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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a myocardial revascularization device and
method for making channels in the inside of the heart ventricle to perfuse
the myocardium.
Within this application several publications are references by arabic
numerals within parentheses. Full citations for these and other references
may be found at the end of the specification immediately preceding the
claims. The disclosures of all of these publications in their entireties
are hereby incorporated by reference into this application in order to
more fully describe the state of the art to which this invention pertains.
It is well known that coronary artery disease is a pervasive disease
afflicting many people in this country. Many of these people are treatable
by coronary artery bypass surgery. However, alternative methods of
myocardial revascularization are required for patients with coronary
artery disease not amenable to coronary artery bypass. Investigators have
used the CO.sub.2 laser in arrested hearts to create transmural channels
from the epicardial surface. The channels increase cardiac perfusion by
shunting blood from the ventricle to myocardial sinusoids, and can
endothelialize and remain patent indefinitely. In this approach, the
energy is delivered from outside the ventricle, and the channels formed by
the laser energy penetrate the full thickness through the ventricular
wall.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method
for myocardial revascularization to increase blood flow to the myocardium
from the endocardium without using the native diseased coronary arteries.
It is an object of the present invention to provide an apparatus and method
for myocardial revascularization to be used with patients having extensive
coronary atherosclerosis in whom bypass surgery is not possible.
It is an object of the present invention to provide an apparatus and method
for myocardial revascularization which avoids forming channels which
penetrate the full thickness through the ventricular wall.
The present invention provides a method for cardiac revascularization using
a transendocardial approach with an energy source such as a
thulium-holmium-chromium: YAG (THC-yittrium aluminum garnet) laser. This
approach can be used on a beating heart, concentrates its effects on the
endocardium, which is the surface at highest risk for ischemia, and
reduces potential risk of bleeding and aneurysmal formation associated
with transmural channels.
According to one aspect of the invention, a method for myocardial
revascularization of the heart in a patient is provided, comprising
positioning a channel forming energy emitter inside the ventricle of the
heart, and directing energy from the channel forming energy emitter toward
the ventricular wall in an amount sufficient to form at least one channel
in the ventricular wall into the myocardium to thereby increase blood flow
from the endocardium to the myocardium. which identifies the location of
the emitted energy from the channel forming energy emitter, locating an
aiming beam energy detector outside the heart at a position adjacent a
desired channel forming site, and wherein the step of directing energy
from the channel forming energy emitter is performed after the aiming beam
energy detector detects aiming beam energy to thereby indicate that the
channel forming energy emitter is directed to the desired channel forming
site. The desired channel forming site may be based on familiar epicardial
anatomic landmarks, such as the epicardial branches of the coronary
arteries.
According to another aspect, the present invention provides a method for
myocardial revascularization of the heart in a patient, comprising
entering the ventricle of the heart with a catheter having a lumen which
houses a fiber which emits energy at a fiber end, locating the fiber end
proximate to the ventricular wall, and emitting energy from said fiber end
in an amount sufficient to form a channel in the ventricular wall into the
myocardium to thereby increase myocardial blood flow from the endocardium
to the myocardium.
A myocardial revascularization device is also provided in accordance with
the invention, comprising a handpiece having at least one lumen, and
having an insertable end and a handling end, a fiber for carrying energy
from an energy source to a fiber end from which the energy is emitted,
said fiber being received in one of said lumens, means for moving the
fiber within the lumen to different stop positions, whereby the fiber end
extends from the handpiece insertable end at different sites of a
ventricular wall corresponding to said stop positions, and means for
transmitting energy to said fiber end in an amount sufficient to form a
channel in the ventricular wall into the myocardium at each of said sites,
to thereby increase myocardial blood flow from the endocardium to the
myocardium.
The present invention also provides a myocardial revascularization device,
comprising a channel forming energy emitter means, for insertion into the
ventricle cavity of a heart, for emitting energy to form at least one
channel in the ventricular wall into the myocardium, an aiming beam energy
emitter means for emitting an aiming beam which identifies the location of
energy emitted from the channel forming energy emitter means, an aiming
beam energy detector, for placing against the exterior of the heart, for
detecting an aiming beam from the aiming beam energy emitter means, and
means for energizing the channel forming energy emitter means in response
to detection of an aiming beam by the aiming beam energy emitter. The
aiming beam energy detector location may be selected on the basis of
familiar epicardial anatomic landmarks, those being the epicardial
branches of the coronary arteries.
