Note: Descriptions are shown in the official language in which they were submitted.
1~75556
The present invention relates to a cardiac assisting
device and, more particularly, to a multipurpose cardiocir-
culatory assist cannula.
The clinical management of myocardial failure and
impending cardiogenic shock following acute ~yocardial in-
farction remains one of the most challenging and important
problems facing clinicians. Equally as important is the
vexing problem of sudden cardiac dea~h associated with
cardiac arrhythmia.
The prevention of such myocardial failure and
cardiogenic shock rests upon the consideration of the patho-
physiologic mechanism thereof. M~tabolic derangements pro-
duced by myoeardi~l ischemia result in a profound deteriora- ;
tion of myocardial performance involving dyskinesia. There
is a decrease of diastolic compliance o the myocardium as
well as a diminished contractile potential. ~his leads to
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an increase of end-diastolic and left atrial pressures and
volumes. The end results of this cycle is cardiogenic shock
and death.
In many instances, coronary artery disease and/or
arterial sclerotic heart disease in themselves must be con-
sidered somewhat distinct from the terminal state or its
causal relationship to any precipitating factors. The de-
generative disease is a result of a progression of perhaps
many years' duration. At some point in time, the heart
sustains an insult to which it is incapable of adjusting or
responding, let alone reversing the process by its own
mechanism and power. Cardiocirculatory support and assist-
ance, for whatever period, becomes critical if the system
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is to be alLowed to correct the effects and maintain vital
homeostatic processes.
There is still another factor which has played an
important, though somewhat elusive role -~ namely, the
question of sudden cardiac death resulting from the effects
of uncontrolled and irreversible arrhythmia. Decreased
myocardial perfusion resulting from coronary occlusive
diseases i9 believed to be principally responsible for
those conditions leading to myocardial catabolic derange-
ments. Acidosis and electrolyte imbalance crea~e a hyper~
sensitive intrinsic conductive mechanism w lnerable to
erratic triggering. The Pnd result is often ventricular
extrasystoles followed by fatal arrhythmia.
Thus, a heart may be found which already suffers
from some degree of degenerative disease of the myocardium
and of the coronary arteries including interstitial fibrosis
leading to decreased levels of myocardial perfusion. Up to
this point and within rather critical lim~ts this heart is
capable of carrying on its normal function and responding
to increased demands of stress. However, for any number
of reasons, at some point in time the scales are tipped
and inadequate cardiac output results from the synergistic
insult o~ decreased coronary perfusion coupled with and
aggravated by a decrease in the contractile force of the
heart. The decreased cardiac output precipitates a vaso-
motor response leading to increased peripheral resistance.
This further aggravates the problem of inadequate cardiac
return and of tissue perfusion leading to severe metabolic
derangement and as a consequence vasomotor collapse~ thus
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completing the syndrome of the picture of myocardial-
circulatory failure.
Whatever triggers the above sequence of events, most
investigators agree that the myocardium responding to a
compromised circulation (insuffifiency of myocardial per-
fusion) undergoes a somewhat rapid and devolutionary
course leading to myocardial failure, cardiogenic shock
and death. The other sequence of events is that of cardiac
arrhythmia and sudden death.
Prior art cardiac assist pumps provide an intra-
aortic occlusion balloon pumping system These devices
are very important for providing intra-arterial cardiac
assistance but are not designed, nor do they accomplish
the improvement of myocardial revascularization or the in-
crease of coronary collateral circulation. Furthermore,
the presently known counterpulsation devices are based on
the phase relationship of the cardiac cycle to the intra-
aortic occlusion balloon. Thus, these devices are prone
to failure if erratic triggering or cardiac arrhythmia
occurs~
It is therefor an object of the present invention
to provide a mul~i-purpose cardiocirculatory assist cannula
whose capability extends beyond that of existing balloon
catheters, and an improved method oftreating cardiovascula-
tory ailments, to augment coronary perfusion, and to in-
crease tissue perfusion.
It is a further object of the present invention to
pace the left ven~ricle thereby counteracting the effects
of arrhythmia crises and death while at the same time
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ensuring proper phasing of the balloon counterpulsation.
