Ventricular fibrillation conduction through an isthmus of preserved myocardium between radiofrequency lesions.

BACKGROUND: Selective local acceleration of myocardial activation during ventricular fibrillation (VF) contributes information on the interactions between neighboring zones during the arrhythmia. This study analyzes these interactions, centering the observations on an isthmus of myocardium between two radiofrequency (RF) lesions. METHODS: In nine isolated rabbit hearts, a gap of preserved myocardium was established between two RF lesions in the anterolateral left ventricle (LV) wall. Before, during, and after increasing the spatial heterogeneity of VF by local myocardial stretching, VF epicardial recordings were obtained. RESULTS: Local stretch in the anterior LV wall decreased the excitable window (17 ± 7 ms vs 26 ± 7 ms; P < 0.05) and increased the dominant frequency (DFr; 18.9 ± 5.0 Hz vs 15.2 ± 3.6 Hz; P < 0.05) in this zone, without changes in the non-stretched posterolateral zone (25 ± 4 ms vs 27 ± 6 ms, ns and 14.1 ± 2.7 Hz vs 14.3 ± 3.0 Hz, ns). The DFr ratio at both sides of the gap was inversely correlated to the excitable window ratio (R = -0.57; P = 0.002). Before (31% vs 26%), during (29% vs 22%), and after stretch suppression (35% vs 25%), the wavefronts passing through the gap from the posterolateral to the anterior LV wall were seen to predominate. The number of wavefronts that passed from the anterior to the posterolateral LV wall was related to the excitable window in this zone (R = 0.41; P = 0.03). CONCLUSIONS: The VF acceleration induced in the stretched zone does not increase the flow of wavefronts toward the non-stretched zone in the adjacent gap of preserved myocardium. The absence of significant changes in the electrophysiological parameters of the non-stretched myocardium limits the arrival of wavefronts in this zone.

Modificaciones de la fibrilación ventricular y de la capacidad de captura inducidas por una lesión lineal con radiofrecuencia / Modifications in ventricular fibrillation and capture capacity induced by a linear radiofrequency lesion

Introducción y objetivos. Analizar los efectos, en la fibrilación ventricular y en la capacidad de capturar al miocardio mediante estimulación a frecuencias rápidas, de una lesión lineal producida con radiofrecuencia. Métodos. En 22 corazones de conejo aislados y perfundidos, se utilizaron electrodos múltiples epicárdicos para registrar la fibrilación ventricular. Se analizaron los mapas de activación al aplicar trenes de estímulos a tres frecuencias distintas, cercanas a las de la arritmia, en tres situaciones: a) basalmente; b) tras producir con radiofrecuencia una lesión en la pared libre del ventrículo izquierdo (longitud, 10±1mm), y c) tras ampliar su extensión (longitud, 23±2mm). Resultados. Tras la lesión, se observó una disminución de la regularidad de las señales registradas y variaciones significativas en la dirección de los frentes de activación. Con la lesión ampliada, se incrementaron ligeramente los episodios con al menos tres capturas consecutivas al estimular con ciclos un 10% más largos que los de la arritmia (basal, 0,6±0,7; lesión inicial, 1±1, diferencias no significativas; lesión ampliada, 3±2,8; p<0,001), mientras que se redujeron los obtenidos al estimular con ciclos un 10% más cortos que los de la arritmia. Conclusiones. La lesión efectuada con radiofrecuencia aumenta la heterogeneidad de la activación miocárdica durante la fibrilación ventricular y modifica la llegada de los frentes de activación a las zonas adyacentes. La estimulación durante la fibrilación ventricular a frecuencias rápidas provoca capturas ocasionales durante al menos tres estímulos consecutivos. La lesión ampliada incrementa ligeramente la capacidad de captura al utilizar ciclos ligeramente más largos que los de la fibrilación ventricular (AU)

Introduction and objectives. An analysis was made of the effects of a radiofrequency-induced linear lesion during ventricular fibrillation and the capacity to capture myocardium through high-frequency pacing. Methods. Using multiple epicardial electrodes, ventricular fibrillation was recorded in 22 isolated perfused rabbit hearts, analyzing the activation maps upon applying trains of stimuli at 3 different frequencies close to that of the arrhythmia: a) at baseline; b) after radio-frequency ablation to induce a lesion of the left ventricular free wall (length=10 [1]mm), and c) after lengthening the lesion (length=23 [2]mm). Results. Following lesion induction, the regularity of the recorded signals decreased and significant variations in the direction of the activation fronts were observed. On lengthening the lesion, there was a slight increase in the episodes with at least 3 consecutive captures when pacing at cycles 10% longer than the arrhythmia (baseline: 0.6 [0.7]; initial lesion: 1 [1] no significant differences; lengthened lesion: 3 [2.8]; P<.001), while a decrease was observed in those obtained upon pacing at cycles 10% shorter than the arrhythmia. Conclusions. The radio-frequency -induced lesion increases the heterogeneity of myocardial activation during ventricular fibrillation and modifies arrival of the activation fronts in the adjacent zones. High-frequency pacing during ventricular fibrillation produces occasional captures during at least 3 consecutive stimuli. The lengthened lesion in turn slightly increases capture capacity when using cycles slightly longer than the arrhythmia (AU)

