Woodchip bioreactors for saline leachates denitrification can mitigate agricultural impacts in mediterranean areas: The Campo de Cartagena-Mar Menor environmental issue.

Leachates from intensive agriculture containing high nitrate have been identified as a major cause of the severe eutrophication crisis that impacts Mar Menor (SE Spain), the largest hypersaline coastal lagoon in the Mediterranean basin. A best management practice for removing NO3--N is denitrifying bioreactors. This is the first study to assess the efficiency of citrus woodchips bioreactors in treating agricultural leachates that flow to the Mar Menor via surface discharges. Denitrification capacity, woodchip degradation (by weight loss), formation of potentially harmful compounds, and greenhouse gas (GHG) emissions were assessed. Three bioreactors (6 m × 0.98 m x 1.2 m) filled with citrus woodchips (3 m3 d-1 per bioreactor) through which the untreated ditch water over 1.5 years. Bioreactors were operated at 8 h, 16 h, and 24 h hydraulic residence time respectively, in each bioreactor. The main characteristics of the ditch water were: pH ≈ 7.5-8.0, electrical conductivity ≈ 5-8 dS m-1, dissolved organic carbon ≈6-10 mg L-1, and NO3--N ≈ 22-45 mg L-1. Bioreactors were highly efficient in reducing NO3--N. The average RNO3 in effluents was for the complete experimental period 8 g N m-3 d-1, 10.9 g N m-3 d-1, and 12.6 g N m-3 d-1 for 8, 16 and 24 h residence time, respectively. Nitrate reduction efficiency was modulated by seasonal changes in temperature, with an increasing efficiency in warmer periods (maximum ≈ 85-90% for all hydraulic residence time) and decreasing in colder ones (minimum ≈ 12%, 23% and 41% for hydraulic residence time 8, 16 and 24 h respectively). Woodchips degradation was greatest during the first six months (average ≈ 29% weight loss) in the material above the water level, attributable to aerobic mineralization of the organic carbon, while weight loss was ≈11% in woodchip media continuously below the water level. Dissolved organic carbon, sulfide, ammonium, and soluble phosphorus concentrations in the effluents were mostly low, although some peaks in concentrations occurred. Design consideration must be taken to avoid environmental impacts due to the occasional presence of harmful compounds in the effluents.

Woodchip bioreactors provide sustained denitrification of brine from groundwater desalination plants.

Woodchip bioreactors are widely known as a best management practice to reduce excess nitrate loads that are discharged with agricultural leachates. The aim of this study was to evaluate the performance of citrus woodchip bioreactors for denitrification of brine (electrical conductivity ≈ 17 mS cm-1) from groundwater desalination plants with high nitrate content (NO3--N ≈ 48 mg L-1) in the Campo de Cartagena agricultural watershed, one of the main providers of horticultural products in Europe. The performance was evaluated relative to seasonal changes in temperature, dissolved organic carbon (DOC) provided by woodchips, hydraulic residence time (HRT) and woodchip aging. Bioreactors (capacity 1 m3) operated for 2.5 years (121 weeks) in batch mode (24 h HRT) with three batches per week. Denitrification efficiency was modulated by DOC concentration, temperature, hydraulic residence time and the drying-rewetting cycles. High salinity of brine did not prevent nitrate removal from occurring. The high DOC availability (>25 mg C L-1) during the first ≈48 weeks resulted in high nitrate removal rate (>75%) and nitrate removal efficiency (until ≈ 25 g N m-3 d-1) regardless of temperature. Moreover, the high DOC contents in the effluents during this period may present environmental drawbacks. Denitrification was still high after 2.5 years (reaching ≈9.3 g N m-3 d-1 in week 121), but dependence on warm temperature became more apparent with woodchips aging from week ≈49 onwards. Nitrate removal efficiency was highest on the first weekly batch, immediately after woodchips had been unsaturated for four days. It was attributable to a flush of DOC produced by aerobic microbial metabolism during drying that stimulated denitrification following re-saturation. Hence, alternance of drying-rewetting cycles is an operation practice that increase bioreactors nitrate removal performance.

