Control system and method for improved laser angioplasty

A control system and method for laser angioplasty or laser ablation or welding of tissue in general, in which firing of a laser catheter is correlated with movement of a vessel or other body chamber carrying the laser catheter, whereby the laser is fired only during those times its fiberoptic-delivered beam is aimed at plaque or other target in the vessel or chamber.

BACKGROUND OF THE INVENTION 
The invention relates specifically to laser angioplasty and to improved 
methods and apparatus therefor. With this in mind, the invention will be 
specifically described with reference to laser systems and methods for 
ablating plaque, although it has broader applicability. For example, it is 
applicable to the so called hot probe laser approach as described in U.S. 
Pat. No. 4,650,024, entitled "Thermorecanalization Catheter and Method for 
Use", issued March 31, 1987. In its broader sense the invention relates to 
any medical treatment systems and method for effecting treatment to 
selected sites in the body in which cyclic or repetitive movement is 
involved. 
The aiming of laser energy accurately at atherosclerotic plaque within a 
vessel, such as a coronary artery, is negatively affected by the 
continuous movement of the vessel. This movement is associated with 
cardiac contractions, hence relates to phases of the cardiac cycle. As a 
result of such movement a laser catheter positioned within a vessel also 
undergoes relative movement and may at times be aimed at plaque and at 
other times aimed at normal vessel wall. 
Mechanical damage to vessels, including wall perforation, continues to be a 
major problem with laser angioplasty. The aiming of laser energy 
(delivered via a fiberoptic delivery system) is a major task. The 
continuous motion of the vessel wall significantly complicates aiming and 
delivering of laser energy accurately to the atherosclerotic plaque. The 
prior art has treated the movement of coronary arteries and other vessels 
as a problem rather than attempting to take advantage of the repetitive 
nature of the movement of coronary arteries as displayed from one cardiac 
cycle to another. 
The present invention relates to a control system for timing the delivery 
of laser energy such that it accurately impinges on plaque or other 
intended target area. 
SUMMARY OF THE INVENTION 
According to this invention the repetitive motion of the walls of the 
ventricles (or heart chambers in general) and the motion of associated 
vessels during heart cycles is taken advantage of and delivery of laser 
energy for ablation of the plaque (or other type of obstruction or target) 
is provided only during specific, predetermined times or time intervals 
during a cardiac cycle or cycles. Thus, in accordance with this invention 
one takes into account the repetitive nature of the movement of the vessel 
carrying the laser catheter and uses the repetitive nature of the movement 
for timing the firing of the laser only when the laser beam (delivered via 
fiberoptic-based catheter) and the plaque or other obstruction or target 
are coincident i.e., at times when accurate aiming exists. 
In accomplishing this it is necessary to identify, during a number of 
consecutive cardiac cycles, those times during the cycle when the laser 
catheter is aimed at the target area and not at normal vessel wall. It can 
be seen that during certain times of such a cycle repetitive movement of 
the vessel will bring the atherosclerotic lesion i.e., a target area into 
a position where the laser energy will impinge on it. Therefore, the laser 
energy delivery during such time or time intervals will be safer and will 
significantly diminish probability of vessel wall perforation. 
Consequently, the movement of the vessel is no longer treated as a problem 
but rather the motion is taken advantage of by timing its cyclic movement 
and selecting or defining those times or time intervals when the laser 
energy is coincident with respect to the targeted area, for firing the 
laser. 
More specifically, with the proposed invention, after initially positioning 
and aiming the distal end of fiberoptic-based laser catheter at a target 
area such as plaque or some other obstruction or target area within the 
vessel, the entire cardiac cycle is artificially divided into a number of 
fixed time intervals, as determined by the physician-operator. For the 
purpose of establishing a cardiac cycle, the QRS complex from an 
electrocardiogram may be used to establish the beginning and end points of 
a repetitive cycle to be used. During a plurality of times within such a 
cycle an image or signal indicative of the position of the distal end of a 
laser catheter, relative to the target, may be obtained during each of 
those times. Such an image or signal (more than one may be involved and 
used) are stored, preferably in an electronic storage media such as a 
digital memory or video tape, for later review and use. 
Images may include fluoroscopic or angiographic (both radiographic) images 
and or images from a fiberoptic angioscope. Signals may be also obtained 
from an ultrasound transducer mounted at the distal tip of a laser 
catheter. Also, laser induced fluorescence signals (plaque and normal 
vessel walls fluoresce differently in response to a laser radiation) may 
be used alone or simultaneously with other signals and/or images 
throughout any predetermined number of cardiac cycles. 
