Myocardial Repolarization Dispersion and Autonomic Nerve Activity in a Canine Experimental Acute Myocardial Infarction Model

Abstract

Background Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI the relationship between stellate ganglionic nerve and vagal nerve activities (SGNA/VNA) progressively increases.

Objective We evaluated 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 9 dogs. From a total 48 short-term electrocardiographic segments, 24 recorded before and 24 seven weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QTe (from q wave T to wave end), QTp (from q wave to T wave peak) and Te (from T wave peak to T wave end) variability index (QTeVI, QTpVI, TeVI). We also performed a heart rate variability power spectral analysis on the same segments.

Results After MI, all the QT variables increased QTeVI (median [interquartile range]) (from - 1.76[0.82] to −1.32[0.68]), QTeVI (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 indexes decreased (p<0.001 for all). Distinct circadian rhythms in QTeVI (p<0.05,) QTpVI (p<0.001) and TeVI (p<0.05) appeared after MI with circadian variations resembling that of SGNA/VNA. The morning QTpVI and TeVI acrophases approached the SGNA/VNA acrophase. Conversely, the evening QTeVI acrophase coincided with another SGNA/VNA peak. After MI, regression analysis detected a positive relationship between SGNA/VNA and TeVI (R2: 0.077; β: 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.