Development and Long-Term Follow-Up of an Experimental Model of Myocardial Infarction in Rabbits.

A chronic model of acute myocardial infarction was developed to study the mechanisms involved in adverse postinfarction ventricular remodeling. In an acute myocardial infarction (AMI), the left circumflex coronary artery of New Zealand White rabbits (n = 9) was occluded by ligature for 1 h, followed by reperfusion. A specific care protocol was applied before, during, and after the intervention, and the results were compared with those of a sham operated group (n = 7). After 5 weeks, programmed stimulation and high-resolution mapping were performed on isolated and perfused hearts using the Langendorff technique. The infarct size determined by 2,3,5-triphenyltetrazolium chloride inside of the area at risk (thioflavin-S) was then determined. The area at risk was similar in both groups (54.33% (experimental infarct group) vs. 58.59% (sham group), ns). The infarct size was 73.16% as a percentage of the risk area. The experimental infarct group had a higher inducibility of ventricular arrhythmias (100% vs. 43% in the sham group, p = 0.009). A reproducible chronic experimental model of myocardial infarction is presented in which the extent and characteristics of the lesions enable the study of the vulnerability to develop ventricular arrhythmias because of the remodeling process that occurs during cardiac tissue repair.

Ranolazine-Mediated Attenuation of Mechanoelectric Feedback in Atrial Myocyte Monolayers.

BACKGROUND: Mechanical stretch increases Na+ inflow into myocytes, related to mechanisms including stretch-activated channels or Na+/H+ exchanger activation, involving Ca2+ increase that leads to changes in electrophysiological properties favoring arrhythmia induction. Ranolazine is an antianginal drug with confirmed beneficial effects against cardiac arrhythmias associated with the augmentation of I NaL current and Ca2+ overload. OBJECTIVE: This study investigates the effects of mechanical stretch on activation patterns in atrial cell monolayers and its pharmacological response to ranolazine. METHODS: Confluent HL-1 cells were cultured in silicone membrane plates and were stretched to 110% of original length. The characteristics of in vitro fibrillation (dominant frequency, regularity index, density of phase singularities, rotor meandering, and rotor curvature) were analyzed using optical mapping in order to study the mechanoelectric response to stretch under control conditions and ranolazine action. RESULTS: HL-1 cell stretch increased fibrillatory dominant frequency (3.65 ± 0.69 vs. 4.35 ± 0.74 Hz, p < 0.01) and activation complexity (1.97 ± 0.45 vs. 2.66 ± 0.58 PS/cm2, p < 0.01) under control conditions. These effects were related to stretch-induced changes affecting the reentrant patterns, comprising a decrease in rotor meandering (0.72 ± 0.12 vs. 0.62 ± 0.12 cm/s, p < 0.001) and an increase in wavefront curvature (4.90 ± 0.42 vs. 5.68 ± 0.40 rad/cm, p < 0.001). Ranolazine reduced stretch-induced effects, attenuating the activation rate increment (12.8% vs. 19.7%, p < 0.01) and maintaining activation complexity-both parameters being lower during stretch than under control conditions. Moreover, under baseline conditions, ranolazine slowed and regularized the activation patterns (3.04 ± 0.61 vs. 3.65 ± 0.69 Hz, p < 0.01). CONCLUSION: Ranolazine attenuates the modifications of activation patterns induced by mechanical stretch in atrial myocyte monolayers.

Modifications of short-term intrinsic pacemaker variability in diet-induced metabolic syndrome: a study on isolated rabbit heart.

