Pacemaker with activity-dependent rate limiting

A pacemaker with activity-dependent rate limiting, comprising:

• an atrial sensing circuit responsive to electrical activity in an atrium of a patient's heart for producing a first control signal indicative of a predetermined atrial electrical activity;
• a pacing circuit responsive to said first control signal and an upper rate limit for electrically stimulating a ventricle of said heart subsequent to said predetermined atrial electrical activity and at a ventricular pacing rate limited by said upper rate limit;
• and
• a control circuit responsive to an activity signal, from activity sensing circuit means, indicative of the patient's level of activity and including an upper rate limit control unit for varying said upper rate limit according to the patient's level of activity.

An atrioventricular pacemaker with activity-dependent rate limiting, comprising:

• an atrial sensing circuit response to electrical activity in a patient's heart for producing a first control signal indicative of an atrial depolarization;
• an atrial refractory circuit for inhibiting said atrial sensing circuit for an atrial refractory period after said atrial depolarization;
• an atrial refractory control unit responsive to a blood temperature in said heart indicative of the patient's level of activity for varying said atrial refractory period according to the patient's level of activity;
• an upper rate limit control unit responsive to said blood temperature for varying an upper rate limit according to the patient's level of activity;
• a lower rate limit control unit responsive to said blood temperature for varying a lower rate limit according to the patient's level of activity;
• a ventricular sensing circuit responsive to said electrical activity for producing a second control signal indicative of a ventricular depolarization;
• a ventricular refractory circuit for inhibiting said second sensing circuit for a ventricular refractory period;
• a ventricular refractory control unit responsive to said blood temperature for varying said ventricular refractory period according to the patient's level of activity;
• a pacing circuit responsive to said first and second control signals for electrically stimulating an atrium and a ventricle of said heart on demand at a pacing rate limited by said upper and lower rate limits;
• a delay circuit responsive to said first control signal for delaying electrically stimulating said ventricle for a predetermined delay period after said atrial depolarization;
• and
• a delay control unit responsive to said blood temperature for varying said delay period according to the patient's level of activity.

An atrioventricular pacemaker with activity-dependent rate limiting, comprising:

• first sensing means for sensing electrical activity in a patient's heart, said sensing means including means for detecting predetermined electrical activity indicative of a P-wave;
• second sensing means for sensing a patient's level of activity other than said predetermined electrical activity;
• control circuit means coupled to said second sensing means for generating an upper and a lower rate limit for the patient's level of activity;
• and
• pacing circuit means for generating a ventricular pulse after a predetermined AV delay period in response to detection of said predetermined electrical activity by said first sensing means, whereby the ventricular pulse rate normally equals the sensed atrial rate, said pacing circuit means including means for limiting the ventricular pulse rate to within a range restricted by said upper and lower rate limits, said control circuit means including means for varying said upper rate limit according to the patient's level of activity, whereby the ventricular pulse rate follows the sensed atrial rate up to said upper rate limit determined by the patient's cardiac output requirement.