Mechanical Valve Replacement
Memory loss.
Micro-emboli travelling to brain at rate of 5 - 6 a minute. During surgery
(OHS) these micro-emboli develop. Interest amongst stroke neurologists, cardiologists
and cardiothoracic surgeons. Memory loss not likely to be caused by
micro-emboli but is most probably a consequence of cardiac surgery. It is
increasingly recognised that cardiopulmonary bypass and other steps has
damaging effects on brain. Using sensitive neuropsychological methods it has
been shown that majority of elderly patients undergoing OHS suffer subtle
cognitive difficulties for several months post-operatively. Problem improves
with time and is reversible in most patients.
The transcranial
doppler (TCD) used to count micro-emboli relatively recent test that is
believed to be predictive of the risk of stroke in high-risk cardio-embolic
situations. Frequency of micro-emboli (HITS) shown to correlate with future
stroke risk. Not conclusively proven but felt that response of HITS frequency
to treatment (coumadin, aspirin, heparin) is predictive of such therapy
preventing stroke. Not all micro-emboli are clots. Air bubbles can cause
similar signals. Methods proposed to distinguish clots or platelets from gas
but not routinely practised except in academic or research applications. The
use of TCD for predicting stroke risk and monitoring in prosthetic valve
patients is especially problematic. Several indicators that appear to imply
that majority of micro-emboli are gaseous from "microcavitation" of
blood from turbulence around the valve. No clear response of the HITS frequency
is noted with coumadin and other therapies that are known to be highly
efficacious in preventing strokes in the prosthetic valve situation.
St. Jude Medical
announces the SJM(R) Sequin annuloplasty ring implants in France and
Netherlands - 22.5.96. An annuloplasty ring is a heart valve repair product for
patients whose heart valve disease can be managed through valve repair instead
of replacement. The SJM¨ Seguin ring product offers annular remodelling and
tri-dimensional flexibility in a semi-rigid design and is used in the repair of
diseased mitral valves. Seguin is Professor Jacques Seguin, France. Licensed on
an exclusive basis this product for use in valve repair procedures performed
with conventional surgery. The SJM¨ product will also be used with Heartport's
innovative Port-Accessª technology. This offers to clinicians and their
patientsÔ solutions to heart valve disease. Repair segment of prosthetic heart
valve market is relatively small
Use of the SJM¨
Seguin ring with Port-Access technology. About 6% heart valve surgical
procedures involve heart valve repair. Port-Access heart valve surgery being
actively pursued. Mechanical heart valve will be used in conjunction with
Port-Access technology to perform less invasive heart valve repair surgery.
Cardiopulmonary bypass (CPB) allows support of circulation during surgery.
Temporarily and safely stop, empty and protect the heart. Creates a still and
bloodless field in which to operate - highest degree of technical precision and
accuracy. Key factor in achieving excellent long-term clinical outcomes. Most
CABG requires turning and manipulating the stopped heart to reach bottom,
sides, and back. Also the front to re-establish blood flow to the three major
vascular beds. Valve surgery requires opening the stopped heart to perform
surgery on its interior structures. Conventional surgery involved opening the
chest and stopping the exposed heart. The trauma, pain and suffering, healing
time and scarring associated with this procedure (12 - 15" incision in
breastbone) were all major disadvantages.
Despite these
drawbacks open-chest surgery using conventional CPB has become the gold
standard because of its excellent clinical outcomes. But now there is
HeartportÕs endovascular CPB technology. This is a novel system (HeartportÕs
EndoCPB© System) and allows stopping the heart without the need to split the
breastbone. The system comprises of a series of proprietary catheters and other
devices that are introduced through peripheral vessels, accessed most often via
a small incision in the neck and groin area . This avoids directly puncturing
or manipulating the heart, vena cava and aorta as is done in conventional
open-chest CPB.
Using HeartportÕs
Port-Access©Mitral Valve Replacement and Repair (Port-Access MVR) System or
Port-Access©Coronary Artery Bypass Grafting (Port-Access CABG) System in
conjunction with the EndoCPB© System, high-precision heart surgery can be
performed through small incisions ("ports") between the ribs. This
enables surgeons to achieve excellent clinical outcomes equal to conventional
procedures in heart surgery with the added benefit of reduced trauma, pain and scarring
and shortened hospital stays and recovery time.
Mitral Valve
Surgery
Open-Heart
Surgery was born on 6.5.53 by John Gibbon when 1st successful open-heart
operation on human patient using heart-lung machine. Mitral valve insufficiency
was first corrected by Lillehei in 1956. Mitral valve replacement first
reported 22.7. 55 performed in England by Judson Cheesterman. In last ten years
mitral valve repair for stenosis and regurgitation (leaking valve) has
increased dramatically. Mitral valve replacement is associated with long-term
complications (also due to anticoagulation) and surgeons have gradually
improved techniques for valve repair and have increased understanding of
functional defects of mitral valve and associated components. The most frequent
cause of bioprosthetic (biological) valve failure is primary tissue
degeneration - overgrowth and calcification. So the focus has been on
techniques to improve conventional prostheses by studying possible alternative
methods of preservation and in vitro endothelialisation, elimination of toxic
agents and antimineralisation.