Metabolic syndrome (MetS) describes a condition associated with multiple diseases concomitantly such as diabetes, hypertension, obesity, and dyslipidemia. It has been linked with higher prevalence of cardiovascular disease, atrial fibrillation, and sudden cardiac death. One of the underlying mechanisms could be altered automaticity, which would reflect modifications of sinus node activity. These phenomena can be evaluated analyzing the components of heart rate variability (HRV). Our aim was to examine the modifications of sinus node variability in an isolated heart model of diet-induced obesity and MetS. Male NZW rabbits were randomly assigned to high-fat (HF, n = 8), control (HF-C, n = 7), high-fat, high-sucrose (HFHS, n = 9), and control (HFHS-C, n = 9) groups, fed with their respective diets during 18/28 weeks. After euthanasia, their hearts were isolated in a Langendorff system. We recorded 10-15 min of spontaneous activity. Short RR time series were analyzed, and standard HRV parameters were determined. One-way ANOVA, Kruskal-Wallis test, and bivariate correlation were used for statistical analysis (p < 0.05). We did find an increase in the complexity and irregularity of intrinsic pacemaker activity as shown by modifications of approximate entropy, sample entropy, minimum multiscale entropy, and complexity index in HFHS animals. Even though no differences were found in standard time and frequency-domain analyses, spectral heterogeneity increased in HFHS group. Animal weight and glucose intolerance were highly correlated with the modifications of intrinsic pacemaker variability. Finally, modifications of intrinsic HRV seemed to be reliant on the number of components of MetS present, given that only HFHS group showed significant changes towards an increased complexity and irregularity of intrinsic pacemaker variability.

Effect of chronic exercise on myocardial electrophysiological heterogeneity and stability. Role of intrinsic cholinergic neurons: A study in the isolated rabbit heart.

A study has been made of the effect of chronic exercise on myocardial electrophysiological heterogeneity and stability, as well as of the role of cholinergic neurons in these changes. Determinations in hearts from untrained and trained rabbits on a treadmill were performed. The hearts were isolated and perfused. A pacing electrode and a recording multielectrode were located in the left ventricle. The parameters determined during induced VF, before and after atropine (1µM), were: fibrillatory cycle length (VV), ventricular functional refractory period (FRPVF), normalized energy (NE) of the fibrillatory signal and its coefficient of variation (CV), and electrical ventricular activation complexity, as an approach to myocardial heterogeneity and stability. The VV interval was longer in the trained group than in the control group both prior to atropine (78±10 vs. 68±10 ms) and after atropine (76±8 vs. 67±10 ms). Likewise, FRPVF was longer in the trained group than in the control group both prior to and after atropine (53±8 vs. 42±7 ms and 50±6 vs. 40±6 ms, respectively), and atropine did not modify FRPVF. The CV of FRPVF was lower in the trained group than in the control group prior to atropine (12.5±1.5% vs. 15.1±3.8%) and, decreased after atropine (15.1±3.8% vs. 12.2±2.4%) in the control group. The trained group showed higher NE values before (0.40±0.04 vs. 0.36±0.05) and after atropine (0.37±0.04 vs. 0.34±0.06; p = 0.08). Training decreased the CV of NE both before (23.3±2% vs. 25.2±4%; p = 0.08) and after parasympathetic blockade (22.6±1% vs. 26.1±5%). Cholinergic blockade did not modify these parameters within the control and trained groups. Activation complexity was lower in the trained than in the control animals before atropine (34±8 vs. 41±5), and increased after atropine in the control group (41±5 vs. 48±9, respectively). Thus, training decreases the intrinsic heterogeneity of the myocardium, increases electrophysiological stability, and prevents some modifications due to muscarinic block.

Effects of the Inhibition of Late Sodium Current by GS967 on Stretch-Induced Changes in Cardiac Electrophysiology.

PURPOSE: Mechanical stretch increases sodium and calcium entry into myocytes and activates the late sodium current. GS967, a triazolopyridine derivative, is a sodium channel blocker with preferential effects on the late sodium current. The present study evaluates whether GS967 inhibits or modulates the arrhythmogenic electrophysiological effects of myocardial stretch. METHODS: Atrial and ventricular refractoriness and ventricular fibrillation modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts (n = 28) using epicardial multiple electrodes and high-resolution mapping techniques under control conditions and during the perfusion of GS967 at different concentrations (0.03, 0.1, and 0.3 µM). RESULTS: On comparing ventricular refractoriness, conduction velocity and wavelength obtained before stretch had no significant changes under each GS967 concentration while atrial refractoriness increased under GS967 0.3 µM. Under GS967, the stretch-induced changes were attenuated, and no significant differences were observed between before and during stretch. GS967 0.3 µM diminished the normal stretch-induced changes resulting in longer (less shortened) atrial refractoriness (138 ± 26 ms vs 95 ± 9 ms; p < 0.01), ventricular refractoriness (155 ± 18 ms vs 124 ± 16 ms; p < 0.01) and increments in spectral concentration (23 ± 5% vs 17 ± 2%; p < 0.01), the fifth percentile of ventricular activation intervals (46 ± 8 ms vs 31 ± 3 ms; p < 0.05), and wavelength of ventricular fibrillation (2.5 ±0.5 cm vs 1.7 ± 0.3 cm; p < 0.05) during stretch. The stretch-induced increments in dominant frequency during ventricular fibrillation (control = 38%, 0.03 µM = 33%, 0.1 µM = 33%, 0.3 µM = 14%; p < 0.01) and the stretch-induced increments in arrhythmia complexity index (control = 62%, 0.03µM = 41%, 0.1 µM = 32%, 0.3 µM = 16%; p < 0.05) progressively decreased on increasing the GS967 concentration. CONCLUSIONS: GS967 attenuates stretch-induced changes in cardiac electrophysiology.