All such data may be stored electronically for subsequent review by a 
physician-operator of the system. After sufficient data has been 
accumulated in the storage medium the images and signals may be reviewed 
frame by frame. It is preferable to review at the same time all images and 
signals which were obtained at the same time in the cycle. Window type 
presentation of multiple images and signals on one screen is also 
preferable. The review is not done in real time but at a speed convenient 
for the physician-operator. The review of the collected data allows the 
physician-operator to determine those times of the cycle during which the 
laser catheter is accurately aimed at the target area. Through the use of 
a microcomputer or other computer means, appropriate programming may then 
be placed into operation to control the firing of the laser catheter for 
delivery of laser radiation during upcoming cardiac cycles and only during 
those times or time intervals when it has been determined that the laser 
beam is aimed directly at or coincident with the target area. 
In a simple system only one image or signal may be utilized to verify 
aiming. However, in a more sophisticated system, wherein one or more 
images and/or signals are stored for review, all of the images and signals 
which have been obtained simultaneously from several sources during given 
times of a cycle may be used to confirm the accurate or inaccurate aiming 
of the laser catheter at the target area. 
Agreement concerning aiming between different sources of data confirms for 
the physician-operator those time intervals of the cycle when it is safe 
to activate the laser for ablating the target area. Trains of ablative 
laser pulses throughout these safe times or time intervals, which may be 
one time or time interval of one cycle or several cycles or several times 
or time intervals extending over a number of cycles may be utilized. Such 
a system of aiming verification will provide improved operation of a laser 
angioplasty system and is most preferred. 
As indicated above, the QRS complex of an ECG may be used for establishing 
a cycle representative of the vessel movement and is preferred. However, 
other sources for establishing representative cycles may be used such as 
the blood pressure in the aorta, blood flow in the cardiac ventricle or 
aorta or an artificial pacing cycle may be established with the pacing 
pulse used as a reference.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In its preferred form, this invention will be practiced in combination with 
the laser catheter described in copending application Ser. No. 066,937, 
entitled Laser Angioplasty and filed June 25, 1987. That application is 
assigned to the same assignee as in this application. Its contents are 
incorporated herein by reference. The following description of the subject 
invention refers particularly to an overall system and method and not to 
any particular catheter construction. 
FIG. 1 shows an embodiment of the invention. In the Figure a computer 
system 10 includes computer hardware 12 and software program means 14. 
Hardware 12 includes storage means (not shown). Also connected to computer 
10 are a display CRT 18 and a user input device such as a keyboard, mouse, 
light pen or joy stick arrangement or others 20. The storage means is 
constructed and arranged such that signals, such as electrocardiogram data 
including QRS complex time points or other cardiac cycle time points, may 
be used to trigger acquisition and/or storage of images and other data 
concerning the relative positions of the laser catheter and a target area 
in a vessel or chamber carrying the laser catheter. The images and other 
data may be generated by one or more various means 24 and 26 and are 
introduced into the storage means hardware. 
Storage and digital image subsequent processing may be accomplished by a 
system such as the Trapix 5500 digital image processor available from 
Recognition Concepts Inc., 341 Skiway, P.O. Box 8510, Incline Village, 
Nev., 89450. Another imaging system known as View 2000 is available from a 
company known as Virtual Imaging, 725 Kieffer Rd., Sunnyvale, Calif. 
94086. 
The various positional data means indicated at 24 and 26 may take various 
forms. For example, one of these may take the form of an imaging system in 
which an image showing the relative positions of the laser catheter and 
the target area may be generated angiographically, including utilization 
of Digital subtraction Angioplasty (DSA) if necessary, or angioscopically 
and stored in the storage means for display on CRT 18. From such images 
one can determine if the laser catheter is accurately aimed at selected 
target area. 
In addition to or in lieu of actual images, various sensing arrangements 
which generate a signal indicative of a positional relationship of the 
laser vis-a-vis the target area may also be used with the present 
invention. As already indicated, the fluorescence effect exhibited by 
plaque is different than the fluorescence effect exhibited by a vessel 
wall, the florescence being in response to impinging low level radiation. 
See the abstract of a presentation entitled Fiberoptic Laser-Induced 
Fluorescence Detection of Atherosclerosis and Plaque Ablation; Potential 
for Laser Angioplasty Guidance". by Decklebaum, Stetz, Lam, Clubb, 
Cutruzzola, Cabin and Long given at the American Heart Association in 
Dallas, Tex. and abstracted as paper #27 (II-7) in the Part 2, Volume 74, 
Number 4, October 1986, Manograph Number 124, Circulation Supplements, 
Abstracts from the 59th Scientific Sessons, American Heart Association. 
