Implantable cardioverter/defibrillator device having means for determining and treating low amplitude ventricular fibrillation and method thereof

A method for use within an implantable stimulation device for detecting and responding to ventricular fibrillation when R-waves associated with such ventricular fibrillation are sufficiently low in amplitude to prevent their being sensed, the implantable stimulation device having sensing means for sensing cardiac activity, pacing means for generating pacing pulses on demand, and shocking means for generating a shocking pulse in order to terminate the ventricular fibrillation, the method comprising the steps of:

• (a) determining if a given pacing pulse generated by the pacing means has caused capture;
• (b) increasing the energy of the pacing pulses generated by the pacing means in the event capture does not occur in step (a);
• (c) repeating steps (a) and (b) until either the energy of the pacing pulses has increased to a predetermine value or capture occurs;
• and
• (d) in the event capture does not occur, delivering a shocking pulse from the shocking means.

An implantable pacing and shocking device comprising:

• sensing means for sensing cardiac activity, the sensing means including means for sensing a first type of cardiac fibrillation characterized by a sustained rhythm of cardiac activity at a rate faster than a prescribed rate;
• pacing means for generating pacing pulses at a plurality of energy levels on demand;
• means for generating shocking pulses upon sensing cardiac activity indicative of the first type of cardiac fibrillation;
• and
• determining means for determining the presence of a second type of cardiac fibrillation, the second type of cardiac fibrillation being characterized by a low amplitude cardiac activity that cannot be sensed by the sensing means, the determining means including:
• capture-determining means for determining if a given pacing pulse generated by the pacing means has effectuated capture, the absence of capture corresponding to the second type of cardiac fibrillation and the presence of capture corresponding to an energy level that was too low to ensure capture, and
• decision-determining means responsive to the capture-determining means for determining the presence of the second type of cardiac fibrillation.

An implantable pacemaker and shocking device comprising:

• pulse generator means for generating stimulation pulses on demand at a selected programmed energy;
• autocapture means for determining whether a given stimulation pulse has effectuated capture;
• first processing means responsive to a determination by the autocapture means that capture has not been effectuated by the given stimulation pulse, for automatically increasing the energy of a next stimulation pulse;
• and
• second processing means, responsive to a determination by the autocapture means that capture has not been effectuated by a stimulation pulse having a predetermined energy, for determining that a low amplitude ventricular fibrillation condition is present;
• and
• a high energy pulse generator means for generating a high energy shocking pulse in response to a determination by the second processing means that a low amplitude ventricular fibrillation condition is present.