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Opposite effects of myocardial stretch and verapamil on the complexity of the ventricular fibrillatory pattern: an experimental study.

CHORRO, F.J., et al.: Opposite Effects of Myocardial Stretch And Verapamil on The Complexity of The Ventricular Fibrillatory Pattern: An Experimental Study. An experimental model is used to analyze the effects of ventricular stretching and verapamil on the activation patterns during VF. Ten Langendorff‐perfused rabbit hearts were used to record VF activity with an epicardial multiple electrode before, during, and after stretching with an intraventricular balloon, under both control conditions and during verapamil (Vp) infusion (0.4–0.8 μmol). The analyzed parameters were dominant frequency (FrD) spectral analysis, the median (MN) of the VF intervals, and the type of activation maps during VF (I = one wavelet without block lines, II = two simultaneous wavelets with block lines, III = three or more wavelets with block lines). Stretch accelerates VF (FrD: 22.8 ± 6.4 vs 15.2 ± 1.0 Hz, P < 0.01; MN: 48 ± 13 vs 68 ± 6 ms, P < 0.01). On fitting the FrD time changes to an exponential model after applying and suppressing stretch, the time constants (stretch: 101.2 ± 19.6 s; stretch suppression: 97.8 ± 33.2 s) do not differ significantly. Stretching induces a significant variation in the complexity of the VF activation maps with type III increments and type I and II decrements (control: I = 17.5%, II = 50.5%, III = 32%; stretch: I = 7%, II = 36.5%, III = 56.5%, P < 0.001). Vp accelerates VF (FrD: 20.9 ± 1.9 Hz, P < 0.001 vs control; MN: 50 ± 5 ms, P < 0.001 vs control) and diminishes activation maps complexity (I = 25.5%, II = 60.5%, III = 14%, P < 0.001 vs control). On applying stretch during Vp perfusion, the fibrillatory process is not accelerated to any greater degree. However, type I and II map decrements and type III increments are recorded, though reaching percentages similar to control (I = 16.5%, II = 53%, III = 30.5%, NS vs control). The following conclusions were found: (1) myocardial stretching accelerates VF and increases the complexity of the VF activation pattern; (2) time changes in the FrD of VF during and upon suppressing stretch fit an exponential model with similar time constants; and (3) although stretching and verapamil accelerate the VF process, they exert opposite effects upon the complexity of the fibrillatory pattern.

Modifications of mechanoelectric feedback induced by 2,3-butanedione monoxime and Blebbistatin in Langendorff-perfused rabbit hearts.

Myocardial stretching is an arrhythmogenic factor. Optical techniques and mechanical uncouplers are used to study the mechanoelectric feedback. The aim of this study is to determine whether the mechanical uncouplers 2,3‐butanedione monoxime and Blebbistatin hinder or modify the electrophysiological effects of acute mechanical stretch.

Mapping of atrial activation patterns after inducing contiguous radiofrequency lesions: an experimental study.

CHORRO, F.J., et al.: Mapping of Atrial Activation Patterns After Inducing Contiguous Radiofrequency Lesions: An Experimental Study. High resolution mapping techniques are used to analyze the changes in atrial activation patterns produced by contiguous RF induced lesions. In 12 Langendorff‐perfused rabbit hearts, left atrial activation maps were obtained before and after RF induction of epicardial lesions following a triple‐phase sequential protocol: (phase 1) three separate lesions positioned vertically in the central zone of the left atrial wall; (phase 2) the addition of two lesions located between the central lesion and the upper and lower lesions; and (phase 3) the placement of four additional lesions between those induced in the previous phases. In six additional experiments a pathological analysis of the individual RF lesions was performed. In phase 1 (lesion diameter = 2.8 ± 0.2 mm, gap between lesions = 3 ± 0.8 mm), the activation process bordered the lesions line in two (2.0‐ms cycles) and four experiments (1.0‐ms cycles). In phase 2, activation bordered the lesions line in eight (2.0‐ms cycles, P < 0.01 vs control) and nine experiments (1.0‐ms cycles, P < 0.001), and in phase 3 this occurred in all experiments except one (both cycles, P < 0.001 vs control). In the experiments with conduction block, the increment of the interval between activation times proximal and distal to the lesions showed a significant correlation to the length of the lesions (r = 0.68, P < 0.05, 100‐ms cycle). In two (17%) experiments, sustained regular tachycardias were induced with reentrant activation patterns around the lesions line. In conclusion, in this acute model, atrial RF lesions with intact tissue gaps of 3 mm between them interrupt conduction occasionally, and conduction block may be frequency dependent. Lesion overlap is required to achieve complete conduction block lines. Tachycardias with reentrant activation patterns around a lesions line may be induced.