These and other advantages will become apparent from the detailed
description accompanying claims and attached drawing figures.
DESCRIPTION OF THE DRAWING
FIG. 1 is a cross-sectional view of a ventricular wall of a heart, showing
the epicardium, myocardium, endocardium and a channel formed by a laser
energy source according to the present invention;
FIG. 2A is a myocardial revascularization device according to the
invention;
FIG. 2B shows in more detail gripping means such as suction cups on the
insertable end of the catheter;
FIG. 3 shows an aiming grid to focus a transatrial laser at specific sites
based on visible epicardial landmarks with the heart surgically exposed;
and
FIG. 4 shows a transthoracic aiming thorascope according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
According to one aspect of the invention, a method for myocardial
revascularization of the heart in a patient is provided, comprising
positioning a channel forming energy emitter inside the ventricle of the
heart, and directing energy from the channel forming energy emitter toward
the ventricular wall in an amount sufficient to form at least one channel
in the ventricular wall into the myocardium to thereby increase blood flow
from the endocardium to the myocardium. The energy emitter may be a laser.
The steps of positioning and directing are preferably repeated to form
channels at different sites in the ventricular wall.
The method preferably includes the steps of positioning an aiming beam
energy emitter inside the ventricle of the heart, said aiming beam energy
emitter having an emitting beam which identifies the location of the
emitted energy from the channel forming energy emitter, locating an aiming
beam energy detector outside the heart at a position adjacent a desired
channel forming site. The channel forming site may be selected based on
familiar epicardial anatomic landmarks, those being the epicardial
branches of the coronary arteries. Further, the step of directing energy
from the channel forming energy emitter is preferably performed after the
aiming beam energy detector detects aiming beam energy to thereby indicate
that the channel forming energy emitter is directed to the desired channel
forming site.
The present invention also provides, in a patient, a method for myocardial
revascularization of the heart, comprising entering the ventricle of the
heart with a catheter having a lumen which houses a fiber which emits
energy at a fiber end, locating the fiber end proximate to the ventricular
wall, and emitting energy from said fiber end in an amount sufficient to
form a channel in the ventricular wall into the myocardium to thereby
increase myocardial blood flow from the endocardium to the myocardium. The
fiber is preferably connected to a laser, so that the fiber end emits
laser energy.
The steps of locating and emitting are preferably repeated to form channels
at different sites in the ventricular wall. The step of locating
preferably comprises advancing the fiber end relative to the catheter a
selected distance, whereby channels are formed in the ventricular wall at
said selected distances.
According to another aspect of the invention, a myocardial
revascularization device is provided, comprising a handpiece having at
least one lumen, and having an insertable end and a handling end, a fiber
for carrying energy from an energy source to a fiber end from which the
energy is emitted, said fiber being received in one of said lumens, means
for moving the fiber within the lumen to different stop positions, whereby
the fiber end extends from the handpiece insertable end at different sites
of a ventricular wall corresponding to said stop positions, and means for
transmitting energy to said fiber end in an amount sufficient to form a
channel in the ventricular wall into the myocardium at each of said sites,
to thereby increase myocardial blood flow from the endocardium to the
myocardium.
The means for moving the fiber preferably comprises means for moving the
fiber within the lumen to different stop positions each a selected
distance apart. The means for transmitting energy preferably comprises a
laser. The handpiece may include means for supplying medicinal fluid, and
may have means for supplying the medicinal fluid under pressure. The
medicinal fluid may be heparin, for example.
The means for moving the fiber may comprise servomotor means for moving the
fiber a selected distance, and may comprise a foot switch to activate the
servomotor means. The handpiece insertable end may include gripping means
extending therefrom to grip a ventricular wall. The gripping means may
comprise three suction cups.
According to another aspect of the invention, a myocardial
revascularization device is provided, comprising a channel forming energy
emitter means, for insertion into the ventricle cavity of a heart, for
emitting energy to form at least one channel in the ventricular wall into
the myocardium, an aiming beam energy emitter means for emitting an aiming
beam which identifies the location of energy emitted from the channel
forming energy emitter means, an aiming beam energy detector, for placing
against the exterior of the heart, for detecting an aiming beam from the
aiming beam energy emitter means, and means for energizing the channel
forming energy emitter means in response to detection of an aiming beam by
the aiming beam energy emitter. The aiming beam energy detector location
may be selected on the basis of familiar epicardial anatomic landmarks,
those being the epicardial branches of the coronary arteries. The aiming
beam energy detector may comprise an array of detector elements.
