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1.
Rev. esp. cardiol. (Ed. impr.) ; 67(12): 993-998, dic. 2014.
Article in Spanish | IBECS | ID: ibc-130166

ABSTRACT

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)


Subject(s)
Animals , Male , Female , Long QT Syndrome/physiopathology , Long QT Syndrome/veterinary , Systole , Models, Animal , Electrophysiology/methods , Electrophysiology/trends , Cardiac Electrophysiology/methods , Cardiac Electrophysiology/trends , Electric Stimulation/methods , Animal Experimentation , Cardiac Pacing, Artificial/methods , Cardiac Pacing, Artificial/veterinary , Hypothermia/physiopathology , Hypothermia , Hypothermia/veterinary , Arrhythmias, Cardiac/veterinary , Arrhythmia, Sinus/veterinary
2.
Rev Esp Cardiol (Engl Ed) ; 67(12): 993-8, 2014 Dec.
Article in English | MEDLINE | ID: mdl-25432709

ABSTRACT

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.


Subject(s)
Heart Rate/physiology , Pericardium/physiology , Animals , Arrhythmias, Cardiac/etiology , Arrhythmias, Cardiac/physiopathology , Cold Temperature/adverse effects , Electric Stimulation , Electrocardiography , Heart Conduction System/physiology , Hot Temperature/adverse effects , Rabbits , Ventricular Function/physiology
3.
Med Eng Phys ; 33(5): 653-9, 2011 Jun.
Article in English | MEDLINE | ID: mdl-21256794

ABSTRACT

Cardiac electrical activity is influenced by temperature. In experimental models, the induction of hypothermia and/or hyperthermia has been used for the study of mechanisms of cardiac arrhythmia. A system that allows for localized, controlled induction, besides simultaneously recording electrical activity in the same induced area, needs to be developed ad hoc. This article describes the construction and application of a new system capable of locally modifying the epicardial temperature of isolated hearts and of carrying out cardiac mapping with sufficient spatial resolution. The system is based on a thermoelectric refrigerator and an array of 128 stainless steel unipolar electrodes in encapsulated epoxy of good thermal conductivity. The surface of the electrode is shaped to match the ventricular curvature. The electrode-device was tested on 7 isolated perfused rabbit hearts following the Langendorff technique. Quality recordings were obtained for the left ventricle at temperatures of 37° C, 22° C and 42° C. The effects of temperature were explored in relation to two electrophysiological parameters: the QT interval during sinus rhythm and the VV interval during ventricular fibrillation. The results indicate that this is a suitable method for creating and analyzing electrophysiological heterogeneities induced by temperature in the experimental model.


Subject(s)
Electrophysiological Phenomena , Epicardial Mapping/instrumentation , Temperature , Animals , Heart Rate/physiology , Heart Ventricles/physiopathology , Rabbits , Ventricular Fibrillation/physiopathology , Ventricular Function/physiology
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