Heart rate correlation, response time and effect of previous exercise using an advanced pacing rate algorithm for temperature-based rate modulation.

A temperature-based algorithm to produce pacing rate that resembles chronotropic response to activity was developed. Measurement criteria for the algorithm included workload dependent rate increases with activity and response time within 60 seconds of exercise onset. To evaluate the algorithm, right ventricular blood temperature was recorded during rest and treadmill exercise in 25 patients with implanted Kelvin 500 pacemakers (Cook Pacemaker). Patients included 16 males and nine females, ages 44-81 (mean 72). Indications for pacing were sinus node disease, atrioventricular block and atrial fibrillation with slow ventricular response. Temperature changes reflected physical activity as well as emotional stress. The algorithm was based on the rate of change (dT/dt), the relative change (delta T) and the baseline history (T) of temperature. At exercise onset, a rapid, brief drop in temperature (dT/dt) typically occurred due to peripheral vasodilation, causing prompt increase in pacing rate. As exercise continued, the increase in metabolic rate caused dT/dt as well as delta T to increase, further increasing pacing rate. After exercise, temperature returned to resting level which correspondingly decreased the pacing rate. Sensitivity of the algorithm to temperature variations, and the upper and lower pacing rate limits were programmable to adapt to individual patient needs. The rates produced by the algorithm mimicked intrinsic rate response for various activity levels and produced a mean response time of 16 seconds from exercise onset. Previous exercise had no significant effect on response time. Correlation between normal chronotropic response and simulated pacing rate from five exercise tests was 0.92. These results show good specificity and refute the statement that blood temperature yields a slow response.