Abstract 15428: Development of Instability in QT Interval Dynamics Before the Onset of Ventricular Fibrillation
INTRODUCTION: Experimental evidence indicates that unstable repolarization dynamics plays an important role in the initiation of ventricular fibrillation (VF). However, assessing repolarization instability before VF onset in the clinic remains a daunting task.
HYPOTHESIS: The QT interval (QTI) in the ECG is a manifestation of ventricular repolarization. We have developed and reported a novel algorithm that detects instability in QTI dynamics. We hypothesize that QTI dynamics tends to become unstable in the approach to VF onset.
METHODS: One hour-long ECG recordings (one per patient) were collected right before VF onset from 17 patients admitted to Johns Hopkins Hospital, and were assembled into a VF group. From each of the 11 patients who did not have cardiac events, one hour-long ECG was randomly selected and assembled into a CONTROL group. All ECGs were subdivided into 1-min episodes termed minECGs. The latter were annotated to obtain QTI and RR intervals (RRIs). Each QTI within a given minECG was defined as a function of QTIs and RRIs of several prior beats. The stability of this function, which describes QTI dynamics of the given minECG, was determined dichotomously in the z-domain. For both VF and COTROL groups, the number of patients who had unstable QTI dynamics, N, was counted every five minutes. Linear regression analysis was performed to determine the trends in the value of N in both groups. Paired t-test was used to compare N between VF and CONTROL groups.
RESULTS: Linear regression results show a significant increase (p=0.002, R2=0.62) in the value of N in the VF group (Figure) but not in CONTROL (p=0.43). In the VF group, N increased from 7 (first 5 minutes) to 13 (last 5 minutes). The mean N of the VF group (9.33±1.8) was significantly (p<0.0001) larger than that of COTROL (2.75±0.75).
CONCLUSONS: More VF patients had unstable QTI dynamics as compared to CONTROL patients. QTI dynamics has a tendency to become unstable in the approach to VF onset.
- © 2011 by American Heart Association, Inc.