Darbepoetin inhibits proliferation of hepatic cancer cells in the presence of TGF-ß.

Darbepoetin (DPO), an erythropoietin (EPO) derivative, was licensed in 2002 to treat patients with solid tumors suffering from chemotherapy-dependent anemia, although various tumors express EPO to improve vascularization, thus favoring tumor growth and spreading. Therefore, we wanted to investigate direct effects of DPO on the liver tumor cell lines HepG2, SkHep1, Huh-7, AKN1, HCC-T and HCC-M, as well as on primary human hepatocytes (hHeps). DPO (0-40 ng/ml) did not affect viability of hHeps, HepG2, SkHep1, AKN1, HCC-T and HCC-M cells, as determined by Resazurin conversion. However, Huh-7 cells' viability dose-dependently decreased from 5 ng/ml DPO on. Lack of LDH release into culture medium and negative DNA laddering excluded apoptosis or necrosis as the cause for the reduced Resazurin conversion. In Huh-7 cells, DPO increased the expression of p53. Interestingly, Huh-7 cells showed the highest basal TGF-ß1 expression as compared to the other cell lines. Upon inhibition of TGF-ß1 signaling, DPO no longer reduced viability in Huh-7 cells. On the contrary, co-incubation with TGF-ß1 made the other cell lines responsive to DPO. Summarizing our data, we show that DPO reduces the growth of Huh-7 cells by up-regulation of the tumor-suppressor gene p53. This mechanism seems to be dependent on a strong TGF-ß expression and corresponding signaling in these cells, as other cell lines became responsive to DPO with TGF-ß1 supplementation. The knowledge of this mechanism offers great perspectives for the understanding and treatment of solid liver tumors.

Narrow irregular QRS tachycardia with AV dissociation: what is the mechanism?

A 39-year-old woman with no structural heart disease and frequent episodes of sudden onset palpitations was referred for the electrophysiological study. During the study, a slightly irregular narrow QRS tachycardia with AV dissociation was repeatedly induced and spontaneously terminated. Apparently, irregular cycles and termination of the tachycardia were related to the dissociated sinus rhythm: atrial depolarizations timed when the AV junction was refractory were able to reset the tachycardia, while early atrial depolarizations caused its termination. This observation was enough to diagnose the tachycardia mechanism in our case.

Multiple interatrial electrical connection after heart transplantation.

A 62-year-old woman who underwent heart transplantation 6 years later presented a regular atrial tachycardia. Electrophysiologic evaluation showed an atrial arrhythmia in the recipient atrium with 2:1 conduction to the donor atrium, with a confusing electroanatomical map. With the suspect of alternant conduction through two different breakthroughs, the map was split in two concordant maps, corresponding to two connections that were successfully ablated. Later on, a third connection was detected and therefore ablated.

Mentoring: what to expect from our surgical mentors in Colombia? A Latin American example.

OBJECTIVE: Identifying the scope of surgical mentoring at Pontificia Universidad Javeriana and compare the perceptions of teachers and students to recognize characteristics and competences of such practice and future needs. METHOD: Two surveys were designed to evaluate the existence and importance of mentoring and inquire about the characteristics, qualities and skills expected on mentors. RESULTS: Both groups agree on the importance of having a mentor. 84.2% of teachers consider themselves mentors, however, only 38.6% of students considered them as such. The most relevant quality of the mentor recognized by students was the willingness and ability to teach, while for teachers it was respect. For the students, the most important competence was the ability to explain and teach about the procedures to be performed, while for teachers it was the ability to provide confidence and security. CONCLUSIONS: There is a paradoxical behavior, most students consider they do not have a mentor while most teachers consider to be such. The need to expand the literature regarding mentoring in Colombia specifically in the surgical field was identified.

