Endothelial hypoxic preconditioning in rat hypoxic isolated aortic segments.

Our aim was to analyse endothelial hypoxic preconditioning after hypoxia-reperfusion (HR). Endothelial functionality was analysed through the vasorelaxation responses to acetylcholine (Ach) and the level of serine1177 phosphorylated endothelial nitric oxide synthase (eNOS) (ser1177-eNOS) measured by Western blot in in vitro hypoxic preconditioned (P + HR) isolated rat aortic segments. Relaxation in response to Ach was reduced in phenylephrine-precontracted aortic segments after HR (control: IC50, 5 +/- 2.5 x 10(-8) mol l(-1); HR: IC50, 3 +/- 1.2 x 10(-7) mol l(-1); P < 0.05). Ach-dependent vasodilatation was improved by P + HR. The content of ser1177-eNOS in the HR segments was 1.5-fold lower than in P + HR. Confocal microscopy showed an increased content of both superoxide anion and peroxynitrite in the vascular wall of HR aortic segments, which it was reduced by P + HR. Geldanamycin (10 microg ml(-1)), an agent known to inhibit heat shock protein 90 (hsp90), reduced the level of ser1177-eNOS in P + HR aortic segments. However in the presence of geldanamycin, endothelial hypoxic preconditioning persisted. We conclude that short periods of hypoxia induced endothelial hypoxic preconditioning that was accompanied by enhanced levels of ser1177-eNOS in the vascular wall. The fact that endothelial hypoxic preconditioning persisted in the presence of geldanamycin suggests that other molecular mechanisms are involved in the endothelial adaptation to HR injury.

Significance of the morphological patterns of electrograms recorded during ventricular fibrillation: an experimental study.

Mapping techniques are used to study the significance of the morphological patterns of the electrograms (EGMs) obtained during VF in an experimental model. In 24 isolated rabbit heart preparations recordings were made of activation during VF using a multiple electrode (121 unipolar electrodes) positioned on the lateral wall of the left ventricle. Three types of activation maps were selected: (A) with functional block of an activation front; (B) with epicardial breakthrough; and (C) with a single broad wavefront without block lines. The EGMs were classified as negative (Q), positive-negative with a predominance of the negative (rS) or positive wave (Rs), and positive (R). In 60 type A maps the morphology in the zone limiting the block line corresponded to an R wave in 55 (92%) cases and to Rs in 5 (8%) cases. In 67 type B maps, the EGM in the earliest activation zone most often showed Q wave morphology (48 [72%] cases), followed by rS (18 [27%] cases), and Rs morphology (1 [1%] case); in no case was R wave morphology seen. Finally, in 78 type C maps the morphology corresponded to a Q wave in 15 (19%) cases, rS in 38 (49%), Rs in 24 (31%), and R in a 1 (1%) case. The differences between the three types of maps were significant (P < 0.0001). Q wave EGM sensitivity for indicating the existence of an epicardial breakthrough pattern was 72%, with a specificity of 89%, and positive and negative predictive values of 76% and 87%, respectively. R wave EGM sensitivity for indicating the existence of conduction block was 92%, with a specificity of 99%, and positive and negative predictive values of 98% and 97%, respectively. R wave morphology is highly sensitive and specific for indicating conduction block. EGM recordings with initial positivity predominance are infrequent in the earliest activation zones of epicardial breakthrough during VF. The recording of the EGM with Q wave morphology indicates centrifugal activation from the explored zone.

[Effects of myocardial stretching on excitation frequencies determined by spectral analysis during ventricular fibrillation]. / Efecto del estiramiento micárdico sobre las frecuencias de activación determinadas mediante análisis espectral durante la fibrilación ventricular.

