Abstract 241: Amplitude Spectrum Area as a Tool to Identify the Circulatory Phase of Ventricular Fibrillation
Background: Ventricular fibrillation (VF) cardiac arrest (CA) is characterized by 3 time dependent phases: electrical (shorter than 4min), circulatory (4-10min), and metabolic (longer than 10min). These phases reflect the progressive increase of myocardial ischemia and suggest the potentially optimal treatment. During the electrical phase, immediate defibrillation is likely to be successful, while during the circulatory phase, the success of defibrillation diminishes without CPR. In the metabolic phase, there is low likelihood of successful resuscitation and probably a longer CPR interval prior to defibrillation is necessary. In the out-of-hospital (OH) setting, most patients may have passed the electrical phase when EMS arrives. Identification of the VF phase may therefore facilitate the proper CPR treatment. We used AMSA to determine if patients were in circulatory or in metabolic phase at EMS arrival.
Methods: Data from an Utstein-compliant registry along with electronic ECG records were collected on consecutive adult OHCA patients treated by 2 EMS agencies over a 2 year period. Patients with bystander witnessed CA and with VF as initial CA rhythm were included (n=41). AMSA was calculated in earliest pause without compression artifacts, using a 2 sec ECG with a Tukey (0.2) FFT window. VF duration was calculated as the sum of the time interval from collapse to defibrillator on and the time interval from defibrillator on to first CPR interruption for defibrillation delivery.
Results: VF duration ranged between 6.5 and 29.6 min (11.3+4.1 min), with a corresponding AMSA between 2.1 and 16.4 mV-Hz (9.4+4.2 mV-Hz). AMSA measured in the circulatory phase (N=19) was significantly higher than that in the metabolic phase (N=22) (8.14+3.17 vs. 5.98+2.88, p=0.03). Linear regression revealed that AMSA decreases by 0.22 mV-Hz for every min of VF. AMSA was able to predict circulatory phase with an accuracy of 0.7 in ROC area. An AMSA threshold of 10 mV-Hz was able to predict the circulatory phase with sensitivity of 32%, specificity of 95%, PPV of 86%, NPV of 62% and overall accuracy of 66%.
Conclusions: AMSA is a good indicator of downtime in OHCA with initial rhythm of VF. AMSA could be used to identify VF phase and thereby suggest for the proper CPR intervention.
- © 2013 by American Heart Association, Inc.