TREA

Method and apparatus for delivering pre-shock defibrillation therapy

Follow

Information

  • Patent Grant
  • 7089055
  • Patent Number
    7,089,055
  • Date Filed
    Friday, June 28, 2002
    22 years ago
  • Date Issued
    Tuesday, August 8, 2006
    17 years ago
Information
Abstract
An apparatus and method is presented for improving cardiac function after successful termination of a tachyarrhythmia such as ventricular fibrillation. A series of electrical stimulation pulses are delivered prior to a defibrillation shock if one or more specific criteria are met.
Description
FIELD OF THE INVENTION

This invention pertains to apparatus and methods for treating cardiac arrhythmias and improving cardiac function.


BACKGROUND

Tachyarrhythmias are abnormal heart rhythms characterized by a rapid heart rate. Examples of ventricular tachyarrhythmias include ventricular tachycardia (VT) and ventricular fibrillation (VF). Both ventricular tachycardia and ventricular fibrillation can be hemodynamically compromising, and both can be life-threatening. Ventricular fibrillation, however, causes circulatory arrest within seconds and is the most common cause of sudden cardiac death. Cardioversion (an electrical shock delivered to the heart synchronously with an intrinsic depolarization) and defibrillation (an electrical shock delivered without such synchronization) can be used to terminate most tachyarrhythmias, including VT and VF. As used herein, the term defibrillation and cardioversion should be taken to mean an electrical shock delivered either synchronously or not in order to terminate a fibrillation. In electrical defibrillation, a current depolarizes a critical mass of myocardial cells so that the remaining myocardial cells are not sufficient to sustain the fibrillation.


Implantable cardioverter/defibrillators (ICDs) provide electro-therapy by delivering a shock pulse to the heart when fibrillation is detected by the device. The ICD is a computerized device containing a pulse generator that is usually implanted into the chest or abdominal wall. Electrodes connected by leads to the ICD are placed on the heart, or passed transvenously into the heart, to sense cardiac activity and to conduct the impulses from the shock pulse generator. The device delivers a defibrillation shock pulse to the heart in response to a detected tachyarrhythmia by impressing a voltage between shock electrodes in contact with the heart.


SUMMARY OF THE INVENTION

The present invention relates to an apparatus and method for preventing post-shock hypotension after termination of ventricular fibrillation. The invention may be incorporated in an ICD or an external defibrillation device. Post-shock cardiac function is improved by delivering a series of electrical stimulation pulses prior to a defibrillation shock while the heart is in fibrillation. In order to avoid delaying an initial defibrillation shock, such pre-shock stimulation therapy is only applied after one or more failed defibrillation attempts, according to the duration of the tachyarrhythmia, or according to the energy level of the defibrillation shock.





BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1 is a system diagram of an exemplary cardiac rhythm management device in which may be incorporated the present invention.



FIGS. 2A through 2D illustrate exemplary algorithms for delivering stimulation pulses to improve cardiac function.





DETAILED DESCRIPTION

It has been found that transient hypotension often occurs following defibrillation shocks. This hypotension may last for seconds, minutes, or even hours and can result in post-shock fatigue in some patients. Some evidence suggests that the likelihood of post-shock hypotension is related to the duration of the fibrillation, and that arterial pressure will quickly return to normal if successful cardioversion occurs within approximately thirty seconds in most patients. Patients who remain in VF for a longer period of time, especially after repeated defibrillation attempts, are more likely to experience transient hypotension after successful cardioversion.


In order to improve post-shock cardiac function, and in some cases increase the likelihood of successful cardioversion, a series of electrical stimulation pulses can be delivered prior to the defibrillation shock. By way of example but not by way of limitation, such pulses may be delivered as a pulse train at a frequency range between 10 and 100 Hz, at an amplitude between 15 and 200 volts, and for a duration of between 100 milliseconds and 2 seconds. Delivering such stimulation pulses while the heart is in fibrillation allows the pulses to be delivered without regard to the intrinsic heart rhythm. Since a patient in VF is in circulatory arrest, however, it is normally considered desirable to delivery defibrillation therapy as soon as possible. In accordance with the present invention, therefore, a series of stimulation pulses are delivered during VF and before a defibrillation shock only after an initial defibrillation shock has failed to cardiovert the patient. In other embodiments, decision algorithms may use additional criteria before delivering pre-shock stimulation therapy such as the duration of the VF, the number of failed defibrillation attempts, and the energy level of defibrillation shock in cases where shocks of increasing magnitude are delivered. By invoking pre-shock stimulation therapy in only these situations, no delay of initial therapy occurs, and the therapy is applied only when it is needed most.


