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? Design: Clinical study. Setting: University hospital. Patients: Phase 1 patients attended for myocardial perfusion imaging. Phase 2 patients were recruited during cardiac arrest. This group included nonarrest controls. Interventions: The impedance cardiogram was recorded through defibrillator/electrocardiographic pads oriented in the standard cardiac arrest position. Measurements and Main Results: Phase 1: Stroke volumes from gated myocardial perfusion imaging scans were correlated with parameters from the impedance cardiogram system (dZ/dtmax 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/dtmax 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.

[2]  Colin Turner,et al.  The impedance cardiogram recorded through two electrocardiogram/defibrillator pads as a determinant of cardiac arrest during experimental studies* , 2008, Critical care medicine.

[3]  Trygve Eftestøl,et al.  Automatic Identification of Return of Spontaneous Circulation During Cardiopulmonary Resuscitation , 2008, IEEE Transactions on Biomedical Engineering.

[4]  Trygve Eftestøl,et al.  Thoracic-impedance changes measured via defibrillator pads can monitor signs of circulation. , 2007, Resuscitation.

[5]  R. Patterson,et al.  The Minnesota impedance cardiograph- theory and applications. , 1974, Biomedical engineering.

[6]  R. Koster,et al.  Use of automated external defibrillator by first responders in out of hospital cardiac arrest: prospective controlled trial , 2003, BMJ : British Medical Journal.

[7]  Gust H. Bardy,et al.  Tripling Survival From Sudden Cardiac Arrest Via Early Defibrillation Without Traditional Education in Cardiopulmonary Resuscitation , 2002, Circulation.

[8]  P. Vries,et al.  The technique of impedance cardiography. , 1997, European heart journal.

[9]  Milton Packer,et al.  Utility of impedance cardiography for the identification of short-term risk of clinical decompensation in stable patients with chronic heart failure. , 2006, Journal of the American College of Cardiology.

[10]  M. Hazinski,et al.  The most important changes in the international ECC and CPR guidelines 2000. , 2000, Resuscitation.

[11]  M. Hazinski,et al.  Guidelines based on fear of type II (false-negative) errors : why we dropped the pulse check for lay rescuers. , 2000, Circulation.

[12]  A A Adgey,et al.  The transthoracic impedance cardiogram is a potential haemodynamic sensor for an automated external defibrillator. , 1998, European heart journal.

[13]  M. Mehra.  Optimizing outcomes in the patient with acute decompensated heart failure. , 2006, American heart journal.

[14]  M. Hazinski,et al.  The most important changes in the international ECC and CPR guidelines 2000. , 2000, Circulation.

[15]  Trygve Eftestøl,et al.  Thoracic impedance changes measured via defibrillator pads can monitor ventilation in critically ill patients and during cardiopulmonary resuscitation* , 2006, Critical care medicine.

[16]  A. Handley,et al.  Single rescuer adult basic life support. An advisory statement from the Basic Life Support Working Group of the International Liaison Committee on Resuscitation (ILCOR) , 1997, Resuscitation.

[17]  D P Bernstein,et al.  A new stroke volume equation for thoracic electrical bioimpedance: Theory and rationale , 1986, Critical care medicine.

[18]  W. G. Kubicek,et al.  On the source of peak first time derivative (dZ/dt) during impedance cardiography , 2006, Annals of Biomedical Engineering.

[19]  W. Dick,et al.  Checking the carotid pulse check: diagnostic accuracy of first responders in patients with and without a pulse. , 1996, Resuscitation.

[20]  A. Handley,et al.  Single-rescuer adult basic life support: an advisory statement from the Basic Life Support Working Group of the International Liaison Committee on Resuscitation. , 1997, Circulation.

[21]  F. H. Bonjer,et al.  The Origin of the Variations of Body Impedance Occurring during the Cardiac Cycle , 1952, Circulation.

[22]  Thomas D Rea,et al.  Public Access Defibrillation in Out-of-Hospital Cardiac Arrest: A Community-Based Study , 2004, Circulation.