Aortic valve replacement (AVR) is the only life-saving treatment for patients with severe symptomatic aortic stenosis. Bioprosthetic valves are used in 90% of AVRs because they do not require lifelong anticoagulation. The major limitation of bioprosthetic valves is their limited durability compared to mechanical valves. In addition, bioprosthetic valves still carry a 2-3% risk of symptomatic valve thrombosis, stroke, and thromboembolism in the first 30 days after implantation, and a 1% annual risk thereafter. The risk of subclinical valve thrombosis is around 10% at 30 days and 25% at 1 year, and prevention of subclinical valve thrombosis is hypothesized to reduce the risk of clinical thrombotic events and perhaps even improve valve durability, although high-quality evidence is lacking.
This doctoral thesis comprises 7 chapters of varied methodology that summarize the evidence behind current recommendations for antithrombotic therapy after bioprosthetic AVR, identify evidence gaps, and present the design a randomized trial that aims to address some of these evidence gaps.
Chapter 1 introduces each included study with a brief summary.
Chapter 2 is a narrative review summarizing guideline recommendation for antithrombotic therapy after bioprosthetic AVR and the evidence upon which they are based.
Chapter 3 is an observational study describing antithrombotic prescribing practices in the VISION Cardiac Surgery cohort study.
Chapter 4 is a systematic review and network meta-analysis of randomized studies of antithrombotic therapy after transcatheter aortic valve replacement.
Chapter 5 is a systematic review and meta-analysis of randomized and observational studies of subclinical valve thrombosis.
Chapter 6 presents the design and rationale of a feasibility trial of direct oral anticoagulants versus vitamin K antagonists in patients with a new surgical bioprosthetic AVR and atrial fibrillation.
Chapter 7 discusses the implications, limitations, and future avenues of the research presented in this doctoral thesis. / Thesis / Doctor of Philosophy (PhD) / More than 10,000 Canadians require aortic valve replacement each year. Bioprosthetic valves (made out of cow or pig tissue) are often preferred over mechanical valves (made out of metal) because the risk of blood clots forming on the valve or causing a stroke is lower. The disadvantage of bioprosthetic valves is that they can wear out and require re-replacement. The reason why bioprosthetic valves wear out is uncertain, but it may be related to small blood clots on the valve that are only detectable on a CT scan. This doctoral thesis explores the use of blood thinners for patients with bioprosthetic aortic valve replacement. Ideally, blood thinners would be able to prevent blood clots and stroke, and to improve the durability of bioprosthetic valves, without causing too much bleeding. The thesis reviews the available evidence, identifies unanswered questions, and ends with a proposal for a study to generate new data.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/28913 |
| Date | 11 1900 |
| Creators | Eikelboom, Rachel |
| Contributors | Whitlock, Richard, Health Research Methodology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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