Modifications in ventricular fibrillation and capture capacity induced by a linear radiofrequency lesion.

INTRODUCTION AND OBJECTIVES: An analysis was made of the effects of a radiofrequency-induced linear lesion during ventricular fibrillation and the capacity to capture myocardium through high-frequency pacing. METHODS: Using multiple epicardial electrodes, ventricular fibrillation was recorded in 22 isolated perfused rabbit hearts, analyzing the activation maps upon applying trains of stimuli at 3 different frequencies close to that of the arrhythmia: a) at baseline; b) after radio-frequency ablation to induce a lesion of the left ventricular free wall (length=10 [1] mm), and c) after lengthening the lesion (length=23 [2] mm). RESULTS: Following lesion induction, the regularity of the recorded signals decreased and significant variations in the direction of the activation fronts were observed. On lengthening the lesion, there was a slight increase in the episodes with at least 3 consecutive captures when pacing at cycles 10% longer than the arrhythmia (baseline: 0.6 [0.7]; initial lesion: 1 [1], no significant differences; lengthened lesion: 3 [2.8]; P<.001), while a decrease was observed in those obtained upon pacing at cycles 10% shorter than the arrhythmia. CONCLUSIONS: The radio-frequency -induced lesion increases the heterogeneity of myocardial activation during ventricular fibrillation and modifies arrival of the activation fronts in the adjacent zones. High-frequency pacing during ventricular fibrillation produces occasional captures during at least 3 consecutive stimuli. The lengthened lesion in turn slightly increases capture capacity when using cycles slightly longer than the arrhythmia.

Pharmacological modifications of the stretch-induced effects on ventricular fibrillation in perfused rabbit hearts.

Stretch induces modifications in myocardial electrical and mechanical activity. Besides the effects of substances that block the stretch-activated channels, other substances could modulate the effects of stretch through different mechanisms that affect Ca(2+) handling by myocytes. Thirty-six Langendorff-perfused rabbit hearts were used to analyze the effects of the Na(+)/Ca(2+) exchanger blocker KB-R7943, propranolol, and the adenosine A(2) receptor antagonist SCH-58261 on the acceleration of ventricular fibrillation (VF) produced by acute myocardial stretching. VF recordings were obtained with two epicardial multiple electrodes before, during, and after local stretching in four experimental series: control (n = 9), KB-R7943 (1 microM, n = 9), propranolol (1 microM, n = 9), and SCH-58261 (1 microM, n = 9). Both the Na(+)/Ca(2+) exchanger blocker KB-R7943 and propranolol induced a significant reduction (P < 0.001 and P < 0.05, respectively) in the dominant frequency increments produced by stretching with respect to the control and SCH-58261 series (control = 49.9%, SCH-58261 = 52.1%, KB-R7943 = 9.5%, and propranolol = 12.5%). The median of the activation intervals, the functional refractory period, and the wavelength of the activation process during VF decreased significantly under stretch in the control and SCH-58261 series, whereas no significant variations were observed in the propranolol and KB-R7943 series, with the exception of a slight but significant decrease in the median of the fibrillation intervals in the KB-R7943 series. KB-R7943 and propranolol induced a significant reduction in the activation maps complexity increment produced by stretch with respect to the control and SCH-58261 series. In conclusion, the electrophysiological effects responsible for stretch-induced VF acceleration in the rabbit heart are reduced by the Na(+)/Ca(2+) exchanger blocker KB-R7943 and by propranolol but not by the adenosine A(2) receptor antagonist SCH-58261.

[Changes in the spectral characteristics of ventricular fibrillation in lesions produced by radiofrequency ablation. An experimental study]. / Modificaciones de las características espectrales de la fibrilación ventricular en las lesiones producidas con radiofrecuencia. Estudio experimental.

