Each day thousands of Americans are victims of cardiac emergencies. Cardiac emergencies typically strike without warning, oftentimes striking people with no history of heart disease. The most common cardiac emergency is sudden cardiac arrest ("SCA"). It is estimated that more than 1000 people per day are victims of SCA in the United States alone.
SCA occurs when the heart stops pumping blood. Usually SCA is due to abnormal electrical activity in the heart, resulting in an abnormal rhythm (arrhythmia). One such abnormal rhythm, VF, is caused by abnormal and very fast electrical activity in the heart. During VF the heart cannot pump blood effectively. Because blood may no longer be pumping effectively during VF, the chances of surviving decrease with time after the onset of the emergency. Brain damage can occur after the brain is deprived of oxygen for four to six minutes.
VF is treated by applying an electric shock to the patient's heart through the use of a defibrillator. The shock clears the heart of the abnormal electrical activity (in a process called "defibrillation") by depolarizing a critical mass of myocardial cells to allow spontaneous organized myocardial depolarization to resume.
Other forms of abnormal cardiac rhythms, such as bradycardia (slow heart rate) and tachycardia (rapid heart rate) can be treated with a low voltage pacing pulse, which assists the heart's natural pacemakers.
External defibrillators send electrical pulses to the patient's heart through electrodes applied to the patient's torso. External defibrillators are typically located and used in hospital emergency rooms, operating rooms, and emergency medical vehicles. Of the wide variety of external defibrillators currently available, AEDs are becoming increasingly popular because they can be used by relatively inexperienced personnel. Such defibrillators can also be especially lightweight, compact, and portable. Because of the lightweight and portable nature of currently available AEDs it would be desirable to add additional features, such as pacing in order to increase the number of cardiac emergencies the device can treat. Unfortunately, the addition of such advanced features also requires the addition of circuitry to accommodate the features. This additional circuitry necessarily increases the weight and size of the defibrillator, thus reducing the compactness and portability. For example, currently available defibrillators with pacing capabilities typically includes two power sources, two capacitors, and two control mechanisms--one for the high energy defibrillation pulse and one for the lower energy pacing pulses. This double circuitry ultimately increases the weight and size of the device.
What is needed, therefore, is a defibrillator capable of pacing which uses a single power source, a single high energy capacitor and a single control mechanism to deliver either defibrillation or pacing energy.