized. Imaging could play and plays an important role in sensing devices for ambient intelligence. Computer vision can for instance be used for recognising persons and objects and recognising behaviour such as illness and rioting. Having a wireless camera as a camera mote opens the way for distributed scene analysis. More eyes see more than one and a camera system that can observe a scene from multiple directions would be able to overcome occlusion problems and could describe objects in their true 3D appearance. In real-time, these approaches are a recently opened field of research. In this thesis we pay attention to the realities of hardware/software technologies and the design needed to realize systems for distributed monitoring, attempting to propose solutions on open issues and filling the gap between AmI scenarios and hardware reality. The physical implementation of an individual wireless node is constrained by three important metrics which are outlined below. Despite that the design of the sensor network and its sensor nodes is strictly application dependent, a number of constraints should almost always be considered. Among them: • Small form factor to reduce nodes intrusiveness. • Low power consumption to reduce battery size and to extend nodes lifetime. • Low cost for a widespread diffusion. These limitations typically result in the adoption of low power, low cost devices such as low powermicrocontrollers with few kilobytes of RAMand tenth of kilobytes of program memory with whomonly simple data processing algorithms can be implemented. However the overall computational power of the WNS can be very large since the network presents a high degree of parallelism that can be exploited through the adoption of ad-hoc techniques. Furthermore through the fusion of information from the dense mesh of sensors even complex phenomena can be monitored. In this dissertation we present our results in building several AmI applications suitable for a WSN implementation. The work can be divided into two main areas:Low Power Video Sensor Node and Video Processing Alghoritm and Multimodal Surveillance . Low Power Video Sensor Nodes and Video Processing Alghoritms In comparison to scalar sensors, such as temperature, pressure, humidity, velocity, and acceleration sensors, vision sensors generate much higher bandwidth data due to the two-dimensional nature of their pixel array. We have tackled all the constraints listed above and have proposed solutions to overcome the current WSNlimits for Video sensor node. We have designed and developed wireless video sensor nodes focusing on the small size and the flexibility of reuse in different applications. The video nodes target a different design point: the portability (on-board power supply, wireless communication), a scanty power budget (500mW),while still providing a prominent level of intelligence, namely sophisticated classification algorithmand high level of reconfigurability. We developed two different video sensor node: The device architecture of the first one is based on a low-cost low-power FPGA+microcontroller system-on-chip. The second one is based on ARM9 processor. Both systems designed within the above mentioned power envelope could operate in a continuous fashion with Li-Polymer battery pack and solar panel. Novel low power low cost video sensor nodes which, in contrast to sensors that just watch the world, are capable of comprehending the perceived information in order to interpret it locally, are presented. Featuring such intelligence, these nodes would be able to cope with such tasks as recognition of unattended bags in airports, persons carrying potentially dangerous objects, etc.,which normally require a human operator. Vision algorithms for object detection, acquisition like human detection with Support Vector Machine (SVM) classification and abandoned/removed object detection are implemented, described and illustrated on real world data. Multimodal surveillance: In several setup the use of wired video cameras may not be possible. For this reason building an energy efficient wireless vision network for monitoring and surveillance is one of the major efforts in the sensor network community. Energy efficiency for wireless smart camera networks is one of the major efforts in distributed monitoring and surveillance community. For this reason, building an energy efficient wireless vision network for monitoring and surveillance is one of the major efforts in the sensor network community. The Pyroelectric Infra-Red (PIR) sensors have been used to extend the lifetime of a solar-powered video sensor node by providing an energy level dependent trigger to the video camera and the wireless module. Such approach has shown to be able to extend node lifetime and possibly result in continuous operation of the node.Being low-cost, passive (thus low-power) and presenting a limited form factor, PIR sensors are well suited for WSN applications. Moreover techniques to have aggressive power management policies are essential for achieving long-termoperating on standalone distributed cameras needed to improve the power consumption. We have used an adaptive controller like Model Predictive Control (MPC) to help the system to improve the performances outperforming naive power management policies.

