One of the indicators of metabolic demand that has been used for controlling the rate of pacemakers is central venous blood temperature (CVT).
In 1983, Bill Cook and Dr. Neal Fearnot began to work under the Cook Pacemaker Company on developing the technology developed by Dr. Fearnot at Purdue University into an improved prototype for a temperature-based exercise responsive pacemaker that was released in 1988 as the Kelvin Sensor rate-responsive pacemaker. One of the first CVT rate-adaptive pacemakers was the Cook Model Kelvin 500 series.
Another one of the first CVT rate-adaptive pacemakers was the Intermedics Nova MR, which differs from the Kelvin 500 series in that its pacing algorithm had a more dynamic HR response. Like the Kelvin 500 series pacemaker, the Nova MR not only modulated the heart rate according to the derivative of the CVT versus time curve as well as the instantaneous CVT, but it also took into account the initial dip in temperature. Intermedis then came out with the Circadia pacemaker that improved beyond the Nova MR through algorithms that better simulated the rate of a normal, healthy heart under conditions such as rest, circadian rhythm, exercise, and fever.
Temperature-sensing pacemakers did not gain wide acceptance, mostly because of their specialized, rather unreliable sensing lead. The last CVT-sensing pacemaker in production (ca. 1994) was the Cook Sensor model 510.
A very detailed engineering discussion on CVT-sensing pacemakers is available at Mayotte MJ. “Rate adaptation by temperature.” In: Webster JG, ed. Design of Cardiac Pacemakers. IEEE Press, Piscataway, NJ, 1995: 335–368.