Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-02-04
2002-07-16
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06421565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cardiac monitoring device of the type having a component for transmitting a signal and receiving at least one echo of the signal reflected from at least one cardiac segment, a position of which, at least when reflecting the signal is related to the cardiac performance of a heart, and circuitry to determine a delay between the transmission of the signal and the receipt of the echo, and to derive from the delay the position of the cardiac segment.
The invention also relates to a rate responsive pacemaker system containing such a device.
2. Description of the Prior Art
Since a device of the above type is particularly suited for an application wherein it is arranged to register the position of a cardiac wall segment, it will, by way of example only, be described in relation to such an application hereinafter. Thereby, the cardiac performance refers to cardiac output and/or other parameters related to cardiac frequency, such as beat volume, cardiac contractility etc.
A device of the above type is described in U.S. Pat. No. 3,938,502, which describes a device for examining a hollow organ, such as a heart, having a catheter which is to be placed inside the hollow organ and which is provided at its end with circumferentially arranged, equidistantly distributed elements, each of which serves both for the transmission and reception of ultrasonic waves. In order to make it possible to completely visualize the moving cardiac structure, such as heart walls and heart valves, surrounding the catheter, at any moment, the device presents a large number of elements which show very little directivity in a plane perpendicular to the axis of the catheter, the elements being so dimensioned in the axial direction that the major part of acoustic energy in transmission is confined to a plane perpendicular to the axis of the catheter. Additionally, this known device includes an excitation unit which successively excites groups of adjacently arranged elements at a rate of at least 25 times per second. The transmitted and the received pulses for the elements of a group are respectively delayed so that the differences in travel times among the elements for the pulses to or from a line in the plane perpendicular to the catheter axis and being perpendicular to the center line of the group are compensated. This known device further includes an adder for the summation of the echo pulses brought into coincidence by the time delays. The known device is used for visually displaying the part of the examined hollow organ surrounding the catheter. This patent teaches the use of the equipment for direct imaging by means of a so called brightness mode (B-mode) ultrasound. The catheter described is primarily intended for examining a visualizing a heart, but is obviously not meant for implantation and would not possibly be used for such a purpose as it is considered highly energy consuming and would be of unacceptable size and weight for operation as an implantable equipment.
European Application 0 503 839 discloses a method and an apparatus for chronologically monitoring the hemodynamic state of a patient using Doppler ultrasound. Such a method and apparatus are used for regulating blood flow within the cardiovascular system in a closed-loop control system using ultrasound measurement techniques to determine a hemodynamic status of a patient and to derive a control parameter for modulating the hemodynamics of the system using electrical or pharmaceutical therapy. Heart contractility and the blood flow output from the heart is monitored in order to control an implantable cardiac assist or therapy device to maintain cardiac output without invading the left heart or the arterial system of the patient, Thus, the pacing rate of a cardiac pacemaker may be based on the determination of the cardiac output estimated by this device. The device is arranged to measure the cardiac output using Doppler ultrasound techniques in which a measuring transducer is implanted within the right heart and directed towards the left ventricle or aortic root. The transducer radiates acoustic energy at ultrasonic frequencies, then the device determines blood flow velocity by receiving and processing the resulting echo signals and measuring the shift in frequency of the returning echoes in comparison to the transmitted waves. The integral of the mean velocity curve is an accurate representation of stroke volume and cardiac output. However, the device is not provided to register the delay between the transmission of the signals and the receipt of the echoes thereof in order to derive from the delay a position of a certain cardiac segment. Moreover, the Doppler equipment to be used in the above application requires quite a lot of energy for its operation, and the output acoustic energy is likely to be too high to be used for permanent operation in a human body.
However, a device as disclosed in European Application 0 503 839 offers a possibility to register the hemodynamic situation in the systemic high pressure circulation of a heart, that is in the left atrium and left ventricle thereof, without needing to be located in said high pressure system. This is an advantage in comparison to prior pacemaker systems that are developed primarily to detect physiologic changes in the right atrium and/or right ventricle even though the action of the pulmonary or right side of the heart is only minimally representative of the hemodynamic situation in the high pressure part of the heart system,
According to modern research and scientific publications as by Baan et at (Baan J. Jong I T. Kerkhof P L. Moene R i. van Dijk A D. van der Velde E I. Koops J. Continuos stroke volume and cardiac output from intra-ventricular dimensions obtained with impedance catheter. Cardiovascular Research 1981 June;15(6):328-34), a very good correlation exists between left ventricular diameter and cardiac output performance. The changes in intra-ventricular dimensions have been measured by means of electrical impedance. For this purpose, a catheter has been equipped with a number of electrodes spaced over a distance equal to the long axis of the left ventricle into which the catheter has been introduced. A constant current was imposed between the outermost electrodes while the inner ones were used to measure resistance of volume segments of the blood contained within the ventricular cavity. The difference in resistance at the beginning and the end of ejection was proportional to the contribution of each segment to stroke volume. The best correlation of left ventricular diameter to cardiac output performance was obtained when measuring in the middle of the axial length of the left ventricle.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a cardiac monitoring device which permits to estimate the total cardiac performance of a heart, including the performance of the high pressure side of said heart, without interfering the function of the heart or being easily interfered by the function of the heart. Moreover, the device should be of a type that is implantable in mammals, and particularly human beings, and which permits to be used in such an application for a significant period of time. The device should also be of a type that requires a minimum of power consumption and is simple as to its construction.
The above object is achieved in accordance with the principles of the present invention in an implantable cardiac monitoring device having an A-mode ultrasound probe which is adapted to be positioned in the right ventricle at a heart, and which emits an ultrasound signal which is reflected from at least one cardiac segment of the left ventricle of the heart, the ultrasound probe receiving the resulting echo signal, and circuitry for determining a delay between the emission of the ultrasound signal and the reception of the resulting echo, and for determining, from this delay, a position of the cardiac segment, the position of this cardiac segment, at least when reflecting th
Getzow Scott M.
Pacesetter AB
Schiff & Hardin & Waite
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