Limitations of open-chest cardiac massage after prolonged, untreated cardiac arrest in dogs

Study objectives: Open-chest cardiac massage is an effective method of resuscitation if instituted within 15 minutes of normothermic cardiac arrest that has failed to respond to ongoing closed-chest CPR efforts. The usefulness of invasive forms of CPR after various periods of untreated cardiac arrest is less certain. This study was performed to determine the effectiveness of open-chest resuscitation after prolonged periods of untreated cardiac arrest. Setting and design: Prospective, controlled laboratory investigation using an animal model of cardiac arrest. Open-chest cardiac massage initially was compared to standard closed-chest compression CPR. The efficacy of open-chest CPR then was evaluated after ten and 40 minutes of untreated ventricular fibrillation. Type of participants: Twenty mongrel dogs (24 ± 1 kg). Measurements and main results: After 20 minutes of untreated ventricular fibrillation, open-chest resuscitation was significantly better than closed-chest efforts for the production of coronary perfusion pressure (58 ± 14 vs 2 ± 1 mm Hg; P < .05) and initial resuscitation success (five of five vs one of five; P < .03). Open-chest cardiac massage was equally effective for initial resuscitation if begun after ten or 20 minutes of untreated ventricular fibrillation (five of five vs five of five), but if untreated ventricular fibrillation continued for 40 minutes prior to instituting open-chest massage, no resuscitation benefit was found (none of five; P < .005). There were marked differences in 24-hour survival depending on the length of time untreated cardiac arrest continued prior to instituting open-chest resuscitation efforts. After 20 minutes of ventricular fibrillation, initial resuscitation was successful with open-chest massage, but long-term survival was poor. Conclusion: Open-chest cardiac massage did not produce long-term survival if untreated cardiac arrest persisted for 20 or more minutes prior to invasive resuscitation efforts.