The means for energizing may comprise control means for receiving an EKG
signal from a patient. The channel forming energy emitter means preferably
is energized in response to detection of an aiming beam by the aiming beam
energy emitter and at a suitable time in the EKG cycle.
The myocardial revascularization device may comprise a magnetic element on
the channel forming energy emitter means, and an electromagnet on the
aiming beam energy detector, for electromagnetically coupling the channel
forming energy emitter and detector, for stabilizing the channel forming
energy emitter.
Referring now to the Figures, as shown in FIG. 1, a ventricle wall 10 has
an epicardium 12, myocardium 14 and endocardium 16. A laser channel 18 is
also shown, which extends into the ventricle wall 10 sufficiently to
communicate with the myocardium layer but which does not extend entirely
through the ventricle wall to and through the epicardium. The laser
channel 18 was formed using the method and apparatus according to the
present invention.
FIG. 2A shows a myocardial revascularization device according to the
present invention, which can be used to perform the method according to
the present invention. The device 20 comprises a catheter 22 having at
least one lumen, and having an insertable end 24, and an operating end 26
to be held by a physician. An energy source, such as a laser 28, which may
be a THC:YAG laser, has connected to it a fiber optic 30, which may be one
or more quartz fibers. The fiber optic 30 is received through the catheter
lumen and is shown having an end 32 extending from the insertable end 24
of the catheter. A servomotor 36 serves to advance the fiber end 32 to
stop positions spaced certain distances from each other. The spacing may
be 1 to 10 mm. for example. The servomotor 36 is connected to and
controlled by a foot activator 40. The foot activator is also connected to
and controls the firing of the laser 28 when the fiber end is at the stop
positions.
The device of FIG. 2A also has means for introducing medicinal fluid to the
site, in the preferred form of heparin. The heparin is introduced under
pressure as shown at 41 in FIG. 2A. A diaphragm 42 inside the catheter
prevents the pressurized heparin from flowing out of the operating end 26
of the catheter.
As shown in FIG. 2B the insertable end 24 of the device has gripping means
extending therefrom in the form of three suction cups 44. These cups 44
provide a means to removably mount and stabilize the insertable end 24 to
the inner ventricular wall, and serve as a tripod for the end 24, and the
fiber end 32.
FIG. 3 shows an aiming grid and aiming beam arrangement useful for locating
the desired target positions to fire the laser which creates the channels.
This arrangement could be used in open chest surgery and can be used in a
procedure as an adjunct to coronary bypass or other procedures.
This arrangement comprises an aiming grid 50 having sensors in the form of
photodiodes 52 located in an array on a suitable sheet material. The grid
50 is adapted to be positioned inside of the thoracic cavity adjacent the
heart outside the ventricular wall in which laser channels are desired.
The grid 50 is connected to a controller 54 by cable 56.
A handpiece 60, having a shell of suitable plastic material, for example,
houses an aiming bean source 62. The aiming beam source may be an 808 nm
diode laser, but could also be other sources of electromagnetic,
ultrasonic or magnetic energy. The aiming beam grid 50 has sensors
compatible with and adapted to detect the energy source. The handpiece 60
may actually be a catheter having two lumens. Also disposed in the
handpiece is a fiber optic end 64 for projecting a laser beam, similar to
that of FIGS. 1 and 2. The fiber optic end 64 is connected, by a fiber
optic 67 within the handpiece, to a laser 66 outside the handpiece.
Control means to fire the laser 66 is provided in controller 66. The
controller, by way of cable 68, also provides a means to control the
servomotor 70, located in the base of the handpiece 60, for advancing the
fiber optic end 64 to selected stop positions similarly as in FIGS. 1 and
2. The controller 54 is also connected to receive signals from a surface
EKG by way of cable 72.
