Method and apparatus for generating adaptive n-phasic defibrillation waveforms

Details

Inventors: Lang, Douglas J.; Swanson, David K.;
Assignee: Cardiac Pacemakers, Inc. (St. Paul, MN)
Primary Examiner: Kamm; William E.
Assistant Examiner: Getzow; Scott M.
Attorney, Agent or Firm: Keck, Mahin & Cate

A method and apparatus for delivering an adaptive n-phasic waveform to the heart in either a fixed-tilt delivery mode or a fixed-duration delivery mode. A first phase of a first polarity is delivered to the heart. The first phase is set to terminate upon decaying to a preset level. If the first phase does not decay to the preset level within a predetermined maximum period of time, the first phase is terminated and the subsequent phases are delivered in a fixed-duration delivery mode. Because the first phase did not decay fast enough, it is determined that the patient has a relatively high system impedance. Therefore, subsequent phases will be delivered to the patient in a fixed-duration mode to insure the defibrillation is reversed. Otherwise, if the first phase decays to the preset level in less than the maximum predetermined period of time, it is determined that the patient has a relatively low system impedance and subsequent phases should be delivered in a fixed-tilt mode.

DETAILED DESCRIPTION It is a primary feature of the present invention to provide a method and apparatus for n-phasic defibrillation capable of automatically selecting the particular defibrillation duration and tilt parameters to minimize the defibrillation energy requirements.
It is an additional feature of the present invention to provide a method and apparatus for generating n-phasic truncated defibrillation waveforms which adjust to the magnitude of the patient's system impedance to minimize the level of the defibrillation energy delivered to the patient.
It is a further feature of the present invention to provide a method for defibrillating the heart by combining the advantages of a fixed-tilt defibrillation mode and a fixed-duration defibrillation mode into a single adaptive n-phasic device to provide a therapy option that is automatically optimized for each patient.
The n-phasic defibrillation system and method of the present invention is adaptable to shock a patient with low impedances in a fixed-tilt mode with variable duration and to shock a patient with higher impedances in a fixed-duration mode with variable waveform tilt.
The shape of the waveform is programmable by specifying the percentage duration of a particular phase relative to the overall duration or by specifying the percentage voltage tilt at the termination of a particular phase relative to the initial capacitor voltage.
In addition, a maximum time switch duration is programmable corresponding to the maximum amount of time the system stays in the fixed-tilt mode before switching to the fixed-duration mode.
Thus, by setting a maximum limit on the duration of the shock, the adaptive method of the present invention optimizes energy delivered to the patient.
Furthermore, by switching to a fixed-duration mode at higher impedances, waveforms, e.
g.
, that are more rectangular (having higher trailing edge voltages), may be produced.
Once an arrhythmia is initially detected, a n-phasic shock is delivered to the patient initially in the fixed-tilt mode

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