Method for stimulating heart muscle activity during the refractory period

Abstract

A system and method for improving heart contractions during a heart function cycle (heartbeat) of a patient requires detecting a local electrical event (depolarization) during the cycle. This local electrical event is then used to trigger a stimulation interval Δt at a time t.sub.0. Importantly, the stimulation interval Δt is set to end at a time t.sub.1 during the absolute refractory period of the heart function cycle. At the time t.sub.1, a stimulator is triggered to stimulate a local sympathetic nerve on the epicardial surface of the heart. With this stimulation the sympathetic nerve secretes norepinephrine to improve a subsequent contraction of the heart.

Claims

1. A method for electrically stimulating a sympathetic nerve of a patient with at least one electrical pulse to improve heart function, the method comprising the steps of: pre-programming each electrical pulse with an intensity having a magnitude and a duration, wherein the magnitude is as much as but less than three times a threshold value that would otherwise directly stimulate the heart muscle; positioning an electrode/sensor in an epicardial vein, on the epicardial surface of the heart adjacent the sympathetic nerve; using a pacing device to detect a local electrical event at a distance from the electrode/sensor to trigger a start time to for a predetermined stimulation interval; waiting a predetermined time interval Δt after the start time to, until a time t.sub.1, wherein t.sub.1 is in the absolute refractory period of the patient's natural heart muscle cycle (t.sub.1−t.sub.0=Δt; activating a stimulator at the time t.sub.1 to electrically stimulate the sympathetic nerve with at least one electrical pulse from the electrode/sensor for a release of norepinephrine during the absolute refractory period; and controlling the pre-programmed intensity of each pulse during the activating step to indirectly assist a subsequent natural stimulation of the heart muscle for improved contractions of the heart muscle after the absolute refractory period.

2. The method as recited in claim 1 wherein Δt constitutes the stimulation interval, and the method further comprises the step of consecutively repeating the stimulation interval.

3. The method as recited in claim 1 wherein Δt is in a range of 100-120 msec.

4. A method for electronically stimulating a sympathetic nerve of a patient with at least one electrical pulse to improve heart muscle function, the method comprising the steps of: pre-programming each electrical pulse with an intensity having a magnitude and a duration wherein, the magnitude is as much as but less than three times a threshold value that would otherwise directly stimulate the heart muscle; positioning an electrode/sensor in an epicardial vein adjacent the sympathetic nerve, wherein the sympathetic nerve is located on the epicardial surface over the left ventricle of the heart muscle; using a pacing device to trigger a start time t.sub.0 for a stimulation interval, wherein t.sub.0 is selected from the group consisting of a local event detected by the pacing device and a time t.sub.0 established by the pacing device; stimulating the sympathetic nerve at the end of the stimulation interval with at least one electrical pulse from the electrode/sensor during the absolute refractory period in the heart muscle cycle to secrete norepinephrine from the sympathetic nerve; controlling the pre-programmed intensity of each pulse during the stimulating step to indirectly assist a subsequent natural stimulation of the heart muscle for improved contractions of the heart muscle after the absolute refractory period; and repeating the stimulating step during each successive heart function cycle.

5. The method as recited in claim 4 further comprising the steps of: pacing a sequence of stimulation intervals with the pacing device; and coordinating the stimulating step with the pacing step to stimulate the sympathetic nerve.

6. The method as recited in claim 5 comprising the step of engaging the pacing device with a timer t.sub.0 establish a stimulation interval Δt, wherein the stimulation interval Δt begins at a start time t.sub.0 and ends at a time t.sub.1.

7. The method as recited in claim 6 wherein the time t.sub.1 is in the absolute refractory period of the heart muscle function cycle.

8. The method as recited in claim 6 wherein t.sub.0 is outside the absolute refractory period.

9. The method as recited in claim 6 wherein the stimulating step is accomplished at the time t.sub.1.

10. The method as recited in claim 7 wherein the start time t.sub.0 is triggered by a local electrical event in the patient's heart muscle during diastole of the heart muscle.

