Experimental study of the so called left ventricular isovolumic relaxation phase.

INTRODUCTION AND OBJECTIVES: Left ventricular filling begins in the ventricular isovolumic relaxation phase. According to the Torrent-Guasp myocardial band theory, this phase results from the contraction of the final portion of the myocardial band: the ascending segment of the apical loop. The objectives were to study the myocardial mechanisms influencing transmitral flow during early diastole and to determine whether the rapid ventricular filling phase involves contraction or relaxation. METHODS: An experimental in vivo pig model was used. Regional contractility in three segments of the myocardial band was assessed using piezoelectric crystals and mitral flow was measured by echo-Doppler ultrasonography at baseline and after akinesia had been induced in the ascending segment by 2.5% formaldehyde infusion. Changes in intracavitary pressure in the left ventricle and left atrium and flow alterations in the aortic root were recorded. The start of the isovolumic relaxation phase was identified using the time at which the ejection of blood ceases, as indicated by aortic flow measurements. RESULTS: During the left ventricular isovolumetric relaxation phase, the ascending segment of the apical loop was undergoing contraction. The infusion of formaldehyde into this segment affected the extent to which the intraventricular pressure could decrease, prolonged the isovolumic relaxation phase and resulted in a lower minimum pressure. It also produced a significant decrease in transmitral flow velocity in early diastole and an increase at end-diastole. CONCLUSIONS: The rapid ventricular filling phase is characterized by contraction.

Estudio experimental de la llamada fase de relajación isovolumétrica del ventrículo izquierdo / Experimental study of the so called left ventricular isovolumic relaxation phase

Introducción y objetivos. El llenado del ventrículo izquierdo se inicia con la fase de relajación isovolumétrica ventricular. En la teoría de la banda miocárdica de Torrent-Guasp, esta fase se produce como consecuencia de la contracción de la porción final de la banda muscular, el segmento ascendente de la lazada apexiana. El objetivo es estudiar los mecanismos miocárdicos involucrados en el flujo transmitral durante la protodiástole y discernir si la fase de llenado rápido ventricular es un proceso de relajación o de contracción. Métodos. Modelo experimental in vivo en cerdos. Se estudia la contractilidad regional con cristales piezoeléctricos en tres segmentos de la banda miocárdica y el flujo transmitral con eco-Doppler, en situación basal y tras la producción de acinesia del segmento ascendente mediante la infiltración con formaldehído al 2,5%. Se registran las curvas de presión intracavitarias del ventrículo izquierdo y la aurícula izquierda y el flujo en la raíz aórtica. Para determinar el inicio de la fase de relajación isovolumétrica, hemos identificado el final de la expulsión de sangre en la curva del flujo aórtico. Resultados. Durante la fase de relajación isovolumétrica del ventrículo izquierdo, el segmento ascendente de la lazada apexiana está contrayéndose. La infiltración con formaldehído de este segmento afecta a la capacidad de reducir la presión intraventricular, y la duración de la fase de relajación isovolumétrica se prolonga y se alcanza una menor presión mínima. Se produce un descenso significativo en las velocidades del flujo transmitral de la protodiástole y un incremento en la telediástole. Conclusiones. La fase de llenado rápido ventricular es un proceso de contracción (AU)

Introduction and objectives. Left ventricular filling begins in the ventricular isovolumic relaxation phase. According to the Torrent-Guasp myocardial band theory, this phase results from the contraction of the final portion of the myocardial band: the ascending segment of the apical loop. The objectives were to study the myocardial mechanisms influencing transmitral flow during early diastole and to determine whether the rapid ventricular filling phase involves contraction or relaxation. Methods. An experimental in vivo pig model was used. Regional contractility in 3 segments of the myocardial band was assessed using piezoelectric crystals and mitral flow was measured by echo-Doppler ultrasonography at baseline and after akinesia had been induced in the ascending segment by 2.5% formaldehyde infusion. Changes in intracavitary pressure in the left ventricle and left atrium and flow alterations in the aortic root were recorded. The start of the isovolumic relaxation phase was identified using the time at which the ejection of blood ceases, as indicated by aortic flow measurements. Results. During the left ventricular isovolumetric relaxation phase, the ascending segment of the apical loop was undergoing contraction. The infusion of formaldehyde into this segment affected the extent to which the intraventricular pressure could decrease, prolonged the isovolumic relaxation phase and resulted in a lower minimum pressure. It also produced a significant decrease in transmitral flow velocity in early diastole and an increase at end-diastole. Conclusions. The rapid ventricular filling phase is characterized by contraction (AU)

Effect of short-duration electrically induced tachycardia on regional myocardial contractility.

BACKGROUND: Tachycardia is a physiological mechanism for adapting cardiac output to modifications in energy consumption in the organism. The repercussions that short-duration tachycardia has on myocardial contractility have not been sufficiently studied.
To study the effects of short-duration tachycardia on regional myocardial function in the anterior face of the left ventricle depending on the rate, duration, and origin of the electrical stimulation producing the tachycardia. MATERIAL/METHODS: Two series were studied in an in vivo canine experimental model. Stimulation was performed in the right atrium and in the base of the left ventricle at a frequency 20 and 40% above the basal rate. The duration of each pacing episode was 10, 20, and 40 minutes followed by a recovery period of 40 minutes. ECG, left ventricular pressure, and regional function curves of a myocardial segment were studied. RESULTS: During atrial pacing there was a similar decrease in both regional segment lengths (end-systolic and end-diastolic lengths) and no variation in the shortening fraction or in hemodynamic parameters. During ventricular pacing, systolic pressure in the left ventricle decreased, end-diastolic pressure increased, end-diastolic length shortened (meaning less ventricular filling), and the end-systolic length increased, leading to a reduced shortening fraction or regional contractility alteration which was temporarily maintained once pacing ceased. CONCLUSIONS: The transient persistence of segment dysfunction after induced ventricular tachycardia ceases indicates the activation of a different, unknown mechanism.