INTRODUCTION AND OBJECTIVES: Although electro- physiological databases contain information about changes in the time domain in lesions produced by radiofrequency ablation, very few data on changes in the frequency domain are available. The aim of this study was to investigate changes in the spectral characteristics of ventricular fibrillation in zones with radiofrequency lesions. METHODS: Recordings of ventricular fibrillation were obtained in 11 isolated perfused rabbit heart preparations using a multiple epicardial electrode located on the left ventricular free wall. Spectral parameters derived by Fourier analysis before and after the creation of transmural radiofrequency lesions were compared. RESULTS: In the ablated zones, significant reductions were observed in the spectral density of the dominant (0.168+/-0.113 mV(2)/Hz vs 0.025+/-0.018 mV(2)/Hz; P< .001) and mean frequencies (0.053+/-0.057 mV(2)/Hz vs 0.012+/-0.016 mV(2)/Hz; P< .001), the normalized energy around the dominant frequency (0.860+/-0.570 vs 0.128+/-0.091; P< .001), and the standard deviation of the power spectrum (0.031+/-0.020 mV(2)/Hz vs 0.004+/-0.001 mV(2)/Hz; P< .001). There was no significant change in the dominant (16.2+/-5.6 vs 14.8+/-1.8 Hz) or mean frequency (17.7+/-3.4 vs 16.6+/-1.3 Hz). The spectral parameters that could be used in a multivariate model to identify the lesion were the standard deviation of the power spectrum and the spectral density of the mean frequency. CONCLUSIONS: During ventricular fibrillation, the spectral parameters associated with spectral power and spectral energy were significantly altered in zones with radiofrequency lesions and could be used to identify those zones. There was no significant change in either the dominant or mean frequency in these zones.

Modificaciones de las características espectrales de la fibrilación ventricular en las lesiones producidas con radiofrecuencia. Estudio experimental / Changes in the spectral characteristics of ventricular fibrillation in lesions produced by radiofrequency ablation. An experimental study

Introducción y objetivos. Aunque se dispone de información sobre las modificaciones en el dominio del tiempo de los registros electrofisiológicos en zonas lesionadas con radiofrecuencia, los datos disponibles en el dominio de la frecuencia son muy escasos. Se analizan las modificaciones de las características espectrales de la fibrilación ventricular en zonas lesionadas con radiofrecuencia. Métodos. En 11 preparaciones de corazón aislado y perfundido de conejo, se registra la fibrilación ventricular con un electrodo múltiple epicárdico situado en la pared libre ventricular izquierda. Se comparan los parámetros espectrales obtenidos mediante análisis de Fourier antes y después de practicar lesiones transmurales con radiofrecuencia. Resultados. En las zonas lesionadas disminuye significativamente la densidad espectral de las frecuencias dominante (0,168 ± 0,113 y 0,025 ± 0,018 mV2/Hz; p < 0,001) y media (0,053 ± 0,057 y 0,012 ± 0,016 mV2/Hz; p < 0,001), la energía normalizada alrededor de la frecuencia dominante (0,860 ± 0,570 y 0,128 ± 0,091; p < 0,001) y la desviación típica del espectro de potencias (0,031 ± 0,020 y 0,004 ± 0,001 mV2/Hz; p < 0,001). No se modifican significativamente las frecuencias dominante (16,2 ± 5,6 y 14,8 ± 1,8 Hz) y media (17,7 ± 3,4 y 16,6 ± 1,3 Hz). Los parámetros espectrales aceptados en el modelo multivariable para indicar que los registros se efectúan en la lesión son la desviación típica del espectro de potencias y la densidad espectral de la frecuencia media. Conclusiones. Durante la fibrilación ventricular, los parámetros relacionados con la potencia y la energía espectral muestran modificaciones significativas en las zonas lesionadas con radiofrecuencia y pueden ayudar a identificarlas. Las frecuencias dominante y media no se modifican significativamente en las zonas lesionadas

Introduction and objectives. Although electro- physiological databases contain information about changes in the time domain in lesions produced by radiofrequency ablation, very few data on changes in the frequency domain are available. The aim of this study was to investigate changes in the spectral characteristics of ventricular fibrillation in zones with radiofrequency lesions. Methods. Recordings of ventricular fibrillation were obtained in 11 isolated perfused rabbit heart preparations using a multiple epicardial electrode located on the left ventricular free wall. Spectral parameters derived by Fourier analysis before and after the creation of transmural radiofrequency lesions were compared. Results. In the ablated zones, significant reductions were observed in the spectral density of the dominant (0.168±0.113 mV2/Hz vs 0.025±0.018 mV2/Hz; P<.001) and mean frequencies (0.053±0.057 mV2/Hz vs 0.012±0.016 mV2/Hz; P<.001), the normalized energy around the dominant frequency (0.860±0.570 vs 0.128±0.091; P<.001), and the standard deviation of the power spectrum (0.031±0.020 mV2/Hz vs 0.004±0.001 mV2/Hz; P<.001). There was no significant change in the dominant (16.2±5.6 vs 14.8±1.8 Hz) or mean frequency (17.7±3.4 vs 16.6±1.3 Hz). The spectral parameters that could be used in a multivariate model to identify the lesion were the standard deviation of the power spectrum and the spectral density of the mean frequency. Conclusions. During ventricular fibrillation, the spectral parameters associated with spectral power and spectral energy were significantly altered in zones with radiofrequency lesions and could be used to identify those zones. There was no significant change in either the dominant or mean frequency in these zones

