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Abstract

A cardiac rhythm management device is described in which the rate controlling parameter of a rate adaptive pacemaker is the heart's total active time. The active time is evaluated using the intraventricular impedance technique, the active time being the length of the interval between the onset of contraction and the point where a line passing through two points on the fast filling segment of the impedance wave form reaches the impedance level corresponding to the end-diastole impedance of the preceding beat. The approach results in a upper rate limit corresponding to the maximum heart rate that does not compromise circulatory function, e.g., result in a decrease in cardiac output, or an increase in cardiac workload without an associated increase in cardiac output. The application also teaches the use of the heart's total active time as an indication of hemodynamic instability for triggering a defibrillation.

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