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.