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Abstract
Aortic valve replacement is the standard treatment for severe aortic stenosis and aortic regurgitation. Internationally and in Australia, there is limited clinical trial evidence for valve devices, and scant information about real-world use, benefits and harms once these devices are adopted into clinical practice. Data generated by the routine operation of health systems are being employed increasingly to provide real-world evidence for the study of valve devices. Longitudinal and population-level data generated within the Australian health system provides a unique opportunity to investigate the use and outcomes of aortic valve devices.
This thesis profiles the use of aortic valve replacement (AVR) procedures — including surgical aortic valve replacement (SAVR) and the newer, less-invasive, transcatheter aortic valve implantation (TAVI)— in the population of New South Wales (NSW), Australia. It addresses important evidence gaps, including: (i) how the use of AVR devices has changed over time; (ii) whether there are differences in patient outcomes between types of valve prostheses: mechanical valves (MV) and bioprosthetic valves (BV); and (iii) whether patients are receiving guideline-recommended antithrombotic medicines following TAVI.
The analyses reported here identified changing trends over time in the type of SAVR procedures being used in NSW between 2001-2013, with increasing use of BV (from 9 to 18 per 100,000 population ) and decreasing use of MV (7 to 4 per 100,000 population). TAVI is now established as the new standard of care among patients aged over 80 years, although it is also being increasingly used in younger patients, particularly those funded privately.
Comparative analyses of age-specific incidence rates of clinical outcomes for patients implanted with BV and MV found that after 5 years of follow-up, patients aged 18-64 years who were implanted with BV had higher rates of reoperation, but lower rates of stroke and haemorrhage. Among patients aged 65+ years, those implanted with BV had lower rates of acute myocardial infarction (AMI), haemorrhage and mortality. After 6-10 years of follow-up, rates of AMI were lower among patients aged 18-64 years implanted with BV, and among patients aged 65+ years, rates of cardiovascular and all-cause mortality remained significantly lower for patients implanted with BV. Further analyses for patients aged <65 years found further age-specific differences in risks of reoperation and mortality over time: patients aged 18-54 years who received BV were consistently at greater risk of reoperation over 15-years of follow-up, whereas patients aged 55-64 years only had a greater risk of reoperation beyond 10 years. Although there was no difference in mortality by valve type in patients aged 18-54 years, patients aged 55-64 years who received BV had a greater risk of mortality after 10 years of follow-up.
Finally, analyses of post-TAVI dispensing found that one-third of patients receiving TAVI were not dispensed guideline-recommended antithrombotic therapy, within 30-days of discharge. The strongest predictor of dispensing was prior exposure to antithrombotic medicines, suggesting that there may be potential gaps in adherence to clinical guidelines for patients who are new to the therapy.
These findings highlight the importance of monitoring the use and outcomes of aortic valve devices in the long-term. They also demonstrate how routinely collected data sources, used in combination with appropriate methods, can offer valuable insight into clinical practice relating to medical devices. Real-world evidence generated using these data complement clinical trials and registries, offering a scalable solution for the challenges of evaluating device-related outcomes in the long-term.
