Aortic valve

Valve Problems. The primary solution to valve problems has been implantable replacement valves. The introduction of these devices necessitates open-heart surgery. There are two types of valves available tissue (porcine and bovine) and mechanical. The disadvantage of tissue valves is that these have a limited life of about seven years before they calcify, stiffen, and have to be replaced. The mechanical valves can last a lifetime, but require anticoagulant therapy. In some patients, anticoagulants may not be feasible or may be contraindicated. Of the valves which require replacement, 99% are mitral and aortic valves. The valves on the left side of the heart are under much greater pressure because the left ventricle is pumping blood out to the entire body, instead of only to the lungs. Occasionally, two valves are replaced in the same procedure. 

The semilunar valves separate the ventricles from their associated arteries. The pulmonary valve is found between the right ventricle and the pulmonary artery and the aortic valve is found between the left ventricle and the aorta. These valves prevent backward flow of blood from the pulmonary artery or the aorta into their preceding ventricles when the ventricles relax. The semilunar valves also have three cusps. There are no valves between the venae cavae or the pulmonary veins and the atria into which they deliver blood. The closure of the valves causes the "lub-dub" associated with the heart beat. Tire first heart sound, or the "lub," occurs when the ventricles contract and the AV valves close. The second heart sound, or the "dub," occurs when the ventricles relax and the semilunar valves close. 

Aortic valve Closed Closed Open Closed... 

Left Ventricle (LV) A simple inverted U curve is drawn that has its baseline between 0 and 5 mmHg and its peak at 120 mmHg. During diastole, its pressure must be less than that of the CVP to enable forward flow. It only increases above CVP during systole. The curve between points A and B demonstrates why the initial contraction is isovolumic. The LV pressure is greater than CVP so the mitral valve must be closed, but it is less than aortic pressure so the aortic valve must also be closed. The same is true of the curve between points C and D with regards to IVR. 

Aorta A familiar arterial pressure trace. Its systolic component follows the LV trace between points B and C at a slightly lower pressure to enable forward flow. During IVR, closure of the aortic valve and bulging of the sinus of Valsalva produce the dicrotic notch, after which the pressure falls to its diastolic value. 

B End of IVC. The LV pressure rises above aortic pressure. Aortic valve opens and blood flows into the circulation. 

C Start of IVR. The LV pressure falls below aortic pressure and the aortic valve closes (S2). 

Fig. 6.2 (A) The Impella pump is a miniature flow mounted pump. It comes in two different sizes and can produce cardiac output of 2.5-5 1/min. (B) The Impella pump is placed across the aortic valve, where it aspirates blood from the left ventricle and propels it into the ascending aorta...

Transendocardial injection is performed via a percutaneous femoral approach. An injection-needle catheter is advanced in retrograde fashion across the aortic valve and positioned against the... 

Fig. 7.11 (Left) Myostar catheter with attached syringe. (Right) Artist s illustration showing the catheter traversing the aortic valve and transendocardial extension of the needle with cell dehvery (inset). Reprinted from [26]...

Check the cardiac valves. The tricuspidal atrioventricular valve on the right side comprises three cusps. The mitral AV valve on the left side comprises two cusps. Both AV valves are linked to papilla-shaped muscles via tendinous ligaments. The pulmonal and aortic valves also have three semilunar cusps, respectively. 

Rosado MF. Thrombosis of a prosthetic aortic valve disclosing a hazardous interaction between warfarin and a commercial ginseng product. Cardiology 2003 99 111. 

Ginseng Unknown Decreased INR thrombosis of a prosthetic aortic valve ... 

Decreased INR associated with the use of P. ginseng was reported in a 47-year-old patient who had been stabilized on warfarin (25). Another case of inadequate anticoagulation with ginseng product resulting in thrombosis on a mechanical aortic valve prosthesis was reported in a 58-year-old patient (26). Additional details of these two case reports are discussed in Chapter 5. 

In patients with cardiac hypertrophy from chronically pressure-loaded human left ventricles due to aortic valve stenosis, a general reduction in gap junction surface area per unit cell volume by about 40% (0.0031 versus 0.0051 pm2/ pm3) has been observed [Peters et al., 1993]. The gap junctions in the pathological tissue were larger than normal. The estimated gap junction content per cell was reduced [Peters et al., 1993]. A reduction by 30% in the gap junction surface per cell was observed [Peters, 1996]. However, the number of intercalated disks per myocyte and the mean density of packing of connexons at freeze-fracture in these hearts remained unchanged as compared to control hearts. 

Billiar, K.L., and Sacks, M.S. (2000) Biaxial mechanical properties of native and glutaraldehyde-treated aortic valve cusp Part II - A structural constitutive model. Journal of Biomechanical Engineering 122, 327-335... 

The commonest cause of stenosis in patients below 60 years of age is a congenitally bicuspid aortic valve with fused commissures and/or dysplastic leaflets. Overtime calcification and fibrosis may cause the valve to become rigid and obstructive. Coexisting regurgitation of these valves is common. 

Hywel Davies reported of temporarily treatment of aortic regurgitation with a parachute valve mounted onto a catheter tip in 1965 (34). Twenty-seven years later Andersen and his colleagues described the first experience with a bioprosthetic valve attached to a wire-based stent and mounted on a balloon valvuloplasty catheter (35). In 2002, Alain Cribier performed the first transcatheter valve implantation in an elderly patient with inoperable aortic stenosis using a prototype of a stent-mounted, pericardial, tricuspid aortic valve (36). 

Approaching the aortic valve with a catheter can be achieved via the venous (antegrade, transseptal) or the arterial routes (retrograde) (37,38). The delivery assembly is positioned within the diseased native valve. Before expansion of the valve mounted balloon rapid pacing (>200 beats/min) is performed to lower stroke volume during the implantation sequence. The balloon is inflated fixing the stented valve to the implantation site. Immediately after balloon deflation... 

The procedures may be performed under local anesthesia and mild sedation or general anesthesia with heparin anticoagulation. Aspirin (160mg, p.o.) and a loading dose of clopidogrel (300 mg, p.o.) are administered 24 hours before intervention for the aortic valve. Antibiotics (e.g., first generation cephalosporin, i.v.) are given before the procedure and continued for 48 hours, After the procedure aspirin is continued for three to six months,... 

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