Does the division of shock energy or prior administration of verapamil or propranolol reduce cardiac damage caused by transthoracic countershock in dogs?
In a canine model, multiple low-energy shocks and prior administration of verapamil reduced myocardial damage from transthoracic countershocks, suggesting a role for calcium accumulation in shock-induced cardiac necrosis.
Myocardial damage by transthoracic countershocks was assessed by observation for electrocardiographic loss of R waves and elevation of ST segments, creatine kinase depletion, and histologic evidence of necrosis in damaged areas, and by excision and examination, 3 days later, of all tissue macroscopically observed to be damaged. When 4000 J of stored energy was passed across the chest of dogs anesthetized with pentobarbital sodium (30 mg/kg), more damage was caused when the energy was divided among 10 shocks than when it was applied in 20 or 40 shocks (at intervals of 0.5 min). The prior intravenous administration of verapamil (1 mg/kg) reduced the weight of damaged shocks. Propranolol (0.4 mg/kg) had no effect. These results give further evidence for the role of calcium accumulation in cardiac necrosis after direct current countershocks. Multiple low-energy shocks cause less cardiac damage than do a few high-energy shocks of similar total energy.
Patton et al. (Wed,) studied this question.