Defibrillator with scheduled and continuous modes of operation

#The invention relates to an improved apparatus and method for treating victims of cardiac arrest, and in particular for those patients who require a treatment regime consisting of cardiopulmonary resuscitation (CPR) and defibrillation electrotherapy.

#A defibrillator delivers a high-voltage impulse to the heart in order to restore normal rhythm and contractile function in patients who are experiencing arrhythmia, such as ventricular fibrillation (“VF”) or ventricular tachycardia (“VT”) that is not accompanied by spontaneous circulation. There are several classes of defibrillators, including manual defibrillators and automated external defibrillators (“AEDs”). AEDs differ from manual defibrillators in that AEDs can automatically analyze the electrocardiogram (“ECG”) rhythm to decide if defibrillation is necessary. After deciding that a shock is needed, the AED arms itself for delivering an electrotherapeutic shock, and then the AED advises the user to press a shock button to deliver the defibrillation shock. An AED that operates in this manner is called semi-automatic. Fully automatic AEDs deliver the defibrillation shock without any user input. Fully automatic AEDs are generally called fully automatic defibrillators in order to reduce confusion in terminology.

#FIG. 1 is an illustration of a defibrillator 1 being applied by a user 2 to resuscitate a patient 4 suffering from cardiac arrest. The defibrillator 1 may be in the form of an AED or a fully automatic defibrillator capable of being used by a first responder. The defibrillator 1 may also be in the form of a manual defibrillator for use by paramedics or other highly trained medical personnel. Two or more electrodes 6 are applied across the chest of the patient 4 by the user 2 in order to acquire an ECG signal from the patient's heart. The defibrillator 1 then analyzes the ECG signal for signs of arrhythmia with a shock analysis algorithm. Only if a shockable rhythm, such as VF or a non-perfusing ventricular tachycardia (VT), is detected does the defibrillator 1 arm itself to deliver a high voltage shock. The defibrillator 1 signals the user 2 via aural or visual prompts that a shock is advised. The user 2 then presses a shock button on the defibrillator 1 to deliver a defibrillation shock.

#FIG. 1 illustrates a defibrillator and its use during a cardiac rescue, according to the prior art.

#FIG. 2a illustrates one process flow embodiment of the inventive algorithm for analyzing ECG in the presence of noise artifact from CPR compressions.

#FIG. 2b illustrates a process flow for determining a shockable cardiac rhythm from the analyzed ECG, according to one embodiment of the present invention.

#The inventive shock advisory algorithm, called the Optimized Arrhythmia Recognition Technology (ART), generally applies the principles of the afore-described wavelet transform analysis to a stream of ECG signals, but instead replaces the wavelet transform with a series of fixed-frequency band pass filters. The set of band pass filters is preferably constructed to have frequency windows shaped like the Gaussian windows that are used to produce traditional Morlet wavelets.

#The ART algorithm suppresses CPR artifact related noise by selectively passing relatively high frequency components of a potentially corrupted ECG signal. ART is based on the inventors' realization that, while CPR and an organized cardiac rhythm can occur at similar repetition rates of about 1 to 2 Hz, typical CPR noise has relatively few high frequency components in its signal, i.e. the signal tends to be a rounded waveform. Cardiac activity tends to have relatively numerous high frequency components due to the rapid polarization and depolarization of the heart over a single cycle. It is these high frequency components that are to be captured and analyzed by ART.

#Now turning to the illustrations, FIG. 2a illustrates a process flow embodiment of the inventive ART algorithm 200 for analyzing ECG in the presence of noise artifact from CPR compressions. At step 202, the method first receives an ECG signal, preferably from two or more electrodes which are arranged in electrical contact with a patient's skin. The ECG signal is a time-varying voltage whose source is the patient's heart as well as possibly voltages induced by CPR compressions being applied to the patient. The signal may also include other artifact signals that are external to the patient, such as patient jostling and motion, external electrical noise, etc. The ECG signal is preferably digitized into a stream of signal data.