Adaptive refractory period within implantable cardioverter-defibrillator

An implantable cardioverter-defibrillator (ICD) comprising:

• stimulation means for generating electrical stimulation pulses and delivering said pulses to a patient's heart in accordance with a prescribed stimulation regime;
• sensing means for sensing intrinsic cardiac depolarization signals of the patient's heart, said sensing means including first and second sensing channels having first and second refractory periods, respectively, said first and second refractory periods each beginning following a depolarization of the patient's heart, said first and second sensing channels being prevented from sensing any depolarization signals during their respective refractory periods,
• said first sensing channel being adapted to sense normal depolarizations and tachycardias following said first refractory period as a function of a first sensitivity setting, and
• said second sensing channel being adapted to sense fibrillation following said second refractory period as a function of a second sensitivity setting;
• and
• control means for defining said first and second refractory periods, said first and second sensitivity settings and said prescribed stimulation regime.

A method of distinguishing normal cardiac activity, including a tachycardia, from cardiac fibrillation comprising the steps of:

• (a) electrically sensing depolarization signals;
• (b) simultaneously processing the depolarization signals sensed in step (a) in first and second signal processing channels;
• (c) making the first signal processing channel refractory during a first refractory period that begins at the beginning of a cardiac cycle, said cardiac cycle beginning following a sensed or paced depolarization, the duration of said first refractory period being selected to prevent sensing of the afterpotential and repolarization;
• (d) applying a first sensitivity setting to the first signal processing channel that is adapted to sense depolarization signals representative of normal depolarization and tachycardia;
• (e) recognizing the presence of a normal depolarization if a depolarization signal is sensed by said first signal processing channel subsequent to the termination of said first refractory period and prior to the beginning of the next cardiac cycle when the sensed depolarization signal conforms to normal depolarization criteria, and recognizing the presence of a tachycardia if a depolarization signal is sensed by said first signal processing channel subsequent to the termination of said first refractory period and prior to the beginning of the next cardiac cycle when the sensed depolarization signal conforms to tachycardia criteria;
• (f) making the second signal processing channel refractory during a second refractory period that begins at the beginning of said cardiac cycle, the duration of said second refractory period being selected to prevent falsely identifying the paced event afterpotential as a second intrinsic depolarization;
• (g) applying a second sensitivity setting to the second signal processing channel that is adapted to sense depolarization signals representative of fibrillation;
• and
• (h) recognizing the presence of fibrillation if a depolarization signal is sensed by said second signal processing channel subsequent to the termination of said second refractory period and before the beginning of the next cardiac cycle when the sensed depolarization signal conforms to prescribed fibrillation criteria.

A method of treating tachycardia and fibrillation with an implantable cardioverter-defibrillator (ICD) device comprising:

• (a) sensing cardiac depolarization signals in a first signal processing channel within said ICD device, said first signal processing channel having a first refractory period and a sensitivity setting adapted to sense cardiac depolarization signals representative of normal cardiac depolarization, including depolarization associated with tachycardia;
• (b) determining the rate of the cardiac depolarization signals sensed in the first signal processing channel and determining whether such depolarization signals are representative of a normal cardiac rhythm or a tachycardia rhythm;
• (c) applying a prescribed antitachycardia therapy through said ICD device in response to determining that a tachycardia rhythm is present;
• (d) sensing cardiac depolarization signals in a second signal processing channel within said ICD, said second signal processing channel having a second refractory period and a sensitivity setting adapted to sense cardiac depolarization signals representative of fibrillation;
• (e) determining whether the cardiac depolarization signals sensed in the second signal processing channel, in combination with other prescribed criteria, are representative of fibrillation;
• and
• (f) applying a prescribed fibrillation therapy through said ICD device in response to determining that a fibrillation is present.