Mechanical valves
limited primarily by thromboembolism and anticoagulant-related haemorrhage.
Mechanical valves do not undergo degeneration like the biological valves but to
decide which valve to implant complications related to thromboembolism and
anticongulant therapy must be considered.
Mitral valve
replacement vs. repair? Reconstruction techniques - repair and save valve
instead of replacement with artificial prosthesis - were successfully used as
early as 1956. Mitral valve replacement, however, became the more widely used
procedure . Recently repair can constitute up to 70% mitral valve operations as
opposed to replacement. One cause of mitral valve incompetence (leaking) is a
prolapse - when organ or body part falls or sinks out of place - of the
anterior mitral valve leaflet due to ruptured chordae tendineae (chorda - any
string-like structure like the tendinous chords attaching valves of heart).
Reconstruction is performed by cutting and resecting a group of chordae from
posterior leaflet and transplanting them to the anterior leaflet.
The
reconstruction is completed by a mitral valve annuloplasty ring implantation.
Another possible cause is a prolapse of the middle part of the posterior
leaflet due to ruptured chordae. A quadrangular resection is performed by cut
ting away the prolapsed excess valve tissue. The annulus is shortened and the
leaflets sutured. A mitral valve annuloplasty ring is finally implanted. If there
is a prolapse of the posterior leaflet (too much tissue) as well as ruptured
chordae causing incompetence of the valve, a quadrangular resection is
performed (cutting away excess valve tissue). The posterior leaflet is cut from
the valve annulus and the annulus is shortened. A "sliding leaflet"
plastic is performed by readapting the posterior leaflet into the shortened
valve annulus.
The posterior
mitral valve leaflet is reconstructed. The exact measurement of the size of the
mitral valve ring to be implanted is done using a special "sizer".
Sutures are put into the mitral valve annulus followed by the mitral valve
ring. The reconstructed valve is tested by flushing water into the heart. If
this is successful there will be no residual incompetence. Assessment of the
mitral valve may show annular dilation (natural enlargement of mitral valve
ring) resulting in incompetence of the valve. After "sizing" the
mitral valve ring (to reduce the size of the mitral valve annulus) sutures are
put into the valve annulus and then the ring. To reconstruct the mitral valve
(by reducing the enlarged valve annulus) a mitral valve ring is implanted into
the valve annulus. This results in the repaired valve by implantation of a
ring, reducing the enlarged annulus and conferring competent closure of the
valve leaflets.
Coronary bypass
and other valves may constitute combined procedures. Aortic Valve Surgery
Experimental study of aortic valvulotomy reported in 1947 by Smithy and Parker
at University of South Carolina in Charleston. Clinical attempts were made by
Bailey and colleagues in Philadelphia in the early 1950's to relieve severe
aortic stenosis. In 1951, Hufnagel in Washington developed a ball valve
prosthesis for rapid insertion into the descending aorta. More effective
approaches began with the advent of clinical cardio-pulmonary bypass in 1954
and 1955. Initially, aortic vavlulotomy and decalcification were all that could
be done. Then the single-leaflet prosthesis was developed and became
commercially available (Bahnson et al and Hufnagel and Conrad). Aortic valve
surgery was placed on a firm footing when Harken and Starr (1960) introduced
the ball valve prosthesis.
Indications are
the classic triad of effort - dyspnoea (shortness of breath), angina and
syncope. Syncope is a fainting attack or sudden loss of consciousness due to
sudden reduction of blood flow to the brain. Results from rhythm disturbance of
the heart or mechanical obstruction to the pump action of the heart. This
occurs in about one third of patients with aortic stenosis (due to calcific,
rheumatic or arteriosclerotic (degenerative) aortic valve stenosis. The main
reason for aortic incompetence are rheumatic (due to annuloaortic ectosia,
endocarditis and aortitis. So, after induction of circulatory support by
extracorporeal circulation (cardiopulmonary bypass) and cooling the patient and
the heart, the aorta is x-clamped and the aortic valve exposed (aorta already
opened). This valve is examined and excised for subsequent aortic valve
replacement. The aortic annulus is "sized" to select the correct
aortic valve prosthesis. Valve sutures are placed in the aortic valve annulus
and into the heart valve prosthesis to tie the prosthesis and secure into the
valve annulus. The aorta is closed, the heart de-aired and the operation is
finished.