Encroachment with selective

Implantable valves, particularly mechanical valves which continue to encroach on tissue valves, are unique. Methods such as valvuloplasty, mitral valve repair, or use of ultrasound are unlikely to reduce the number of valve replacements into the twenty-first century. Valve selection remains in the hands of the surgeon because of the critical nature of the procedure. If anything goes wrong, the result can be catastrophic to the patient. Cost of a valve, from 3000— 4000, is a relatively small part of the cost of open-heart surgery which can mn as high as 30,000. Growth of the cardiovascular valve market has slowed in the United States with the decline of the threat of rheumatic fever. 

The Si consumption can be beneficial in that a more intimate contact between W and Si is promoted.25 It can, however, lead to encroachment problems that will be discussed later. As in the blanket tungsten deposition case, film resistivities are higher than bulk. For selective deposition, thinner films are useful, so it is important to recognize that resistivity varies with film thickness, as shown in Figure 16.26... 

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