1. Hardware Platform


The present invention may be incorporated into either an external defibrillator or an ICD. The description that follows, however, will principally refer to an ICD configured and programmed to carry out the method of delivering pre-shock stimulation therapy described above. Cardiac rhythm management devices such as ICDs are typically implanted subcutaneously on a patient's chest and have leads threaded intravenously into the heart to connect the device to electrodes used for sensing and delivery of defibrillation shocks. A programmable electronic controller causes defibrillation shocks to be delivered when an arrhythmia is detected. The controller also controls the output of pacing pulses in the case of an ICD with pacemaker functionality. The present invention may be incorporated into an ICD or incorporated into an external defibrillation device. For illustrative purposes, however, a block diagram of an implantable device with cardioversion/defibrillation capability is shown in FIG. 1. The controller of the device is made up of a microprocessor 10 communicating with a memory 12, where the memory 12 may comprise a ROM (readonly memory) for program storage and a RAM (random-access memory) for data storage. The controller could be implemented by other types of logic circuitry (e.g., discrete components or programmable logic arrays) using a state machine type of design, but a microprocessor-based system is preferable.


The device has a sensing channel for sensing cardiac electrical activity and a stimulation channel for delivering stimulation pulses. The device would normally be implanted such that the ventricles are sensed and stimulated by the respective channels. Each channel in this embodiment utilizes a single lead connected to the device that includes a ring electrode 43a and tip electrode 43b for bipolar sensing and stimulation. In certain embodiments, the device may incorporate a pacemaker functionality in which case the stimulation channel may also be used for delivering paces to the heart in accordance with a pacing algorithm. A MOS switching network 70 controlled by the microprocessor is used to switch the electrodes to the input of a sense amplifier 41 for the sensing channel or to the output of a pulse generator 42 for the stimulation channel. The switching network may also be used to connect only one of either the ring or tip electrode to the pulse generator 42 or sensing amplifier 41 for unipolar sensing or stimulation, in which case the conductive case of the device or can 60 is used as the other electrode. A channel interface 40 which communicates bidirectionally with a port of microprocessor 10 may include an analog-to-digital converter for digitizing sensing signal inputs from the sensing amplifier, registers that can be written to for adjusting the gain and threshold values of the sensing amplifier, and registers for controlling the output of stimulation pulses and/or changing the stimulation pulse amplitude or frequency. A defibrillation shock pulse generator 50 with shock leads 50a and 50b for delivering cardioversion/defibrillation shocks to the ventricles is also interfaced to the controller. In an alternative embodiment, the stimulation channel may use the shock leads rather than the sensing lead for delivering stimulation pulses.


The microprocessor 10 controls the overall operation of the device in accordance with programmed instructions stored in memory. The sensing channel detects a chamber sense, either an atrial sense or ventricular sense, when an electrogram signal (i.e., a voltage sensed by an electrode representing cardiac electrical activity) generated by the channel exceeds a specified detection threshold. The time intervals between such senses are measured in order to detect tachyarrhythmias so that appropriate therapy can be delivered by the device. Upon detection of a tachyarrhythmia warranting intervention (e.g., ventricular fibrillation), the controller causes the delivery of a shock pulse to the heart. As described below with reference to different embodiments, the controller is also programmed to deliver pre-shock stimulation pulses via the stimulation channel when certain criteria are met.


2. Exemplary Decision Algorithms



FIGS. 2A through 2D illustrate decision algorithms for delivering pre-shock stimulation therapy as could be implemented in the programming of the device in FIG. 1. Referring first to FIG. 2A, the cardiac rhythm is monitored at step A1 by detecting ventricular senses (R waves) and determining if a ventricular tachyarrhythmia such as VF exists. If a ventricular tachyarrhythmia has been detected, a defibrillation shock is delivered at step A2. This defibrillation shock is delivered without delay and not preceded by stimulation pulses. At step A3, it is determined whether the tachyarrhythmia is still present. If the patient has been successfully cardioverted, the device returns to step A1. If the tachyarrhythmia is still present, a series of stimulation pulses at a specified frequency, magnitude, and duration is delivered at step A4 before the next defibrillation shock is delivered at step A5. The device then returns to step A3 to see if the defibrillation shock was successful. Thus, in this embodiment, pre-shock stimulation therapy for improving cardiac function is delivered prior to each defibrillation shock only after an initial failure of a defibrillation shock delivered immediately after detection of the tachyarrhythmia.