Patrones de activación durante la fibrilación auricular en un modelo experimental

Introduccion y objetivos En la fibrilacion auricular junto a los mecanismos de reentrada y de activacion aleatoria se han descrito patrones de activacion focal que se han atribuido tanto a propagacion desde el endocardio como a la existencia de zonas de actividad automatica. Los objetivos del presente estudio son analizar y cuantificar los patrones de activacion auricular en un modelo experimental de fibrilacion. Material y metodos Se estudian 11 preparaciones de corazon aislado de conejo segun la tecnica de Langendorff en los que se inducen episodios de fibrilacion auricular mediante sobreestimulacion tras haber provocado dilatacion auricular derecha con un balon intraauricular. Utilizando un electro-do multiple compuesto por 121 electrodos, situado en la pared lateral de la auricula derecha, se construyen los mapas de activacion correspondientes a 10 segmentos de 100 ms en 11 episodios distintos de fibrilacion auricular sostenida. Resultados De los 110 segmentos analizados, en 44 de ellos (40%) se observan patrones de activacion aleatoria. En 15 segmentos (14%) se observan reentradas completas y en ellas el numero de giros consecutivos esta comprendido entre 1 y 2,25 (promedio 1,4 ± 0,4). En 49 segmentos (44%) se evidencia o bien un frente unico de activacion que atraviesa sin bloquearse el area de registro, o bien dos frentes simultaneos que no reexcitan la zona activada por el otro. En 2 segmentos (2%) se obtiene un patron de activacion focal sin evidencia de propagacion desde el epicardio que rodea a la zona activada. Conclusiones . a) en el modelo estudiado los patrones de activacion aleatoria son mas frecuentes que los de reentrada completa; b) la reentrada completa puede ocurrir en areas menores de 1 cm2, y c) la activacion focal durante la fibrilacion auricular es un fenomeno raro.

Características de los electrogramas auriculares registrados en las líneas de bloqueo producidas con radiofrecuencia en un modelo experimental

Objetivos Analizar y cuantificar las modificaciones de los electrogramas auriculares tras la realizacion de lesiones lineales en la pared auricular utilizando procedimientos de ablacion con radiofrecuencia. Metodos En 12 preparaciones de corazon aislado de conejo segun la tecnica de Langendorff se ha utilizado un electrodo multiple epicardico (221 electrodos unipolares) para analizar la activacion auricular antes y despues de la realizacion de una lesion lineal en la pared auricular izquierda mediante aplicaciones sucesivas de radiofrecuencia. Tras comprobar la existencia de bloqueo de la conduccion en la zona lesionada mediante cartografia epicardica y analisis de los vectores de propagacion, en cada experimento se han seleccionado seis electrodos en la zona lesionada y otros seis en la no lesionada. En ambas zonas se ha comparado la amplitud, la maxima pendiente negativa y la morfologia de los electrogramas antes (control) y despues de las aplicaciones de radiofrecuencia. Resultados El analisis de la reproducibilidad de las mediciones en dos ciclos consecutivos ha puesto de manifiesto una variacion en la amplitud de un 1 ± 5% (NS) y en la pendiente de un 1 ± 9% (NS). En la zona no lesionada, la amplitud (105 ± 22%) y la pendiente (92 ± 16%) (valores normalizados con respecto a los obtenidos en el control) no han variado significativamente tras las aplicaciones de radiofrecuencia, y los registros de electrogramas simples han sido los mas frecuentes (el 82 frente al 83% en el control; NS). En la zona lesionada, la amplitud (19 ± 7%, p Conclusiones Los electrogramas obtenidos directamente sobre lineas de bloqueo originadas con radiofrecuencia se caracterizan por presentar una reduccion significativa de la amplitud y de la maxima pendiente negativa. En estos registros predominan los electrogramas dobles cuyos dos componentes representan la activacion a ambos lados de la lesion. En la linea de bloqueo pueden registrarse tambien en un porcentaje reducido de casos electrogramas simples y multiples. Palabras clave: Ablacion con radiofrecuencia Lesiones lineales. Activacion auricular. Cartografia. Electrofisiologia cardiaca. Modelos experimentales.

