New markers for the risk of sudden death: Analysis of ventricular depolarisation

The identification of patients at high risk of sudden cardiac death is one of the greatest challenges for cardiologists. Non-invasive methods have, ch aracteristically, low predictive sensitivities and specificities. The role of abnormalities of ventricular repolarisation (QT interval) in the genesis of ventricular arrhythmias has been well established by experimental data. For this reason, parameters of ventricular repolarisation on the surface e lectrocardiogram have been proposed. However, taken in isolation, these mar kers are limited in terms of arrhythmic risk stratification. This report an alyses the value of the different parameters of ventricular repolarisation in the identification of high risk : QT dispersion, QT dynamics and T wave alternans. The dispersion of the QT interval is a marker of unhomogenous ventricular d epolarisation. This concept must be applied differently in such pathologica lly dissimilar diseases such as myocardial infarction, cardiomyopathy or th e long QT syndrome. Moreover, methodological problems make the interpretati on of many experimental studies very delicate. Frequency dependence of the QT helps select high risk patients after myocar dial infarction or with dilated cardiomyopathy. A common feature of patholo gical ventricular myocardium is the more pronounced frequency-dependency of the QT interval. The predictive value of this new index should be evaluate d and compared with other non-invasive risk factors in prospective trials. Studies of T wave alternans in selected high risk populations, essentially patients with coronary artery disease and dilated cardiomyopathy, have show n this parameter to be predictive of arrhythmia. The predictive value requi res confirmation in much larger populations at lower levels of risk of arrh ythmia and sudden death in prospective trials. A new field of research has opened up in the study of ventricular repolaris ation. Many studies have been undertaken on the duration of the QT interval , the morphology of the QT (including T wave alternans and post-pause chang es) and, finally, the dynamics of the QT interval. By regrouping, analysing and using these data correctly, we should be able to identify new markers of high arrhythmic risk.