Cardiac arrhythmia analysis system

• US 4,473,078 A
• Filed: 05/24/1982
• Issued: 09/25/1984
• Est. Priority Date: 05/24/1982
• Status: Expired due to Term

• Current Assignee: Cardiac Resusitator Corporation
• Original Assignee: Cardiac Resuscitator Corp.
• Inventors: Angel, James H.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Foley, Deidre A.
• Application Number:
  US06/381,644
• Time in Patent Office: 855 Days
• Field of Search: 128/419 D, 128/419 PG, 128/702, 128/704, 128/705, 128/706, 128/703
• US Class Current: 607/6
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3904 External heart defibrillators [EHD]

Abstract

A method and apparatus for analyzing cardiac electrical activity and other life signs, and triggering a therapeutic current. A signal representative of cardiac electrical activity is analyzed by two distinct analog circuits and a logic protocol is provided to identify cardiac arrhythmia based on the outputs of the circuits and the presence or absence of respiration. One circuit employs comparison of the electrical signal with a previous peak value thereof, and is characterized by its tendency to double-count some QRS complexes. The other circuit compares the sum of the rectified and low-pass filtered signal plus the derivative of the signal to a reference level, and compares the rectified and filtered signal to a threshold level, to identify QRS complexes while largely ignoring ventricular fibrillation. Defibrillation is triggered if either the second circuit produces output pulses greater than or equal to 200 pulses per minute, or the first circuit produces output pulses greater than 200 pulses per minute and the second circuit produces pulses at a rate less than half the pulse rate of the first circuit. Pacing is triggered if both circuits produce pulses at a rate less than 25 pulses per minute. Tachycardia and/or ventricular fibrillation must be apparently identified several times, and lack of respiration must be established, within a predetermined time period in order for defibrillation to be triggered. Defibrillation is inhibited as a result of interference which could produce unreliable measurements.

Claims

1. A system for monitoring the cardiac electrical activity and at least one other selected life sign of a patient, and triggering the application of appropriate therapeutic current to said patient, comprising:

(a) input means for receiving from said patient an electro-cardiac signal representative of said electrical activity of said patient'"'"'s heart and a second signal derived from said other selected life sign and indicative of a second criterion for the identification of selected cardiac arrhythmia;

(b) V-fib circuit means, responsive to said electro-cardiac signal, for repetitively producing V-fib pulses at a rate greater than or equal to a first predetermined rate in response to the occurrence of ventricular fibrillation and for producing at least one V-fib pulse in response to the occurrence in sid electro-cardiac signal of a QRS complex;

(c) QRS circuit means, responsive to said electro-cardiac signal, for producing a QRS pulse in response to the occurrence in said electro-cardiac signal of a QRS complex while producing in response to ventricular fibrillation QRS pulses at less than half the rate of V-fib pulses produced by said V-fib circuit means; and

(d) logic means, for producing a defibrillation trigger signal, said logic means having clock means for establishing a rate measurement period, means for counting the number of QRS and V-fib pulses during said rate measurement period to determine the respective rates thereof and for producing a defibrillation request pulse if, during said rate measurement period, either the number of V-fib pulses equals or exceeds said first predetermined rate while the number of QRS pulses is less than half the V-fib pulse rate or the number of QRS pulses equals or exceeds said first predetermined rate, accumulator means responsive to said defibrillation request pulse for counting the number of said request pulses during an accumulation period, and output means, responsive to said timing means and to said second signal for producing a defibrillation trigger signal upon the occurrence of three defibrillation pulses within said accumulation period and of said second criterion for a predetermined period.

2. The system of claim 1, wherein said other selected life sign is respiration, said second criterion being the absence thereof.

3. A method for determining whether or not to defibrillate a patient based upon the identification of apparent ventricular fibrillation, represented by a fibrillation pulse or tachycardia represented by a tachycardia pulse, from analysis of cardiac electrical activity during a predetermined measurement period, comprising:

(a) requiring the identification of three occurrences of either defibrillation or tachycardia pulses and no respiration within a first period in order to fibrillation;

(b) restarting said first period if following a first identification a second identification does not occur within a second predetermined period;

(c) restarting said first period if following said second identification a third identification does not occur within a third predetermined period;

(d) restarting said first period if for a fourth predetermined period following said third identification there has been respiration during a preceeding fifth predetermined period, the total of said second, third and fourth periods equalling said first period.