Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-08-20
2002-03-19
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S017000
Reexamination Certificate
active
06360126
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of methods and medical devices for modulating cardiac muscle contractility and more specifically to apparatus and methods for determining the parameters of delivery of excitable tissue controller (ETC) signals under a variety of cardiac conditions.
BACKGROUND OF THE INVENTION
Excitable tissue controllers (ETCs) are devices which modulate the activity of excitable tissues by application of non-excitatory electrical stimulation to the excitable tissue through suitable electrodes in contact with the tissue. For example, ETC devices may be used, inter alia, to increase or decrease the contractility of cardiac muscle in vitro, in vivo and in situ., as disclosed in detail in PCT application, International Publication Number WO 97/25098 to Ben-Haim et al., titled “ELECTRICAL MUSCLE CONTROLLER”, incorporated herein by reference. Other methods and applications of ETC devices are disclosed in PCT applications commonly-assigned to the assignee of the present application, International Publication Number WO 98/10828, titled “APPARATUS AND METHOD FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference, International Publication Number WO 98/10829, titled “DRUG-DEVICE COMBINATION FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference and International Publication Number WO 98/10830, titled “FENCING OF CARDIAC MUSCLES” to Ben Haim et al., incorporated herein by reference, International Publication Number WO 98/10831 to Ben Haim et al., titled “CARDIAC OUTPUT CONTROLLER”, incorporated herein by reference.
Further applications of the ETC including devices combining cardiac pacing and cardiac contractility modulation are disclosed in PCT Application, International Publication No. WO 98/10832, titled “CARDIAC OUTPUT ENHANCED PACEMAKER” to Ben Haim et al., co-assigned to the assignee of the present application. Such ETC devices function by applying non-excitatory electrical field signals of suitable amplitude and waveform, appropriately timed with respect to the heart's intrinsic electrical activity to selected cardiac segments. The contraction of the selected segments can be modulated to increase or decrease the stroke volume of the heart. The timing of the ETC signals must be carefully controlled since application of the ETC signal to the myocardium at inappropriate times may be arrhythmogenic. The ETC signals must therefore be applied to the selected cardiac segment within a defined time interval during which the selected cardiac segment will not be stimulated by the ETC signals.
As disclosed in International Publication No. WO 98/10832, the ETC signals may be timed relative to a trigger signal which is also used as a pacing trigger, or may be timed relative to locally sensed electrogram signals.
U.S. Patent Application to Mika et al., Ser. No. 09/276,460, Titled “APPARATUS AND METHOD FOR TIMING THE DELIVERY OF NON-EXCITATORY ETC SIGNALS TO A HEART”, filed Mar. 25, 1999 and assigned to the common assignee of the present application, the entire specification of which is incorporated herein by reference, discloses a method for timing the delivery of non-excitatory ETC signals to a heart using, inter alia, an alert window period for reducing the probability of delivering an improperly timed ETC signal to the heart due to spurious detection of noise or ectopic beats.
U.S. patent application Ser. No. 09/328,068 to Mika et al., filed Jun. 8, 1999, assigned to the common assignee of the present application, titled “APPARATUS AND METHOD FOR COLLECTING DATA USEFUL FOR DETERMINING THE PARAMETERS OF AN ALERT WINDOW FOR TIMING DELIVERY OF ETC SIGNALS TO A HEART UNDER VARYING CARDIAC CONDITIONS”, now U.S. Pat. No. 6,223,072, the entire specification of which is incorporated herein by reference, discloses, inter alia, apparatus and methods for collecting data from a patient's heart. The collected data is processed to obtain a data set which may be used in an ETC device for dynamically setting the parameters of an alert window used for detecting a depolarization event to trigger the delivery of ETC signals to the heart.
U.S. patent application to Mika et al., filed Jun. 23, 1999, Ser. No. 09/338,649, assigned to the common assignee of the present application, titled “APPARATUS AND METHOD FOR SETTING THE PARAMETERS OF AN ALERT WINDOW USED FOR TIMING THE DELIVERY OF ETC SIGNALS TO A HEART UNDER VARYING CARDIAC CONDITIONS”, the entire specification of which is incorporated herein by reference, discloses, inter alia, apparatus and methods for using the data set obtained in U.S. patent application Ser. No. 09/328,068, now U.S. Pat. No. 6,223,072, to Mika et al., referenced hereinabove, for dynamically setting the parameters of an alert time window on a beat by beat basis.
These methods take into account changes in the velocity of propagation of the depolarization wave in the myocardium caused by various cardiac conditions such as pacing of the heart, prior delivery of ETC signals to the myocardium and the beat to beat cycle length (which is indicative of the instantaneous heart rate).
ETC devices effect their influence on the electrochemical/electromechanical dynamics of the tissue through electrical currents delivered to the tissue after it has been stimulated and while it is undergoing active depolarization and repolarization.
However, when attempting to control the contractility of the heart using ETC devices, currents forced through the tissue past the effective refractory period (ERP) may be arrhythmogenic.
Typically, in ETC therapy the duration of the effective refractory period and other parameters of interest such as, inter alia, the action potential duration, the dispersion of repolarization and the activation velocity are estimated under physician supervision during or after the implantation of an implanted ETC device, or after the implantation of electrodes in the patient's heart and the connection of the implanted electrodes to a non-implantable ETC device disposed outside the patient's body. Such devices are disclosed, inter alia, in U.S. patent applications Ser. Nos. 09/276,460 and 09/328,068 to Mika et al. and in U.S Patent Application to Mika et al., filed Jun. 23,1999, cited hereinabove. The ERP and the other parameters of interest may then be periodically estimated during follow-up visits of the patient
Unfortunately, since the refractory period of the myocardium may change as a function of various of factors such as, inter-alia, the state of the tissue, the level of circulating hormones, such as, but not limited to cathecholamines, the presence and level of pharmacological agents, artificial cardiac stimulation (e.g. pacing), as well as the previous application of ETC signals, a-priori assessment of the duration of the ERP may not be possible.
Moreover, even if it was possible to assess a mean duration of the ERP for some of the above mentioned cardiac conditions, this only represents an average value which may not be valid for each individual cardiac beat cycle, since the ERP duration value may still fluctuate for individual beats occurring under similar cardiac conditions.
Furthermore, certain pathological conditions such as myocardial ischemia, tachycardia and premature ventricular contractions may result in gradual or even abrupt changes in the cardiac action potential parameters which may result in respective gradual or abrupt changes in the ERP duration, Such changes may increase the probability of delivery of ETC signals in the vulnerable time period outside of the ERP duration, unduly increasing the risk of induced arrhythmia.
Another problem which may be encountered during delivery of cardiac ETC therapy, is that the efficacy of the therapy may change as a result of changes in the cardiac action potential duration (APD). This stems from the fact that the ETC signal effectiveness may vary as a function of the timing of the ETC signal delivery within the non vulnerable portion of the cardiac action potentia
Mika Yuval
Prutchi David
Cowan Liebowitz & Latman P.C.
Dippert William H.
Impulse Dynamics N.V.
Layno Carl
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