[Effect of streptomycin on stretch-induced change in myocardial activation during ventricular fibrillation]. / Efectos de la estreptomicina en las modificaciones de la activación miocárdica durante la fibrilación ventricular inducidas por el estiramiento.

The aim of this study was to determine whether the changes in myocardial activation pattern resulting from acute stretching during ventricular fibrillation can be counteracted by administering a compound that blocks receptors sensitive to stretch. The study involved 16 isolated rabbit hearts, in which refractoriness and activation frequency during ventricular fibrillation were measured before, during and after localized acute stretching of the left ventricular free wall, either without (series A, n=8) or with (series B, n=8) the presence of streptomycin, 200 micromol. At baseline and during and after stretching, ventricular fibrillation was slower with streptomycin perfusion in series B than in series A (dominant frequency at baseline, 13+/-2 Hz vs. 16+/-2 Hz, respectively; P< .005; dominant frequency with stretching, 14+/-2 Hz vs. 19+/-3 Hz, respectively; P< .005). Streptomycin attenuated the electrophysiological changes produced by stretching and had a direct effect on refractoriness and activation frequency during ventricular fibrillation.

Efectos de la estreptomicina en las modificaciones de la activacion miocardica durante la fibrilacion ventricular inducidas por el estiramiento / Effect of streptomycin on stretch-induced change in myocardial activation during ventricular fibrillation

Se ha evaluado si las modificaciones en la activación miocárdica durante la fibrilación ventricular producidas por el estiramiento agudo pueden ser contrarrestadas por un bloqueador de los receptores sensibles al estiramiento. En 16 corazones aislados de conejo, se ha analizado la refractariedad y la frecuencia de activación durante la fibrilación ventricular antes, durante y después de producir un estiramiento agudo localizado en la pared libre del ventrículo izquierdo, en ausencia (serie A, n = 8) o en presencia (serie B, n = 8) de estreptomicina 200 μmol. Durante la perfusión de estreptomicina (serie B), tanto basalmente como durante y después del estiramiento, la fibrilación ventricular ha sido más lenta que en la serie A (frecuencia dominante basal, 13 ± 2 Hz frente a 16 ± 2 Hz; p < 0,005; frecuencia dominante estiramiento, 14 ± 2 Hz frente a 19 ± 3 Hz; p < 0,005). La estreptomicina ha atenuado las modificaciones electrofisiológicas producidas por el estiramiento y ha tenido efecto directo en la refractariedad y la frecuencia de activación durante la fibrilación ventricular (AU)

The aim of this study was to determine whether the changes in myocardial activation pattern resulting from acute stretching during ventricular fibrillation can be counteracted by administering a compound that blocks receptors sensitive to stretch. The study involved 16 isolated rabbit hearts, in which refractoriness and activation frequency during ventricular fibrillation were measured before, during and after localized acute stretching of the left ventricular free wall, either without (series A, n=8) or with (series B, n=8) the presence of streptomycin, 200 μmol. At baseline and during and after stretching, ventricular fibrillation was slower with streptomycin perfusion in series B than in series A (dominant frequency at baseline, 13±2 Hz vs. 16±2 Hz, respectively; P<.005; dominant frequency with stretching, 14±2 Hz vs. 19±3 Hz, respectively; P<.005). Streptomycin attenuated the electrophysiological changes produced by stretching and had a direct effect on refractoriness and activation frequency during ventricular fibrillation (AU)

[Influence of recording mode (unipolar or bipolar) on the spectral characteristics of epicardial recordings in ventricular fibrillation. An experimental study]. / Influencia del tipo de registro (unipolar o bipolar) en las características espectrales de los registros epicárdicos de la fibrilación ventricular. Estudio experimental.

