Improved rate adaptive pacemaker apparatus

Claim 2

Demand pacer apparatus (50) for pacing a patient, having stimulus means for delivering stimulus pulses and sensing means for sensing natural heartbeats, first means for sensing a patient variable indicative of desired pacing rate (70 or 114), and rate means for modifying the rate of delivery of stimulus pulses by said stimulus means as a correlation function of said sensed patient variable (114), characterized by: second means for sensing at least another patient variable indicative of desired pacing rate (116, 126), and correlation control means for controlling said correlation function in accordance with said another patient variable (130).

Claim 3

The pacer apparatus as described in claim 1, wherein said first means comprises QT means (70) for sensing the QT interval of a cycle of said pacer.

Claim 4

The demand pacer apparatus as described in claim 1, wherein said second means comprises means for processing said sensed natural heartbeats (116).

Claim 5

The apparatus as described in claim 2, wherein said QT interval is sensed following delivery of a stimulus pulse, and said rate means controls the pacing interval of said stimulus means as a function of the sensed QT interval following each delivered stimulus (102, 114).

Claim 6

The apparatus as described in claim 4, wherein said rate means comprises means for decreasing said pacing interval at a predetermined rate following sensing of a natural heartbeat (108), whereby said pacer rate rises so that a stimulus pulse is delivered after one or more naturally occurring heartbeats and said QT interval is again measured.

Claim 7

The apparatus as described in claim 1, comprising limit means (131) for limiting said correlation function within a predetermined limit.

Claim 8

The apparatus as described in claim 1, wherein said second means comprises means for accumulating patient data over a plurality of cycles (126).

Claim 9

The apparatus as described in claim 1, comprising external means (Fig. 3) for obtaining patient data, said second means being further characterized by means for receiving said external patient data.

Claim 10

Demand pacer apparatus having stimulus means for delivering stimulus pulses, and sensing means for sensing natural heartbeats, comprising: QT means for sensing the QT interval following each delivered stimulus (114): rate means for modifying the pacing interval of said stimulus means as a correlation function of said sensed QT intervals (114); overdrive means for decreasing the escape interval of said stimulus means following at least one natural heartbeat so as to overdrive the natural rate and deliver a stimulus pulse, whereby the QT interval can be sensed and said rate means can modify the pacing interval in accordance with at least one sensed QT interval (102 - 104, 108).

Claim 11

Demand pacer apparatus having stimulus means for delivering stimulus pulses, and sensing means for sensing natural heartbeats, comprising: QT means for sensing the QT interval following each delivered stimulus (114): rate means for modifying the pacing interval of said stimulus means as a correlation function of said sensed QT intervals (114); overdrive means for decreasing the escape interval of said stimulus means following at least one natural heartbeat so as to overdrive the natural rate and deliver a stimulus pulse, whereby the QT interval can be sensed and said rate means can modify the pacing interval in accordance with at least one sensed QT interval (102 - 104, 108).

Claim 12

The demand pacer apparatus as described in claim 9 , wherein said overdrive means decreases said escape interval continuously from cycle to cycle until a stimulus is delivered.

Claim 13

The demand pacer apparatus as described in claim 10, wherein said overdrive means operates to deliver an early stimulus after detecting natural heartbeats over a predetermined duration.

Claim 14

A cardiac pacing system employing demand pacer apparatus comprising: sensing means (102) for sensing when a natural heartbeat occurs and pacer interval means (108) for decreasing the pacer escape interval when at least one such natural heartbeat is sensed, until at least one stimulus pulse is delivered, and measuring means (114) for measuring the QT interval following said at least one stimulus pulse.

Claim 15

A cardiac pacing system employing demand pacer apparatus comprising: sensing means (102) for sensing when a natural heartbeat occurs and pacer interval means (108) for decreasing the pacer escape interval when at least one such natural heartbeat is sensed, until at least one stimulus pulse is delivered, and measuring means (114) for measuring the QT interval following said at least one stimulus pulse.