FIG. 2B shows an alternative embodiment in which an additional step A33 is performed after it is determined that a tachyarrhythmia is still present at step A3. Step A33 adds the requirement that at least N previous unsuccessful defibrillation shocks must have been applied before pre-shock stimulation therapy is delivered at step A4. FIG. 2C shows another embodiment in which step A34 is added after step A3 in order to test the duration of the tachyarrhythmia. In this case, pre-shock stimulation therapy is delivered at step A4 only if it is determined that the tachyarrhythmia has been present for at least M seconds.



FIG. 2D shows an embodiment in which pre-shock stimulation therapy is applied or not in accordance with the energy level of the defibrillation shock. Ventricular fibrillation is a phenomena that exhibits a threshold with respect to the shock magnitude and duration needed to terminate the fibrillation by changing the transmembrane potential in a critical mass of myocardial cells. The ventricular defibrillation threshold (VDFT), for example, is defined the smallest amount of energy that can be delivered to the heart to reliably convert ventricular fibrillation to normal sinus rhythm. The larger the magnitude of the shocks delivered by an ICD, the more the battery is drained, thus decreasing the longevity of the device, and the more discomfort is inflicted upon the patient. It is desirable, therefore, for defibrillation shocks to be as small and close to the VDFT as possible. When a defibrillation shock is unsuccessful in terminating a tachyarrhythmia, however, an ICD may be programmed to increase the energy of the defibrillation shock. The magnitude of the defibrillation shock may be increased after each successive failed shock or after a specified number of failed shocks to implement a kind of tiered therapy with respect to shocking energy level. The embodiment of FIG. 2D adds step A31 to increase the energy level of the defibrillation shock up to a specified maximum after each failed defibrillation attempt. Step A35 then determines if the energy level of the defibrillation shock is at least K joules before pre-shock stimulation therapy is delivered at step A34.


In an alternative embodiment, once the controller 10 detects a tachyarrhythmia warranting intervention, a command may also be issued to the drug delivery interface 330. The drug delivery interface then actuates a drug delivery apparatus 331 incorporated into the device that delivers a quantity of a pharmacological or neurohumoral agent for improving post-shock cardiac function. (e.g., epinephrine or norepinephrine). The drug delivery apparatus may take a number of forms. One example of such an apparatus is a pump and a drug reservoir located within a header portion of the device, where the pump communicates with an intravenously disposed catheter. The drug delivery interface within the housing communicates with the pump by control wires that pass into the header through a feedthrough. Upon actuation by the drug delivery interface 330, the pump pumps a quantity of drug from a reservoir into the lumen of the catheter.


Although the invention has been described in conjunction with the foregoing specific embodiment, many alternatives, variations, and modifications will be apparent to those of ordinary skill in the art. Such alternatives, variations, and modifications are intended to fall within the scope of the following appended claims.

