Dual sensor rate response pacemaker

An implantable pacing system for providing pacing pulses to a patient, the system comprising:

• at least one lead adapted to be implanted adjacent the heart of the patient so as to be able to deliver pacing pulses to the heart of the patient;
• an activity sensor adapted to be implanted within the body of the patient, wherein the activity sensor periodically produces an activity signal corresponding to the sensed level of activity of the patient;
• a metabolic sensor adapted to be implanted within the body of the patient, wherein the metabolic sensor periodically produces a metabolic signal corresponding to the sensed metabolic demand of the patient;
• a control unit adapted to be implanted within the body of the patient, wherein the control unit receives the activity signal and periodically determines an activity indicated rate therefrom indicative of a pacing rate corresponding to the sensed level of activity of the patient, wherein the control unit also receives the metabolic signal and periodically determines a metabolic indicated rate therefrom indicative of a pacing rate corresponding to the sensed metabolic demand of the patient, wherein the metabolic indicated rate and the activity indicated rate are scaled so as to correspond to each other and wherein the control unit periodically determines a dual indicated rate by selecting the greater of the activity indicated rate and the metabolic indicated rate, wherein the activity indicated rate is generally more indicative of the patient's physiological need during periods of low exercise and initiation of exercise and is selected to have a higher magnitude than the metabolic indicated rate during these periods such that during periods of low exercise and initiation of exercise, the dual indicated rate generally corresponds to the activity indicated rate and induces the delivery of pacing pulses to the heart of the patient via the at least one lead so that the heart rate of the heart is maintained at a rate corresponding to the dual indicated rate.

A method of determining a pacing rate of a heart of a patient, the method comprising:

• sensing an activity parameter of the patient comprising sensing the acceleration of the patient's body to obtain an indication of the level of activity of the patient;
• sensing a metabolic parameter of the patient;
• determining an activity indicated rate based upon the sensed activity parameter of the patient;
• determining a metabolic indicated rate based upon the sensed metabolic parameter of the patient;
• and
• setting a dual indicated rate to be the greater of the activity indicated rate or the metabolic indicated rate, wherein the dual indicated rate corresponds to the rate at which the heart rate of the heart of the patient is to be maintained to meet the metabolic needs of the patient based upon the sensed activity and metabolic parameters.

A pacing system comprising:

• a plurality of independently functioning rate sensors, said plurality comprising activity rate sensor means and metabolic sensor means;
• the activity rate sensor means, functioning independently from the metabolic sensor means, for generating an activity indicated rate signal dependent upon the sensed activity of the patient;
• the metabolic rate sensor means, functioning independently from the activity rate sensor means, for generating a metabolic indicated rate signal dependent upon a metabolic demand of the patient in response to physical activity of the patient;
• dual indicated rate determining means for determining, based upon the activity indicated rate signal and the metabolic indicated rate signal, a dual indicated rate for pacing the patient, wherein the dual indicated rate determining means sets the dual indicated rate to correspond to the greater of the activity indicated rate signal or the metabolic indicated rate signal;
• and
• pacing means for providing pacing signals to the heart of the patient in response to the dual indicated rate.

A method of determining a pacing rate of a heart of a patient, the method comprising the steps of:

• sensing an activity parameter of the patient;
• sensing a metabolic parameter of the patient;
• determining an activity indicated rate based upon the sensed activity parameter of the patient;
• determining whether the activity indicated rate exceeds a preselected maximum rate;
• setting the activity indicated rate to the preselected maximum rate when the activity indicated rate exceeds the preselected maximum rate;
• determining a metabolic indicated rate based upon the sensed metabolic parameter of the patient;
• and
• setting a dual indicated rate to be the greater of the metabolic indicated rate and the activity indicated rate, wherein the dual indicated rate corresponds to the rate at which the heart rate of the heart of the patient is to be maintained to meet the metabolic needs of the patient based upon the sensed activity and metabolic parameters.

A method of determining a pacing rate of a heart of a patient, the method comprising the steps of:

• sensing an activity parameter of the patient
• sensing a metabolic parameter of the patient;
• determining an activity indicated rate based upon the sensed activity parameter of the patient;
• determining a metabolic indicated rate based upon the sensed metabolic parameter of the patient;
• and determining whether the activity indicated rate is less than a preselected threshold value when the metabolic indicated rate exceeds a preselected threshold value and wherein setting a dual indicated rate, when the activity indicated rate is less than a preselected threshold value and when the metabolic indicated rate exceeds a preselected value, comprises setting the dual indicated rate to an intermediate value which is between the metabolic indicated rate and the activity indicated rate to thereby slow the heart rate more slowly, wherein the dual indicated rate corresponds to the rate at which the heart rate of the heart of the patient is to be maintained to meet the metabolic needs of the patient based upon the sensed activity and metabolic parameters.

A method of determining a pacing rate of a heart of a patient, the method comprising the steps of:

• sensing an activity parameter of the patient;
• sensing a metabolic parameter of the patient;
• determining an activity indicated rate based upon the sensed activity parameter of the patient;
• determining a metabolic indicated rate based upon the sensed metabolic parameter of the patient;
• determining whether the activity indicated rate or the metabolic indicated rate indicates that the patient is at rest;
• and
• setting a dual indicated rate to a rest rate when it is determined that the patient is at rest, otherwise setting the dual indicated rate to be the greater of the activity indicated rate or the metabolic indicated rate, wherein the dual indicated rate corresponds to the rate at which the heart rate of the heart of the patient is to be maintained to meet the metabolic needs of the patient based upon the sensed activity and metabolic parameters.