These and other objects are accomplished by the
present device which involves a cannula~ preferably hav-
ing three functions, which may be inserted into the axil- -
lary or subclavian arteries and fed through the aorta
until the tip extends into the left ventricle. This can-
cula (1) acts as a blood pump which withdraws blood from
the left ventricle and reinfuses it into the coronary
sinuses; (2) it acts as a balloon pump in the aorta to
further decrease the workload of the heart; and (3) it
acts as a heart pacer wh;ch supplies direct ventricular
pacing.
Since the myocardium receives most of its blood
flow during diastole, the reinfusion of blood via the can-
nula during this period will increase coronary flow and
hence myocardial perfusion pressure. Further, inflation
of the balloon at this time augments this flow pressure
relationship and hence is optionally effective in assist-
ing the ischemic heart thereby reversing the serious im-
pending catabolic-biochemical imbalance which oftentimes
heralds,if not precipitates, arrhythmia. The phase rela-
tionship is extremely important to the successful operation
of counterpulsation balloon devices of whatever configura--
tion. The present device is capable of dealing with the
question by the simple expediency of controlling heart
rate and the balloon in such a fashion so as to ensure
the proper phasing of each cycle.
The further nature and advantages of the present
invention will be more apparent from the following detailed
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description taken in conjunction with the drawings where-
in:
Fig. 1 is an elevational view of the multipurpose
cardiocirculatory assist cannula of the present invention;
Fig. 2 is a partly broken away perspective view of
the cannula of the present invention;
Fig. 3 is a cross-sectional view through line 3-3
of Fig. 2;
Fig. 4 is a cross-sectional view of another embodi-
ment at a location similar to that of Fig. 3; and --
Fig. 5 is a block diagram indicating the various
subsystems necessary for the complete operation of the
present device.
The device consists of a cannula 10 (Figs. 1 and 2)
which may be fabricated from reinforced organo-silicon
polymers such as Silastic (registered trademark) or other
blood compatible m~terials, or at least coated with such
a material. The proximal end of the cannula 10 consists
of a nozzle 11 which may advantageously be made of Teflon *
(polytetrafluoroethylene). The nozzle 11 is designed to
allow for quick connection to suitable drive means and
consoles (Fig. 5), the nature of which will be clear to
those having knowledge of the present field.
Surrounding the base of the nozzle 11 and the hous-
ing 18 of the cannula is an outer housing 19. The outer
housing 19 around the area at the base of the nozzle 11 is
flanged outwardly in order to define an annular chamber 17
around the cannula housing 18. An inlet valve 12 leads
through the outer housing 19 for attachment to the pneumatic
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drive of the balloon control for the balloon section 41 of
the device lO. The pneumatic chamber 17 is preferably
constructed with an airtight elastic recoil-type diaphragm
20 extending between the housing 18 and outer housing 19
below the inlet opening 12.
Extending distally from the pneumatic chamber 17 is
a pneumatic conduit 13 between the housing 18 and the outer
housing 19. The conduit 13 may be in the form of small
tubes 38 which are held in place on the outside of the hous-
ing 18 by outer housing 19 as seen in Fig. 3. In this em-
bodiment the rigid material of the outer housing 19 which
makes upthe wall of chamber 17 is molded to a more flexible
material 37 at a point below the chamber 17, which flexible
material 37 is laminated to the housing 18 around tubes 38.
The flexible material 37 is still considered a part of
outer housing 19.
Alternatively, the outer housing 19 can remain
rigid all the way to the balloon portion 41 in order to
define an annular conduit 39 as seen in Fig. 4. The con-
duit 13 empties directly into the balloon 14 which has been
molded onto the outer surface of the cannula at approximately
the midpoint thereof.
If diaphragm 20 were omitted it is apparent that the
gas (preferably a low density gas such as C02) entering
opening 12 would pass through chanber 17 and directly into
conduit 13 and the balloon portion 41, thereby inflating
the balloon 14. In the preferred embodiment, however, a
predetermined pressure is sealed into the balloon 14, con-
duit 13 and chamber 17 up to the diaphragm 20. Gas coming
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through opening 12 into the chamber 17 will depress elastic
diaphragm 20 forcing inflation of the balloon 14. This
arrangement prevents the direct flow of gas from the drive
means to the balloon 14. Consequently, in the event of
accidental rupture of the balloon 14, an excessive amount
of gas will not be infused into the artery.