Claims
  • 1. A cardiac rhythm management device, comprising: a sensing channel for generating electrograms reflecting cardiac electrical activity;a defibrillation shocking channel for delivering a defibrillation shock pulse to the heart;a stimulation channel for delivering stimulation pulses to improve post-shock cardiac function;a controller for causing the defibrillation shocking channel to deliver a first defibrillation shock with no preceding stimulation pulses upon detection of a tachyarrhythmia from the sensed electrogram;wherein the controller is programmed to deliver subsequent defibrillation shocks with increasing energy until the tachyarrhythmia is terminated or a specified maximum energy is reached; and,wherein the controller is programmed to cause the delivery of a series of stimulation pulses to the heart prior to delivery of a subsequent defibrillation shock if the energy of the subsequent defibrillation shock is above a specified threshold and if the tachyarrhythmia has been present for a minimum specified time.
  • 2. The device of claim 1 wherein the stimulation channel is additionally utilized as a pacing channel by the controller.
  • 3. The device of claim 1 wherein the defibrillation shocking channel includes a pair of shock electrodes and further wherein the stimulation channel utilizes the shock electrodes for delivering stimulation pulses.
  • 4. The device of claim 1 wherein the stimulation pulses are in a frequency range approximately between 10 and 100 Hz.
  • 5. The device of claim 1 wherein the series of stimulation pulses delivered to the heart prior to delivery of a subsequent defibrillation shock is a pulse train of a duration on the order of 100 milliseconds to 2 seconds.
  • 6. The device of claim 1 wherein the stimulation pulses are of a magnitude on the order of 15 to 200 volts.
  • 7. The device of claim 1 wherein the controller is programmed to increase the energy of a subsequent defibrillation shock if a specified number of previous defibrillation shocks were unsuccessful in terminating the tachyarrhythmia.
  • 8. A method for operating a cardiac rhythm management device, comprising: generating electrograms reflecting cardiac electrical activity;delivering a first defibrillation shock upon detection of a tachyarrhythmia from a sensed electrogram;delivering subsequent defibrillation shocks with increasing energy until the tachyarrhythmia is terminated or a specified maximum energy is reached; and,delivering of a series of stimulation pulses to the heart prior to delivery of a subsequent defibrillation shock if the energy of the subsequent defibrillation shock is above a specified threshold and if the tachyarrhythmia has been present for a minimum specified time.
  • 9. The method of claim 8 wherein the stimulation pulses are in a frequency range approximately between 10 and100 Hz.
  • 10. The method of claim 8 wherein the series of stimulation pulses delivered prior to delivery of a subsequent defibrillation shock is a pulse train having a duration between 10 and 100 milliseconds.
  • 11. The method of claim 8 wherein the stimulation pulses have an amplitude between 15 and 200 volts.
  • 12. The method of claim 8 further comprising increasing the energy of subsequent defibrillation shocks if a specified number of previous defibrillation shocks were unsuccessful in terminating the tachyarrhythmia.
US Referenced Citations (201)