Ricerche di campo per lo sviluppo della tecnologia del maschio sterile nella lotta ad Aedes albopictus (Skuse)

Aedes albopictus (Skuse), comunemente detta Zanzara Tigre, ha invaso, negli ultimi anni, molti paesi, soprattutto in modo passivo attraverso il commercio di pneumatici usati. Questa specie è particolarmente adatta all'applicazione della tecnica dell'insetto sterile (SIT), basata su allevamento massale, sterilizzazione e rilascio in campo di un gran numero di maschi della specie vettrice. I maschi sterili rilasciati devono essere in grado di volare, di disperdersi sul territorio, di sopravvivere, di essere sessualmente attivi abbastanza a lungo per coprire il tempo tra una fase di rilascio e la successiva, di individuare le femmine vergini selvatiche e competere con successo per l'accoppiamento con i maschi selvatici. La dispersione e la sopravvivenza dei maschi di Ae. albopictus allevati in laboratorio, sono state studiate mediante tecniche di marcatura, rilascio e ricattura. Le catture sono state eseguite da tecnici specializzati, in un raggio di 350 m dal sito di rilascio. Gli esperimenti condotti hanno dimostrato che i maschi sono in grado di disperdersi, dal sito di rilascio, per circa 200 m ma la loro longevità in campo è fortemente dipendente dalle condizioni climatiche. In studi di semi-campo e di campo è stato valutato uno speciale dispositivo progettato per essere incluso nella stazione di rilascio dei maschi in grado di fornire loro fonti energetiche per migliorarne le prestazioni. I risultati ottenuti sono stati positivi. Studi di competitività sono stati condotti in tunnel costruiti in un ambiente naturale al fine di validare un protocollo per studi sulla competitività dei maschi in questo modello sperimentale. Maschi irraggiati mediante l'applicazione di raggi gamma alla dose di 30 Gy sono stati messi in competizione con maschi fertili per l'accoppiamento con femmine vergini con diversi rapporti. I risultati ottenuti hanno dimostrato le buone prestazioni e l'affidabilità di questo modello sperimentale rimanendo però irrisolto il problema dell’elevata variabilità.

Untersuchung der Auswirkungen verschiedener Variationsbereiche des differenziellen Lernens und Lehrens im weiten Sinn auf ausgewählte technische Grundfertigkeiten im Hallenhockey

Die Frage wie großmotorische Bewegungen gelernt werden beschäftigt nicht nur Sportler, Trainer und Sportlehrer sondern auch Ärzte und Physiotherapeuten. Die sportwissenschaftlichen Teildisziplinen Bewegungs- und Trainingswissenschaft versuchen diese Frage sowohl im Sinne der Grundlagenforschung (Wie funktioniert Bewegungslernen?) als auch hinsichtlich der praktischen Konsequenzen (Wie lehrt man Bewegungen?) zu beantworten. Innerhalb dieser Themenfelder existieren Modelle, die Bewegungslernen als gezielte und extern unterstützte Ausbildung zentralnervöser Bewegungsprogramme verstehen und solche, die Lernen als Selbstorganisationsprozess interpretieren. Letzteren ist das Differenzielle Lernen und Lehren (Schöllhorn, 1999) zuzuordnen, das die Notwendigkeit betont, Bewegungen durch die Steigerung der Variationen während der Aneignungsphase zu lernen und zu lehren. Durch eine Vielzahl an Variationen, so die Modellannahme, findet der Lernende ohne externe Vorgaben selbstorganisiert ein individuelles situatives Optimum. Die vorliegende Arbeit untersucht, welchen Einfluss Variationen verschiedener Art und Größe auf die Lern- und Aneignungsleistung großmotorischer Bewegungen haben und in wie fern personenübergreifende Optima existieren. In zwei Experimenten wird der Einfluss von räumlichen (Bewegungsausführung, Bewegungsergebnis) und zeitlichen Variationen (zeitliche Verteilung der Trainingsreize) auf die Aneignungs- und Lernleistung großmotorischer sportlicher Bewegungen am Beispiel zweier technischer Grundfertigkeiten des Hallenhockeys untersucht. Die Ergebnisse der Experimente stützen die bisherige Befundlage zum Differenziellen Lernen und Lehren, wonach eine Zunahme an Variation in der Aneignungsphase zu größeren Aneignungs- und Lernleistungen führt. Zusätzlich wird die Annahme bestätigt, dass ein Zusammenhang von Variationsbereich und Lernrate in Form eines Optimaltrends vorliegt. Neu sind die Hinweise auf die Dynamik von motorischen Lernprozessen (Experiment 1). Hier scheinen individuelle Faktoren (z. B. die Lernbiografie) als auch die Phase im Lernprozess (Aneignung, Lernen) Einfluss zu haben auf den Umfang und die Struktur eines für die optimale Adaptation notwendigen Variationsbereichs. Darüber hinaus weisen die Befunde auf verschiedene Aneignungs- und Lerneffekte aufgrund alleiniger Variation der zeitlichen Verteilung bei ansonsten gleichen Trainingsreizen hin (Experiment 2). Für zukünftige Forschungsarbeiten zum Erlernen großmotorischer Bewegungen und für die sportliche Praxis dürfte es daher erkenntnisreich sein, die Historie der intrinsischen Dynamik der lernenden Systeme stärker zu berücksichtigen. Neben Fragestellungen für die Grundlagenforschung zum (Bewegungs-)Lernen ließen sich hieraus unmittelbar praxisrelevante Erkenntnisse darüber ableiten, wie Bewegungslernprozesse mittels verschiedener Variationsbereiche strukturiert und gesteuert werden könnten.

