Myocardial repolarization dispersion and autonomic nerve activity in a canine experimental acute myocardial infarction model

BACKGROUND Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI, the relationship between stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) progressively increases. OBJECTIVE The purpose of this study was to evaluate how autonomic nervous system activity influences temporal myocardial repolarization dispersion at this period. METHODS We analyzed autonomic nerve activity as well as QT and RR variability from recordings previously obtained in nine dogs. From a total of 48 short-term ECG segments, 24 recorded before and 24 recorded 7 weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QT(e) (from Q-wave to T-wave end), QT(p) (from Q-wave to T-wave peak), and T-e (from T-wave peak to T-wave end) variability index (QT(e)VI, QT(p)VI, TeVI). We also performed heart rate variability power spectral analysis on the same segments. RESULTS After MI, all the QT variables increased QT(e)VI (median [interquartile range]) (from -1.76[0.82] to -1.32[0.68]), QT(e)VI (from -1.90[1.01] to -1.45[0.78]), and TeVI (from -0.72[0.67] to -0.22[1.00]), whereas all RR spectral indices decreased (P < .001 for all). Distinct circadian rhythms in QT(e)VI (P < .05,) QT(p)VI (P < .001) and TeVI (P < .05) appeared after MI with circadian variations resembling that of SGNA/VNA. The morning QT(p)VI and TeVI acrophases approached the SGNA/VNA acrophase. Conversely, the evening QT(e)VI acrophase coincided with another SGNA/VNA peak. After MI, regression analysis detected a positive relationship between SGNA/VNA and TeVI (R-2: 0.077; beta: 0.278; p < 0.001). CONCLUSION Temporal myocardial repolarization dispersion shows a circadian variation after MI reaching its peak at a time when sympathetic is highest and vagal activity lowest.