Threshold energy dose for enzyme release after direct-current countershock

Serum cardiac markers response to biphasic and monophasic electrical cardioversion for supraventricular tachyarrhythmia—a randomised study

BACKGROUND

Electrical cardioversion in patients with various types of supraventricular tachyarrhythmia (SVT) may induce serum cardiac markers elevation. Only a few studies have evaluated the impact of the type of shock waveform on electrical myocardial injury. The aim of our study was to compare the response of serum cardiac markers to biphasic and monophasic cardioversion for SVT.

METHODS

One hundred and forty one patients with various SVTs referred for electrical cardioversion were randomised to monophasic (MP) or biphasic (BP) cardioversion. Serum levels of creatine kinase (CK), MB fraction of CK (CK-MB), myoglobin and troponin I were analysed before cardioversion and 254+/-58 min after the procedure.

RESULTS

Average age of the patients was 67.9+/-11.3 years, 71 underwent BP and 70 MP cardioversion. In MP group, cumulative energy (CE)>150J was associated with significant elevation of CK and myoglobin levels after cardioversion (1.52+/-3.81 microkat/l and 187+/-433 microg/l), while CE<150J was not (-0.04+/-0.34 and 4+/-11, p<0.05). In BP group, CE>150J was associated with significant but smaller CK elevation (0.27+/-1.09 microkat/l, p<0.05) and comparable myoglobin elevation (80.7+/-21.4 microg/l, p<0.05). CE>150J was the only independent positive predictor for CK and myoglobin elevation in both groups. No significant changes in CK-MB and Troponin I levels after cardioversion were identified.

CONCLUSIONS

According to our study, electrical cardioversion for SVTs is not associated with biochemical signs of myocardial injury. Application of CE>150J can be followed by CK and myoglobin elevation most likely due to skeletal muscle damage. This reaction is more pronounced in MP than in BP cardioversion.

Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?

Sufficiently strong defibrillation shocks will cause temporary or permanent damage to the heart. Weak defibrillation shocks do not cause any damage to the heart but also do not defibrillate. A relevant and practical question is what range of shock energies is most likely to defibrillate while not causing damage to the heart. This question is most difficult to answer in the pre-hospital defibrillation setting where the patients' size and shape vary, placement of the defibrillation patches vary, and the etiology of their arrhythmia varies. Unlike internal defibrillators, which are tested at implantation, efficacy of an external defibrillator is determined only once, when it is most needed. This review discusses shock damage and dysfunction caused by monophasic waveforms as well as biphasic waveforms. Evidence is presented suggesting that for perfused hearts, the threshold for damage is well above any shock size delivered clinically. For non-perfused hearts, both in humans and animals, evidence is presented that monophasic shocks of up to 5 J/kg do not cause any more cardiac damage/dysfunction than that associated with smaller shocks and that much of this damage is caused by the ischemic period itself rather than the shock. Although many patients can be defibrillated with 150 J (2.2 J/kg) biphasic shocks, some patients may require biphasic shocks up to 360 J (5 J/kg) to be defibrillated. Studies still need to be performed comparing the efficacy and damaging effects of 360 J biphasic shocks to 150 J biphasic shocks. Until those studies are completed, it seems reasonable to use the same 360 J (5 J/kg) energy limit for biphasic shocks as for monophasic shocks.