11. The method as recited in claim 9 wherein Δt is in a range of 100-120 msec.

12. The method as recited in claim 11 wherein the electrical pulse for stimulating the sympathetic nerve has a predetermined intensity less than three times the intensity required for activating a contraction of the heart muscle.

13. A method for electronically stimulating a sympathetic nerve of a patient with at least one electrical pulse to improve heart muscle function, the method comprising the steps of: pre-programming each electrical pulse with an intensity having a magnitude and a duration, wherein the magnitude is as much as but less than three times a threshold value that would otherwise directly stimulate the heart muscle; pacing a sequence of heart muscle cycles with an electronic pacing device wherein the pacing device is positioned on the patient at a distance from the heart muscle to detect a local electrical event with which to trigger a start time t.sub.0 for a predetermined stimulation interval; positioning an electrode/sensor in an epicardial vein adjacent the sympathetic nerve, wherein the sympathetic nerve is located on the epicardial surface over the left ventricle of the heart muscle; engaging the pacing device and the electrode/sensor with a timer to establish an electrode activation at the start time t.sub.0 for the stimulation interval; stimulating the sympathetic nerve with at least one electrical pulse at a time t.sub.1 for a release of norepinephrine during the absolute refractory period; controlling the pre-programmed intensity of each pulse during the stimulating step to indirectly assist a subsequent natural stimulation of the heart muscle for improved contractions of the heart muscle after the absolute refractory period; repeating the stimulating step during each successive heart function cycle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:

(2) FIG. 1 is a depiction of a system in accordance with the present invention shown together with the intended environment of its operation;

(3) FIG. 2 is a functional layout of the components employed in a system of the present invention;

(4) FIG. 3 is a time-line depiction of a heart muscle cycle with an operation of the present invention superposed thereon in its relation to the absolute refractory period; and

(5) FIG. 4 is a logic flow chart for the functional tasks that are required during an operation of the computer-controlled system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) Referring initially to FIG. 1, a system for electrically stimulating a sympathetic nerve of a patient to improve heart function is shown and is generally designated 10. As shown, the system 10 includes a deployment catheter 12 which has a sensor 14 and an electrode 16 that are mounted in combination at the distal end of the deployment catheter 12. In addition to the mechanical components mentioned above, the system 10 also includes various electronic components which are disclosed below with reference to FIG. 2. As disclosed below, these electronic components are mounted in the console 18 and interact with each other to provide operational control over the system 10. For purposes of the present invention, it is to be appreciated that the console 18 may be either extracorporeal or implantable. For example, as an implantable, the console 18 may be part of a pacemaker or a defibrillator.

(7) Still referring to FIG. 1, a heart muscle 20 is shown as the surgical target for the present invention. Anatomically, a view of the diaphragmatic surface of the heart muscle 20 shows its coronary sinus 22 and several connecting veins. In particular, the posterior vein 24 of the left ventricle, and the middle cardiac vein 26 are shown. Also shown are sympathetic nerve(s) 28 in the nervous system, of which the nerve bundles 28a, 28b and 28c are only exemplary. Importantly, the nerves 28 are located on the epicardial surface of the left ventricle, and they are adjacent to either the coronary sinus 22 or one of the veins connected with the coronary sinus 22 (e.g. veins 24 or 26).

(8) Referring now to FIG. 2, it will be seen that a computer 30 is provided for the system 10, and that the computer 30 is electronically connected with a switch 32, a timer 34, a stimulator 36 and a voltage source 38. Optionally, a pacing device 40 can also be electronically incorporated with the aforementioned components. As will be best appreciated by cross-reference between FIG. 1 and FIG. 2, the switch 32, the timer 34, the stimulator 36, and the voltage source 38, as well as the pacing device 40, can all be mounted on the extracorporeal console 18. On the other hand, as disclosed above, the sensor 14 and the electrode 16 are incorporated into the deployment catheter 12.

