Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Patent
1996-12-05
2000-06-20
Schaetzle, Kennedy J.
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
600513, A61B 502
Patent
active
060772360
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for monitoring cardiac contractility. A Particular embodiment of the invention is suitable for application in pacemakers and in defibrillators, to permit the collection via telemetry of data relating to myocardial contractility and to monitor and control pharracological treatment, provided either by infusion or by conventional methods.
The use of accelerometers inserted in the heart by means of an intravascular catheter is known from French Pat. No. 2.224.752 of 9.4.73 held by Thomson medical Telco and from the publication "contractility studies using a catheter tip accelerometer in the left ventricle" by J. J. Schipper Heijn et al, in "International Conference on Biomedical Transducers", Nov. 7, 1975, Paris, France, which describes the acute and temporary application of the accelerometric device covered by the aforesaid French patent.
More recently, the publication "Characterisation of natural and total artificial heart acceleration" by Pantalos et al. in Vol. XXXV, Transactions of the American Society Artificial Internal Organs 1989, also described the application of an accelerometer to the epicardium of an animal's heart, to measure the variations in natural heart acceleration (NHA) due to the infusion of a drug which acts on the cardiovascular system.
Acceleration sensors have also already been used as sensors in an implantable system, and there are rate-responsive electronic stimulators whose control is based on the measurement of vibrations in the 3-70 Hz band, in Medtronic's Activitrax, or of vibrations below 8 Hz in CPI's Excel.
However, these sensors are disposed in the subcutaneous control unit, and are therefore sensitive only to vibrations and inertial forces transmitted through and to the whole body, and do not pick up the acceleration generated autonomously by the myocardium during the heart's operating cycle.
Application of endocardial acceleration in an implantable device is described in EP-A-0515319 of 12.05.92, "A cardiostimulator device of the rate responsive type" by Sorin Biomedica, which describes an electronic stimulator of the rate responsive type controlled by an acceleration sensor located in the tip of the electronic stimulation catheter, where the control signal is obtained by processing the measured acceleration component.
The invention is based on the realisation that the accelerometric system described in EP-A-0515319 does not allow the real endocardial acceleration to be measured properly during the cardiac cycle, for the following reasons:
a) The accelerometer measures the component of acceleration in one direction only, which in known devices normally corresponds to the longitudinal axis of the electrode which incorporates the acceleration sensor.
It has been shown in practice that it is totally impossible to orientate and keep orientated the axis of the electrode perpendicular to the part of the myocardial wall which is displaced rhythmically following the contraction of the heart. Consequently, the acceleration measured by the uniaxial sensor is related to the real acceleration by the cosine of the angle between the axis of the electrode and the direction of the cardiac acceleration vector. If this angle has a value of 90.degree., the corresponding cosine is zero, and therefore the value of any signal produced by the sensor will be equal to zero.
b) Research into heart kinetics has demonstrated that the displacement of the ventricle wall to which the electrode with the acceleration sensor is fixed is never unidirectional, but is expressed in ways which vary from one point to the next, generally as a complex vector which is given by the sum of the translatory and rotational components.
c) As described for example in Technical Note TN-008, Silicon Accelerometers, by IC Sensors-Eurosensor, the principle on which all uniaxial accelerometers are based may be reduced to the measurement of one component of the force in the specified direction exerted by a seismic mass subjected to the acceleration which is the subject of the measurement, wher
REFERENCES:
patent: 5304208 (1994-04-01), Inguaggiato et al.
patent: 5425750 (1995-06-01), Moberg
patent: 5480412 (1996-01-01), Mouchawar et al.
patent: 5496351 (1996-03-01), Plicchi et al.
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