Implantable cardiac stimulation device having an improved backup mode of operation and method thereof

An implantable cardiac stimulation device, comprising:

• sensing means for sensing a physiological parameter of a patient;
• control means, in response to the sensing means, for providing an output signal indicating one of timing and amplitude of a stimulation pulse in accordance with a set of stored instructions;
• pulse generating means for providing stimulation pulses to the patient's heart in response to the output signal;
• first memory means for storing a first set of instructions that, when executed, controls operation of the control means based on the sensed physiological parameter;
• second memory means for storing a second set of stored instructions that, when executed, controls operation of the control means based on the sensed physiological parameter;
• and
• error detection means, operatively coupled to at least one of the control means and the first memory, for detecting the occurrence of an error in operation of the device, to thereby detect possible corruption of the first set of stored instructions, the error detection means providing an error indication in response thereto;
• wherein the control means includes:
• means for operating in a first mode of operation in response to the first set of stored instructions when there has been no error indication, and
• means for operating in a second mode in response to the error indication in which its operation is governed by the second set of stored instructions;
• whereby the control means continues to control the operation of the device based on-the sensed physiological parameter of the patient, notwithstanding the error indication.

An implantable cardiac stimulation device, comprising:

• error detection means for detecting errors;
• telemetry means for producing a digital signal responsive to communication received from outside the body;
• control means for determining at least one of timing and magnitude of stimulation pulses in response to each of two alternative sets of stored program instructions, a first set being associated with a first mode and a second set being associated with a second mode;
• watchdog means, in communication with the control means, for requiring the control means to acknowledge proper operation;
• pulse generating means for generating stimulation pulses supplied to the heart in response to one of the control means and the watchdog means;
• timing means, selectively activated by the watchdog means, for triggering the pulse generating means to generate stimulation pulses at a fixed rate independent of the control means;
• and
• processing means for controlling the pulse generating means to deliver stimulation pulses with a hierarchy of pacing modes, the processing means including:
• means for controlling the pulse generating means to operate in a first mode corresponding to a first level of the hierarchy which includes telemetry control, wherein the digital signal provides the telemetry means with the ability to selectively place the control means in at least the first mode based upon the first set of stored program instructions;
• means for controlling the pulse generating means to operate in a second pacing mode corresponding to a second level of the hierarchy which includes watchdog control, wherein the watchdog means includes means for triggering the pulse generating means, when correct acknowledgment is not received, to generate the stimulus in accordance with the fixed-rate timing means and not in response to the control means;
• and
• means for controlling the pulse generating means to operate in a third pacing mode corresponding to a third level of the hierarchy which includes error detection control, wherein the error detection means includes means for triggering the control means to switch from the first mode to the second mode, and thereby rely upon the second, alternative set of stored program instructions in response to error detected in the first mode.

A method for controlling an implantable cardiac stimulation device to provide an electrical stimulus to the heart, the method using a control means, an error detection means and at least two areas of memory that each have a set of stored instructions that direct actions by the control means, the method comprising the steps of:

• executing a first set of the stored instructions to direct the actions of the control means in providing the stimulus to the heart, the first set of stored instructions providing at least one automatic function;
• detecting errors in operation of the implantable cardiac stimulation device using the error detection means;
• and
• executing a second set of the stored instructions in response to the detection of an error, so that the actions of the control means in providing the stimulus are determined by the second set of stored instructions which also provides at least one automatic function.