Résumé
Resumen. Introducción: La prolongación del intervalo QT en el electrocardiograma es un conocido factor de riesgo para desarrollar eventos cardiovasculares. En Latinoamérica existe poca evidencia acerca de la epidemiología de este tipo de alteraciones electrocardiográficas. El objetivo de este estudio fue evaluar la prevalencia del intervalo QT corregido largo según cuatro fórmulas. Metodología: Estudio descriptivo retrospectivo. Se realizó una revisión de 156 registros electrocardiográficos de 12 derivaciones realizados a pacientes mayores a 40 años. Las medidas se realizaron manualmente y posteriormente los valores se ajustaron a la frecuencia cardiaca mediante cuatro fórmulas validadas existentes. Se consideró intervalo QT largo cuando la duración sobrepasaba los 470 ms. Resultados: De los 156 registros analizados, 55.7% de los registros pertenecieron a pacientes de sexo femenino y la edad media fue 70.3 ± 9.7 años. 9.6% de los registros fueron considerados como largos mediante la fórmula de Bazzet, 4.4% mediante la fórmula de Hodges, 3.8% mediante la fórmula de Fridericia y 3.2% mediante la fórmula deFramingham. La fórmula de Fridericia fue hallada como la más consistente para ajustar el intervalo QT a la frecuencia cardiaca. Conclusión: Dependiendo de la fórmula utilizada la prevalencia del intervalo QT largo varió significativamente. La fórmula de Fridericia fue la que demostró mejor consistencia.
Abstract. Introduction: The prolongation of the QT interval in the electrocardiogram is a well-known risk factor for developing cardiovascular events. In Latin America there is no much evidence about the epidemiology of electrocardiographic alterations. The objective of this study was to evaluate the prevalence of long corrected QT interval according to four formulas. Methodology: Retrospective descriptive study. A total of 156 electrocardiographic records of 12 referrals made to patients older than 40 years were review. The measurements were made manually and later the values were adjusted to the heart rate by means of four existing validated formulas. The long QT interval was considered when the duration exceeded 470ms. Results: Of the 156 records analyzed, 55.7% of the records belonged to female patients and the mean age was 70.3 ± 9.7 years. 9.6% of the records were considered long using the Bazzet formula, 4.4% according to the Hodges formula, 3.8% according to the Fridericia formula and 3.2% according to the Framingham formula. The formula of Fridericia was found to be the most consistent to adjust the QT interval to the heart rate. Conclusion: Depending on the formula used, the prevalence of the long QT interval varied significantly. The formula of Fridericia was the one that showed the best consistency.
Resumo. Introdução: O prolongamento do intervalo QT no eletrocardiograma é um fator de risco conhecido para o desenvolvimento de eventos cardiovasculares. Na América Latina, há poucas evidências sobre a epidemiologia desse tipo de alteração eletrocardiográfica. O objetivo deste estudo foi avaliar a prevalência do intervalo QT longo corrigido de acordo com quatro fórmulas. Metodologia: Estudo descritivo retrospectivo. Uma revisão de 156 registros eletrocardiográficos de 12 derivações realizadas em pacientes com mais de 40 anos foi realizada. As medidas foram feitas manualmente e posteriormente os valores foram ajustados à freqüência cardíaca por meio de quatro fórmulas validadas existentes. O intervalo QT longo foi considerado quando a duração ultrapassou 470 ms. Resultados: Dos 156 prontuários analisados, 55,7% dos prontuários pertenciam a pacientes do sexo feminino e a média de idade foi de 70,3 ± 9,7 anos. 9,6% dos registros foram considerados longos usando a fórmula de Bazzet, 4,4% usando a fórmula de Hodges, 3,8% usando a fórmula de Fridericia e 3,2% usando a fórmula de Fraingham. A fórmula de Fridericia foi considerada a mais consistente para ajustar o intervalo QT à frequência cardíaca. Conclusão: Dependendo da fórmula utilizada, a prevalência do intervalo QT longo variou significativamente. A fórmula da Fridericia foi a que apresentou a melhor consistência.
Résumé
Long QT interval syndrome ( LQTS ) is an ion channelopathy disease which holds the characteristics of the prolongation of QT interval on electrocardiogram ( ECG ) and ventricular arrhythmia ( VT) . The occurrence of this disease is associated with mutations among potassium channel protein,sodium channel protein,calcium channel related factor,and membrane adaptation protein. Now,there were 13 genes that their mutation results in LQTS. The clinical feature is mainly manifested on the abnormal prolongation of QT interval,the giant T wave alternans on the ECG and the syncope or cardiac sudden death resulted from torsades de pointes(TdP) ventricular tachycardia. Arrhythmic events are closely related with the gene type involved. On LQTS1,the arrhythmia was normally triggered by sports and emotional excitement,and LQTS2 was by loud noises. The emergency treatment is required when the TdP occurred, because it will result in rapid deterioration of circulatory perfusion and sudden death. The emergency treatment includes intravenous administration of magnesium sulfate,synchronized or nonsynchronized DC shock for cardioversion,correcting internal environmental disturbance such as hypokalemia,and terminating the use of certain drugs which could cause the prolongation of QT interval. The long term management of LQTS includes lifestyle intervention, oral administration of β-blockers, implantation of implantable cardioverter defibrillator ( ICD ) , left cardiac sympathetic denervation and certain target drugs.
Résumé
Long QT interval syndrome ( LQTS ) is an ion channelopathy disease which holds the characteristics of the prolongation of QT interval on electrocardiogram ( ECG ) and ventricular arrhythmia ( VT) . The occurrence of this disease is associated with mutations among potassium channel protein,sodium channel protein,calcium channel related factor,and membrane adaptation protein. Now,there were 13 genes that their mutation results in LQTS. The clinical feature is mainly manifested on the abnormal prolongation of QT interval,the giant T wave alternans on the ECG and the syncope or cardiac sudden death resulted from torsades de pointes(TdP) ventricular tachycardia. Arrhythmic events are closely related with the gene type involved. On LQTS1,the arrhythmia was normally triggered by sports and emotional excitement,and LQTS2 was by loud noises. The emergency treatment is required when the TdP occurred, because it will result in rapid deterioration of circulatory perfusion and sudden death. The emergency treatment includes intravenous administration of magnesium sulfate,synchronized or nonsynchronized DC shock for cardioversion,correcting internal environmental disturbance such as hypokalemia,and terminating the use of certain drugs which could cause the prolongation of QT interval. The long term management of LQTS includes lifestyle intervention, oral administration of β-blockers, implantation of implantable cardioverter defibrillator ( ICD ) , left cardiac sympathetic denervation and certain target drugs.