The haemodynamics of rate adaptive pacing: Use of an ambulatory nuclear monitor.

This thesis evaluates the optimal pacing haemodynamics during rate adaptive pacing using an ambulatory nuclear monitor (Capintec VEST). Comparisons of different pacing modes were performed; i) VVI with DDD. ii) DDD with optimal AV delay at rest with VVIR. iii) DDD with optimal AV delay with DDD with a short AV delay in patients with normal and impaired left ventricles. iv) DDD with DDDR in chronotropically incompetent and competent patients. Relative cardiac output was measured and significant variation was assessed by statistical methods. The optimal pacing rate for constant exercise was studied for WIR pacing and an algorithm to produce optimal haemodynamics was investigated. DDD pacing was found to be superior to VVI during activities of daily living. However, no advantage was detected between DDD over VVIR pacing during exercise, except in patients with impaired left ventricles. An optimal rate band was defined and shown to increase non linearly with increasing work load. No correlation was found between the mean of this band and predicted peak heart rate. It was therefore not possible to predict this mean rate by straightforward means. A new parameter 'Total Active Time' (TAT) was defined, as the time from the beginning of cardiac contraction to the end of the filling phase. TAT was calculated from the optimal rate data. This was transformed into a heart rate and plotted against the paced rate. The intersection was defined as the Haemodynamic Maximum Sensor Rate (HMSR) and this rate was shown to lie within the optimal rate band. In conclusion, the optimal pacing rate is an individual parameter and not age related. It is proposed that the HMSR can be used to dynamically limit the upper rate in order to automatically optimise pacing haemodynamics. This method is considered superior to the development of dual sensor devices.