M. Min, A. Kink, T. Parve, and I. Rätsep (Estonia)
Cardiac pacemakers, rate adaptive pacing control, pacing rate limits, intracardiac bioimpedance, myocardium's energy balance.
The unhealthy heart can not operate at both, significantly high and low rates because of reducing of the myocardium's energy supply E (in comparison with energy consumption for work W), which is proportional to the blood inflow equal to P/R, where P is the blood pressure difference, and R is the hydraulic resistance of the vascular system of the heart itself (Fig.1). The limits between which the heart is able to operate without any danger to the myocardium can vary depending on the actual status of an unstably operating diseased organism. The limits of pacing rate can be made dynamically changeable in implantable cardiac pacemakers through the keeping of myocardium's energy consumption and supply in balance automatically. The energy balance of the myocardium can be estimated indirectly by the aid of measurement of the intracardiac bioimpedance. All the information needed for adaptive control of the pacing rate limits (both, higher and lower limits), can be obtained from analysis of dynamic variations of the measured bioimpedance. There are certain medical routines established for determining the maximum and minimum cardiac pacing rate values, allowable for the patient with a diagnosed disease [1]. These settings are to be determined as the constants before implantation of the pacemaker, which are periodically re-programmable also after implantation.
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