In addition to this safety feature, the use of an
elastic diaphragm 20 in the gas chamber 17 will permit al-
most instantaneous loading and unloading of the balloon 14
and will prevent the balloon 14 from completely collaps~ng
becsuse of the preset pressure therewithin. The balloon
14 therefore will maintain a certain configuration in its
deflated mode such that streamlined blood flow around the
balloon 14 is provided, thereby avoiding further turbulence
to the blood flow. It should be understood that the dia-
phragm may be placed at any point between the cannula and
the gas pump.
Be~ween the balloon 14 and the distal end of the
cannula i9 a blood pump section 51. Here are located
several mul~-fenestrated unidirectional elastic recoil out-
let valves 15. When properly positioned these outlet valves
15 will come to lie with the sinus of Valsalva. The outer
; valves 15 are an integral part of a recoil band 21 which
is laminated to the cannula housing 18 and is preferably
constructed of the same material as the cannula hous~ng 18.
, A plurality of fenestrae 22 through ~he cannula housing 18
lead to outlet valves 15.
Between the ou~let valves 15 and the distal tip of
the cannula lie multi-fenestrated inlet valves 16. The
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valves 16 are an integral part of a band 23 laminated to
the inside diameter of the cannula and cover a plurality
of fenestrae 24 through the ca~nula housing 18. The inlet
valves 16 permit blood to be removed from the left ventricle
to be subsequently reinfused through the outlet valves 15
into the coronary ostia.
The tip 25 of the cannula 10 is an obturator to
permit passage of the device beyond the aortic valves. The
tip is preferably made of a methyl methacrylate-type poly-
mer such as Lucite or Plexiglas, possibly coated with a
blood compatible material such as Silastic. A pressure
transducer 26 may be attached to tip 25 to determine the
diastolic pressure within the left ventricle. Suitable
electrical leads (not shown) pass through the cannula to
a suitable means to translate the signals from the trans-
ducer 26.
A pacing electrode 27 is encapsulated within the
housing 18 of the cannula 10 in a separate cable 28. The
electrode 27 may be advanced independently of the tip of
the cannula within cable 28 and may be freely rotated by
means of a mechanism located in the area of the inlet
nozzle 11. This mechanism is provided with a handle 29
and a plunger 30 which are illustrated schematically in
Fig. 2. The tip of the electrode 31 may advantageously
be formed in the shape of a grappling hook which opens when
the electrode 27 is being extended and closes when it is
withdrawn.
Thus the electrode tip 31 may be maneuvered into
the optimal position within the ventricle for its pacing
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function and then secured there by closing the hook onto
a fiber of the ventricle wall. When the electrode 27 is
eventually removed the fiber may be broken with no adverse
effect. Since the electrQde 27 is made to operate inde-
pendently of the cannula 10, once positioned the cannula
10 may be removed from the ventricle while the electrode
27 remains behind for the purpose of pacing the heart. Of
course, handle 29 would have to be removed to permit this
operation.
Referring to Fig. 5, the blood pump section 51 is -
provided with suitable driving means 32 located in a con-
sole near the patient. Blood is removed through the inlet
valves 16 and reinfused through outlet valves 15. The pump
and inner lumen may be primed wqth the patient's blood to
begin the pumping operation. Preferably the device should
~, be capable of removing up to 20 cc of blood from the left
ventricle and reinfusing the same quantity into the sinus
of Valsalva.
, The balloon pump 41 is also provided with a driving
means 33 located in the console. A pneumatic system 36 is
connected thereto for inflAting the balloon 14 within a
period of time commensurate with the length of time of the
, cardiac cycle. The actual balloon pumping will be control-
led by a delayed mode triggered by the heart pacer 34. The
pacer 34 is connected to an electrocardiograph which in
turn controls the phases of the blood pump drive means 32
, and balloon pump drive means 33.