Effects of S-Nitrosoglutathione on Electrophysiological Manifestations of Mechanoelectric Feedback.

Electromechanical coupling studies have described the intervention of nitric oxide and S-nitrosylation processes in Ca2+ release induced by stretch, with heterogeneous findings. On the other hand, ion channel function activated by stretch is influenced by nitric oxide, and concentration-dependent biphasic effects upon several cellular functions have been described. The present study uses isolated and perfused rabbit hearts to investigate the changes in mechanoelectric feedback produced by two different concentrations of the nitric oxide carrier S-nitrosoglutathione. Epicardial multielectrodes were used to record myocardial activation at baseline and during and after left ventricular free wall stretch using an intraventricular device. Three experimental series were studied: (a) control (n = 10); (b) S-nitrosoglutathione 10 µM (n = 11); and (c) S-nitrosoglutathione 50 µM (n = 11). The changes in ventricular fibrillation (VF) pattern induced by stretch were analyzed and compared. S-nitrosoglutathione 10 µM did not modify VF at baseline, but attenuated acceleration of the arrhythmia (15.6 ± 1.7 vs. 21.3 ± 3.8 Hz; p < 0.0001) and reduction of percentile 5 of the activation intervals (42 ± 3 vs. 38 ± 4 ms; p < 0.05) induced by stretch. In contrast, at baseline using the 50 µM concentration, percentile 5 was shortened (38 ± 6 vs. 52 ± 10 ms; p < 0.005) and the complexity index increased (1.77 ± 0.18 vs. 1.27 ± 0.13; p < 0.0001). The greatest complexity indices (1.84 ± 0.17; p < 0.05) were obtained during stretch in this series. S-nitrosoglutathione 10 µM attenuates the effects of mechanoelectric feedback, while at a concentration of 50 µM the drug alters the baseline VF pattern and accentuates the increase in complexity of the arrhythmia induced by myocardial stretch.

An Experimental Model of Diet-Induced Metabolic Syndrome in Rabbit: Methodological Considerations, Development, and Assessment.

In recent years, obesity and metabolic syndrome (MetS) have become a growing problem for public health and clinical practice, given their increased prevalence due to the rise of sedentary lifestyles and unhealthy eating habits. Thanks to animal models, basic research can investigate the mechanisms underlying pathological processes such as MetS. Here, we describe the methods used to develop an experimental rabbit model of diet-induced MetS and its assessment. After a period of acclimation, animals are fed a high-fat (10% hydrogenated coconut oil and 5% lard), high-sucrose (15% sucrose dissolved in water) diet for 28 weeks. During this period, several experimental procedures were performed to evaluate the different components of MetS: morphological and blood pressure measurements, glucose tolerance determination, and the analysis of several plasma markers. At the end of the experimental period, animals developed central obesity, mild hypertension, pre-diabetes, and dyslipidemia with low HDL, high LDL, and an increase of triglyceride (TG) levels, thus reproducing the main components of human MetS. This chronic model allows new perspectives for understanding the underlying mechanisms in the progression of the disease, the detection of preclinical and clinical markers that allow the identification of patients at risk, or even the testing of new therapeutic approaches for the treatment of this complex pathology.