Integrated Geophysical Investigation of the St. James Fault Complex: A Case Study

We noninvasively detected the characteristics and location of a regional fault in an area of poor bedrock exposure complicated by karst weathering features in the subsurface. Because this regional fault is associated with sinkhole formation, its location is important for hazard avoidance. The bedrock lithologies on either side of the fault trace are similar; hence, we chose an approach that capitalized on the complementary strengths of very low frequency (VLF) electromagnetic, resistivity, and gravity methods. VLF proved most useful as a first-order reconnaissance tool, allowing us to define a narrow target area for further geophysical exploration. Fault-related epikarst was delineated using resistivity. Ultimately, a high-resolution gravity survey and subsequent inverse modeling using the results of the resistivity survey helped to further constrain the location and approximate orientation of the fault. The combined results indicated that the location of the fault trace needed to be adjusted 53 m south of the current published location and was consistent with a north-dipping thrust fault. Additionally, a gravity low south of the fault trace agreed with the location of conductive material from the resistivity and VLF surveys. We interpreted these anomalies to represent enhanced epikarst in the fault footwall. We clearly found that a staged approach involving a progression of methods beginning with a reconnaissance VLF survey, followed by high-resolution gravity and electrical resistivity surveys, can be used to characterize a fault and fault-related karst in an area of poor bedrock surface exposure.

Time-Resolved Ultra–High Resolution Optical Coherence Tomography for Real-Time Monitoring of Selective Retina Therapy

Purpose: Selective retina therapy (SRT) is a novel treatment for retinal pathologies, solely targeting the retinal pigment epithelium (RPE). During SRT, the detection of an immediate tissue reaction is challenging as tissue effects remain limited to intracellular RPE photodisruption. Time-resolved ultra-high axial resolution optical coherence tomography (OCT) is thus evaluated for the monitoring of dynamic optical changes at and around the RPE during SRT. Methods: An experimental OCT system with an ultra-high axial resolution of 1.78 µm was combined with an SRT system and time-resolved OCT M-scans of the target area were recorded from four patients undergoing SRT. OCT scans were analyzed and OCT morphology was correlated with findings in fluorescein angiography, fundus photography and cross-sectional OCT. Results: In cases where the irradiation caused RPE damage proven by fluorescein angiography, the lesions were well discernible in time-resolved OCT images but remained invisible in fundus photography and cross-sectional OCT acquired after treatment. If RPE damage was introduced, all applied SRT pulses led to detectable signal changes in the time-resolved OCT images. The extent of optical signal variation seen in the OCT data appeared to scale with the applied SRT pulse energy. Conclusion: The first clinical results proved that successful SRT irradiation induces detectable changes in the OCT M-scan signal while it remains invisible in conventional ophthalmoscopic imaging. Thus, real-time high-resolution OCT is a promising modality to monitor and analyze tissue effects introduced by selective retina therapy and may be used to guide SRT in an automatic feedback mode.

Cathodal HD-tDCS on the right V5 improves motion perception in humans

Brain lesions in the visual associative cortex are known to impair visual perception, i.e., the capacity to correctly perceive different aspects of the visual world, such as motion, color, or shapes. Visual perception can be influenced by non-invasive brain stimulation such as transcranial direct current stimulation (tDCS). In a recently developed technique called high definition (HD) tDCS, small HD-electrodes are used instead of the sponge electrodes in the conventional approach. This is believed to achieve high focality and precision over the target area. In this paper we tested the effects of cathodal and anodal HD-tDCS over the right V5 on motion and shape perception in a single blind, within-subject, sham controlled, cross-over trial. The purpose of the study was to prove the high focality of the stimulation only over the target area. Twenty one healthy volunteers received 20 min of 2 mA cathodal, anodal and sham stimulation over the right V5 and their performance on a visual test was recorded. The results showed significant improvement in motion perception in the left hemifield after cathodal HD-tDCS, but not in shape perception. Sham and anodal HD-tDCS did not affect performance. The specific effect of influencing performance of visual tasks by modulating the excitability of the neurons in the visual cortex might be explained by the complexity of perceptual information needed for the tasks. This provokes a "noisy" activation state of the encoding neuronal patterns. We speculate that in this case cathodal HD-tDCS may focus the correct perception by decreasing global excitation and thus diminishing the "noise" below threshold.