INTRODUCTION AND OBJECTIVES: The aim of this study was to analyze the effects of myocardial stretching on excitation frequencies, as determined by spectral analysis, during ventricular fibrillation. METHODS: In 12 isolated rabbit heart preparations, ventricular activation during ventricular fibrillation was recorded with multiple electrodes. Recordings were obtained before, during and after ventricular dilatation produced with an intraventricular balloon. The dominant frequency of the signals obtained with each of the electrodes was determined by spectral analysis. RESULTS: During the control phase, the mean, minimum and maximum dominant frequencies were, respectively, 14.3 1.7, 12.5 1.7, and 16.2 1.4 Hz, and the average difference between the maximum and minimum frequencies was 3.6 2.1 Hz. This difference was over 4 Hz in four cases, and in no case did it exceed 8 Hz. During ventricular stretching, the mean dominant frequency increased significantly (21.1 6.1 Hz; p < 0.0001), as did the minimum values (14 2.6 Hz; p < 0.05) and especially the maximum values (26.6 7.7 Hz; p < 0.0001). The difference between the maximum and minimum frequencies (12.6 6.4 Hz; p < 0.001) was over 4 Hz in all cases except one, and over 8 Hz in 9 cases. The maximum values were distributed heterogeneously during ventricular stretching. Upon suppressing ventricular stretching, the dominant frequency did not differ from controls. CONCLUSIONS: Myocardial frequency maps during ventricular fibrillation show limited variations in the dominant frequency of the signals recorded in the lateral wall of the left ventricle. During stretching, the patterns were heterogeneous, due mainly to the marked increase in the maximum dominant frequency. In the experimental model used, the effects of stretching remitted after suppressing ventricular dilatation.

Effects of acute reduction of temperature on ventricular fibrillation activation patterns.

Because of its electrophysiological effects, hypothermia can influence the mechanisms that intervene in the sustaining of ventricular fibrillation. We hypothesized that a rapid and profound reduction of myocardial temperature impedes the maintenance of ventricular fibrillation, leading to termination of the arrhythmia. High-resolution epicardial mapping (series 1; n = 11) and transmural recordings of ventricular activation (series 2; n = 10) were used to analyze ventricular fibrillation modification during rapid myocardial cooling in Langendorff-perfused rabbit hearts. Myocardial cooling was produced by the injection of cold Tyrode into the left ventricle after induction of ventricular fibrillation. Temperature and ventricular fibrillation dominant frequency decay fit an exponential model to arrhythmia termination in all experiments, and both parameters were significantly correlated (r = 0.70, P < 0.0001). Termination of the arrhythmia occurred preferentially in the left ventricle and was associated with a reduction in conduction velocity (-60% in left ventricle and -54% in right ventricle; P < 0.0001) and with activation maps predominantly exhibiting a single wave front, with evidence of wave front extinction. We conclude that a rapid reduction of temperature to <20 degrees C terminates ventricular fibrillation after producing an important depression in myocardial conduction.

Efecto del estiramiento miocárdico sobre las frecuencias de activación determinadas mediante análisis espectral durante la fibrilación ventricular / Effects of myocardial stretching on excitation frequencies determined by spectral analysis during ventricular fibrillation

Introducción y objetivos. Analizar mediante técnicas espectrales los efectos del estiramiento miocárdico sobre las frecuencias de activación durante la fibrilación ventricular (FV). Métodos. En 12 preparaciones de corazón aislado de conejo se ha registrado la activación durante la fibrilación ventricular utilizando un electrodo múltiple antes, durante y después de la dilatación ventricular producida con un balón intraventricular y se ha determinado (análisis espectral) la frecuencia dominante de las señales obtenidas. Resultados. Durante el control, la frecuencia dominante media, mínima y máxima ha sido de 14,3 ñ 1,7; 12,5 ñ 1,7 y 16,2 ñ 1,4 Hz, y el promedio de las diferencias entre la máxima y la mínima ha sido de 3,6 ñ 2,1 Hz. Esta diferencia ha sido superior a 4 Hz en 4 casos y en ningún caso ha sido superior a 8 Hz. Durante la dilatación ventricular, la frecuencia dominante media ha aumentado significativamente (21,1 ñ 6,1 Hz; p < 0,0001), así como los valores mínimos (14 ñ 2,6 Hz; p < 0,05) y en mayor medida los máximos (26,6 ñ 7,7 Hz; p < 0,0001) y la diferencia entre máximos y mínimos (12,6 ñ 6,4 Hz; p < 0,001) que ha sido superior a 4 Hz en todos los casos excepto en uno y superior a 8 Hz en 9 casos. Los valores máximos se han distribuido de manera heterogénea durante la dilatación y, al suprimirla, los valores de la frecuencia dominante no han presentado diferencias con respecto al control. Conclusiones. Los mapas de frecuencias durante la fibrilación ventricular ponen de manifiesto variaciones limitadas en la frecuencia dominante de las señales registradas en la pared lateral del ventrículo izquierdo. Durante la dilatación, los patrones observados se caracterizan por su heterogeneidad debido, fundamentalmente, al acentuado incremento de las frecuencias máximas. En el modelo utilizado, los efectos del estiramiento revierten una vez suprimida la dilatación (AU)

