| OBJECTIVES:The purpose of this study was to assess a number of non-invasive cardiac electrical indicators (TWA, HRV, HRT, NSVT, VPBs, VLP, QTc) to identify AMI patients at increased risk for SCD, and designed to evaluate the value of all indicators as predictors of SCD in the early post MI period and to find the optimal way to combine and use these noninvasive techniques in clinical practice.METHODS:289consecutive post-MI patients were enrolled in the study. Body electrocardiograph, Ambulatory ECG-based measures and signal-averaged electrocardiography were performed within2weeks after AMI. The duration of QRS wave and the QTc interval were measured by body electrocardiograph. The wide QRS wave was defined as its duration longer than110ms. The extended QTc interval was defined as its value longer than450ms for male or460ms for female. The analysis of VLP is based on the quantitative time-domain measurements of the filtered vector magnitude of the orthogonal Frank X, Y, and Z leads. VLP were considered to be present when the three criteria (RMS40≤20mV+f-QRS≥114ms, and/or LAS40≥38ms) were met. We analyzed hazard ratios using the previously determined47μV TWA cutpoint. Impaired HRT was defined by abnormalities in either HRT onset (TO value of>0) or slope (TS value of<2.5ms/per normal-to-normal interval).The standard deviation of all normal-to-normal R-R intervals (SDNN) was chosen as a parameter of HRV in this study, and a value of<70ms was pre-defined as abnormal. VPBs (30or more VPBs per hour) and NSVT (≥3consecutive ventricular premature beats at a rate of100beats/min) were also recorded by an ambulatory ECG. The left ventricular dysfunction was defined as LVEF lower than35%. The primary outcome was prospectively defined as sudden cardiac death or life-threatening ventricular arrhythmic events. All cause mortality and cardiac deaths categorized as nonarrhythmic were secondary outcomes.RESULTS:The duration of follow-up was11±3months.15(5%) patients died suddenly. Compared to the patients in survived group, the patient with SCD had lower LVEF[35%(28%-52%) vs50%(33%-60%), P<0.0001], longer duration of QRS wave[115(88,152)ms vs105(91,136)ms, P=0.0222] and longer QTc interval [458(416,513)ms vs450(394,493)ms, P=0.1836]. Multivariate Cox Regression Analyses showed that an ambulatory ECG-based TWA, VLP, TS and present NSVT were predictors of the primary outcome. A hazard ratio for TWA was15.07(95%CI2.88to78.68; p=0.001), for VLP was6.49(95%CI2.13to19.77; p=0.0031), for TS was4.21(95%CI1.18to14.99; p=0.026) and for NSVT was16.78(95%CI3.68to44.41; p<0.0001). Moreover, patients with≥5TWA episodes≥47μV were at higher risk for SCD [Hazard ratio=18.24(95%CI,4.20to83.68), p=0.0004]. United TWA and TS can improve VLP predictive capability, the hazard ratio (HR), respectively, from6.49to16.07and14.21.CONCLUSIONS:TWA (≥47μV) monitored within2weeks after AMI predicted heightened risk of SCD. Prediction is improved when the frequency of TWA episodes≥47μV is analyzed. Patients were found to be at the higher risk if they met the both positive VLP and TS or TWA.
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