Prolongation of the QT c interval is a sign of prolonged repolarisation of the ventricular myocardium. severe bradycardia (especially complete heart block).cerebrovascular disease (subarachnoid haemmorhage, ischaemic stroke).electrolyte abnormality (hypokalaemia, hypomagnesaemia).cardiac pathology (heart failure, ischaemia, myocarditis).Jervell and Lange-Nielsen syndrome (cardiacĪbnormality - autosomal dominant & associated.Romano-Ward syndrome (autosomal dominant). The QT interval is the time between the initiation of the QRS complex and the termination of the T wave in the electrocardiogram.Ĭongenital (at least six genetic mutations identified) In children up to the age of 15, the upper limit of normal is 440 ms. The observed QT (QT o) interval can be corrected (QT c) for heart rate by using the following formula where RR is the interval in seconds between two successive R waves on the ECG.Ī QT c interval of 430 milliseconds (ms) is accepted as the upper limit of normal for men and 450 ms as the upper limit of normal for women. A diurnal variation of the QT interval associated with the variations in sympathetic tone has also been described. The QT interval is dependent on heart rate, age and gender. When multiple leads are used the longest QT interval is considered to be the true QT interval. This 'T wave dispersion' occurs when the terminal portion of the T wave is isoelectric in some leads. There is commonly a variation in the QT interval measured in the various leads of the ECG. It represents the duration between the onset of depolarisation and the completion of repolarisation of the myocardium. The QT interval is the time between the start of the QRS complex and the end of the T wave in the ECG ( Fig.
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