OBJETIVO: Identificar el alcance del mentoring quirúrgico en la Facultad de Medicina de la Pontificia Universidad Javeriana y comparar las percepciones de docentes y estudiantes, con el fin de reconocer características y competencias de dicha práctica y necesidades a futuro. MÉTODO: Se diseñaron dos encuestas para evaluar la existencia y la importancia del proceso de mentoring e indagar acerca de las características, las cualidades y las competencias esperadas de los mentores. RESULTADOS: Ambos grupos coinciden en la importancia de contar con un mentor. El 84.2% de los docentes consideran ser mentores, pero solo el 38.6% de los estudiantes los consideraron a ellos como tales. Las cualidad más relevantes del mentor reconocidas por los estudiantes fueron la disposición y la habilidad para enseñar, mientras que para los docentes fue el respeto. Para los estudiantes, la competencia más importante fue la capacidad de explicar y enseñar sobre los procedimientos a realizar, mientras que para los docentes fue la capacidad de brindar confianza y seguridad. CONCLUSIONES: Existe un comportamiento paradójico, pues los estudiantes no consideraron contar con un mentor mientras que los docentes sí estimaron serlo. Se identificó la necesidad de ampliar la literatura respecto al mentoring en Colombia, específicamente en el ámbito quirúrgico.

Ablation of Premature Ventricular Complexes Triggering Ventricular Fibrillation in a Patient with Long QT Syndrome.

We describe the case of a patient with long QT syndrome and recurrent ventricular fibrillation, triggered by premature ventricular complexes (PVCs) with a left bundle branch block pattern and inferior axis of the QRS. Activation mapping demonstrated the origin of the PVCs to be in the right ventricular outflow tract. Ventricular fibrillation (VF) was successfully treated by catheter ablation of the triggering PVCs and there has been no recurrence of VF during a follow-up period of 14 months.

Emergency department attendance and reasons for consultation after cryoballoon ablation for pulmonary vein isolation of atrial fibrillation.

INTRODUCTION AND OBJECTIVES: There are few data on emergency visits after cryoballoon-based pulmonary vein isolation. The aim of this study was to quantify emergency department visits during the first 3 months after the procedure and to identify the reasons for consultation, final diagnoses, and the therapeutic approach. METHODS: Observational, retrospective study of 330 consecutive patients undergoing a first cryoballoon-based ablation procedure. Patients were followed up for 90 days after the procedure. We recorded emergency visits, symptoms, electrocardiographic data, and the therapeutic approach. Final diagnoses were classified as rhythm disorder, confirmed complication, possible complication, and unrelated to the procedure or to the arrhythmic disorder. RESULTS: A total of 112 (34%) patients attended the emergency department, 50 (44.6%) for palpitations. Sustained atrial arrhythmias were documented in 44 (39.3%) patients. Among the 29 (25.9%) visits for complications potentially related to the procedure, 5 were confirmed inguinal puncture complications and 10 were classified as unconfirmed possible complications. Forty-one visits were unrelated to the procedure or to the arrhythmic disorder. A total of 21.4% of the visits were due to palpitations requiring no therapeutic action. CONCLUSIONS: A third of the patients attended the emergency department at least once, with the most frequent reason being arrhythmia-related symptoms. Late complications were rare and generally mild. Up to 20% of emergency visits could potentially be avoided by the availability of a teleconsulting system with remote electrocardiogram transmission.

[Healthcare for migrants on the high seas. The case of the operation EUNAVFOR MED "Sophia".] / El caso de la operación EUNAVFOR MED "Sophia".

Since 2015, the Spanish Navy participates in the Operation EUNAVFOR MED Sophia, a naval operation of the European Union against the trafficking of human beings in the Mediterranean in which our ships carry out an important humanitarian work in the rescue and assistance of migrants on the sea. The attention and health care of these migrants lies mainly in the military Health Group and it is based on a series of principles and procedures among which the application of a triage adapted to the special conditions of rescue and assistance on the sea and in the diagnosis and treatment of various pathologies present among migrants. In this context, a series of epidemiological data is provided, especially the most frequent pathologies attended by rescued migrants and emphasizing the importance of adopting a series of measures to prevent the transmission of infectious pathologies that are rare or already eradicated in our country.

