Abstract 2088: The Impedance Cardiogram Recorded Through the Two Electrocardiogram/Defibrillator Pads as a Determinant of Cardiac Arrest in Experimental and Clinical Studies
Objective: Can the impedance cardiogram be used as a marker of cardiac arrest when recorded through 2 EKG/defibrillation pads placed trans - thoracically?
Background: First responders are poor at emergency pulse checks having a sensitivity of 90% and specificity 55% when detecting the absence of a pulse. As such, guidelines recommend that pulse checks should not be performed creating the potential for suboptimal management of cardiac arrest. The impedance cardiogram (ICG; dZ/dt) is used to measure stroke volume. Can a novel ICG electrode configuration be used to identify circulatory arrest?
Methods: Experimentally, cardiac arrests were induced in 20 pigs (2 sets, 10 training and 10 validation). Fourty epochs of sinus rhythm (20 prior to ventricular fibrillation and 20 after successful defibrillation), 40 during ventricular fibrillation, 20 during pulseless electrical activity and 20 during asystole were recorded in each set. Each epoch lasted 5 seconds. The Fast Fourier Transform (FFT) of dZ/dt was assessed to identify changes in the frequency spectrum of the ICG with the onset of cardiac arrest. Clinically, 132 ‘cardiac arrest’ patients (53 Training, 79 Validation sets) and 97 controls (47 Training, 50 Validation sets) were studied. Four second epochs for dZ/dt were analyzed in triplicate (blocks of 3 epochs) using a selective filter technique. Similar results were required in 2 of the 3 consecutive epochs to confirm the diagnosis of circulatory arrest.
Results: Experimentally, a peak FFT amplitude of ≤ 4 dB.ohms.rms indicated cardiac arrest with sensitivities and specificities of 94% and 98% (Training set) and 86% and 90% (Validation set) respectively. In clinical patients, sensitivities and specificities of 89.7% and 99.4% (Training) and 82.9% and 98.1% (Validation) were found.
Conclusions: The FFT of the ICG waveform is a powerful clinical marker of circulatory collapse and as such has the potential to improve emergency care by first responders using automated defibrillators.