RESUMO
BACKGROUND: Abnormal dynamicity of repolarization is considered to be a marker of myocardial vulnerability contributing to increased risk of arrhythmic events and sudden death. However, little is known about QT dynamics in hypertrophic cardiomyopathy (HCM). In this study, we aimed to evaluate ventricular repolarization by QT dynamicity in patients with HCM, focusing on its value to define if it is able to differentiate among low- and high-risk HCM patients. METHODS: The linear regression slopes of the QT interval, measured to the apex and to the end of the T wave plotted against RR intervals (QTapex/RR and QTend/RR slopes, respectively) were calculated from 24-hour Holter recordings using a standard algorithm in 36 HCM patients and 64 control subjects. RESULTS: QTapex/RR and QTend/RR slopes were significantly steeper in the HCM patients in contrary to healthy control subjects (QTapex/RR = 0.22 + 0.08 vs 0.20 + 0.05, P = 0.0367; QTend/RR = 0.25 + 0.10 vs 0.20 + 0.06, P = 0.023). Moreover, the slopes of QTend/RR and QTapex/RR of high-risk patients were significantly steeper than those of control subjects while no significant differences were found among low-risk HCM patients and control subjects and only QTe/RR of high-risk patients was significantly different between low- and high-risk HCM patients. CONCLUSIONS: Our study results suggest that QT dynamicity is impaired in patients with HCM and may help to differentiate among low- and high-risk patients. Further studies are needed to elucidate the prognostic significance and clinical implications of impaired ventricular repolarization in patients with HCM.
Assuntos
Arritmias Cardíacas/complicações , Arritmias Cardíacas/fisiopatologia , Cardiomiopatia Hipertrófica/complicações , Cardiomiopatia Hipertrófica/fisiopatologia , Eletrocardiografia Ambulatorial , Frequência Cardíaca/fisiologia , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , RiscoRESUMO
BACKGROUND: Left ventricular hypertrophy (LVH) is associated with an increased risk of death, vulnerability to ventricular arrhythmia, and multiple electrophysiological abnormalities. OBJECTIVES: The purpose of the present study was to determine the gender-dependent differences in electrical remodeling and the susceptibility to ventricular arrhythmias in a rabbit model of renovascular hypertension. METHODS: Rabbits of both sexes underwent unilateral renal artery banding and contralateral nephrectomy or were placed in the control group. Data are expressed as mean +/- standard error of the mean. RESULTS: The duration of action potentials was prolonged in the LVH group compared with the control group in both male (123 +/- 2.4 ms and 151 +/- 2.3 ms vs. 180 +/- 5.1 ms and 196 +/- 3.1 ms for action potential duration [APD](90 Epi) and APD(90 Endo) of control [n = 5] and LVH rabbits [n = 8], respectively; P<.05) and female rabbits (131 +/- 1.9 ms and 166 +/- 2.0 ms vs. 156 +/- 4.2 ms and 175 +/- 2.2 ms for APD(90 Epi) and APD(90 Endo) of control [n = 5] and LVH rabbits [n = 7], respectively; P<.05). Moreover, the gender-dependent differences in repolarization were opposite to those seen under control conditions. In LVH rabbits, APD(90) was greater in males than in females. The changes induced in APD lead to a greater transmural dispersion of repolarization (38 +/- 6.6 ms vs. 19 +/- 6.5 ms for males and females, respectively; P<.05). In addition, while control rabbits did not show induction of arrhythmias, an enhanced susceptibility to ventricular arrhythmia was seen in LVH male rabbits (6/8 male vs. 1/7 female LVH rabbits; P<.05). CONCLUSION: We conclude that the electrical remodeling associated with LVH inverted the gender-dependent differences, with male rabbits now exhibiting action potentials with longer durations both in the endocardial and epicardial surface of the left ventricle, increased dispersion of repolarization, and increased vulnerability to ventricular arrhythmia induction.
Assuntos
Hipertrofia Ventricular Esquerda/complicações , Taquicardia Ventricular/etiologia , Taquicardia Ventricular/fisiopatologia , Remodelação Ventricular/fisiologia , Potenciais de Ação/fisiologia , Animais , Modelos Animais de Doenças , Ecocardiografia , Feminino , Hipertrofia Ventricular Esquerda/diagnóstico por imagem , Hipertrofia Ventricular Esquerda/fisiopatologia , Masculino , Coelhos , Fatores SexuaisRESUMO
INTRODUCTION: Repolarization heterogeneity has been shown to constitute a substrate for malignant ventricular arrhythmias. Noninvasive measurement of abnormal repolarization through assessment of QT interval dispersion from the resting standard 12-lead ECG initially had shown promise in assessing arrhythmia risk but was challenged recently. The relative T wave residuum (TWR) has been proposed recently to reflect regional repolarization dispersion more accurately. We analyzed the role played by the dipolar and nondipolar components in determining TWR. METHODS AND RESULTS: Singular value decomposition was applied to the repolarization signals obtained from isolated rabbit hearts using a 5 x 8 array multielectrode recording system during premature beats (N = 11) and after d-sotalol (N = 9) exposure. Both the dipolar and nondipolar components of the T wave increased significantly during premature stimulation and after d-sotalol exposure. The relative TWR decreased significantly during premature stimulation but did not change after d-sotalol. Changes in the dipolar and nondipolar components of the second half of the T wave were significantly greater than those corresponding to the first half during premature stimulation, and a significant correlation was observed between the nondipolar components of the second half of the T wave and the T(peak-end) interval. CONCLUSION: Conditions exist during which both the dipolar and nondipolar components can change simultaneously. Under these conditions, the relative TWR may not reflect regional heterogeneity of repolarization with accuracy. The nondipolar components of the second half of the T wave can be linked to assessment of the transmural dispersion of repolarization.