Development and characterization of an experimental model of diet-induced metabolic syndrome in rabbit.

Metabolic syndrome (MetS) has become one of the main concerns for public health because of its link to cardiovascular disease. Murine models have been used to study the effect of MetS on the cardiovascular system, but they have limitations for studying cardiac electrophysiology. In contrast, the rabbit cardiac electrophysiology is similar to human, but a detailed characterization of the different components of MetS in this animal is still needed. Our objective was to develop and characterize a diet-induced experimental model of MetS that allows the study of cardiovascular remodeling and arrhythmogenesis. Male NZW rabbits were assigned to control (n = 15) or MetS group (n = 16), fed during 28 weeks with high-fat, high-sucrose diet. We measured weight, morphological characteristics, blood pressure, glycaemia, standard plasma biochemistry and the metabolomic profile at weeks 14 and 28. Liver histological changes were evaluated using hematoxylin-eosin staining. A mixed model ANOVA or unpaired t-test were used for statistical analysis (P<0.05). Weight, abdominal contour, body mass index, systolic, diastolic and mean arterial pressure increased in the MetS group at weeks 14 and 28. Glucose, triglycerides, LDL, GOT-AST, GOT/GPT, bilirubin and bile acid increased, whereas HDL decreased in the MetS group at weeks 14 and 28. We found a 40% increase in hepatocyte area and lipid vacuoles infiltration in the liver from MetS rabbits. Metabolomic analysis revealed differences in metabolites related to fatty acids, energetic metabolism and microbiota, compounds linked with cardiovascular disease. Administration of high-fat and high-sucrose diet during 28 weeks induced obesity, glucose intolerance, hypertension, non-alcoholic hepatic steatosis and metabolic alterations, thus reproducing the main clinical manifestations of the metabolic syndrome in humans. This experimental model should provide a valuable tool for studies into the mechanisms of cardiovascular problems related to MetS, with special relevance in the study of cardiovascular remodeling, arrhythmias and SCD.

Effects of JTV-519 on stretch-induced manifestations of mechanoelectric feedback.

JTV-519 is a 1,4-benzothiazepine derivative with multichannel effects that inhibits Ca2+ release from the sarcoplasmic reticulum and stabilizes the closed state of the ryanodine receptor, preventing myocardial damage and the induction of arrhythmias during Ca2+ overload. Mechanical stretch increases cellular Na+ inflow, activates the reverse mode of the Na+ /Ca2+ exchanger, and modifies Ca2+ handling and myocardial electrophysiology, favoring arrhythmogenesis. This study aims to determine whether JTV-519 modifies the stretch-induced manifestations of mechanoelectric feedback. The ventricular fibrillation (VF) modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts using epicardial multiple electrodes under control conditions (n=9) or during JTV-519 perfusion: 0.1 µmol/L (n=9) and 1 µmol/L (n=9). Spectral and mapping techniques were used to establish the baseline, stretch and post-stretch VF characteristics. JTV-519 slowed baseline VF and decreased activation complexity. These effects were dose-dependent (baseline VF dominant frequency: control=13.9±2.2 Hz; JTV 0.1 µmol/L=11.1±1.1 Hz, P<.01; JTV 1 µmol/L=6.6±1.1 Hz, P<.0001). The stretch-induced acceleration of VF (control=38.8%) was significantly reduced by JTV-519 0.1 µmol/L (19.8%) and abolished by JTV 1 µmol/L (-1.5%). During stretch, the VF activation complexity index was reduced in both JTV-519 series (control=1.60±0.15; JTV 0.1 µmol/L=1.13±0.3, P<.0001; JTV 1 µmol/L=0.57±0.21, P<.0001), and was independently related to VF dominant frequency (R=.82; P<.0001). The fifth percentile of the VF activation intervals, conduction velocity and wavelength entered the multiple linear regression model using dominant frequency as the dependent variable (R=-.84; P<.0001). In conclusion, JTV-519 slowed and simplified the baseline VF activation patterns and abolished the stretch-induced manifestations of mechanoelectric feedback.