Desde 2015, la Armada española participa en la operación EUNAVFOR MED Sophia, una operación naval de la Unión Europea contra el tráfico de seres humanos en el Mediterráneo, en la que nuestros buques realizan una importante labor humanitaria en el rescate y asistencia de migrantes en la mar. La atención y asistencia sanitaria de estos migrantes recae principalmente en el Grupo de Sanidad militar, y se basa en una serie de principios y procedimientos entre los que destacan la aplicación de un triaje adaptado a las especiales condiciones del rescate y asistencia en alta mar, así como en el diagnóstico y tratamiento de diversas patologías presentes entre los migrantes. En este sentido, este trabajo proporciona una serie de datos epidemiológicos, incidiendo en las patologías más frecuentes entre los migrantes rescatados, y destacando la importancia de la adopción de una serie de medidas para prevenir la transmisión de patologías infecciosas poco frecuentes o ya erradicadas en nuestro país.

Bioreactors for brine denitrification produced during polluted groundwater desalination in fertigation areas of SE Spain: batch assays for substrate selection.

Increasing knowledge of nitrate removal using denitrifying bioreactors has illustrated the usefulness of this management practice for treating discharge water from agricultural land uses. The objective of this study was to assess the viability of almond shell, chopped carob, olive bone, and citrus woodchip as carbon media for denitrification of brine with high nitrate load (EC ≈ 20 dS m-1, NO3--N concentration ≈ 65-80 mg NO3--N L-1) in bioreactors. To the authors' knowledge, this is the first test of denitrifying brine using organic wastes as the carbon substrate, and the first use of these carbon media for that purpose. Nitrate removal efficiency and efficiency:cost ratio were considered. The results indicated that the best removal efficiency and cheapest cost were provided by citrus woodchip (3.02 ± 0.15 mg NO3--N m-3 d-1) at a cost of ≈ 6€ m-3, followed by almond shell (1.54 ± 0.20 mg NO3--N m-3 d-1) at a cost of ≈ 19€ m-3. Chopped carob and olive bone showed negligible nitrate removal in the brine; chopped carob generated acidic leachate with extremely high dissolved organic carbon, and olive bone resulted in a highly saline leachate. Of the four media tested, the results of this study indicated that citrus woodchip was the most suitable media for denitrification of the brine.

Spectral analysis of intracardiac electrograms during induced and spontaneous ventricular fibrillation in humans.

AIMS: Very limited data are available on the differences between spontaneous and induced episodes of ventricular fibrillation (VF) in humans. The aim of the study was to compare the spectral characteristics of the electrical signal recorded by an implantable cardioverter defibrillator (ICD) during both types of episodes. METHODS AND RESULTS: Thirteen ICD patients with at least one spontaneous and one induced VF recorded by the device were included in the study. A spectral representation was obtained for the first 3 s of the intracardiac unipolar electrogram during VF. The dominant frequency (f(d)), the peak power at f(d), an organization index (OI), a bandwidth measurement, and an estimate of the correlation with a sinusoidal wave (leakage) were estimated for each episode. The f(d) was higher in induced episodes (4.75 +/- 0.57 vs. 3.95 +/- 0.59 Hz for the spontaneous episodes, P = 0.002), as well as the degree of organization assessed by the OI, bandwidth, and leakage parameters. CONCLUSION: Clinical and induced VF episodes in humans have different spectral characteristics. Changes in the electrophysiological substrate or in the location of the arrhythmia wavefront at onset could play a role to explain the observed differences.

ICD proarrhythmia as a consequence of an interaction with an algorithm to prevent atrial arrhythmias.

An episode of device-related proarrhythmia is reported. Ventricular tachycardia was induced by ventricular pacing in a dual-chamber implantable cardioverter-defibrillator due to an inappropriate interaction of programmed device settings with the atrial preference pacing, an automatic algorithm designed to prevent atrial tachyarrhythmias.

Medium- and long-term outcome after a single second-generation cryoballoon ablation in patients with paroxysmal and persistent atrial fibrillation.

