PREHOSPITAL CARDIAC-ARREST TREATED BY URBAN 1ST-RESPONDERS - PROFILE OF PATIENT RESPONSE AND PREDICTION OF OUTCOME BY VENTRICULAR-FIBRILLATION WAVE-FORM

Study objectives: To determine the speed and characteristics of patien t response to urban first-responder defibrillation and to determine wh ether amplitude of ventricular fibrillation (VF) can predict outcome i n these patients. Type of participants: All adult patients in prehospi tal VF treated by fire department first-responders (265). Design and i nterventions: A prospective observational study occurring between Febr uary 1, 1989, and January 1, 1991. Patients were defibrillated accordi ng to advanced cardiac life support and first-responder protocols. ECG and time data were recorded digitally. Main results: Sixty-five perce nt of patients converted from VF to a more stable rhythm at least once during first-responder monitoring. Fifty-four percent of converted pa tients refibrillated at least once, and 42% of all stable conversions occurred after at least one episode of refibrillation. Seventy percent of all refibrillations occurred less than six minutes after the defib rillator was turned on, and 23% occurred after more than ten minutes. The proportion of stable conversions decreased from 30% on first conve rsion to 2% on fourth conversion. With each successive conversion the interval to refibrillation grew shorter, and development of a pulse or blood pressure became less likely. Presence of blood pressure or puls e after conversion had a sensitivity for hospital discharge of 54% and a specificity of 98%. Maximum VF amplitude before countershock was hi ghly predictive of post-shock rhythm, stable conversion in the field, time interval before refibrillation, inpatient admission, and hospital discharge. VF amplitude was unrelated to response interval or interva l to defibrillation but was positively related. to bystander CPR. Logi stic regression identified VF amplitude as the most important predicto r of hospital discharge; traditional variables such as response interv al and bystander CPR were not predictive once amplitude had been accou nted for. Changes in VF amplitude during the course of resuscitation e fforts were frequent and also predictive of outcome.Conclusion: Patien ts in VF who were treated by early counter-shock refibrillated much mo re frequently than previously reported. Refibrillations occur both ear ly and late. Initial VF maximum amplitude is strongly predictive of ou tcome. Future reports of VF cardiac arrest should control for this pre viously neglected variable. Increased amplitude of VF during repeated refibrillation episodes is associated with increased hospital discharg e, so future studies of advanced cardiac life support interventions sh ould explore changes in VF amplitude as an outcome variable.