Estudio experimental de los efectos de EIPA, losartán y BQ-123 sobre las modificaciones electrofisiológicas inducidas por el estiramiento miocárdico / Experimental study of the effects of EIPA, Losartan, and BQ-123 on electrophysiological changes induced by myocardial stretch

Introducción y objetivos: Se han implicado diversos mecanismos en la respuesta mecánica al estiramiento miocárdico, que incluyen la activación del intercambiador Na+/H+ por acciones autocrinas y paracrinas. Se estudia la participación de estos mecanismos en las respuestas electrofisiológicas al estiramiento agudo miocárdico mediante el análisis de los cambios inducidos con fármacos. Métodos: Se analizan las modificaciones de la fibrilación ventricular inducidas por el estiramiento agudo miocárdico en corazones de conejo aislados y perfundidos utilizando electrodos múltiples epicárdicos y técnicas cartográficas. Se estudian 4 series: control (n = 9); durante la perfusión del antagonista de los receptores de la angiotensina II, losartán (1 miM, n = 8); durante la perfusión del bloqueador del receptor de la endotelina A, BQ-123 (0,1 miM, n = 9), y durante la perfusión del inhibidor del intercambiador Na+/H+, EIPA (5-[N-ethyl-N-isopropyl]-amiloride) (1 miM, n = 9). Resultados: EIPA atenuó el aumento de la frecuencia dominante de la fibrilación producido por el estiramiento (control = 40,4%; losartán = 36% [no significativo]; BQ-123 = 46% [no significativo], y EIPA = 22% [p < 0,001]). Durante el estiramiento, la complejidad de los mapas de activación fue menor en la serie con EIPA (p < 0,0001) y también en esta serie fue mayor la concentración espectral de la arritmia (mayor regularidad): control = 18 ± 3%; EIPA = 26 ± 9% (p < 0,02); losartán = 18 ± 5% (no significativo), y BQ-123 = 18 ± 4% (no significativo). Conclusiones: El inhibidor del intercambiador Na+/H+ EIPA atenúa los efectos electrofisiológicos responsables de la aceleración y del aumento de la complejidad de la fibrilación ventricular producidos por el estiramiento agudo miocárdico. Por el contrario, el antagonista de los receptores de la angiotensina II, losartán, y el del receptor A de la endotelina, BQ-123, no modifican estos efectos (AU)

Introduction and objectives: Mechanical response to myocardial stretch has been explained by various mechanisms, which include Na+ /H+ exchanger activation by autocrine-paracrine system activity. Drug-induced changes were analyzed to investigate the role of these mechanisms in the electrophysiological responses to acute myocardial stretch. Methods: Multiple epicardial electrodes and mapping techniques were used to analyze changes in ventricular fibrillation induced by acute myocardial stretch in isolated perfused rabbit hearts. Four series were studied: control (n = 9); during perfusion with the angiotensin receptor blocker losartan (1 mM, n = 8); during perfusion with the endothelin A receptor blocker BQ-123 (0.1 mM, n = 9), and during perfusion with the Na+ /H+ exchanger inhibitor EIPA (5-[N-ethyl-N-isopropyl]-amiloride) (1 mM, n = 9). Results: EIPA attenuated the increase in the dominant frequency of stretch-induced fibrillation (control = 40.4%; losartan = 36% [not significant]; BQ-123 = 46% [not significant]; and EIPA = 22% [P < .001]). During stretch, the activation maps were less complex (P < .0001) and the spectral concentration of the arrhythmia was greater (greater regularity) in the EIPA series: control = 18 (3%); EIPA = 26 (9%) (P < .02); losartan = 18 (5%) (not significant); and BQ-123 = 18 (4%) (not significant). Conclusions: The Na+ /H+ exchanger inhibitor EIPA attenuated the electrophysiological effects responsible for the acceleration and increased complexity of ventricular fibrillation induced by acute myocardial stretch. The angiotensin II receptor antagonist losartan and the endothelin A receptor blocker BQ-123 did not modify these effects (AU)

Ranolazine Attenuates the Electrophysiological Effects of Myocardial Stretch in Langendorff-Perfused Rabbit Hearts.