It is usually desired that only specific regions of the myocardium will be
targets. The targets are based on the watershed areas of each of the
coronary branches, such that a region poorly perfused by an occluded
coronary branch would be a target, while an adjacent area might not. There
are virtually no visual landmarks to provide a roadmap of the coronary
branches when the ventricle is viewed from the inside and even if there
were, an optical system would be necessary to visually guide such a
system. The coronary arteries are largely epicardial, and provide readily
interpretable landmarks with which surgeons are quite familiar. The grid
provides an arrangement for lining up the laser beam directly underneath
the target, when the target is best identified by external landmarks.
The operation of the aiming beam grid arrangement is as follows. During
open chest surgery, the grid 50 is positioned inside of the abdominal
cavity adjacent the heart outside the ventricular wall in which laser
channels are desired. The handpiece is inserted into the ventricular
cavity and the aiming beam is energized.
When the aiming beam is sensed by the photodiode 52, indicating the proper
location for a channel to be formed in the ventricular wall, the
controller enables or automatically fires the laser 66. The controller
also senses EKG signals and enables or automatically fires the laser only
at the proper time in the heart cycle.
The handpiece is moved to different positions inside the ventricular cavity
and when the aiming beam is sensed by another photodiode in the grid, the
laser is enabled to create another channel in the ventricular wall. This
process is continued until the desired number of channels is created. The
controller may be provided with circuitry to determine whether a
particular photodiode has previously sensed an aiming beam, so that when a
channel has been created at that location, the laser will be prevented
from being enabled at that location again, to thereby avoid firing the
laser at a location where a channel has previously been created.
The controller may also be provided with means to detect the distance
between the aiming beam source 62 (the end of the handpiece) and the grid
50, and the signal strength received. This computed distance and signal
strength may be used to control the intensity of the laser energy used to
create the channel and thus the size and depth thereof. The signal
strength of the aiming beam received would indicate the ventricular wall
thickness and dictate the channel depth desired.
The arrangement of FIG. 3 allows a physician to focus a retrograde
transatrial laser at specific sites based on visible epicardial landmarks
with the heart surgically exposed.
FIG. 4 shows a transthoracic aiming thorascope according to the invention
for focusing a percutaneously introduced laser catheter at specific sites
based on epicardial landmarks. In this arrangement a single photodiode 52
is mounted at the end of a first handpiece 80 which is adapted to be
inserted through adjacent ribs in the ribcage and positioned with its end
against the exterior of the heart. The photodiode is connected to
controller 54 by cable 50. The controller is also connected by cable 68 to
a servomotor 70 in a second handpiece 90. A laser 66 is also connected to
the controller 54, which controls the laser, and its output is through a
fiber optic 67, which fiber optic extends throughout the length of the
second handpiece and terminating at an end 64.
The second handpiece 90 also houses an aiming beam source 62, similar to
that in FIG. 3. The second handpiece may be a catheter having two lumens
as in the arrangement of FIG. 3. The controller 54 receives EKG signals
similarly as in FIG. 3.
Similarly to the operation of the device of FIG. 3, the second handpiece 90
is inserted into the ventricular cavity. The aiming beam from source 62
projects from the second handpiece 90, and when the first handpiece 80 is
aligned to have photodiode 52 receive the aiming beam from the second
handpiece 90, the controller enables the laser 66 to fire and create a
channel in the interior ventricular wall.
An electromagnet 92 may be mounted in the end of the first handpiece 80,
and a metallic ring 94 may be mounted in the second handpiece 90. Magnetic
force could be used to stabilize the first handpiece end against the
endocardium directly opposite the aiming scope. The first handpiece 80,
sometimes referred to an aiming scope, may be provided with appropriate
imaging optics 96, connected to visual monitor 98, for direct
visualization of the region. The details of this feature are well known to
those skilled in the art.
An experiment conducted using the method according to the invention will
now be described.
MATERIALS AND METHODS
The left anterior descending artery (LAD) of 18 dogs (10 laser, eight
control) was ligated distal to the first diagonal, and the area at risk
(AAR) was mapped with methylene blue dye. In laser animals, a catheter
containing the laser fiber was passed through the left atrium, stabilized
against the contracting left ventricular wall, and nontransmural channels
(600 u diameter, about 4 channels/cm.sup.2) were lasered through the
endocardium (800 mJ pulses; frequency 3 Hz) until epicardial blanching was
noted. Survivors (laser, 9/10; controls, 4/8) were sacrificed at six
weeks, and the infarct size was outlined using triphenyltetrazolium
chloride (TTC). Ventriculograms were done after the animals were killed by
ligating the coronary arteries, clamping across the mitral and aortic
valves, and instilling radiopaque dye into the ventricle.