Physical oceanography during METEOR cruise M60/3 at the Logatchev hydrothermal field in the mid-Atlantic

The R/V METEOR cruise M60/3 took place from January 13 through February 14, 2004. Target area was the Logatchev hydrothermal field situated on the Mid-Atlantic Ridge (MAR) with main spots around 14°45'N and 44°59'W and 14°55'N and 44°55'W. The active Logatchev hydrothermal field lies on a small plateau on the eastern flank of the inner rift valley in 2900 m to 3060 m water depth. It is characterized by sites of active, high-T fluid emanation and sulfide precipitation as well as by inactive sites. CTD data for 17 stations located in the vicinity of the Logatchev hydrothermal field were recorded using a SEABIRD CTD Type 911, mostly for the entire water column. CTD sensors had been calibrated by SEABIRD directly before the cruise; additional calibrations of the data obtained, e.g. by salinometer measurements of selected samples were not accomplished. For most stations, no indication of hydrothermal plumes could be identified within the CTD-profiles. An exception is station M60/3-37-CTD-R for which the S/T plot evidences the intrusion of a component relatively depleted in salinity for the depth area from 2600m to 2700m water depth.

Gridded bathymetry from multibeam echosounder EM120 data of the cruise M72/1 (2007)

Bathymetry based on data recorded during M72-1 between 07.02.2007 and 20.02.2007 in the Black Sea. The main focus of the cruise were gas vents and seeps in the north-western Black Sea below 700 m water depth which is the zone of gas hydrate stability. The main target area was the deep Dnepr Canyon west of the Crimea Peninsula where previous investigations had indicated the occurrence of gas seepage.

Gridded bathymetry from multibeam echosounder EM710 data of the cruise M72/1 (2007)

Bathymetry based on data recorded during M72-1 between 07.02.2007 and 20.02.2007 in the Black Sea. The main focus of the cruise were gas vents and seeps in the north-western Black Sea below 700 m water depth which is the zone of gas hydrate stability. The main target area was the deep Dnepr Canyon west of the Crimea Peninsula where previous investigations had indicated the occurrence of gas seepage.

Evaluation of mission planning strategies of a robotic aerial vehicle for the AIRC international competition

The International Aerial Robotics Competition (IARC) is an important event where teams from universities design flying autonomous vehicles to overcome the last challenges in the field. The goal of the Seventh Mission proposed by the IARC is to guide several mobile ground robots to a target area. The scenario is complex and not determinist due to the random behavior of the ground robots movement. The UAV must select efficient strategies to complete the mission. The goal of this work has been evaluating different alternative mission planning strategies of a UAV for this competition. The Mission Planner component is in charge of taking the UAV decisions. Different strategies have been developed and evaluated for the component, achieving a better performance Mission Planner and valuable knowledge about the mission. For this purpose, it was necessary to develop a simulator to evaluate the different strategies. The simulator was built as an improvement of an existing previous version.

Epicardial Radiofrequency Ablation Failure During Ablation Procedures for Ventricular Arrhythmias: Reasons and Implications for Outcomes.

BACKGROUND Radiofrequency ablation (RFA) from the epicardial space for ventricular arrhythmias is limited or impossible in some cases. Reasons for epicardial ablation failure and the effect on outcome have not been systematically analyzed. METHODS AND RESULTS We assessed reasons for epicardial RFA failure relative to the anatomic target area and the type of heart disease and assessed the effect of failed epicardial RFA on outcome after ablation procedures for ventricular arrhythmias in a large single-center cohort. Epicardial access was attempted during 309 ablation procedures in 277 patients and was achieved in 291 procedures (94%). Unlimited ablation in an identified target region could be performed in 181 cases (59%), limited ablation was possible in 22 cases (7%), and epicardial ablation was deemed not feasible in 88 cases (28%). Reasons for failed or limited ablation were unsuccessful epicardial access (6%), failure to identify an epicardial target (15%), proximity to a coronary artery (13%), proximity to the phrenic nerve (6%), and complications (<1%). Epicardial RFA was impeded in the majority of cases targeting the left ventricular summit region. Acute complications occurred in 9%. The risk for acute ablation failure was 8.3× higher (4.5-15.0; P<0.001) after no or limited epicardial RFA compared with unlimited RFA, and patients with unlimited epicardial RFA had better recurrence-free survival rates (P<0.001). CONCLUSIONS Epicardial RFA for ventricular arrhythmias is often limited even when pericardial access is successful. Variability of success is dependent on the target area, and the presence of factors limiting ablation is associated with worse outcomes.