METHOD AND APPARATUS FOR PERFORMING TRANSMYOCARDIAL
REVASCULARIZATION
FIELD OF THE INVENTION
The present invention relates generally to laser devices and biomedical
applications thereof. More specifically, the invention relates to laser-based
scanning methods and apparatus for performing transmyocardial
revascularization (TMR).
BACKGROUND OF THE INVENTION
Proper functioning of the heart as a pump requires that the heart
muscles receive a steady uninterrupted supply of fresh (oxygenated) blood
through the coronary arteries. In particular, the blood from the coronary arteries
provides nutrients to the heart muscle through the myocardium by capillaries that
extend from the coronary arteries. These coronary arteries may become blocked
(occluded) or stenosed with fatty plaques, stenoses or the like, from various
diseases. Drugs, such as vasodilators, and angioplasty, where a balloon catheter
is inserted into these coronary arteries and the balloon is expanded at the
stenosis, are common treatments for opening these blockages. When balloon
angioplasty is not expected to solve this problem, a coronary bypass procedure is
often performed, where a portion or portions of the coronary arteries are replaced
by vein grafts, taken from other parts of the body.
However, some patients do not respond to drug therapy and are not
candidates for angioplasty and/or bypass surgery. These patients typically
include those with insufficient strength to withstand the surgery, frail health,
severe reactions to anesthesia and chronic conditions, such as diabetes, poor
ventricular function, and those who have had poor results from previous surgery.
One solution to assist such patients as well as others is by procedures
commonly known as myocardial revasculahzation (MR). These procedures
revascularize the myocardium by creating channels through the ventricular walls,
either from inside the heart, known as Percutaneous Myocardial
Revasculahzation (PMR) or from outside the heart, known as Transmyocardial
Revasculahzation (TMR). These channels serve to direct oxygenated blood
from the ventricles to the myocardium. As reported in Mirhoseini, et al., "Clinical
Report: Laser Myocardial Revasculahzation", in Lasers in Surgery and Medicine,
6:459-461 (1986), early attempts including needle punctures in the left ventricle
were unsuccessful in the long term, as the channels created by these needles
closed due to fibrosis, scarring, and the like.
In order to achieve longer-term success, carbon dioxide lasers were
employed to create channels in the myocardium. However, this procedure
exhibited several drawbacks, as it required high powered lasers of at least
300-350 Watts, when working with beating hearts. See, Mirhoseini et al. (above).
When the heart was cooled and arrested, this procedure could be performed with
carbon dioxide lasers of lower power (80-100 Watts). However, this requires
aorto-coronary vein bypass procedures and placing the patient on a heart-lung
machine, unsuitable for people such as diabetics, and those with similar chronic
conditions.
An alternate TMR approach using laser technology is disclosed in U.S.
Patent No. 5,554,152 (Aita, et al.). The apparatus disclosed is a laser connected
to an optical fiber, in turn connected to a lens for outputting the laser. The
apparatus is inserted into the chest cavity into contact with the heart. The heart is
then irradiated with sufficient laser energy for a sufficient time, to cause a channel
to be formed from the epicardium through the myocardium and the endocardium.
Another alternate TMR approach is disclosed in U.S. Patent 5,125,926
(Rudko, et al.). Here, there is disclosed a pulsed laser system for a carbon
dioxide laser. The laser beam is delivered by an articulated optical arm or a fiber
optic element, in pulses of 50 Joules.
SUMMARY OF THE INVENTION
The present invention improves on the prior art transmyocardial
revasculahzation (TMR) methods by providing TMR methods that employ laser
beam scanning for cutting channels in heart tissue. Scanning is preferably with a
flash scanner, that in conjunction with a laser source, allows for the use of a low
power (approximately 60-200 Watt) laser for producing a controlled beam, for
movement in accordance with a controlled scanning pattern, cutting channel(s) in
the heart that allow for its revasculahzation. These TMR methods of the present
invention may be performed either by open chest surgery or endoscopically.