RESULTS
The AAR was similar in both groups (12.7.+-.2.3 cm.sup.2 vs. 13.0.+-.3.1
cm.sup.2). Compared with controls at six weeks, laser-treated animals had
smaller infarct size (3.67.+-.0.32 cm.sup.2 vs. 0.73.+-.0.13 cm.sup.2,
P<0.02), and lower infarct-to-AAR ratio (0.26.+-.0.05 vs. 0.06.+-.0.02,
P<0.02). Neither bleeding nor aneurysms occurred in any of the animals.
Ventriculograms on control animals showed no perfusion of the free wall;
laser-treated animals had dye-filled sinusoids in the free wall, filling
through short channels originating from the endocardial surface.
DISCUSSION
Transmural channels created with a CO.sub.2 laser increase myocardial
perfusion in experimental models, and have been used clinically as an
adjunct during coronary artery bypass. Postoperative ventriculography and
radionuclide scans have demonstrated perfusion, through laser channels, of
regions not revascularized through bypass grafts. The mechanism is thought
to involve perfusion of the collateral network of myocardial sinusoids by
flow entering the lasered channels from the ventricular cavity during
systole. The channels remain open because carbonization associated with
laser energy has been shown to inhibit lymphocyte, macrophage, and
fibroblast migration. Thus, in contrast to channels created by needle
acupuncture, laser channels heal more slowly and with less scar formation,
which allows endothelialization and long-term patency. Bleeding from the
epicardial site of penetration is usually controlled by clot formation.
To improve myocardial perfusion, the channels must allow communication
between the ventricular cavity and myocardial sinusoids, but do not need
to be transmural. In previous models, transmural channels were a
consequence of the inability to deliver CO.sub.2 laser energy through a
flexible fiberoptic system, mandating application of the laser energy from
the epicardial surface of the ventricle. The far-infrared (10.6 u)
CO.sub.2 laser has been used because of its ability to remove tissue
precisely. The mid-infrared (2.15 u) THC:YAG laser has similar tissue
effects because of a large absorption peak of water for light energy in
the 2 u region. In addition, the wavelength of 2 u radiation is short
enough to be effectively transmitted through low hydroxyl 600 u diameter
quartz fibers. This feature permits application of laser energy from the
endocardial surface of a beating ventricle, avoiding the need to create
transmural channels from the epicardial surface.
Using this approach, the AAR in the experimental group was significantly
decreased after the creation of laser channels, and after six weeks the
laser animals had smaller infarcts, as measured by TTC staining.
Laser-treated and control animals had similar initial AAR. In the
laser-treated animals, but not in the controls, ventriculography at six
weeks demonstrated noncoronary perfusion of myocardial sinusoids in the
area at risk through short channels communicating with the ventricular
chamber. There were no bleeding complications, aneurysms, or permanent
arrhythmias.
In conclusion, laser energy can be transmitted through flexible quartz
fibers to create myocardial channels from the endocardial surface in a
beating heart. The channels improve perfusion acutely and remain patent
for up to six weeks. This technique may be useful as an adjunct to
coronary bypass or, with development of a delivery system, might permit
percutaneous treatment of inoperable patients with diffuse coronary artery
disease.
REFERENCES
1. Michoseini M, Shelgikar S, Cayton M M: New concepts in revascularization
of the myocardium. Ann Thor Surg 45:415-420, 1988.
2. Okada M, Ikuta H, Shimizu K, et al: Alternative method of myocardial
revascularization by laser: Experimental and clinical study. Kobe J Med
Sci 32:151-161, 1986.
3. Hardy R1, Bove K E, James F W, et al: A histologic study of
laser-induced transmyocardial channels. Lasers Surg Med 6:563-573, 1987.
4. Oz M C, Treat M R, Trokel S L, et al: A fiberoptic compatible
mid-infrared laser with CO.sub.2 laser like effect: Application to
atherosclerosis. J Surg Res 47(6):493-501, 1989.
5. Treat M R, Trokel S L, Reynolds, R D, et al: A preliminary evaluation of
a pulsed 2.15 micron laser for endoscopic surgery. Lasers Surg Med
8:322-326, 1988.
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