Diagnosis and risk stratification in patients at risk of sudden cardiac death

Abstract

Patients after acute myocardial infarction suffer from an increased risk of sudden cardiac arrhythmogenic death within a time period of one to two years following the acute event. Despite improving strategies for immediate revascularization in the early phase of the infarction (thrombolysis, acute coronary intervention), the rate of sudden cardiac death remains unchanged. Several non-invasive techniques for risk stratification are established: clinical risk profile, measurement of left ventricular function (LV-ejection fraction), resting ECG (detection of repolarization disorders: QT-dispersion, QT-variability), an ECG stress test (detection and severity of myocardial ischemia), ambulatory ECG monitoring (qualitative and quantative analysis of ventricular arrhythmias, QT-variability), surface high resolution ECG (detection of ventricular late potentials), measurement of T-wave alternans (alternans ratio), measurement of the activity and balance of the autonomic nervous system (heart rate variability, baroreflex sensitivity). In addition, programmed ventricular stimulation (PVS) serves as an invasive risk stratification technique (detection of an arrhythmogenic substrate). All of these parameters have been shown to be indicative of an increased risk of sudden cardiac death. However, the prognostic power of the non-invasive techniques is limited. In general, the prognostic value of a negative test is reasonably high (90–100% depending on the test used), whereas the prognostic value of a positive test is rather low (4–42% depending on the test used). The combination of several non-invasive tests may significantly improve the positive predictive value above 50%. However, this goes along with a significant decrease of sensitivity below 50%. Therefore, a combination of non-invasive tests with an invasive electrophysiologic study (PVS) seems reasonable. Furthermore, with regard to cost intensive therapies, such as implantable cardioverter defibrillator or antiarrhythmic therapies with sever side effects, an optimal selection for different therapies is mandatory. Thus, a combination of pre-selecting patients by non-invasive variables, to enhance sensitivity of following PVS to more accurately discriminate low risk from high risk patients, is important for clinical practice.