Assessment of the impedance cardiogram recorded by an automated external defibrillator during clinical cardiac arrest.
OBJECTIVE
To assess the impedance cardiogram recorded by an automated external defibrillator during cardiac arrest to facilitate emergency care by lay persons. Lay persons are poor at emergency pulse checks (sensitivity 84%, specificity 36%); guidelines recommend they should not be performed. The impedance cardiogram (dZ/dt) is used to indicate stroke volume. Can an impedance cardiogram algorithm in a defibrillator determine rapidly circulatory arrest and facilitate prompt initiation of external cardiac massage?


METHODS
Clinical study.


METHODS
University hospital.


METHODS
Phase 1 patients attended for myocardial perfusion imaging. Phase 2 patients were recruited during cardiac arrest. This group included nonarrest controls.


METHODS
The impedance cardiogram was recorded through defibrillator/electrocardiographic pads oriented in the standard cardiac arrest position.


RESULTS
Phase 1: Stroke volumes from gated myocardial perfusion imaging scans were correlated with parameters from the impedance cardiogram system (dZ/dt(max) and the peak amplitude of the Fast Fourier Transform of dZ/dt between 1.5 Hz and 4.5 Hz). Multivariate analysis was performed to fit stroke volumes from gated myocardial perfusion imaging scans with linear and quadratic terms for dZ/dt(max) and the Fast Fourier Transform to identify significant parameters for incorporation into a cardiac arrest diagnostic algorithm. The square of the peak amplitude of the Fast Fourier Transform of dZ/dt was the best predictor of reduction in stroke volumes from gated myocardial perfusion imaging scans (range = 33-85 mL; p = .016). Having established that the two pad impedance cardiogram system could detect differences in stroke volumes from gated myocardial perfusion imaging scans, we assessed its performance in diagnosing cardiac arrest. Phase 2: The impedance cardiogram was recorded in 132 "cardiac arrest" patients (53 training, 79 validation) and 97 controls (47 training, 50 validation): the diagnostic algorithm indicated cardiac arrest with sensitivities and specificities (+/- exact 95% confidence intervals) of 89.1% (85.4-92.1) and 99.6% (99.4-99.7; training) and 81.1% (77.6-84.3) and 97% (96.7-97.4; validation).


CONCLUSIONS
The impedance cardiogram algorithm is a significant marker of circulatory collapse. Automated defibrillators with an integrated impedance cardiogram could improve emergency care by lay persons, enabling rapid and appropriate initiation of external cardiac massage.
Department of Cardiology, Belfast Heart Centre, Royal Victoria Hospital, Belfast, Northern Ireland. nacromie@doctors.org.uk
Nick Alexander
NA
Cromie
John Desmond
JD
Allen
César
C
Navarro
Colin
C
Turner
John McC
JM
Anderson
A A Jennifer
AA
Adgey
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002302:Cardiac Output; D002307:Cardiography, Impedance / Q000592:standards*; D047548:Defibrillators / Q000592:standards*; D004562:Electrocardiography; D005260:Female; D006323:Heart Arrest / Q000175:diagnosis / Q000503:physiopathology*; D006336:Heart Massage / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D055414:Myocardial Perfusion Imaging; D012680:Sensitivity and Specificity; D013318:Stroke Volume / Q000502:physiology