INTRODUCTION AND OBJECTIVES: To report medium- and long-term results following a single second-generation cryoballoon (CB2)-based ablation procedure in patients with paroxysmal (PAF) and persistent (PeAF) atrial fibrillation. METHODS: A retrospective study was performed of consecutive patients undergoing a first CB2-based ablation procedure in a tertiary center. Cryoenergy was applied for 3 min if a time to effect <60 s was documented or 4 min otherwise, with a bonus application in cases of late isolation or suboptimal temperature. Follow-up was obtained from the regional health electronic records system and by telephone or personal interviews. Recurrence was defined as any atrial arrhythmia >30 s beyond a three-month blanking period. The clinical impact of recurrences was classified using a severity score. RESULTS: A total of 172 patients (134 PAF and 38 PeAF) were included, of whom 25 (14.5%) had structural heart disease and 120 (69.7%) had a normal or mildly dilated left atrium. Acute success was achieved in 167 (97.1%). After a median follow-up of 27 (14-41) months, 100 patients (58.1%) remained free of atrial arrhythmias (64.2% for PAF and 36.8% for PeAF, p=0.006). Left atrial size (p=0.05) and clinical presentation as PeAF (p=0.006) were predictors of recurrence. Of patients with recurrences, 11.1% did not require further therapies and an additional 16.7% had good control with antiarrhythmic drugs. CONCLUSIONS: A single CB2 procedure resulted in 58.1% of patients remaining free of atrial arrhythmias at 27-month follow-up. Conservative management was useful in 27.8% of patients with recurrences.

Alternative explanations to the differences of femoral and brachial saline contrast injections for echocardiographic detection of patent foramen ovale.

Patent foramen ovale (PFO) of the interatrial septum is a cardiac foetal remnant, which frequent persistence in adulthood has important implications in a variety of clinical conditions. Echographic diagnosis of PFO is based on detection of interatrial shunt by means of contrast microbubbles identification after venous injection of a first-generation echographic contrast agent. Current recommendations propose venous femoral injection of contrast for enhanced echographic detection of PFO instead of venous brachial administration, as femoral injection has been shown to have higher sensitivity for PFO detection. Inferior vena cava inflow directed toward interatrial septum has been considered the explanation for increased sensitivity of femoral delivery of contrast. In the present paper, it is hypothesised that the main determinants of these differences between injection sites are technical factors related to right atrial contrast opacification and proper transient right atrial pressure rise, rather than intraatrial flow streaming. Effects of inferior vena cava inflow stream, although significant during foetal life, would be negligible after birth. Rationale and evidence, basis for further research, and practical implications leading to a simpler and safer routine technique for echographic detection of PFO are presented and discussed.

Trastornos de estrés agudo: consideraciones a partir de un caso clínico en el ámbito militar / Acute Stress Disorders: Considerations from a clinical case in the military field

Introducción: Se presenta el caso de un militar de 32 años, varón, diagnosticado de trastorno de estrés agudo durante su despliegue en zona de operaciones en Afganistán. La sintomatología que manifestaba el paciente le incapacitaba para el servicio.Objetivo: El objetivo terapéutico es el control de la sintomatología de estrés del paciente y la normalización de su estado psicológico, para conseguir su completa reincorporación al servicio activo.Material y métodos: Diseño de caso único, pre-postratamiento. Para el diagnóstico y medida postratamiento se utilizó el Cuestionario de Adaptación 6RA, el Inventario de Ansiedad Estado-Rasgo y la escala de Síntomas de Estrés Agudo. Se aplicó un programa terapéutico breve compuesto de 7 sesiones y basado en psicoeducación, reestructuración cognitiva, entrenamiento en técnicas de relajación y exposición en vivo.Resultados: La evaluación postratamiento muestra una notable reducción de la sintomatología de estrés agudo. La normalización del estado psicológico del paciente permitió la reincorporación a su puesto, completando el resto de la misión sin novedad.Conclusiones: El presente trabajo pone de manifiesto la efectividad de las psicoterapias breves para el tratamiento de trastornos de estrés en operaciones militares en el exterior, al permitir al militar mantener su operatividad y reincorporarse al servicio lo más rápidamente posible. Las medidas preventivas previas al despliegue son fundamentales para la adaptación del militar.(AU)

