【正文】 y be a better marker of nonarrhythmic mortality in the present data. Further studies are needed to establish whether HRV has a role in risk stratification for SCD. The predictive value of HRV The shortterm fluctuation in sinus cycle length that follows a VPB. Holter Heart rate turbulence (HRT) indices HRT TO (turbulence onset) 0 (positive), ≤0 (negative)。 TS (turbulence slope) ≥2. 5 mm / s (positive), 2. 5 mm / s (negative)。 Mechanism After a premature beat and a pensatory pause, there is a typical increase in blood pressure due to the prolonged filling in the cycle of the pensatory pause. Reflex parasympathetic activation ensues and slows the heart rate. HRT Heart rate turbulence has been examined primarily in postMI patients. A smaller number of studies of patients with nonischemic dilated cardiomyopathy, chronic congestive heart failure, or hypertrophic cardiomyopathy (HCM) and patients undergoing revascularization have also suggested a predictive value of heart rate turbulence. HRT Abnormal heart rate turbulence is associated with increased mortality. Further studies are needed to establish whether there is clinical utility of this parameter for risk stratification. The predictive value of HRT Exercise Test/Functional Status Heart rate recovery and recovery ventricular ectopy Immediately after graded exercise, heart rate normally falls with an initial rapid decline occurring during the first 30 seconds to 1 minute of recovery. Abnormal indices 1 min heart rate recovery≤12 beats/min 2 min heart rate recovery ≤22 beats/min When a supine recovery,≤18 beats/min There were frequent or severe VPs during 5min recovery. Parasympathetic reactivation likely plays a major role in regulating heart rate recovery. Because impaired parasympathetic tone correlates with increased risk of death,it was hypothesized that an attenuated heart rate recovery would similarly predict an increased risk of death. Heart rate recovery recovery ventricular ectopy Mechanism Heart rate recovery recovery ventricular ectopy a 1minute heart rate recovery 12 beats per minute was associated with a markedly increased risk of allcause death (positive predictive value 19%, negative predictive value 95%, confounderadjusted hazard ratio , 95% CI to ). Heart rate recovery and ventricular ectopy during recovery are new and interesting markers of mortality. Heart rate recovery recovery ventricular ectopy Their value as risk stratification tools for SCD is untested. Exercise Test/Functional Status Twave alternans In 1994, Rosenbaum et al first related Twave alternans to highrisk findings on electrophysiological testing and to an increased risk of serious arrhythmic events. Recently, Twave alternans can be detected by Holter. Exercise Test/Functional Status Twave alternans Twave alternans is a reflection of repolarization alternans at the level of the single cell. and most likely arises when heart rate exceeds the capacity of cardiac cells to cycle intracellular calcium. Microvoltlevel Twave alternans The typical definition for an abnormal Twave alternans test is the occurrence of μV of alternans starting at a heart rate of 110 beats per minute. Twave alternans has been directly linked to a mechanism of arrhythmogenesis. Mechanism Exercise Test/Functional Status Twave alternans moderately reproducible, with concordance on repeated tests of 65% to 75%, and 80% to 90% microvolt Twave alternans may work at least as well as electrophysiological testing for prediction of SCD or major arrhythmic events. Twave alternans may be better than QRS duration for identifying patients likely to benefit from ICDs Exercise Test/Functional Status Twave alternans Twave alternans was associated with substantially increased risk and predicted events as well as or better than other markers, including LVEF, electrophysiological testing, SAECG, BRS, and HRV. A moderate amount of prospective data suggests that abnormal Twave alternans is a risk factor for SCD. Exercise Test/Functional Status Twave alternans Clinical utility to guide selection of therapy has been evaluated, but the results, to date, are not consistent. A summary Slowed conduction Heterogeneities in ventricular repolarization Imbalance in autonomic tone Ventricular ectopy QRS duration late potential HRV, HRT Heart rate recovery QT interval, QTdispersion, T T alternans VPs, NSVT