Also from the same sessions, see Abstract #25 (II-7) entitled "Detection 
of Atherosclerotic Places and Characterization or Arterial wall Structure 
by Laser Induced Fluorescence" by Sartori; Bossaler, Weilbacher, Henry and 
Roberts and see Abstract #26 (II-7) entitled " Laser Induced Placue 
Atherolvsis with Tetracycline" by Abela, Barbieu, Roxey and Conti. In 
accordance with this invention a sensing means responsive to such 
flourescence may be included in the system, the particular type of the 
fluorescence being indicative of when the catheter is on target and when 
it is not. 
Likewise, a data signal may be generated by means of an ultrasound 
tranducer which may be mounted on the distal end of the laser catheter. 
See the abstract of a presentation entitled "Continuous On-Line Assessment 
of Coronary Angioplasty with a Doppler Tipped Balloon Dilatation Catheter" 
by Sibley, Bulle, Baxley, Dean and Whitlow given at the same Scientific 
Sessions above-identified and abstracted as #1828 (II-459). Such data may 
also be stored for later review and use. Ultrasound image or images can be 
reconstructed from such signals or data. 
With constructions such as those described above, after initially 
positioning a laser catheter in a vessel and aiming it at a target area, 
positional images and data and/or signals as described above generated by 
various modalities are obtained at predetermined times throughout any 
desired number of cardiac cycles. Such a cardiac cycle is shown in the 
electrocardiogram of FIG. 2 wherein the repeating cycle is defined by time 
between QRS complex R.sub.1 -R.sub.2 of an ECG. In the cycle illustrated, 
a plurality of time points t.sub.1 . . . t.sub.n represent the times 
during which the images and/or signals are generated to determine whether 
the laser catheter is accurately aimed at the target area or not. 
Simultaneous collection of various positional images, data and/or signal 
by various modalities (whether carried by the catheter or independently 
operative means) such as 24 and 26 may be taken at each point of time 
t.sub.l . . . t.sub.n for storage (on electronic memory means such as 
video tape or optical disc, etc.). Then, all of these images and data may 
be recalled and reviewed frame by frame preferably with simultanteous 
review of images and data from different imaging and data or signal 
sources obtained at the same time in the cardiac cycle. 
This review is not done in real time but at a speed convenient for the 
physician-operator 28. Any number of cardiac cycles and number of times or 
time points per cycle may be selected by the physician-operator. The 
review of this data allows the physician-operator to determine those time 
or time intervals of the cycle during which the laser catheter is reliably 
and consistently aimed at the target area. 
Then and only then, computerized control of the laser actuating mechanism 
30 may be set through input device 20 to energize or trigger the laser or 
allow the laser beam to enter the shooting optical fiber of the laser 
catheter during those times or time intervals of the upcoming cycle when 
the catheter is reliably aimed at the target area. 
If any abnormal pattern of cardiac activity is observed by the 
physician-operator or identified by computerized control system, the 
operator or the computerized control system is arranged to automatically 
block delivery of ablating laser radiation. 
FIG. 3 shows a program flow chart for the operations performed by the 
hardware shown in FIG. 1. FIG. 3 represents the various steps involved in 
selecting times during which to actuate the laser or otherwise allow laser 
radiation to impinge on a target area. The first step in this process 
occurs at 32 when the QRS time points are generated. 32 represents the 
step in which the time period cycle between two consecutive QRS complex 
points R.sub.1 -R.sub.2 are determined. The next step is indicated at 33 
in which the time period R.sub.1 -R.sub.2 is divided into a number of 
times t and n number of images or data signals are obtained and stored 
from one or more instruments which the physician-operator selects for each 
of the time intervals t.sub.1 to t.sub.n during one cycle. During next 
step 34, the images or data readings obtained in step 33 are displayed on 
the CRT in operator selected format. Step 36 indicates the point at which 
it is determined if plaque or other suitable target is present. Step 38 
indicates a decision point in which the operator must decide whether the 
laser is accurately aimed during one or more of the times or time 
intervals. If the laser is not aimed at the plaque during one or more of 
the time intervals, step 40 is executed, which involves adjusting the 
catheter position and returning steps 32-38. If the operator determines 
that the laser is aimed at plaque or the like during one or more time 
intervals, step 42 is performed. Step 42 consists of the operator 
selecting the particular time or time interval during which to fire the 
laser in an upcoming cycle or cycles and inputting this time or time 
intervals and the number of cycles into the computer. The last step 
indicated at 44 is triggering the laser actuation mechanism which either 
activates the laser itself or allows the laser beam to enter the laser 
catheter. 
From the foregoing description it will be seen in accordance with this 
invention that the safe firing of a laser catheter in an angioplasty 
system may be accomplished. Preferably this is done by using various 
modalities associated with the catheter and independent of it to generate 
positional data and confirm the adequacy of the aiming or the need to 
adjust same.