Threshold energy dose for enzyme release after direct-current countershock

Serial measurement of serum total creatine kinase and creatine kinase MB isoenzyme was prospectively performed by photometric assay in 82 consecutive patients (55 male and 27 female; mean age 62 ± 11 years) after elective DC countershock for atrial flutter or fibrillation. Enzyme release is commonly observed to follow DC shock; the related energy threshold for enzyme release, however, a parameter with potential clinical usefulness, has not yet been determined. The energy dose was individually titrated but the anterolateral paddle-electrode location was used in all cases. The mean ± S.D. (range) of shock number, peak energy level and cumulative energy dose normalized to body weight were respectively: 1.7 ± 0.9 (1–5), 228.6 ± 87.6 (75–400) J and 5.26 ± 3.74 (1.0–19.7) J/kg. All these parameters had highly significant positive correlation with enzyme release (P < 0.0001), which peaked 16 h after countershock. Only creatine kinase levels changed significantly vs. baseline (P < 0.0001). As evidenced by dose vs. effect scattergram, the energy threshold value for enzyme release was around 4 J/kg for creatine kinase and 6 J/kg for creatine kinase MB isoenzyme. These energy dose figures may provide clinical usefulness to avoid unnecessary muscle damage; moreover, they may be used as a reference when enzyme elevations interfere with the diagnosis of a concomitant ischemic acute myocardial infarction.