There is disclosed a method where the heart is accessed, by
procedures including conventional surgical open chest access, such that the laser
beam will be in communication with the heart, preferably at an area proximate a
ventricle. Laser firing and ultimately scanning are synchronized by a
synchronization system, that activates and subsequently deactivates the requisite
laser pulse for scanning in accordance with the heartbeat cycle from the
electrocardiogram (ECG) of the instant patient. When the laser source is
activated, a laser beam of a sufficient energy for heart tissue ablation, may be
scanned by the flash scanner, preferably in a controlled spiral pattern, for a time
period sufficient to cut the requisite channel in the heart. Additional channels may
be cut into the heart by repeating this procedure.
A second embodiment of the present invention discloses a TMR
method, similar to the first embodiment, except that the heart is accessed
endoscopicly. The apparatus disclosed for this second embodiment is similar to
that disclosed in the first embodiment, and where necessary, is adapted for
endoscopic use.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described with reference to the
accompanying drawings, wherein like reference numerals identify like or
corresponding components.
In the drawings:
FIG. 1 is a schematic diagram of a first embodiment of the present
invention;
FIG. 2 is diagram of an ECG (ECG signal);
FIG. 3 is a diagram of a spiral scanning pattern generated by the flash
scanner of the present invention;
FIG. 4 is a cross sectional view of a heart with a channel cut therein by
the present invention;
FIG. 5 is a schematic diagram of a second embodiment of the present
invention; FIG. 6 is a cross-sectional of view of the working channel of the
endoscope used in the method shown in Fig. 5; and
FIG. 7 is a photograph of a dog heart treated in accordance with the
present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
FIGs. 1-4 show a first embodiment of the method of the present
invention. This first embodiment involves accessing the heart 20 by opening the
chest of a patient. A surgeon 22 places a flash scanner 24, that emits a focused
beam 24a of laser energy, from a handpiece 25, proximate the heart 20 and in
particular, proximate the epicardium 26. The flash scanner 24 is computer
controlled to scan a target area 28 on the heart 20, preferably in a spiral pattern
30. The flash scanner 24 is connected to a laser source (L) 32, that is coupled to
a synchronization system (SS) 34, that synchronizes laser activation and
deactivation, preferably in the form of pulses of laser energy, based on the
patient's heartbeat cycle, as established by an electrocardiogram (ECG) 36 (the
patient being connected to an ECG machine), the ECG is shown in detail in FIG.
2 and described below. Activation of the laser source 32, begins scanning, that
results in channels 38 in the heart 20 for its revascualrization.
With specific reference to FIG. 1 , the heart (beating) is shown having
been accessed by conventional medical (surgical) procedures well known to
those of skill in the art. The patient is placed on the requisite life support
machinery. The flash scanner 24 is positioned proximate the heart 20, preferably
proximate a ventricle 20a.
The flash scanner 24, handpiece 25, and computer control, employed
with the present invention, are disclosed in commonly assigned U.S. Patent
Application Serial No. 08/346,878, filed November 30, 1994, entitled: METHOD
AND APPARATUS FOR HAIR TRANSPLANTATION USING A SCANNING
CONTINUOUS-WORKING C02 LASER, now allowed, this patent application
being incorporated by reference herein. This flash scanner 24 focuses the laser
energy beam 24a from the laser of the laser source 32 into a spot 40 (FIG. 3).
Alternately, a flash scanner that scans a Lissajou pattern as described in U.S.
Patent No. 5,411 ,502 (Zair) (the '502 patent), this patent being incorporated by
reference herein, may also be employed as the flash scanner 24.
These flash scanners 24 employ mirrors, whose movements can be
continuous or in steps. Continuous mirror movement involves scanning in a
predetermined pattern at a constant speed. Step mirror movement involves
scanning in patterns, that are variable from site to site, creating a scanned pattern
from a multiple of adjacent sites at multiple locations. The above discussed
scanners are designed to employ a suitable handpiece 25 fitted thereto, these
handpieces being disclosed in U.S. Patent Application Serial No. 08/346,878
(above). Both of the flash scanners 24, and all components thereof, employed
with the present invention are electronically controlled and preferably computer
controlled, by conventional computer control hardware (not shown) and software
(not shown).
