Atropine: animal models

The frequency of 'occult' ventricular fibrillation masquerading as a flat line in prehospital cardiac arrest

We investigated the frequency with which a "vector of ventricular fibrillation" may exist in persons in prehospital cardiac arrest. Emergency medical technicians trained in defibrillation were directed to record the rhythm in three different monitor leads whenever they noted an initial flat line. Before these lead switches, the technicians performed a flat line protocol that included inspection of the lead connections to the patient and to the defibrillator, and checks of the calibration and battery status of the devices. They performed this flat line protocol for 127 cardiac arrest patients; 118 were in confirmed asystole after technical problems were corrected. Ventricular fibrillation was detected in only three (2.5%) when the monitor lead was switched. Initial technical problems were more frequent and were identified for ten patients (8%). The frequency of occult ventricular fibrillation (three of 118 asystolic patients) yields a 95% confidence that the true frequency is no greater than 8% to 9%. This suggests that ventricular fibrillation masquerading as asystole is rare. These data do not support protocols for empiric countershocks of patients with an initial flat line on the monitor.

Treatment of presumed asystole during pre-hospital cardiac arrest: superiority of electrical countershock

Standard drug therapy for asystole during cardiac arrest includes epinephrine, atropine, and calcium chloride (CaCl). Recent studies have shown that ventricular fibrillation (VF) can appear to be asystole when recorded from the chest surface. To determine the efficacy of these drugs and electrical countershock for asystole, a group of 83 adult nontraumatic cardiac arrest victims (55 men, 28 women, mean age of 64 +/- 14 years) were studied. Asystole appeared at some time during arrest in 44 patients (53%) and was the initial rhythm in 24 (29%). The rate of survival to hospital discharge was significantly higher in patients whose initial rhythm was VF (46%) than in patients whose initial rhythm was asystole (0%). Epinephrine, CaCl and atropine infrequently changed the rhythm from asystole. Electrical countershock infrequently altered the rhythm from asystole when it appeared as the initial rhythm. However, countershock was significantly more effective than epinephrine (P less than 0.003), atropine (P less than 0.04), or CaCl (P less than 0.03) in altering the rhythm from asystole, which appeared later in resuscitation. Ventricular fibrillation was the most common rhythm appearing after countershock for asystole. Countershock appears to be superior to epinephrine, CaCl, and atropine for treating asystole during the course of resuscitation, suggesting that the rhythm diagnosed as asystole may actually be VF in many cases.