Assuntos
Eletrocardiografia , Sistema de Condução Cardíaco/fisiopatologia , Antagonistas Adrenérgicos beta/farmacologia , Animais , Antiarrítmicos/farmacologia , Modelos Animais de Doenças , Estimulação Elétrica , Técnicas Eletrofisiológicas Cardíacas , Sistema de Condução Cardíaco/efeitos dos fármacos , Masculino , Modelos Cardiovasculares , Coelhos , Sotalol/farmacologia , Função Ventricular/efeitos dos fármacos , Complexos Ventriculares Prematuros/fisiopatologiaRESUMO
OBJECTIVES: Firstly, to compare gender-dependent differences of cardiac repolarization in both adult and young rabbits. Secondly, to analyze the effect of gonadectomy on these gender differences in cardiac repolarization. METHODS: We evaluated potential gender differences in cardiac repolarization with both microelectrode and ECG recordings. QT(end), JT(end), and T(peak-end) intervals and action potential durations at 30%, 50% and 90% of full repolarization were used to assess ventricular repolarization in adult (normal and gonadectomized) and young rabbits of both sexes. RESULTS: Adult rabbits exhibited clear gender-related differences in repolarization evidenced by significantly longer JT(end) and T(peak-end) intervals and significantly longer APD30, APD50 and APD90 in females. These gender-related differences in repolarization were absent in young rabbits and were abolished by gonadectomy. CONCLUSIONS: Developmental changes of repolarization are present in rabbits. These changes are in agreement with those reported in humans and may further support the role played by sex hormones in the modulation of cardiac repolarization.
Assuntos
Hormônios Esteroides Gonadais/fisiologia , Sistema de Condução Cardíaco/fisiopatologia , Coração/crescimento & desenvolvimento , Caracteres Sexuais , Potenciais de Ação/fisiologia , Animais , Eletrocardiografia , Eletrofisiologia , Feminino , Masculino , Microeletrodos , CoelhosRESUMO
INTRODUCTION: The influence of activation sequence on the rate of rise of the depolarization phase of action potentials in atrial or ventricular muscles has been well established. However, whether myocardial fiber orientation is important in modulating the repolarization process is unclear. METHODS AND RESULTS: We examined the influence of activation sequence on the repolarization phase of action potentials in epicardial tissues from the right and left ventricles of domestic pigs. Whereas cells from the right ventricle exhibited direction-dependent differences in action potential duration at 30%, 50%, and 90% of full repolarization (190.6 +/- 31.1 msec vs 181.8 +/- 32.8 msec, 240.3 +/- 23.5 msec vs 236.7 +/- 25.4 msec, and 291.3 +/- 23.7 msec vs 287.4 +/- 25.1 msec for longitudinal and transverse propagation, respectively; P < 0.001), a similar duration of repolarization during both directions of propagation was observed in cells from the left ventricle at 50% and 90% of full repolarization (241.4 +/- 39.4 msec and 285.5 +/- 39.5 msec vs 240.4 +/- 38.9 msec and 284.9 +/- 39.6 msec for longitudinal and transverse propagation respectively; P = NS). A slight but significant difference was found at 30% of full repolarization in cells from the left ventricle (190.4 +/- 39.0 msec vs 187.0 +/- 38.0 msec for longitudinal and transverse propagation, respectively; P < 0.05). In the left ventricle, the duration of repolarization did not change as the distance between the recording site and stimulation site increased. CONCLUSION: The direction of wavefront propagation with respect to fiber orientation may not play an important role in modulating the duration of repolarization in epicardial cells from the left ventricle.