Cartografía epicárdica de la activación reentrante durante la fibrilación ventricular. Estudio experimental

Introduccion y objetivos Analizar las caracteristicas de la activacion reentrante durante la fibrilacion ventricular en un modelo experimental mediante cartografia epicardica de alta resolucion. Metodos En 30 preparaciones de corazon aislado de conejo se ha registrado la actividad fibrilatoria ventricular utilizando un electrodo multiple epicardico. En los mapas de activacion con patrones de activacion reentrante se han determinado el numero de giros consecutivos, la longitud maxima de la zona central de la reentrada, el area abarcada por la zona central y dos electrodos alrededor de la misma y la duracion de los ciclos. Resultados En la mayor parte de los mapas se han observado patrones complejos con dos o mas frentes de activacion que colisionan entre si o quedan separados por lineas de bloqueo funcional (514 mapas; 86%). En 112 mapas (19%) se han obtenido patrones compatibles con afloramiento epicardico del proceso de activacion. Se ha detectado actividad reentrante en 42 mapas (7%) y el numero maximo de giros consecutivos ha sido de 3 (promedio de 1,3 ± 0,5 giros). La longitud maxima de la zona central de la reentrada ha estado comprendida entre 3 y 7 mm (promedio de 5 ± 1 mm), y el area abarcada por esta zona mas dos electrodos alrededor de la misma entre 35 y 55 mm2 (promedio de 45 ± 6 mm2). La duracion de los ciclos reentrantes (promedio de 47 ± 8 ms) ha demostrado una relacion lineal con la longitud maxima de la zona central de la reentrada (ciclo = 4,52 × longitud + 24,6; r = 0,7; p Conclusiones a) La cartografia epicardica permite objetivar patrones de activacion reentrante durante la fibrilacion ventricular en el modelo utilizado; b) la activacion reentrante detectada es poco frecuente e inestable, y c) existe una relacion lineal entre la duracion de los ciclos definidos por este tipo de activacion y la longitud maxima de la zona central de la reentrada.

Effects of local temperature variation on ventricular fibrillation dominant frequency

By inducing controlled changes in the electrophysiologic properties of the whole heart, numerous studies have analysed the onset and maintenance mechanisms of ventricular arrhythmias. In this contribution a new method that cause local heterogeneities in the cardiac tissue is explained. A specific device, based on the Peltier effect, has been developed to quantify, in an experimental model (Langendorff-perfused), the temperature dependence of the dominant frequency (DF) during ventricular fibrillation (VF). This device performs changes of temperature above and below the basal value. With a drop of temperature, a valuable decrease of DF in the affected area, was observed. The differences between every step and control (37/spl deg/C) were significant, and the correlation of DF with temperature was high. At 42/spl deg/C the fibrillation signals showed the main degree of organization, and the highest DF value.

Changes in ventricular refractoriness and conduction velocity induced by local hypothermia and hyperthermia

VF pattern is related to the electrophysiological parameters of the myocardium. Although the influence of global temperature on these parameters is known, the effects of its regional variations have not been sufficiently studied. We examined the effects of local hypothermia and hyperthermia on refractoriness and conduction velocity (VC), during constant pacing at cycle lengths of 250 ms. In an experimental model (rabbit isolated heart) we used a new method to perform epicardial cooling and heating on the registered surface. The results show that local variations of temperature generate heterogeneity in the electrophysiological properties of the heart. Hypothermia prolongs refractoriness and decreases VC, in a reversible manner. Hyperthermia (42degC) has the opposite effects. The wavelength of the cardiac impulse is not altered because of the opposite and proportional actions on functional refractory period and VC

QT dispersion induced by local temperature variations

Abnormally long and short QT intervals (QTi) have been shown to be associated with an increased risk for life-threatening ventricular arrhythmias and sudden cardiac death. Because of its electrophysiological effects temperature can influence this parameter. Therefore hypothermia or/and hyperthermia can be used for modulate QTi in studies with experimental models. In this work, a novel electrode-device to perform epicardial mapping and simultaneous thermal modifications is presented. In ten preparations of isolated rabbit hearts (Langendorff-perfused) changes in QTi was analyzed in two different left ventricular areas. One area was thermally modified, while the other remained in basal conditions, the QTi were measured in both areas. During hypothermia the differences between them increased mainly due to the prolongation of the QTi in altered area. hyperthermia had the opposite effect.