Introduction: The case of a 32-year-old military man diagnosed with acute stress disorder during his deployment to the area of ​​operations in Afghanistan is presented. The symptoms manifested by the patient incapacitated him for the service.Objective: The therapeutic objective is to control the patient's stress symptoms and to normalize their psychological condition, to achieve their full return to active duty.Material and Methods: Single case design, pre-post treatment. The instruments used for the diagnosis and post-treatment measure were the Adaptation Questionnaire 6RA, the State-Trait Anxiety Inventory and the Acute Stress Symptoms Scale. A short therapeutic program of 7 sessions was applied, based on psychoeducation, cognitive restructuring, training in relaxation techniques and live exposure.Results: The post-treatment evaluation shows a significant reduction in the symptoms of acute stress. The normalization of the patient's psychological condition allowed him to return to work, completing the rest of the mission without incident.Conclusions: This paper shows the effectiveness of brief psychotherapies for the treatment of stress disorders in military operations abroad. These psychotherapies allow the military to maintain its operability and rejoin the military service as soon as possible. Pre-deployment preventive measures are essential for the military's adaptation.(AU)

Frecuentación y motivos de asistencia en el servicio de urgencias tras la ablación de fibrilación auricular con criobalón / Emergency department attendance and reasons for consultation after cryoballoon ablation for pulmonary vein isolation of atrial fibrillation

Introducción y objetivos Existe poca información sobre la frecuentación a urgencias en las semanas siguientes a un procedimiento de aislamiento de venas pulmonares con criobalón. El objetivo del estudio es cuantificar las visitas a urgencias en los primeros 3 meses tras el procedimiento, evaluando los motivos, el diagnóstico final y la actitud terapéutica. Métodos Estudio observacional retrospectivo sobre 330 pacientes sometidos a un primer procedimiento de crioablación de fibrilación auricular. Se realizó un seguimiento de 90 días tras el procedimiento durante el que se registraron las visitas a urgencias con los síntomas que motivaron la consulta, electrocardiograma, actitud terapéutica y diagnóstico final, clasificado como alteración del ritmo, complicación confirmada, complicación posible y sin relación con el procedimiento ni con el trastorno arrítmico. Resultados Un total de 112 pacientes (34%) consultaron en urgencias, 50 de ellos (44,6%) por palpitaciones. En 44 pacientes (39,3%) se documentó una arritmia auricular sostenida. De las 29 consultas (25,9%) por síntomas potencialmente relacionados con complicaciones del procedimiento, 5 fueron complicaciones confirmadas de la punción inguinal, 10 quedaron con diagnóstico no confirmado de posible complicación y 41 visitas no guardaron relación con el procedimiento. El 21,4% del total de consultas fueron por palpitaciones en las que no se tomó ninguna medida terapéutica. Conclusiones Un tercio de los pacientes consultaron en urgencias al menos 1 vez, y los síntomas arrítmicos fueron el motivo más frecuente. Las complicaciones diferidas del procedimiento son raras y, en general, benignas. La disponibilidad de un sistema de teleconsulta con transmisión del ECG a distancia podría evitar hasta un 20% de los desplazamientos a urgencias. (AU)