Number Name Date Kind
3692027 Ellinwood, Jr. Sep 1972 A
4003379 Ellinwood, Jr. Jan 1977 A
4146029 Ellinwood, Jr. Mar 1979 A
4271192 Wurtman et al. Jun 1981 A
4281664 Duggan Aug 1981 A
4299220 Dorman Nov 1981 A
4417038 Vogel et al. Nov 1983 A
4470987 Wurtman et al. Sep 1984 A
4544371 Dormandy, Jr. et al. Oct 1985 A
4556063 Thompson et al. Dec 1985 A
4559946 Mower Dec 1985 A
4651716 Forester et al. Mar 1987 A
4674518 Salo Jun 1987 A
4686987 Salo et al. Aug 1987 A
4693253 Adams Sep 1987 A
4871351 Feingold Oct 1989 A
4880005 Pless et al. Nov 1989 A
4897987 Spalla Feb 1990 A
4904472 Belardinelli et al. Feb 1990 A
4924875 Chamoun May 1990 A
4944299 Silvian Jul 1990 A
4980379 Belardinelli et al. Dec 1990 A
4987897 Funke Jan 1991 A
5002052 Haluska Mar 1991 A
5014698 Cohen May 1991 A
5040533 Fearnot Aug 1991 A
5041107 Heil, Jr. Aug 1991 A
5042497 Shapland Aug 1991 A
5058581 Silvian Oct 1991 A
5087243 Avitall Feb 1992 A
5113869 Nappholz et al. May 1992 A
5127404 Wyborny et al. Jul 1992 A
5137019 Pederson et al. Aug 1992 A
5190035 Salo et al. Mar 1993 A
5215083 Drane et al. Jun 1993 A
5220917 Cammilli et al. Jun 1993 A
5269301 Cohen Dec 1993 A
5282836 Kreyenhagen et al. Feb 1994 A
5284136 Hauck et al. Feb 1994 A
5305745 Zacouto Apr 1994 A
5330505 Cohen Jul 1994 A
5334222 Salo et al. Aug 1994 A
5342408 deCoriolis et al. Aug 1994 A
5353800 Pohndorf et al. Oct 1994 A
5354317 Alt Oct 1994 A
5366485 Kroll et al. Nov 1994 A
5368028 Palti Nov 1994 A
5391190 Pederson et al. Feb 1995 A
5404877 Nolan et al. Apr 1995 A
5405362 Kramer et al. Apr 1995 A
5416695 Stutman et al. May 1995 A
5417717 Salo et al. May 1995 A
5431682 Hedberg Jul 1995 A
5441525 Shelton et al. Aug 1995 A
5456692 Smith, Jr. et al. Oct 1995 A
5460605 Tuttle et al. Oct 1995 A
5464434 Alt Nov 1995 A
5487752 Salo et al. Jan 1996 A
5496360 Hoffmann et al. Mar 1996 A
5499971 Shapland et al. Mar 1996 A
5501701 Markowitz et al. Mar 1996 A
5540728 Shelton et al. Jul 1996 A
5551953 Lattin et al. Sep 1996 A
5556421 Prutchi et al. Sep 1996 A
5562711 Yerich et al. Oct 1996 A
5562713 Silvian Oct 1996 A
5579876 Adrian et al. Dec 1996 A
5584868 Salo et al. Dec 1996 A
5586556 Spivey et al. Dec 1996 A
5603331 Heemels et al. Feb 1997 A
5607418 Arzbaecher Mar 1997 A
5607463 Schwartz et al. Mar 1997 A
5634899 Shapland et al. Jun 1997 A
5662689 Elsberry et al. Sep 1997 A
5676686 Jensen et al. Oct 1997 A
5690682 Buscemi et al. Nov 1997 A
5690683 Haefner et al. Nov 1997 A
5693075 Plicchi et al. Dec 1997 A
5703125 Bovy et al. Dec 1997 A
5706829 Kadri Jan 1998 A
5720770 Nappholz et al. Feb 1998 A
5725561 Stroebel et al. Mar 1998 A
5725562 Sheldon Mar 1998 A
5730125 Prutchi et al. Mar 1998 A
5749900 Schroeppel et al. May 1998 A
5782879 Rosborough et al. Jul 1998 A
5800464 Kieval Sep 1998 A
5800498 Obino et al. Sep 1998 A
5814089 Stokes et al. Sep 1998 A
5817131 Elsberry et al. Oct 1998 A
5833603 Kovacs et al. Nov 1998 A
5836935 Ashton et al. Nov 1998 A
5851220 Murphy Dec 1998 A
5874420 Pelleg Feb 1999 A
5876353 Riff Mar 1999 A
5893881 Elsberry et al. Apr 1999 A
5899928 Sholder et al. May 1999 A
5913879 Ferek-Petric et al. Jun 1999 A
5919210 Lurie et al. Jul 1999 A
5925066 Kroll et al. Jul 1999 A
5949659 Lesche Sep 1999 A
5954761 Macheck et al. Sep 1999 A
5957861 Combs et al. Sep 1999 A
5957957 Sheldon Sep 1999 A
5967986 Cimochowski et al. Oct 1999 A
5978705 KenKnight et al. Nov 1999 A
5991668 Leinders et al. Nov 1999 A
6016443 Ekwall et al. Jan 2000 A