; In operation the cannula 10 is inserted into any
accessable artery leading to aorta, preferably the axillary
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or subclavian arteries, through a direct incision necessi-
tating only a minor surgical procedure. It is then passed
retrograde so that the tip 25 and the multifenestrated inlet
portion 24 as well as the paclng electrode 27 come to lie
below the aortic valve within the left ventricle. In this
position the outflow tract 15 of the device will be within
the sinus of Valsalva thus directing flow into both the
left and right coronary orifices.
The balloon 14 will then lie in the transverse
aortic arch distal to the carotid outflow tract. The tip
of the electrode 31 is maneuvered to the most effective
region of the left ventricle and is embedded in place. The
most effective place is where the pacer has the best effect
as shown by the electrocardiograph 35, which is determined
by trial. Once positioned the device is ready to be put
into operation.
First, the device can be made simply to unload the
left ventricle directly, by withdrawing up to 30 ml of blood
with each stroke and reinfusing this volume into the coronary
sinuses durlng the diastolic phase of the cardiac cycle
(pump systole).
Secondly, if it becomes necessary to decrease the
workload of the heart further and increase coronary per~u-
sion, the balloon 14 through a separate pneumatic conduit ~ -
can be utilized. During cardiac diastole the resistance
to flow in the vessels of the heart, i.e. the coronary ar-
teries, is at a minimum. Inflation of the balloon 14 at
th~s time increases the flow through the coronary arteries
and pumps blood along the aorta toward the neck and head
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and toward the kidneys, liver, stomach and other organs.
Deflation of the balloon 14 at the end of cardiac diastole
aids the heart by reducing the pressure in the aorta which
the heart mMst normally pump against during cardiac systole.
This permits the heart to pump a large volume of blood
with each contraction and also reduces the pressure in
the left ventricle at the end of cardiac diastole.
Thirdly, to avoid problems of phase relationship of
the device to the cardiac cycle, direct ventricular pacing
is simultaneously started by means of the pacing electrode
27 located at the tip of the device.
In summary, the device is versatile enough so that
during impending left ventricular failure secondary to myo-
cardial infarction, it can directly unload the left vent-
ricle, perfuse the coronary arteries, reduce the afterload
resistance, and pace the left ventricle. As ventricular
function improves and the heart is capable of providing
a more adequate cardiac output, the cannula can be with-
drawn until it lies within the ascending aorta, while the
electrode tip remains behind to continue pacing the heart.
The operation of the blood pump at this time will be ter- -
minated. The left ventricle, once recovered from initial
failure may continue to require additional support by way
of increased coronary circulation while reducing the after-
load resistance and hence cardiac stroke work. The balloon
14 even after partial cannula withdrawal so that the tip
of the device no longer protrudes through the aortic valve,
will still be positioned within the aortic transverse arch
distal to the carotid outflow tract. With proper pacing
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and positioning the cannula with the balloon can be used
as a counterpulsating device.
In the preferred embodiment, the device measures 50
cm end-to-end with an outside diameter of about 1.5 cm and
an inside diameter of .635 cm. The nozzle portion is
approximately 4.5 cm in length. The balloon portion is
approximately 25 cm from the nozzle. The balloon measures
about 5 cm in length and can be inflated to contain about
15 to 20 ~c of gas. The pressure is preset within the dia-
phragm to approximately half that. When fully inflated
the balloon should have a sufficient diameter to occlude
the aorta or about 2.5 cm. The outlet valves are located
some 15-18 cm beyond the balloon and measure approximately
3 cm in length. The tip of the device is about 7 cm from
the outlet valves of whîch the final 3 cm contain the multi-
fenestrated inlet valve. The dimensions given above are
by no means limitative but are meant to provide an example
of workable dimensions for the normal sized human heart
and circulatory system. Any dimensions which will permit
passage of the cannula through the arteries and the posi-
tioning of the various par~s in their operative positions
are comprehended by the present invention.
It should be understood that the present invention
may be fabricated by any presently available technique.
Furthermore, the materials disclosed for the various parts
of the cannula are by no means limitative but any biocom-
patible materials may be used. The pump system used may
be any presently available system including pulsatile,
non-pulsatile or centrifugal. The other electronic and
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pneumatic components of the device are well known in the
art individually and it is well within the skill of the
art to select the proper components which will operate as
described herein.
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