(9) For a disclosure of their interaction with each other, the components mentioned above are shown in FIG. 2 in their relationship with the heart muscle 20. Specifically, the sensor 14 and the electrode 16 are operationally shown in direct contact with the heart muscle 20. Depending on whether the operation of system 10 is to rely on a paced event, which can be alternatively provided using the pacing device 40, the switch 32 is used to alternatively connect the sensor 14 or the pacing device 40 with the timer 34. Further, under the control of the computer 30, the stimulator 36 is energized by the voltage source 38 for a timed activation of the electrode 16. In turn, the electrode 16 will stimulate a sympathetic nerve 28 on the heart muscle 20. As envisioned for the present invention, each pulse that is used to stimulate the sympathetic nerve 28 will have an intensity that is less than about three times the intensity required for activating a contraction of the heart muscle 20.

(10) The depiction of a normal heart function cycle (i.e. a heartbeat) is shown in FIG. 3 and is generally designated 42. As shown, the heart function cycle 42 is depicted by an isoelectric line 44. In this context, the absolute refractory period 46 of the heart function cycle 42 is shown in its overall relationship with the heart function cycle 42. As discussed above, the absolute refractory period 46 is a period of time in which the heart muscle 20 is not able to respond to an electrical stimulation. As also discussed above, the present invention requires there be a stimulation of a sympathetic nerve 28 during the absolute refractory period 46. To do this, the system 10 of the present invention establishes a stimulation interval 48 that will begin with an electrical event 50 at a time t.sub.0 and will end at a time t.sub.1 in the absolute refractory period 46 when a sympathetic nerve 28 is stimulated.

(11) Still referring to FIG. 3 an exemplary electrical event 50 is shown on the isoelectric line 44 to occur at a time t.sub.0. As envisioned by the present invention, the exact time for selection of an occurrence for the electrical event 50 is somewhat arbitrary. Preferably, however, it will be before and relatively near the beginning of the absolute refractory period 46. As indicated above, in an alternate embodiment of the present invention a pacing device 40 can be employed to set the start time t.sub.0. In any event, once a time t.sub.0 has been determined for the electrical event 50, or set by the pacing device 40, the stimulation interval 48 can be established. Mathematically expressed, t.sub.1−t.sub.0=Δt, wherein Δt is the stimulation interval 48. Preferably, Δt will be in an approximate range of 100 to 120 msec. Again, note with reference to FIG. 3 that the time t.sub.1 falls within the absolute refractory period 46.

(12) A logic flow chart for the tasks to be performed during an operation of the present invention is shown in FIG. 4 and is generally designated 52. After the start of an operation, the inquiry block 54 questions whether the sensor 14 is being used. If so, task block 56 requires that the heart muscle function be monitored by the sensor 14. Next, inquiry block 58 asks whether an electrical event 50 has been detected. If not, the sensor 14 continues monitoring the heart function cycle 42. On the other hand, if an electrical event 50 is detected, task block 60 requires the establishment of a stimulation interval 48. As disclosed above, the stimulation interval Δt 48 extends from a time t.sub.0 when the electrical event 50 is detected, to a time t.sub.1 when a pulse(s) is(are) to be fired by the stimulator 36 to stimulate a sympathetic nerve 28. Recall, in an alternate embodiment of the present invention, a pacing device 40, rather than the sensor 14, is used to trigger the stimulation interval 48. Thus, for the alternate embodiment, inquiry block 54 together with task block 62 directs there be an engagement of the timer 34 with the pacing device 40. In all embodiments, however, the inquiry block 64 and task block 66, together, indicate that when the stimulation interval 48 has expired, the stimulator 36 is activated by the computer 30 to stimulate the sympathetic nerve 28. The system 10 then proceeds to monitor the next heart function cycle 42.

(13) While the particular Method for Stimulating Heart Muscle Activity During the Refractory Period as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.