1. Field of the Invention
The present invention is directed to implantable defibrillator systems, and in particular to such systems which include means for permitting communication between components of the implanted system and external, control signal-generating elements.
2. Description of the Prior Art
Implantable defibrillation systems are known in the art which deliver a high-voltage defibrillation pulse to the heart when the onset of fibrillation is detected and/or in the event of a detected complete loss of cardiac output. Such known devices are also capable, if the heart exhibits an arrhythmia such as atrial fibrillation, atrial flutter or tachycardia, or ventricular tachycardia, of cardioverting the heart by delivering a low-voltage pulse in an attempt to regain synchronous operation of the heart, instead of delivering the high voltage defibrillation pulse. In known devices of this type, considerable effort has been devoted to the development of detection circuitry to accurately identify heart arrhythmias which require defibrillation or cardioversion (i.e., insuring true-positives) and for preventing a "no output" situation when an output is actually needed (i.e., preventing true-negatives). In conventional systems of this type, however, adequate steps have not been taken to prevent the delivery of a defibrillation or cardioversion pulse when none is needed (i.e., preventing false-positives).
It is important to provide a safety mechanism for preventing implantable systems of this type from releasing a treatment pulse when the patient feels no need for such a pulse. A false-positive output could result in severe discomfort to the patient, and may trigger ventricular tachycardia, ventricular fibrillation and ultimately death if the system cannot react quickly enough to provide proper treatment to revive the patient.
It is known from U.S. Pat. No. 4,086,916 to contain a cardiac monitoring system in a wristwatch worn by a patient, the system including circuitry for detecting an erratic heartbeat, a missing pulse or other irregularities and providing an alarm indication, audio and visual, when such an event is detected.
It is also known from U.S. Pat. No. 4,088,139 to provide, in an implantable cardiac pacing system, means for generating a marking pulse in the pacemaker monitoring system if an event such as loss of capture occurs. The patient is not immediately informed of the occurrence of such an event, however, the system is provided with telemetry means so that when the recorded data is subsequently read out and examined by a physician, the data will include the marker indicating that loss of capture has occurred. The physician can then take such corrective steps as may be necessary.
An implantable pacing system is disclosed in U.S. Pat. No. 4,102,346 which includes an alarm device as part of the implanted unit which generates an alarm signal to inform the pacemaker user when the battery source of power of the pacemaker is nearing end of life or is malfunctioning.
An implantable tissue stimulating device is disclosed in U.S. Pat. No. 4,345,603 which activates an alarm which informs the patient in whom the system is implanted that the battery is in need of replacement. After the user has been so informed, the user applies a magnet externally in the vicinity of the implanted unit to deactivate the monitoring system and thereby cease the continued operation of the alarm.
A pacemaker for controlling tachycardia is disclosed in U.S. Pat. No. 4,407,289 also disclosing means for informing a pacemaker user of the remaining battery life. The user places a magnet externally in the vicinity of the implanted unit, which thereby causes the implanted unit to generate two pulses, which can be seen on the patient's ECG waveform. The time separation between the two pulses indicates the remaining battery potential. Application of the magnet, after the pulses have been generated, temporarily disables the device.