PURPOSE: Mechanical stretch is an arrhythmogenic factor found in situations of cardiac overload or dyssynchronic contraction. Ranolazine is an antianginal agent that inhibits the late Na (+) current and has been shown to exert a protective effect against arrhythmias. The present study aims to determine whether ranolazine modifies the electrophysiological responses induced by acute mechanical stretch. METHODS: The ventricular fibrillation modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts using epicardial multiple electrodes under control conditions (n = 9) or during perfusion of the late Na(+) current blocker ranolazine 5 µM (n = 9). Spectral and mapping techniques were used to establish the ventricular fibrillation dominant frequency, the spectral concentration and the complexity of myocardial activation in three situations: baseline, stretch and post-stretch. RESULTS: Ranolazine attenuated the increase in ventricular fibrillation dominant frequency produced by stretch (23.0 vs 40.4 %) (control: baseline =13.6 ± 2.6 Hz, stretch = 19.1 ± 3.1 Hz, p < 0.0001; ranolazine: baseline = 1.4 ± 1.8 Hz, stretch =14.0 ± 2.4 Hz, p < 0.05 vs baseline, p < 0.001 vs control). During stretch, ventricular fibrillation was less complex in the ranolazine than in the control series, as evaluated by the lesser percentage of complex maps and the greater spectral concentration of ventricular fibrillation. These changes were associated to an increase in the fifth percentile of VV intervals during ventricular fibrillation (50 ± 8 vs 38 ± 5 ms, p < .01) and in the wavelength of the activation (2.4 ± 0.3 vs 1.9 ± 0.2 cm, p < 0.001) under ranolazine. CONCLUSIONS: The late inward Na(+) current inhibitor ranolazine attenuates the electrophysiological effects responsible for the acceleration and increase in complexity of ventricular fibrillation produced by myocardial stretch.

Experimental Study of the Effects of EIPA, Losartan, and BQ-123 on Electrophysiological Changes Induced by Myocardial Stretch.

INTRODUCTION AND OBJECTIVES: Mechanical response to myocardial stretch has been explained by various mechanisms, which include Na(+)/H(+) exchanger activation by autocrine-paracrine system activity. Drug-induced changes were analyzed to investigate the role of these mechanisms in the electrophysiological responses to acute myocardial stretch. METHODS: Multiple epicardial electrodes and mapping techniques were used to analyze changes in ventricular fibrillation induced by acute myocardial stretch in isolated perfused rabbit hearts. Four series were studied: control (n = 9); during perfusion with the angiotensin receptor blocker losartan (1 µM, n = 8); during perfusion with the endothelin A receptor blocker BQ-123 (0.1 µM, n = 9), and during perfusion with the Na(+)/H(+) exchanger inhibitor EIPA (5-[N-ethyl-N-isopropyl]-amiloride) (1 µM, n = 9). RESULTS: EIPA attenuated the increase in the dominant frequency of stretch-induced fibrillation (control=40.4%; losartan=36% [not significant]; BQ-123=46% [not significant]; and EIPA=22% [P<.001]). During stretch, the activation maps were less complex (P<.0001) and the spectral concentration of the arrhythmia was greater (greater regularity) in the EIPA series: control=18 (3%); EIPA = 26 (9%) (P < .02); losartan=18 (5%) (not significant); and BQ-123=18 (4%) (not significant). CONCLUSIONS: The Na(+)/H(+) exchanger inhibitor EIPA attenuated the electrophysiological effects responsible for the acceleration and increased complexity of ventricular fibrillation induced by acute myocardial stretch. The angiotensin II receptor antagonist losartan and the endothelin A receptor blocker BQ-123 did not modify these effects.

Heterogeneidades inducidas en el intervalo QT mediante enfriamiento/calentamiento epicárdico local. Estudio experimental / QT interval heterogeneities induced through local epicardial warming/cooling. An experimental study