The laser source (L) 32 preferably includes a laser, such as a CW
(continuous working) mode C02 (carbon dioxide) laser or a pulsed mode C02
laser, in accordance with that disclosed in U.S. Patent Application Serial No.
08/346,878 (above), preferably of low power (approximately 60-200 Watts).
Alternate lasers may include pulsed excimer and pulsed Erbium-YAG lasers. The
laser source 32 is also under the control of the above discussed computer control
hardware and software.
The ECG (ECG signal) 36, detailed in FIG. 2, shows the patent's
heartbeat cycle as four different waveforms (waves), Q, R, S, T. The
synchronization system (SS) 34 is connected with the ECG machine (for example,
a type HP78352A from Hewlett Packard Company, Palo Alto, California), and
coordinates laser pulsing (firing), ultimately resulting in scanning, with the
heartbeat cycle based on the patient's ECG. The preferred synchronization
system is that disclosed in U.S. Patent 5,125,926 (Rudko, et al.) (the '926 patent),
this patent being incorporated by reference herein. Pulsing (activation and
deactivation) of the laser of the laser source 32 is in accordance with that
disclosed for the laser in the '926 patent (above), and such pulsing effectuates
scanning for the time period (scanning duration) listed in Table 1 below. It is
highly preferred that pulsing occur in the time interval between the R and T waves
of the ECG (ECG signal) 36, for at this time, the heart is most still and its electrical
sensitivity is minimal (this time period is also known as systole or the systolic
phase). With the laser of the pulsed laser source 32, scanning occurs in
accordance with that disclosed in U.S. Patent Application Serial No. 08/346,878
(above), and scanning parameters are described in TABLE 1 below.
Turning also to FIG. 3, the preferred scanning occurs as the spot 40 is
scanned in a spiral pattern 30, preferably at a constant velocity, to cover the target
area 28, preferably with the C02 laser at a power level of approximately 150
watts, to avoid any possible charring of the heart tissue. Lack of char assures
minimal thermal necrosis on the walls of the channel 38 (FIG. 4) of the heart
tissue. The spot 40 is preferably focused at a focal length of approximately 50
mm to 150 mm, to generate a spot size of a diameter of approximately 0.2 mm.
By utilizing this spiral scanning, target areas 28 of diameters D of approximately
0.8 mm to 1.5 mm can be scanned for creating (cutting) the requisite channel(s) in
the heart 20. Specifically, single or multiple channels 38 may be cut into the heart
20, by this scanning. Preferably, scanning is adjacent to an area, such as a
ventricle 20a, in need of increased blood circulation. However, portions of the
heart other than the ventricles 20a can also be revascularized by this method. A
typical scan to create a single channel 38 takes approximately 10 milliseconds to
approximately 100 milliseconds, is started preferably between the R and T waves
(in the time interval therebetween), and stops preferably approximately 0.2 to 0.4
seconds after the R wave crest, to avoid fibrilations. Parameters for scanning a
channel 38 are listed in the following TABLE 1.
TABLE 1 - PREFERRED FLASH SCANNER SPECIFICATIONS
Focal length 80 mm
Scanning diameters 0.8 - 1.5 mm
Scanning duration 0.1 sec
Spot size 0.2 mm
Scan Velocity (for continuous mirror movements) 200 mm/sec
Instantaneous Dwelling Time (for a step scan with non-continuous scanner mirror movements) 1 millisecond
Scanning pattern a. Continuous mirror movements -
Spiral (constant velocity - Fig. 3 above) b. Non-continuous mirror movements (step scan) - Spiral (as above) or Circular
The scanning is such that once the channel 38 is formed, the portion of
the channel opening through the epicardium 26 is temporarily covered while a
portion of the channel 38 extending through the epicardium 26 seals itself.
