Prehospital cardiac rhythm deterioration in a system providing only basic life support.

Access to an ambulance service trained to provide only basic cardiac life support (BCLS) and adjunctive ventilation with oxygen provided the opportunity to study cardiac rhythms during BCLS in patients with circulatory arrest. Holter monitoring was attempted in 43 patients. Technically adequate traces throughout transport to hospital were obtained in 21. The average monitored time was 11.9 minutes. A tachydysrhythmia (mainly VF/VT) was initially found in 10, heart block or bradycardia in 9, and asystole in 2 persons. During BCLS, six patients with bradycardic rhythms converted temporarily to VF. The first ECG tracing obtained in the hospital revealed, however, that only five were still in a tachydysrhythmia and 15 were asystolic. These data demonstrate that important rhythm changes occur when BCLS is continued for several minutes during circulatory arrest. Although some bradycardic rhythms convert to VF, the VF is not sustained. After an average of 12 minutes, 90% of those initially in bradycardic rhythm and 50% of those initially in VF/VT were asystolic. This study provides further evidence that BCLS does not prevent cardiac deterioration.