Cardio-synchronous impedance measurement system for an implantable stimulation device

An implantable system for providing therapeutic electrical pulses to the heart of a patient comprising:

• delivery means for delivering electrical pulses to a ventricle of the heart;
• control means for controlling the delivery of the electrical pulses to the ventricle of the heart, wherein the control means induces the delivery means to provide a first type of electrical pulse for therapeutic purposes and a second type of electrical pulse for impedance measurement purposes;
• and
• means for adjusting the first electrical pulses to optimize hemodynamics by measuring at least two instantaneous impedance measurements during a window defined by contraction of the ventricle of the heart to determine a single impedance slope representative of the instantaneous impedance slope that corresponds to the contractility of the ventricle of the heart.

A method of providing electrical pulses to the heart of a patient comprising the steps of:

• sensing the occurrence of either an evoke contraction or a naturally occurring contraction;
• providing two impedance measurement pulses to a ventricle of the heart during either the evoked contraction or the naturally occurring contraction;
• obtaining two instantaneous impedance measurements in response to the two impedance measurement pulses;
• determining an impedance slope based on the two instantaneous impedance measurements;
• and
• adjusting the delivery of one or more pacing electrical pulses to the heart based upon the determined impedance slope.

An implantable electrical system for delivering therapeutic stimulation to a patient's heart, the system comprising:

• a lead, which extends into a ventricle of the heart, adapted for delivering electrical pulses;
• a pulse generator, coupled to the lead, that selectively generates one of tissue stimulation pulses or impedance excitation pulses to the ventricle, wherein the impedance excitation pulses are delivered at two different times during a period of ventricular ejection corresponding to contraction of the ventricle;
• an impedance measuring circuit, coupled to the lead, that measures an instantaneous impedance at the two different times the excitation pulses are delivered during the ventricular contraction;
• a processor system, coupled to the impedance sensing circuit and the pulse generator, that determines an impedance slope based on the two instantaneous impedance measurements, the impedance slope being indicative of contractility of the ventricle, and that regulates the generation of the tissue stimulation pulses based on the impedance slope.