Introducción y objetivos. La duración anormal del intervalo QT o su dispersión se han asociado con un incremento en el riesgo de arritmias ventriculares. Se analiza el posible efecto arritmogénico de sus variaciones inducidas mediante enfriamiento y calentamiento local epicárdico. Métodos. En 10 corazones aislados de conejo, se modificó escalonadamente la temperatura de una región epicárdica del ventrículo izquierdo (22 a 42 °C), registrando simultáneamente los electrogramas en dicha zona y en otra del mismo ventrículo. En ritmo sinusal, se determinó el QT y el intervalo de recuperación de la activación y, mediante estimulación programada, la velocidad de conducción y la inducción de arritmias ventriculares. Resultados. En la zona modificada respecto al valor basal (37 °C), el QT se prolongó en hipotermia máxima (195 ± 47 frente a 149 ± 12 ms; p < 0,05) y se acortó en hipertermia (143 ± 18 frente a 152 ± 27 ms; p < 0,05). El intervalo de recuperación de la activación tuvo el mismo comportamiento. La velocidad de conducción disminuyó en hipotermia y aumentó en hipertermia. No hubo cambios en la otra zona. Se observaron respuestas repetitivas en cinco experimentos, pero no se encontró dependencia entre su aparición y las condiciones de hipotermia e hipertermia inducidas (p > 0,34). Conclusiones. En el modelo experimental empleado, las variaciones locales de la temperatura epicárdica modulan el intervalo QT, el intervalo de recuperación de la activación y la velocidad de conducción. Las heterogeneidades inducidas no han favorecido la inducción de arritmias ventriculares (AU)

Introduction and objectives. Abnormal QT interval durations and dispersions have been associated with increased risk of ventricular arrhythmias. The present study examines the possible arrhythmogenic effect of inducing QT interval variations through local epicardial cooling and warming. Methods. In 10 isolated rabbit hearts, the temperatures of epicardial regions of the left ventricle were modified in a stepwise manner (from 22 °C to 42 °C) with simultaneous electrogram recording in these regions and in others of the same ventricle. QT and activation-recovery intervals were determined during sinus rhythm, whereas conduction velocity and ventricular arrhythmia induction were determined during programmed stimulation. This multicenter retrospective study involved patients from the UMBRELLA national registry who underwent replacement due to defibrillator battery depletion. The incidence of ventricular arrhythmias was determined via remote monitoring. Risk factors for sustained ventricular arrhythmia after replacement were analyzed. Results. In the area modified from baseline temperature (37 °C), the QT (standard deviation) was prolonged with maximum hypothermia (195 [47] vs 149 [12] ms; P < .05) and shortened with hyperthermia (143 [18] vs 152 [27] ms; P < .05). The same behavior was displayed for the activation-recovery interval. The conduction velocity decreased with hypothermia and increased with hyperthermia. No changes were seen in the other unmodified area. Repetitive responses were seen in 5 experiments, but no relationship was found between their occurrence and hypothermia or hyperthermia (P > .34). Conclusions. In the experimental model employed, local variations in the epicardial temperature modulate the QT interval, activation-recovery interval, and conduction velocity. Induction of heterogeneities did not promote ventricular arrhythmia occurrence (AU)

QT interval heterogeneities induced through local epicardial warming/cooling. An experimental study.

INTRODUCTION AND OBJECTIVES: Abnormal QT interval durations and dispersions have been associated with increased risk of ventricular arrhythmias. The present study examines the possible arrhythmogenic effect of inducing QT interval variations through local epicardial cooling and warming. METHODS: In 10 isolated rabbit hearts, the temperatures of epicardial regions of the left ventricle were modified in a stepwise manner (from 22°C to 42°C) with simultaneous electrogram recording in these regions and in others of the same ventricle. QT and activation-recovery intervals were determined during sinus rhythm, whereas conduction velocity and ventricular arrhythmia induction were determined during programmed stimulation. RESULTS: In the area modified from baseline temperature (37°C), the QT (standard deviation) was prolonged with maximum hypothermia (195 [47] vs 149 [12] ms; P<.05) and shortened with hyperthermia (143 [18] vs 152 [27] ms; P<.05). The same behavior was displayed for the activation-recovery interval. The conduction velocity decreased with hypothermia and increased with hyperthermia. No changes were seen in the other unmodified area. Repetitive responses were seen in 5 experiments, but no relationship was found between their occurrence and hypothermia or hyperthermia (P>.34). CONCLUSIONS: In the experimental model employed, local variations in the epicardial temperature modulate the QT interval, activation-recovery interval, and conduction velocity. Induction of heterogeneities did not promote ventricular arrhythmia occurrence.

