2.1.6 The use of bare metal stents has not been a substitute for the more expensive existing technologies…
If PTCAs and Stents were perfect substitutes for CABGs we would expect the number of CABGs to decrease while the number of stents and PTCAs would increase by the same proportion. Equally, expenditure on coronary care would be considerably reduced from the improvement in technology. This has not been supported by the data. Indeed, examination of more recent data finds that CABGs have been on the increase. This is seen in Figure 1 showing the number of admissions to New Zealand hospitals for the period 1990-2004 for each procedure.
The fact that we do not see this substitution effect suggests that the existence of stents has increased the number of candidates receiving an intervention. An obvious inference is that patients with low clinical complexity who in the past may not have had an intervention of any kind are now prime candidates for a stent hence the increase in numbers. Moreover, these procedures are performed by an interventional cardiologist and are stimulating and rewarding to do. There is then an incentive for more to be done to seek suitable candidates thus increasing the pool of patients treated for coronary artery disease.
Note: The data is expressed here in terms of calendar years but represents data from mid 1990 to the end of the 2003-04 financial year. The observed decline in 2004 is because we have only included six months of data for that year.
2.1.7 …because the procedures are not interchangeable
Wellington cardiologists stressed that clinicians cannot substitute CABG with angioplasty since there are many instances where CABG is the more appropriate (and safer) option. This depends on:
- the number of vessels which are involved;
- the distance over which the artery has narrowed;
- whether the patient has experienced a heart attack in the past; and
- the size of the blockage.
Therefore continued use of CABG is not necessarily a sign of a lack of technology diffusion but may also reflect the conditions presented by patients. Hence any analysis of new technology uses must also take into account the change in clinical complexity of each case.
Notably, when the health literature debated the relative efficacy of CABGs and stents (Hannan et al. 2005, Hill et. al. 2004, Weinstein 2003, to name just a few), the general view was that stenting was suitable for patients with low clinical complexity or limited disease. A number of studies have pointed to the fact that it is wrong to look at stenting as a “one off” procedure and then compare costs with a CABG since people could have multiple stents before finally coming up for a CABG. It may therefore be better to think of stenting as a strategy rather than a single procedure.
Furthermore, technology has advanced not just in the nature of the devices (e.g. drug eluting stents versus bare metal stents) but also in surgical advances which allow stents to be used in places not previously reachable. Moreover, new technologies enable clinicians to treat people who could not be treated with the older technologies. Consequently, while the cost of a heart operation may fall with advances in technology, the number of people treated increases dramatically thus driving up overall expenditure in the cardiology area.
2.1.8 The evidence on drug eluting stents is inconclusive because the device has only recently been introduced so advisory committees are acting with caution…
Drug eluting stents (DES) have only been used in New Zealand for the past 3 years and are subject to considerable controversy. The actual DES costs on average $5800 while bare metal stents are considerably cheaper at $950. Hence in the absence of international evidence showing outcome advantages for the DES, the bare metal stent would appear more cost effective. However, anecdotal evidence suggests DES have been adopted around New Zealand on the basis of individual judgement so that now, some cardiologists adopt the DES while others stick with the bare metal stent. Evidence from one DHB suggests that there are discrepancies with the use of drug eluting and bare metal stents between neighbouring DHBs. The benefits of using the more expensive drug eluting stents are not conclusive (despite the MSAC findings). Hence some DHBs are opting for bare metal stents in their surgery. However, other DHBs have already adopted the use of drug eluting stents, perhaps because they do not face such tight funding constraints.
The controversy concerns the manner with which this dissemination took place. The DES was not required to pass a clinical trial in New Zealand before being taken into practice. Given its cost and concern over the drug coating of the DES (i.e. possible long term problems outlined in the Australian Productivity Commission Report, 2005), this questions the process through which new technologies are introduced into New Zealand hospitals.
In terms of the data presented here, the International Classification of Diseases (ICD9) makes no distinction between drug eluting and bare metal stents so we cannot see the extent to which one type is used instead of another hence our comments are based on anecdotal evidence from practitioners in different DHBs.
2.1.9 …but there are a number of factors influencing its adoption.
Influence of the patient – Anecdotal evidence suggests that as patients become more well-informed through media or internet, they tend to pressure clinicians for particular procedures. This makes it even more difficult to reverse the trend of a relatively “poor” technology (e.g. less cost effective than alternative choices) in the absence of robust research which may not become available in the short term.
Staffing – Interventional cardiologists and specialised nurses are typically attracted to those DHBs with a specialised research-oriented hospital (such as Capital and Coast District Health Board, Waikato District Health Board and Canterbury District Health Board). Conversely, it is very difficult to attract skilled staff in isolated hospitals outside these DHBs, which may generate inequalities. However, this is not necessarily a bad thing if: (a) a particular safety threshold exists for the number of procedures performed by a cardiologist in a certain time frame; or (b) it is costly to perform only a few such procedures in an institution. Sadly, the data does not decompose to individual clinicians. Nevertheless, it does show each facility (e.g. hospital) in which the procedure is carried out. This means that we can get an idea of the volume of patients treated in a hospital over a particular time period.
Domino effects and Inter-district flows
With regard to technological diffusion, problems exist between neighbouring DHBs. For instance it has been suggested that if Capital and Coast decided to take up the procedure of offering drug eluting stents, Hutt Valley would feel the impact through increased inter-district flows. Work has started in New Zealand to make comparisons across DHBs (Sharpe and Wilkins, 2004) in order to ensure quality and equity in cardiovascular health across the country. Initial results suggest that inequalities do indeed exist particularly when comparing between those hospitals regarded as “intervention” centres and those that are not. The examples used in their study were Waikato and Taranaki hospitals. Significantly higher revascularisation rates were seen at Waikato where management was performed by cardiologists with immediate access to invasive intervention facilities. It is a subject for debate as to whether decision making should take this form (Conaglen et al. 2004). As may be expected, some DHBs cannot afford to take on new technologies. Consequently, technological diffusion may be strongly influenced by the degree to which the DHB is funding constrained.