Características de los electrogramas auriculares registrados en las líneas de bloqueo producidas con radiofrecuencia en un modelo experimental / Characteristics of atrial electrograms recorded in radiofrequency induced block lines in an experimental model

Objetivos. Analizar y cuantificar las modificaciones de los electrogramas auriculares tras la realización de lesiones lineales en la pared auricular utilizando procedimientos de ablación con radiofrecuencia. Métodos. En 12 preparaciones de corazón aislado de conejo según la técnica de Langendorff se ha utilizado un electrodo múltiple epicárdico (221 electrodos unipolares) para analizar la activación auricular antes y después de la realización de una lesión lineal en la pared auricular izquierda mediante aplicaciones sucesivas de radiofrecuencia. Tras comprobar la existencia de bloqueo de la conducción en la zona lesionada mediante cartografía epicárdica y análisis de los vectores de propagación, 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 máxima pendiente negativa y la morfología de los electrogramas antes (control) y después de las aplicaciones de radiofrecuencia. Resultados. El análisis de la reproducibilidad de las mediciones en dos ciclos consecutivos ha puesto de manifiesto una variación en la amplitud de un 1 ñ 5 por ciento (NS) y en la pendiente de un 1 ñ 9 por ciento (NS). En la zona no lesionada, la amplitud (105 ñ 22 por ciento) y la pendiente (92 ñ 16 por ciento) (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 más frecuentes (el 82 frente al 83 por ciento en el control; NS). En la zona lesionada, la amplitud (19 ñ 7 por ciento, p < 0,001) y la pendiente (24 ñ 11 por ciento; p < 0,001) han disminuido significativamente, así como los porcentajes de electrogramas simples (el 6 frente al 86 por ciento en el control; p < 0,001). En esta zona no se ha podido determinar la morfología en un 12 por ciento de los registros, se han obtenido electrogramas múltiples en un 15 por ciento (frente a un 2 por ciento en el control; p < 0,01) y el tipo más frecuente ha correspondido al de electrogramas dobles (el 67 frente al 12 por ciento en el control; p < 0,001) cuyos dos componentes han coincidido en el tiempo con la activación auricular en la zonas situadas proximal y distalmente a la lesión. Conclusiones. Los electrogramas obtenidos directamente sobre líneas de bloqueo originadas con radiofrecuencia se caracterizan por presentar una reducción significativa de la amplitud y de la máxima pendiente negativa. En estos registros predominan los electrogramas dobles cuyos dos componentes representan la activación a ambos lados de la lesión. En la línea de bloqueo pueden registrarse también en un porcentaje reducido de casos electrogramas simples y múltiples (AU)

Some properties of two autolytic-defective mutants of Streptococcus faecalis ATCC 9790.

The isolation and some properties of two mutants of Streptococcus faecalis ATCC 9790 (S. faecium) which autolyze at a much slower rate than the wild type are described. Compared with the wild type, mutant E71 autolyzed more slowly, contained less active but more latent autolysin in the isolated wall fraction, and possessed a wall of very similar chemical composition and degree of cross-bridging. Ultrastructural studies of exponential phase cells showed that cells of E71 were on the average slightly longer and had slightly thickened walls compared to the wild type. Mutant E81 autolyzed much more slowly, grew exponentially in long chains (8 to 40 cells compared with mainly diplococci), contained much less active and latent autolysin in the wall, and possessed a wall of very similar chemical composition but with about twice the content of N-terminal groups. Mutant E81 walls were more susceptible to isolated autolysin but possessed an autolysin of the same specificity as the wild type. Ultrastructurally E81 cells were, on the average, significantly longer and had thicker walls than the wild type. Mutant E71 may be partially blocked at either transport of autolysin to the wall or in conversion of latent to active autolysin. The pleitropic effects noted in mutant E81 have been taken to suggest a possible membrane defect and to support the role of the autolysin in cell separation.