Evaluación de la complejidad de la activación miocárdica durante la fibrilación ventricular. Estudio experimental / Evaluation of the complexity of myocardial activation during ventricular fibrillation. An experimental study

Introducción y objetivos. Analizar en un modelo experimental las características de la fibrilación ventricular en situaciones con distintos grados de complejidad y establecer la relación existente entre los datos aportados por distintos métodos de análisis de la arritmia. Métodos. En 27 preparaciones de corazón aislado de conejo estudiadas bajo la acción de fármacos (propranolol y KB-R7943) o procedimientos físicos (estiramiento) que causan distintos grados de variación de la complejidad de la activación miocárdica durante la arritmia, se han utilizado técnicas espectrales, morfológicas y cartográficas para procesar los registros obtenidos con multielectrodos epicárdicos. Resultados. La complejidad de la fibrilación ventricular objetivada mediante procedimientos cartográficos se ha relacionado con la frecuencia dominante, la energía normalizada del espectro, el índice de regularidad de las señales, sus coeficientes de variación y el área de las regiones de interés identificadas a partir de estos parámetros. En el análisis multivariable, se han aceptado como variables independientes el área de las regiones de interés relacionadas con la energía espectral y el coeficiente de variación de la energía (índice de complejidad = -0,005 × área de las regiones de la energía espectral -2,234 × coeficiente de variación de la energía +1,578; p = 0,0001; r = 0,68). Conclusiones. Los indicadores espectrales, morfológicos y, de manera independiente, los derivados del análisis de las regiones de interés de la energía normalizada permiten aproximarse de manera fiable a la evaluación de la complejidad de la fibrilación ventricular como una alternativa a los complejos procedimientos cartográficos (AU)

Introduction and objectives. An experimental model is used to analyze the characteristics of ventricular fibrillation in situations of variable complexity, establishing relationships among the data produced by different methods for analyzing the arrhythmia. Methods. In 27 isolated rabbit heart preparations studied under the action of drugs (propranolol and KB-R7943) or physical procedures (stretching) that produce different degrees of change in the complexity of myocardial activation during ventricular fibrillation, use was made of spectral, morphological, and mapping techniques to process the recordings obtained with epicardial multielectrodes. Results. The complexity of ventricular fibrillation assessed by mapping techniques was related to the dominant frequency, normalized spectral energy, signal regularity index, and their corresponding coefficients of variation, as well as the area of the regions of interest identified on the basis of these parameters. In the multivariate analysis, we used as independent variables the area of the regions of interest related to the spectral energy and the coefficient of variation of the energy (complexity index = -0.005 × area of the spectral energy regions -2.234 × coefficient of variation of the energy +1.578; P=.0001; r=0.68). Conclusions. The spectral and morphological indicators and, independently, those derived from the analysis of normalized energy regions of interest provide a reliable approach to the evaluation of the complexity of ventricular fibrillation as an alternative to complex mapping techniques (AU)

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.

Evaluation of the complexity of myocardial activation during ventricular fibrillation. An experimental study.

INTRODUCTION AND OBJECTIVES: An experimental model is used to analyze the characteristics of ventricular fibrillation in situations of variable complexity, establishing relationships among the data produced by different methods for analyzing the arrhythmia. METHODS: In 27 isolated rabbit heart preparations studied under the action of drugs (propranolol and KB-R7943) or physical procedures (stretching) that produce different degrees of change in the complexity of myocardial activation during ventricular fibrillation, use was made of spectral, morphological, and mapping techniques to process the recordings obtained with epicardial multielectrodes. RESULTS: The complexity of ventricular fibrillation assessed by mapping techniques was related to the dominant frequency, normalized spectral energy, signal regularity index, and their corresponding coefficients of variation, as well as the area of the regions of interest identified on the basis of these parameters. In the multivariate analysis, we used as independent variables the area of the regions of interest related to the spectral energy and the coefficient of variation of the energy (complexity index=-0.005×area of the spectral energy regions -2.234×coefficient of variation of the energy+1.578; P=.0001; r=0.68). CONCLUSIONS: The spectral and morphological indicators and, independently, those derived from the analysis of normalized energy regions of interest provide a reliable approach to the evaluation of the complexity of ventricular fibrillation as an alternative to complex mapping techniques.

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.