It is more than 50 years since Starr and Edwards’ description of successful prosthetic valve replacement in 1961.Although, Mitral valvotomy for mitral stenosis and other techniques for repair of the diseased mitral valve, particularly mitral valve prolapse, have been developed and refined, valve operation remains as a promising approach and continue to rise in last decades. Each year, approximately 90 000 valve substitutes are now implanted in the United States and 280 000 worldwide.
Types of heart valve prosthesis
- Ball valves: The original Starr-Edwards prosthesis comprised a silastic ball which seated in the sewing ring when closed and moved forward into the cage when open.
- Disc valves: The Bjork-Shiley prosthesis is comprised of a single graphite disc coated with pyrolite carbon which tilts between two struts of the housing which is made of stainless steel or titanium.
- Bileaflet valves: Bileaflet valves have two semicircular leaflets which open and close creating one central and two peripheral orifices. It is now the most commonly implanted type of mechanical prosthesis in the world.
All mechanical prosthesis has an absolute requirement for anticoagulant treatment. The potential advantage of avoiding the hazards of anticoagulation has led to the search for a valve replacement of suitable biological material which would not require long term anticoagulant treatment. A number of different approaches to the problem of finding a suitable biological valve have been made. An autologous or autogeneous valve is fashioned from the patient’s own tissue such as fascia lata or pericardium. An autograft valve is one translocated from one position to another—for example, when the patient’s own pulmonary valve is used to replace a diseased aortic valve. A homograft (or allograft) valve is one transplanted from a human donor. A heterograft (or xenograft) valve is one transplanted from another species such as a pig, or manufactured from tissue such as bovine pericardium. Porcine valves are treated with glutaraldehyde which both sterilises the valve tissue and renders it biologically acceptable to the recipient.
Most bioprosthesis are mounted on stents attached to a sewing ring, but stentless valves which are sewn in free hand have become available. Stentless valves have a greater effective orifice area compared with stented valves, but are technically more difficult to implant.
Bovine pericardial valves are fashioned from bovine pericardium mounted on a stented frame.
Biological prosthesis with stents
Biological prosthesis without stents
Studies comparing different types of mechanical prosthesis
Thromboembolism has been reported as occurring at a higher rate following Starr-Edwards replacement than Bjork-Shiley. Bileaflet prosthesis appears to have the lowest risk of thromboembolism. Rates of thromboembolism are higher following mitral valve replacement than following aortic valve replacement. The criteria in favor of using a mechanical valve include the following:
- the informed patient wants a mechanical valve and has no contraindication for long-term anticoagulation;
- the patient is already on anticoagulation (mechanical prosthesis in another position or at high risk for thromboembolism);
- the patient is at risk of accelerated bioprosthesis structural deterioration (young age, hyperparathyroidism, renal insufficiency); and
- the patients is younger than 65 years of age and has a long life expectancy.
Studies evaluating different types of biological prosthesis
Porcine valve failure is happen seven or more years after implantation, particularly in younger patients. One study compared results with stentless porcine prosthesis with stented prosthesis in the aortic position showed apparently enhanced durability of the stentless prosthesis. Advocates of the stentless prosthesis point to its superior haemodynamics with an effective valve area some 10% larger than stented prosthesis of equivalent size. A bioprosthesis may be preferred rather than mechanical prosthesis in the following situations:
- the informed patient wants a bioprosthesis;
- good-quality anticoagulation is unavailable (contraindication or high risk, compliance problems, lifestyle);
- the patient is older than 65 years of age and/or has limited life expectancy; and
- the patient is a woman of childbearing age. Bioprosthesis degenerate more rapidly in young patients and during pregnancy.
. P. Pibarot, J.G. Dumesnil, “Prosthetic heart valves: selection of the optimal prosthesis and long-term management”, Circulation, 2009; 119: 1034-1048.
. P. Bloomfield, “Choise of heart valve prosthesis”, Heart 2002; 87: 583-589.
Taking aspirin at bedtime instead of in the morning might reduce acute heart events, according a new study presented at the American Heart Association’s Scientific Sessions 2013.
Low-dose daily aspirin is recommended for people at high risk of heart disease and for reducing the risk of recurrent heart events. Aspirin thins the blood and makes it less likely to clot. The tendency for platelet activity to be higher peaks in the morning.
In the randomized, open-label study, 290 patients took either 100 mg of aspirin upon waking or at bedtime during two 3-month periods. At the end of each period, blood pressure and platelet activity was measured.
Blood pressure was not reduced; however, bedtime aspirin platelet activity was reduced by 22 units (aspirin reaction units).