Assuntos
Potenciais de Ação/fisiologia , Estimulação Elétrica/métodos , Sistema de Condução Cardíaco/fisiologia , Função Ventricular , Potenciais de Ação/efeitos dos fármacos , Animais , Anisotropia , Eletrocardiografia , Eletrofisiologia/métodos , Humanos , Técnicas In Vitro , Masculino , Pericárdio/fisiologia , Potássio/farmacologia , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Suínos , TemperaturaRESUMO
En el presente trabajo se vuelca nuestra experiencia en el estudio de la repolarización ventricular. Hemos podido comprobar, en primer lugar, que las caracterísitcas anisotrópicas del tejido cardíaco son capaces de modular la repolarización ya que, en el epicardio del ventrículo derecho los potenciales de acción son más cortos tanto al 30 como al 50 y al 90 por ciento de la repolarización completa, durante la propagación transversal cuando se los compara con los obtenidos durante la propagación longitudinal o paralela al eje mayor de las fibras cardíacas. Sin embargo esto no se cumple en el ventriculo izquierdo (Tabla 1). Este comportamiento diferente en la modulación de la repolarización, probablemente ligado con la presencia de propiedades anisotrópicas no homogéneas entre ambos ventrículos, contribuye a su vez a modular la dispersión de la repolarización ventricular especialmente ante situaciones en las que el efecto electrotónico se vea favorecido por la presencia de conducción lenta. En segundo lugar pudimos comprobar que la evaluación de la dispersión de la repolarización incrementa su poder de discriminación si se la mide con una grilla de electrodos distribuídos homogeneamente en la superficie del tórax. En tercer lugar comprobamos que el incremento en la dispersión de la repolarización ventricular en función del intervalo de acoplamiento de un latido prematuro exhibe un comportamiento diferencial dependiente del sitio de estimulación. Esto es mientras la dispersión de la repolarización se incrementa monotónicamente a medida que se acorta el intervalo de acoplamiento de un latido prematuro cuando el sitio de aplicación de los estímulos se ubica en el ventrículo derecho. Cuando los estímulos fueron aplicados en el ventrículo izquierdo pudimos observar que la dispersión mostró una reducción incicial en función del período de acoplamiento hasta alcanzar un mínimo y a partir de allí exhibe un incremento monotónico. Finalmente, ha sido sugerido que cambios en la forma -mas que cambios en la duración- de la onda T son los que contribuyen a aumentar la heterogeneidad de la repolarización. En este sentido, se ha mostrado que la alternancia en la onda T, que es una manifestación extrema de anormalidades en la forma de la onda T, puede relacionarse con incremento del riesgo a las taquiarritmias ventriculares... (TRUNCADO)
Assuntos
Animais , Coelhos , Anisotropia , Arritmias Cardíacas/fisiopatologia , Bioensaio , Modelos Cardiovasculares , Pericárdio/fisiologia , Potenciais de Ação , Sistema de Condução Cardíaco/fisiologia , Ventrículos do Coração/fisiologia , SuínosRESUMO
En el presente trabajo se vuelca nuestra experiencia en el estudio de la repolarización ventricular. Hemos podido comprobar, en primer lugar, que las caracterísitcas anisotrópicas del tejido cardíaco son capaces de modular la repolarización ya que, en el epicardio del ventrículo derecho los potenciales de acción son más cortos tanto al 30 como al 50 y al 90 por ciento de la repolarización completa, durante la propagación transversal cuando se los compara con los obtenidos durante la propagación longitudinal o paralela al eje mayor de las fibras cardíacas. Sin embargo esto no se cumple en el ventriculo izquierdo (Tabla 1). Este comportamiento diferente en la modulación de la repolarización, probablemente ligado con la presencia de propiedades anisotrópicas no homogéneas entre ambos ventrículos, contribuye a su vez a modular la dispersión de la repolarización ventricular especialmente ante situaciones en las que el efecto electrotónico se vea favorecido por la presencia de conducción lenta. En segundo lugar pudimos comprobar que la evaluación de la dispersión de la repolarización incrementa su poder de discriminación si se la mide con una grilla de electrodos distribuídos homogeneamente en la superficie del tórax. En tercer lugar comprobamos que el incremento en la dispersión de la repolarización ventricular en función del intervalo de acoplamiento de un latido prematuro exhibe un comportamiento diferencial dependiente del sitio de estimulación. Esto es mientras la dispersión de la repolarización se incrementa monotónicamente a medida que se acorta el intervalo de acoplamiento de un latido prematuro cuando el sitio de aplicación de los estímulos se ubica en el ventrículo derecho. Cuando los estímulos fueron aplicados en el ventrículo izquierdo pudimos observar que la dispersión mostró una reducción incicial en función del período de acoplamiento hasta alcanzar un mínimo y a partir de allí exhibe un incremento monotónico. Finalmente, ha sido sugerido que cambios en la forma -mas que cambios en la duración- de la onda T son los que contribuyen a aumentar la heterogeneidad de la repolarización. En este sentido, se ha mostrado que la alternancia en la onda T, que es una manifestación extrema de anormalidades en la forma de la onda T, puede relacionarse con incremento del riesgo a las taquiarritmias ventriculares... (TRUNCADO) (AU)