Death and damage caused by multiple direct current shocks: studies in an animal model

Patients who require multiple defibrillator shocks have a poor prognosis. In healthy greyhounds the acute mortality increased as the number of transthoracic shocks (400 J) applied increased (one shock 0/6: five shocks 8/18: 10 shocks 12/17 dogs died acutely from asystole or electromechanical dissociation). The appearance on electron microscopy of the myocardium of these dogs showed few specific abnormal features to account for the total contractile failure that occurs in these dogs. In the survivors, significant ST segment elevation was recorded from the precordial leads of the dogs receiving five and 10 shocks, but not those receiving a single shock. At three days there was significantly more macroscopic cardiac damage in the 10-shock (13.1 +/- 1.8 g) than in the five-shock (7.2 +/- 2.0) group (P less than 0.05). One shock caused little damage. Hence a single high-energy shock was well tolerated in this model. Multiple shocks caused cardiac injury and acute pump failure. These studies indicate the need to reassess why patients die following multiple shocks, and re-emphasise the need for optimized first-shock effectiveness.