“Because higher platelet activity contributes to a higher risk of acute heart events , this simple intervention – switching aspirin intake from morning to bedtime – could be beneficial for the millions of patients with heart disease who take aspirin on a daily basis,” said Tobias Bonten, M.D., PhD student at the Leiden University Medical Center in the Netherlands.
When Bruce Peterson went to see cardiologist Samuel DeMaio for chest pain, DeMaio put 21 coronary stents in Peterson’s chest over eight months, and in one procedure tore a blood vessel and placed five of the metal-mesh tubes in a single artery. Unneeded stents weakened Peterson’s heart and exposed him to complications including clots, blockages and ultimately his death.
Peterson’s case is part of the expanding impact of U.S. medicine’s binge on cardiac stents – implants used to prop open the arteries of 7 million Americans in the last decade at a cost of more than $110 billion.
These and other acute cases account for about half of the 700,000 stent procedures in the U.S. annually.
These sources point to stent practices that underscore the waste and patient vulnerability in a U.S. health care system that rewards doctors based on volume of procedures rather than quality of care. Cardiologists get paid less than $250 to talk to patients about stents’ risks and alternative measures, and an average of four times that fee for putting in a stent.
“Stenting abuse is by no means the norm, but neither is it a rarity” said Nortin Hadler, a professor of medicine at the University of North Carolina at Chapel Hill.
Two out of three elective stents, or more than 200,000 procedures a year, are unnecessary, according to David Brown, a cardiologist at Stony Brook University School of Medicine in New York.
It means that more than a million Americans in the past decade with implants in their coronary arteries they didn’t need, said William Boden, chief of medicine at a Veterans Administration hospital in Albany, New York. Boden was the principal investigator of a 2007 study known as Courage that found stents added no benefit over medicines, exercise and dietary changes in stable patients.
The procedure of stenting typically involves inserting the stent with a catheter through a small incision in the groin area or wrist and snaking it through to heart vessels. It usually takes less than 45 minutes.
Patients who received them are living with risks including blood clots, bleeding from anti-clotting medicine and blockages from coronary scar tissue, any of which can be fatal, according to Sanjay Kaul, a cardiologist and researcher at Cedars-Sinai Medical Center in Los Angeles.
Cardiac stents were linked to at least 773 deaths in incident reports to the U.S. Food and Drug Administration last year, according to a review by Bloomberg News. That was 71 percent higher than the number found in the FDA’s public files for 2008. The 4,135 non-fatal stent injuries reported to the FDA last year – including perforated arteries, blood clots and other incidents – were 33 percent higher than 2008 levels.
Furthermore, This July, a panel of experts convened by the American Medical Association and the Joint Commission, a hospital accreditor, named elective stenting as one of five overused treatments that too often “provide zero or negligible benefit to patients, potentially exposing them to the risk of harm.”
Elective-stent patients typically see rapid quality-of-life improvements, including in their ability to work and be active, according to Ted Bass, president of the Society for Cardiovascular Angiography and Interventions, whose members specialize in cardiac implants. The Courage trial found stents, compared to medication and lifestyle changes, were better at relieving chest pain for as long as two years after placement – a benefit that ended by 36 months.
Stony Brook’s Brown, and Boden, who led the Courage study, argue that many elective patients should be getting medical therapy before they risk stents. Only 44 percent try medication and lifestyle changes before stenting, a 2011 study in the Journal of the American Medical Association found.
Coronary artery disease (CAD) is caused by “hardening” or “atherosclerosis” of the coronary arteries on the surface of the heart. The interior walls of arteries are normally smooth and flexible, allowing blood to flow easily. But, deposits of fat, or plaques that may build up inside the arterial wall would narrow down the artery and could reduce or even completely stop the blood flow.
Clinical syndromes of the disease, called Angina, include pain and discomfort in the chest, arms and lower jaw. The first suggestion for amelioration and resolution of these symptoms would be a change in one’s lifestyle including smoking cessation, a low fat/cholesterol diet, weight loss, regular exercise, stress management, diabetes control and blood pressure control, in addition to medications. In cases where medicine therapy fails one of the following procedures might be suggested:
Coronary artery bypass
This category of surgeries might be divided into two main subgroups: traditional open heart surgery called coronary artery bypass graft (CABG) and minimally invasive off-pump surgery. The former group includes a complete opening up of the chest with heart beat recessed. Therefore, a heart-lung machine artificially maintains circulation while the surgeon operates on the heart. In more recent techniques called “off-pump coronary artery bypass” or “beating heart”, CABG surgery is performed through relatively small incision in inter-rib spaces so that no cardiopulmonary bypass (heart-lung machine) is required. In bypass surgeries, the surgeon uses a portion of a healthy vessel (either an artery or vein) from the leg, chest, or arm to create a detour or bypass around the blocked portion of the coronary artery. About 10% of the patients require this category of surgery.
