Publication: Validación clínica de una nueva fórmula para el cálculo del intervalo QT corregido
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2018-04-16
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Universidad Complutense de Madrid
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Abstract
El intervalo QT representa Ja duración global de la actividad eléctrica del miocardio ventricular. La repolarización ventricular juega un papel importante en la fisiología cardiaca, y es fundamental en la patogénesis de múltiples arritmias. El alargamiento del QT s un indicador de repolarización anornal, y se ha asociado a arritmias y muerte súbita en varias cardiopatías, e incluso en la población general. El intervalo QT depende de la duración del ciclo cardiaco, por lo que debe corregirse para la frecuencia. A pesar de que se han propuesto muchas fórmulas, para la corrección del intervalo QT, la fórmula de Bazett es la más usada en la práctica: QTc = QT/ √RR. La formula de Bazett no proporciona una buena corrección, pero se continua usando por su aparente sencillez y por el peso de la costumbre. A partir de razonamientos matemáticos, hemos desarrollado una formula muy sencilla. QTc=QT/ (l+RR)/2. Que podría proporcionar una corrección precisa del intervalo QT. Además, nuestra nueva fórmula es la base de un método fácil para diagnosticar "de un vistazo" el alargamiento del QT. Para probar la nueva fórmula, hemos recuperado los datos de QT y RR de 19 estudios poblacionales reportados en la literatura. Los valores de QT y RR se utilizaron para calcular el QT corregido usando nuestra fórmula y las cuatro fórrnulas más usadas en la clínica : Bazett, Fridericia [QTc = QT/3√RR), Hodges (QTc = QT + 1.75 *(HR-60)), and Sagie (QTc = QT + 0.154* (1-RR)). Hemos determinado la pendiente de la línea de regresión de QTc vs RR para cada fórmula en cada estudio. Cuanto más se aproxime a cero esta pendiente, mejor es la corrección de una fórmula. Por otra parte, hemos evaluado las cinco fórmulas en dos grupos de pacientes adultos en nuestro medio. En términos generales, la fórmula de Bazett proporciona la peor corrección, mientras que las otras cuatro (Nueva Fórmula, Fridericia, Sagie y Hodges) tienen un comportamiento similar. Concluimos que la nueva fórmula para la corrección del QT es más exacta que la de Bazett, y más práctica que las otras fórmulas. Pensamos que nuestra nueva fórmula puede ser muy útil en la evaluación clínica diaria del intervalo QT.
The QT interval measures the global duration of the electrical activity of the ventricular myocardium. Repolarization plays a determining role in the normal function of the heart, and is often responsible for the development of arrhythmias. QT prolongation is a marker of abnormal repolarization, and it is a risk factor for arrhythmias and sudden death in many cardiac conditions, and even in the general population. Because the duration of QT interval depends upon the heart rate, the QT interval should be corrected for cardiac frequency. Of the man y formulas proposed for the correction of the QT interval, the one developed by Bazett, remains the most used in practice: QTc = QT/√RR. The popularity of the Bazett formula is based on its apparent simplicity, not on its merit. Based upon mathematical considerations, we hypothesize that the very simple formula: QTc=QT/ (l+RR)/2. would provide an accurate correction. Additionally, our new formula offers an easy, eyeballing method to diagnose QT prolongation. To test our new formula, QT and RR data were recovered from 19 large population studies reported in the literature. The QT and RR intervals were used to calculate the QTc by use of the new formula and other four different heart rate correction formulae: Bazett, Fridericia (QTc = QT/3√RR], Hodges (QTc = QT + 1.75 *(HR-60)], and Framingham (QTc = QT + 0.154*(1-RR)]. The slope of QTc-RR regression line for each QTc formula was detemúned and used to compare QT c formulae. Regression line slopes close to zero indicate a satisfactory correction. Further, we used the five formulae in two samples of adult patients in our setting. Generally, Bazett's formula pro vides the worst correction, the others four formulae have a similar accuracy. We conclude that the new QTc formula is more accurate than Bazett's correction and more convenient than the other formulae. We think that our new formula can be very useful in the routine clinical evaluation of the QT interval.
The QT interval measures the global duration of the electrical activity of the ventricular myocardium. Repolarization plays a determining role in the normal function of the heart, and is often responsible for the development of arrhythmias. QT prolongation is a marker of abnormal repolarization, and it is a risk factor for arrhythmias and sudden death in many cardiac conditions, and even in the general population. Because the duration of QT interval depends upon the heart rate, the QT interval should be corrected for cardiac frequency. Of the man y formulas proposed for the correction of the QT interval, the one developed by Bazett, remains the most used in practice: QTc = QT/√RR. The popularity of the Bazett formula is based on its apparent simplicity, not on its merit. Based upon mathematical considerations, we hypothesize that the very simple formula: QTc=QT/ (l+RR)/2. would provide an accurate correction. Additionally, our new formula offers an easy, eyeballing method to diagnose QT prolongation. To test our new formula, QT and RR data were recovered from 19 large population studies reported in the literature. The QT and RR intervals were used to calculate the QTc by use of the new formula and other four different heart rate correction formulae: Bazett, Fridericia (QTc = QT/3√RR], Hodges (QTc = QT + 1.75 *(HR-60)], and Framingham (QTc = QT + 0.154*(1-RR)]. The slope of QTc-RR regression line for each QTc formula was detemúned and used to compare QT c formulae. Regression line slopes close to zero indicate a satisfactory correction. Further, we used the five formulae in two samples of adult patients in our setting. Generally, Bazett's formula pro vides the worst correction, the others four formulae have a similar accuracy. We conclude that the new QTc formula is more accurate than Bazett's correction and more convenient than the other formulae. We think that our new formula can be very useful in the routine clinical evaluation of the QT interval.
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Medicina, leída el 13/07/2017