INTRODUCTION AND OBJECTIVES: The aim of this study was to examine the hypothesis that the recording mode (i.e., unipolar or bipolar) affects the information obtained using spectral analysis techniques during ventricular fibrillation by carrying out an experiment using epicardial electrodes. METHODS: Recordings of ventricular fibrillation were obtained in 29 isolated rabbit hearts using a multiple-electrode probe located on the left ventricular free wall. The parameter values obtained in the frequency domain (by Fourier analysis) using unipolar or bipolar electrodes, different interelectrode distances, and different orientations (i.e., horizontal, vertical or diagonal) were compared. RESULTS: Changing the recording mode (i.e., unipolar to bipolar) or the interelectrode distance significantly altered the mean frequency (P< .0001) and the normalized energy of the spectrum (+/-1 Hz) around the dominant frequency (P< .05), though the changes were small relative to the dominant frequency. Cross-spectral analysis showed that the coherence between unipolar recordings decreased as the interelectrode distance increased, while the opposite occurred with the coherence between unipolar and bipolar recordings. The two coherences were inversely correlated such that the greater the former coherence, the less the coherence between unipolar and bipolar recordings (r=0.29; P< .0001; n=348). CONCLUSIONS: The recording mode (i.e., unipolar or bipolar) used influenced the information obtained using spectral analysis techniques from epicardial recordings of ventricular fibrillation. Differences were observed in the mean frequency and in the frequency distribution, but they were very small relative to the dominant frequency.

Influencia del tipo de registro (unipolar o bipolar) en las características espectrales de los registros epicárdicos de la fibrilación ventricular. Estudio experimental / Influence of recording mode (unipolar or bipolar) on the spectral characteristics of epicardial recordings in ventricular fibrillation. An experimental study

Introducción y objetivos. Se evalúa la hipótesis de que el tipo de registro (unipolar o bipolar) influye en la información obtenida mediante técnicas espectrales durante la fibrilación ventricular en un modelo experimental que utiliza electrodos epicárdicos. Métodos. En 29 corazones aislados de conejo se obtienen registros de la fibrilación ventricular con un electrodo múltiple situado en la pared libre del ventrículo izquierdo. Se comparan los parámetros obtenidos en el dominio de la frecuencia (análisis de Fourier) al utilizar electrodos unipolares o bipolares con varias separaciones entre los electrodos en distintas direcciones (horizontal, vertical o diagonales). Resultados. La modalidad de registro (unipolar o bipolar) y la separación entre los electrodos han introducido diferencias significativas en la frecuencia media (p < 0,0001) y en la energía normalizada del espectro alrededor de la frecuencia dominante (± 1 Hz) (p < 0,05), pero éstas han sido mínimas al considerar la frecuencia dominante. En el análisis espectral cruzado, se ha observado que la coherencia entre los registros unipolares disminuye al aumentar la separación entre los electrodos, mientras que ocurre lo contrario al analizar la coherencia entre los unipolares y los bipolares. Ambas coherencias se correlacionan inversamente, de tal modo que cuanto mayor es la primera menor es la de los unipolares respecto a los bipolares (r = 0,29; p < 0,0001; n = 348). Conclusiones. El tipo de registro utilizado (unipolar o bipolar) introduce variaciones en la información obtenida mediante técnicas espectrales en los registros epicárdicos de la fibrilación ventricular. Estas diferencias se observan en la frecuencia media y en la distribución de frecuencias del espectro, pero son muy pequeñas al considerar la frecuencia dominante (AU)

Introduction and objectives. The aim of this study was to examine the hypothesis that the recording mode (i.e., unipolar or bipolar) affects the information obtained using spectral analysis techniques during ventricular fibrillation by carrying out an experiment using epicardial electrodes. Methods. Recordings of ventricular fibrillation were obtained in 29 isolated rabbit hearts using a multiple-electrode probe located on the left ventricular free wall. The parameter values obtained in the frequency domain (by Fourier analysis) using unipolar or bipolar electrodes, different interelectrode distances, and different orientations (i.e., horizontal, vertical or diagonal) were compared. Results. Changing the recording mode (i.e., unipolar to bipolar) or the interelectrode distance significantly altered the mean frequency (P<.0001) and the normalized energy of the spectrum (±1 Hz) around the dominant frequency (P<.05), though the changes were small relative to the dominant frequency. Cross-spectral analysis showed that the coherence between unipolar recordings decreased as the interelectrode distance increased, while the opposite occurred with the coherence between unipolar and bipolar recordings. The two coherences were inversely correlated such that the greater the former coherence, the less the coherence between unipolar and bipolar recordings (r=0.29; P<.0001; n=348). Conclusions. The recording mode (i.e., unipolar or bipolar) used influenced the information obtained using spectral analysis techniques from epicardial recordings of ventricular fibrillation. Differences were observed in the mean frequency and in the frequency distribution, but they were very small relative to the dominant frequency (AU)