Angioplasty is the technique of mechanically widening narrowed or obstructed arteries. An empty and collapsed balloon on a guide wire, known as a balloon catheter, is passed into the narrowed locations and then inflated to a fixed size using water pressures. The balloon forces expansion of the inner white blood cell/clot plaque deposits and the surrounding muscular wall, opening up the blood vessel for improved flow, and the balloon is then deflated and withdrawn. A stent may or may not be inserted at the time of ballooning to ensure the vessel remains open. Unlike angioplasty and stents, which pushes the plaques into the vessel wall, atherectomy involves removing the plaque burden within the vessel and four types of devices might be used for this purpose: orbital, rotational, laser, and directional. Typically about one third of CAD patients undergo angioplasty.
Choosing between the two categories depends on surgeon diagnosis, patient preference, as well as physical characteristics of the patient including number and severity of blockage of arteries, medical history, etc.
Dr. Jones a medicine professor at Duke University believes that angioplasty’s main selling point is that it’s much less traumatic than a bypass and one can get back to his/her normal daily life within a few days. But it’s also less permanent. One recent review found that 89% of bypass patients were free of angina one year later, compared with 74% of patients who had an angioplasty. The convenience of angioplasty comes with a price. Up to one-quarter of people who have angioplasty must have it repeated, or have bypass surgery, within a few years. And anyone who gets a drug-eluting stent must take medicine for at least a year to prevent the formation of potentially deadly clots around the stent.
Summarizing the results of the studies up to year 2002 could indicate the relative preference of the two methods in the following situations.
- Narrowing of one, two or three coronary arteries
- When one or two principal coronary arteries are blocked but it’s not located in the beginning part of the artery or the linkage part between two arteries.
- Blockages in two or three coronary arteries, at the junction of two arteries,
- Places where stenting is not very possible due to twisted path
- In a heart with poor pumping power in the left ventricle
- In an individual with diabetes or kidney disease.
This is while a review including 17,000 bypass surgeries and angioplasties performed in 2003 and 2004 indicated that the boundaries could not be set as clearly as the above classification. In this study the investigators compared deaths immediately after these procedures, deaths within 18 months, and heart attacks within 18 months. Bypass surgery was better, but not by much. An extra 1.6% to 2% of people in the bypass group were still alive and had not had a heart attack after 18 months. The biggest difference between the two procedures was in the need for repeat procedures. Among those who initially underwent angioplasty, 30% needed a second procedure within 18 months, compared with 5% in the bypass group. This study collected information from 2003 and 2004, when the use of drug-eluting stents was in full swing. So the results are relevant today. But the cardiologists and patients chose which procedure to have.
Hence, choosing between the two procedures is a complicated task but it could be expected that future comparative studies including more novel technologies like laser atherectomy would shed more light on the issue and facilitate patients’ decisions.
. A.D. Michaels, K. Chatterjee, “Angioplasty Versus Bypass Surgery for Coronary Artery Disease”, Circulation, vol. 106, pp. e187-e190, 2002.
. “Health.com, article Should You Opt for Bypass Surgery or an Angioplasty?”, Health Media Ventures, 2013.
At the end of 2013, the First Annual International Conference on Cardiology & Cardiovascular Medicine Research (CCMR) will be held in Singapore. This conference will be coordinated by high-profile professors of Texas University -Houston and National University of Singapore. This conference is planned to be held on 9th-10th of June.
Professor Mehmanesh suggests this conference to the researcher in the field of cardiovascular medicine to exchange the latest progress of their research.
The research topics discussed in this conference includes:
- Acute Coronary Syndromes (ACS)
- Atrial Fibrillation
- Cardiac Emergencies
- Cardiac Surgeries
- Congenital Heart Disease
- Diagnostic Imaging and Biomarkers
- Genomic Medicine
- Heart & Lung Transplant
- Heart Failure
- Interventional Cardiology
- Lipids and Cardiovascular Risk Management
- Medical Devices in Cardiology
- Vascular Disease
- Vascular Surgery
- Cardiovascular Medical Research
- Preventive Cardiology
- Diseases of the Aorta
- Cardiac Tumors
- Cardiac rehabilitation
- Community Cardiology
- Disorders of the coronary circulation
- Cardiac Arrest
- Disorders of the myocardium (muscle of the heart)
- Disorders of the pericardium (outer lining of the heart)
- Disorders of the heart valves
- Congenital heart defect
- Diseases of blood vessels (vascular diseases)
- Devices used in cardiology
- Diagnostic tests and procedures