Turning now to FIG. 4, there is shown the heart 20 with the resultant
channel 38 cut therein by scanning. While only a single channel 38 is shown in
this drawing figure, multiple channels are also permissible. It is preferred that the
channel 38 extend from the epicardium 26, through the myocardium 44 and
perforating the endocardium 46. These channels 38 should preferably be
scanned to dimensions of approximately 0.8 mm to 1.5 mm in diameter and
approximately 1 cm to 3 cm in depth.
With a first channel 38 formed, additional channels may be formed by
computer controlled repositioning of the mirrors for the flash scanner 24, as
described in U.S. Patent Application Serial No. 08/346,878 (above), to scan
another target area (on the heart 20), similar to the previously discussed target
area 28 (above). This computer-controlled retargeting does not require manual
repositioning of the flash scanner 24. This allows for the efficient scanning of
other areas of the heart 20 for cutting these additional channels.
FIG. 5 shows a second embodiment of the present invention, where
channels 38 are cut into the heart 20 by scanning, similar to the first embodiment,
except that certain instrumentation is adapted for endoscopic use. This method
initially involves making an incision in the chest cavity, preferably subxyphoid, to
access the heart. The heart 20 is accessed, preferably at an area proximate the
ventricle 20a, by conventional instrumentation, including a standard rigid
endoscope 50 (through the incision), that is preferably advanced to a point
approximately 1 mm from the heart 20.
The endoscope 50 is a conventional multiple channel endoscope, and
includes at least two channels, a viewing channel 51 (FIG. 5) and an operating
channel 52 (FIG. 6). This endoscope could also be a conventional thorasoscope
or the like. The viewing channel 51 is fitted with standard optics (not shown) and
conventional image conveying apparatus (not shown) for direct vision on a video
monitor 53 or the like. The operating channel 52 receives the flash scanner (SC)
24', that emits a focused beam 24a' of laser energy. This flash scanner 24' is
similar to the flash scanner 24 described above, except that it has been modified
slightly for endoscopic use. The flash scanner 24' is connected to the laser
source (L) 32 (described above), that is in turn connected to a synchronization
system (SS) 34 (described above), the synchronization system 34 that utilizes the
ECG 36 (described above) of the individual patient, all connections in accordance
with those described above. The endoscope 50 also includes a conventional
control mechanism 54 for steering it, upon its advancement toward the heart 20,
in accordance with conventional surgical techniques.
Turning also to FIG. 6, the focused beam 24a' of laser energy extends
into and through the operating channel 52 of the endoscope 50, during scanning
in accordance with the above detailed laser-beam scanning procedure, in the
above described scanning patterns 28, for cutting a channel(s) 38 in the heart 20.
Once the requisite channel(s) 38 have been cut, all instrumentation (e.g.,
endoscope 50 and other instrumentation associated therewith) is removed in
accordance with conventional surgical procedures.
EXAMPLE 1
In accordance with the first embodiment of the present invention,
detailed above, a live dog (mongril, approximately 30 kilograms) was anesthetized
by conventional surgical techniques, the heart was accessed by conventional
chest opening techniques, and an ECG was taken. Channels 1 , 2, 3, as shown in
FIG. 7, were scanned with the flash scanner (described above) and cut in the
heart by activating a CW C02 laser (as described above) in the time interval
between the R and T waves of the ECG (FIG. 2), for approximately 0.2 seconds,
at an output of 150 watts, the activation ending approximately 0.2 seconds after
the crest of the R wave. Scanning was performed in the spiral shaped pattern in
accordance with FIG. 3. In doing so, the flash scanner was set to a scanning
diameter of 1.0 mm. The channels 1 , 2, 3 extended completely through the heart
(from the endocardium to the epicardium, a depth of approximately 7 mm) and
had a diameter of approximately 1 mm.
While embodiments of the present invention have been described so as
to enable one skilled in the art to practice the present invention, the preceding
description is intended to be exemplary. It should not be used to limit the scope of
the invention, which should be determined by reference to the following claims.