Introduction and objectives There are few data on emergency visits after cryoballoon-based pulmonary vein isolation. The aim of this study was to quantify emergency department visits during the first 3 months after the procedure and to identify the reasons for consultation, final diagnoses, and the therapeutic approach. Methods Observational, retrospective study of 330 consecutive patients undergoing a first cryoballoon-based ablation procedure. Patients were followed up for 90 days after the procedure. We recorded emergency visits, symptoms, electrocardiographic data, and the therapeutic approach. Final diagnoses were classified as rhythm disorder, confirmed complication, possible complication, and unrelated to the procedure or to the arrhythmic disorder. Results A total of 112 (34%) patients attended the emergency department, 50 (44.6%) for palpitations. Sustained atrial arrhythmias were documented in 44 (39.3%) patients. Among the 29 (25.9%) visits for complications potentially related to the procedure, 5 were confirmed inguinal puncture complications and 10 were classified as unconfirmed possible complications. Forty-one visits were unrelated to the procedure or to the arrhythmic disorder. A total of 21.4% of the visits were due to palpitations requiring no therapeutic action. Conclusions A third of the patients attended the emergency department at least once, with the most frequent reason being arrhythmia-related symptoms. Late complications were rare and generally mild. Up to 20% of emergency visits could potentially be avoided by the availability of a teleconsulting system with remote electrocardiogram transmission. (AU)

[A probabilistic model of cardiac electrical activity based on a cellular automata system]. / Desarrollo de un modelo probabilístico de la actividad eléctrica cardíaca basado en un autómata celular.

INTRODUCTION AND OBJECTIVES: Mathematical models of cardiac electrical activity may help to elucidate the electrophysiological mechanisms involved in the genesis of arrhythmias. The most realistic simulations are based on reaction-diffusion models and involve a considerable computational burden. The aim of this study was to develop a computer model of cardiac electrical activity able to simulate complex electrophysiological phenomena but free of the large computational demands required by other commonly used models. MATERIAL AND METHOD: A cellular automata system was used to model the cardiac tissue. Each individual unit had several discrete states that changed according to simple rules as a function of the previous state and the state of the neighboring cells. Activation was considered as a probabilistic process and was adjusted using restitution curves. In contrast, repolarization was modeled as a deterministic phenomenon. Cell currents in the model were calculated with a prototypical action potential that allowed virtual monopolar and bipolar electrograms to be simulated at any point in space. RESULTS: Reproducible flat activation fronts, propagation from a focal stimulus, and reentry processes that were stable and unstable in two dimensions (with their corresponding electrograms) were obtained. The model was particularly suitable for the simulation of the effects observed in curvilinear activation fronts. Fibrillatory conduction and stable rotors in two- and three-dimensional substrates were also obtained. CONCLUSIONS: The probabilistic cellular automata model was simple to implement and was not associated with a high computational burden. It provided a realistic simulation of complex phenomena of interest in electrophysiology.

[Early heart rate increase does not predict the result of the head-up tilt test potentiated with nitroglycerin]. / El incremento temprano de la frecuencia cardíaca no predice el resultado de la prueba de basculación potenciada con nitroglicerina.

INTRODUCTION AND OBJECTIVES: The magnitude of the change in heart rate during the first few minutes of the head-up tilt test has been used to predict the test's result. The aim of this study was to investigate whether the heart rate increase during the head-up tilt test potentiated with nitroglycerin is related to the development of syncope. PATIENTS AND METHOD: The study included 158 consecutive patients with syncope, with stable sinus rhythm, and without structural cardiac disease who were undergoing a head-up tilt test with nitroglycerin. The heart rate increment induced by the tilt maneuver and by nitroglycerin administration was calculated, and its relationship to clinical variables and to the test's results was analyzed. RESULTS: The head-up tilt test gave positive results in 117 patients (74%). The heart rate was 68.7 (11.3) bpm in the decubitus position and 85.1 (15.4) bpm during the first 6 min of tilting. There was strong inverse correlation between the heart rate increase induced by tilting and age (r=--0.63; P<.001), but the increase (16.8 [9.3] bpm in patients with syncope versus 14.9 [11.3] bpm in those without; P=.3) did not predict the result of the test. The heart rate increase induced by nitroglycerin was also similar for patients with and without syncope during the pharmacologic phase of the test (27.3 [12.6] bpm and 26.7 (13.4) bpm, respectively; P=.8). CONCLUSIONS: The magnitude of the heart rate increase during the first few minutes of tilt-testing and after nitroglycerin administration is inversely related to age but does not predict the result of the head-up tilt test with nitroglycerin.