Copyright © 1998 by the European Society of Cardiology.
The transthoracic impedance cardiogram is a potential haemodynamic sensor for an automated external defibrillator
a Regional Medical Cardiology Centre, Royal Victoria Hospital, Belfast
b Northern Ireland Bioengineering Centre, Belfast, Northern Ireland
accepted June 10, 1998
Aims
The American Heart Association has endorsed the concept of Public Access Defibrillation. However, there have been reports of inappropriate direct current shocks from automatic external defibrillators. The specificity of automatic external defibrillators for shockable rhythms may be improved by the incorporation of a haemodynamic sensor.
Methods and Results
This study examined the use of four parameters extracted from the impedance cardiogram i.e. Peak dz/dt (the peak of the impedance cardiogram measured from the line dz/dt=0|gQs–1), Peak-trough (the peak-to-trough measurement of the impedance cardiogram |gQs–1), Area 1 (the area under the C wave of the impedance cardiogram above the line dz/dt=0m|gQ) and Area 2 (the area under the impedance cardiogram 50ms on either side of the Peak and above the line dz/dt=0m|gQ) as predictors of cardiac output.
At 116 cardiac arrest calls the ECG and impedance cardiogram were recorded through two ECG/defibrillator pads placed in an antero-apical position. Nine recordings were rejected for artefact. The rhythm recorded in the remaining 107 calls was asystole (19), ventricular fibrillation (14), agonal rhythm (20), electromechanical dissociation (22), ventricular tachycardia (27) and sinus rhythm (5). These rhythms were divided into those associated with haemo-dynamic collapse i.e. no pulse—asystole, ventricular fibrillation, agonal rhythm, electromechanical dissociation and shockable ventricular tachycardia (associated with loss of consciousness, pulselessness or a systolic blood pressure of <80mmHg) (Group 1) and those associated with a satisfactory cardiac output i.e. non-shockable ventricular tachycardia (conscious with a pulse) and sinus rhythm (Group 2). On univariate analysis each of the four impedance cardiogram parameters were significantly greater in Group 2 than Group 1 (P<0·001). On multivariate analysis the parameters which best differentiated the two groups were Area 1 and Peak-trough.
Conclusion
Thus the impedance cardiogram is a potential haemodynamic sensor for an automatic external defibrillator.
Key Words: Impedance cardiogram • automatic external defibrillator • cardiac arrest
f1 Correspondence: Prof A. A. J. Adgey, Regional Medical Cardiology Centre, Royal Victoria Hospital, Belfast BT12 6BA, Northern Ireland.