6016447 Juran et al. Jan 2000 A
6016448 Busacker et al. Jan 2000 A
6022322 Prutchi Feb 2000 A
6035233 Schroeppel et al. Mar 2000 A
6044297 Sheldon et al. Mar 2000 A
6049735 Hartley et al. Apr 2000 A
6070590 Hoffmann Jun 2000 A
6076015 Hartley et al. Jun 2000 A
6078834 Lurie et al. Jun 2000 A
6104949 Pitts Crick et al. Aug 2000 A
6112116 Fischell et al. Aug 2000 A
6115636 Ryan Sep 2000 A
6128526 Stadler et al. Oct 2000 A
6140740 Porat et al. Oct 2000 A
6141588 Cox et al. Oct 2000 A
6154672 Pendekanti et al. Nov 2000 A
6154675 Juran et al. Nov 2000 A
6155267 Nelson Dec 2000 A
6161042 Hartley et al. Dec 2000 A
6168801 Heil, Jr. et al. Jan 2001 B1
6198394 Jacobsen et al. Mar 2001 B1
6200265 Walsh et al. Mar 2001 B1
6203495 Bardy Mar 2001 B1
6206914 Soykan et al. Mar 2001 B1
6213942 Flach et al. Apr 2001 B1
6221011 Bardy Apr 2001 B1
6231516 Keilman et al. May 2001 B1
6237398 Porat et al. May 2001 B1
6253108 Rosborough et al. Jun 2001 B1
6254573 Haim et al. Jul 2001 B1
6256233 Glass Jul 2001 B1
6259949 Rosborough et al. Jul 2001 B1
6261230 Bardy Jul 2001 B1
6263241 Rosborough et al. Jul 2001 B1
6264606 Ekwall et al. Jul 2001 B1
6266563 KenKnight et al. Jul 2001 B1
6270457 Bardy Aug 2001 B1
6272377 Sweeney et al. Aug 2001 B1
6273377 Sweeney et al. Aug 2001 B1
6277072 Bardy Aug 2001 B1
6277078 Porat et al. Aug 2001 B1
6278894 Salo et al. Aug 2001 B1
6280380 Bardy Aug 2001 B1
6285898 Ben-Haim Sep 2001 B1
6298267 Rosborough et al. Oct 2001 B1
6298272 Peterfeso et al. Oct 2001 B1
6309370 Haim et al. Oct 2001 B1
6312378 Bardy Nov 2001 B1
6317615 KenKnight et al. Nov 2001 B1
6317631 Ben-Haim et al. Nov 2001 B1
6331160 Bardy Dec 2001 B1
6336903 Bardy Jan 2002 B1
6358202 Arent Mar 2002 B1
6358203 Bardy Mar 2002 B1
6361522 Scheiner et al. Mar 2002 B1
6361780 Ley et al. Mar 2002 B1
6368284 Bardy Apr 2002 B1
6370424 Prutchi Apr 2002 B1
6398728 Bardy Jun 2002 B1
6411840 Bardy Jun 2002 B1
6411844 Kroll et al. Jun 2002 B1
6424847 Mastrototaro et al. Jul 2002 B1
6440066 Bardy Aug 2002 B1
6442413 Silver Aug 2002 B1
6443949 Altman Sep 2002 B1
6453195 Thompson Sep 2002 B1
6459917 Gowda et al. Oct 2002 B1
6459929 Hopper et al. Oct 2002 B1
6468263 Fischell et al. Oct 2002 B1
6473640 Erlebacher Oct 2002 B1
6478737 Bardy Nov 2002 B1
6501983 Natarajan et al. Dec 2002 B1
6511477 Altman et al. Jan 2003 B1
6518245 Anderson et al. Feb 2003 B1
6519488 KenKnight et al. Feb 2003 B1
6556865 Walcott et al. Apr 2003 B1
6689117 Sweeney et al. Feb 2004 B1
6760621 Walcott et al. Jul 2004 B1
6813516 Ujhelyi et al. Nov 2004 B1
6892094 Ousdigian et al. May 2005 B1
20010000802 Soykan et al. May 2001 A1
20020026228 Schauerte Feb 2002 A1
20020099328 Scheiner et al. Jul 2002 A1
20030004403 Drinan et al. Jan 2003 A1
20030045805 Sheldon et al. Mar 2003 A1
20030060854 Zhu Mar 2003 A1
20030069606 Girouard et al. Apr 2003 A1
20030153952 Auricchio et al. Aug 2003 A1
20030158584 Cates et al. Aug 2003 A1
20030208240 Pastore et al. Nov 2003 A1
20030233132 Pastore et al. Dec 2003 A1
20040002739 Cates et al. Jan 2004 A1
20040093034 Girouard et al. May 2004 A1
Foreign Referenced Citations (12)
Number Date Country
0054138 Oct 1981 EP
0467695 Jan 1992 EP
0545628 Jun 1993 EP
0620420 Oct 1994 EP
1050265 Nov 2000 EP
WO-9725098 Jul 1997 WO
WO-9733513 Sep 1997 WO
WO-9834537 Aug 1998 WO
WO-0004947 Feb 2000 WO
WO-0007497 Feb 2000 WO
WO-0108748 Feb 2001 WO
WO-0130436 May 2001 WO
Related Publications (1)
Number Date Country
20040002739 A1 Jan 2004 US