This paper provides the background, and context of the draft assessments undertaken for aortic stenosis. These include a Tier 2 aortic stenosis (AS) assessment, a Tier 3 transcatheter aortic valve implantation (TAVI) assessment and a Tier 3 sutureless aortic valve replacement (sutureless AVR) assessment.
This paper positions these assessments within the overall ongoing cardiovascular work stream undertaken by the National Health Committee (NHC) since 2011, and outlines the next steps in the process to finalise these assessments, including consultation with the sector.
Background
At the request of the health sector, the NHC has undertaken multiple cardiovascular assessments since its reconfiguration in 2011. These assessments have tended to focus on very high cost leading edge interventions for elderly patients with established and advanced disease, often with multiple comorbidities. Assessments have included:
The cardiac cluster consultation, published March 2014, ISBN: 978-0-478-42791-2; Recommendations approved by the Minister of Health 30/05/2014. The cluster was a synthesis of recommendations from the assessments of renal denervation, percutaneous left atrial appendage occlusion, percutaneous interventions for the treatment of mitral regurgitation, and cardiac catheter ablation for the treatment of atrial fibrillation.
Percutaneous left atrial appendage occlusion for stroke prevention in patients with atrial fibrillation. An assessment was published in July 2013 and updated May 2015, with updated recommendations approved by the Minister of Health 10/09/2015, ISBN: 978-0-478-44892-4.
Sutureless aortic valve replacement for the treatment of aortic stenosis (Technology Note published May 2012, ISBN: 978-0-478-44894-8).
Transcatheter aortic valve implantation (TAVI) for the treatment of aortic stenosis (Briefing Report published September 2012, ISBN: 978-0-478-44898-6).
Catheter ablation for the treatment of atrial fibrillation (Technology Note published November 2012 and updated July 2013, ISBN: 978-0-478-44897-9).
Percutaneous interventions for the treatment of mitral regurgitation (Technology Note published July 2013, ISBN: 978-0-947491-00-0).
Renal artery denervation for the treatment of refractory hypertension (Technology Note published July 2013, ISBN: 978-0-947491-02-4).
A strategic overview of cardiovascular disease in New Zealand (Tier 1 assessment published December 2013, ISBN: 978-0-947491-03-1).
An overview of ischaemic heart disease (Tier 2 assessment published March 2014, ISBN: 978-0-9922623-1-0).
Five ischaemic heart disease Tier 3 assessments, in the process of development, were derived from the IHD overview. Screening for abdominal aortic aneurysm (AAA); reconfigured Tier 2 assessment of the AAA model of care (in progress).
Cardiovascular assessments have been undertaken using the NHC's previously documented tiered business case for change methodology.1 The assessment work has developed a detailed understanding of the clinical safety and effectiveness of the respective technologies, including the patient sub-groups (if any) most likely to benefit, and the potential health, economic and societal/ethical impact of the technology. The assessments have sought to understand the feasibility of adopting the new interventions, particularly the impact of introducing additional interventions into a fixed capital and operational service delivery model.
The NHC has also funded cardiovascular research through a partnership fund with the Health Research Council, the Health Innovation Partnership, including the evaluation of:
the cost-effectiveness of fractional flow reserve in myocardial infarction; and
a process for improving care processes for patients with possible acute coronary syndrome.
The NHC has maintained an ongoing interest in TAVI and sutureless AVR as the evidence for the technologies has evolved. Both technologies are used for the treatment of severe aortic stenosis. Our current work presents up-to-date (Tier 3) assessments of the technologies alongside a Tier 2 overview document of aortic stenosis. Although the technologies affect a relatively small group of patients, our discussions with the health sector have indicated the opportunity for material change to the overall model of care for severe aortic stenosis.
Severe aortic stenosis and its treatment
Aortic stenosis (AS) is a condition where the main outflow valve of the heart becomes narrowed. AS is a disease largely of the elderly, and is expected to increase in prevalence due to population ageing. Technically, severe symptomatic AS has been defined as a peak aortic valve velocity of >4 m per second, corresponding to a mean aortic valve gradient >40 mm Hg, and an aortic valve area of < 0.8 cm2. There is also a small group of patients that may benefit from aortic valve replacement who have asymptomatic AS, but have left ventricular dysfunction, with a left ventricular ejection fraction of less than 50%.
Without aortic valve replacement, the prognosis for severe symptomatic AS is poor. Patients face a poor prognosis once the disease becomes clinically evident, either with the onset of symptoms or with deterioration in left ventricular function. The life expectancy of patients with clinically evident AS without intervention is two to three years, with sudden death occurring in up to a third of these patients. AS is responsible for the deaths of about 300 New Zealanders a year.
The majority (85%) of patients with severe AS in 2012/13 were suffering from at least one of nine comorbid conditions, and over a quarter (27%) had at least three of these conditions (Figure ). These patients are a lot more likely to have ischaemic heart disease (IHD) and heart failure than a similarly aged group of people. People with IHD have insufficient blood and oxygen flow to the heart muscle. This means not only are these patients suffering from severe AS, but for two-thirds their heart function is additionally compromised due to IHD, warranting best practice treatment. For these patients major interventions may be less appropriate.
Figure : Percentage of people with selected long-term conditions, patients with severe aortic stenosis and a comparator group – 2012/13
Source: 2015 NHC Executive analysis of 2012/13 NZ Health Tracker data
There are few preventative measures for AS and no proven medical therapy to prevent its progression. Medical therapy is instead focused on symptom relief. Patients with asymptomatic AS mostly do not require treatment. For patients with severe symptomatic aortic stenosis, or severe AS with significant left ventricular dysfunction, surgical AVR is the standard of care. There are two types of prosthetic valve: mechanical valves that may last up to 25 years but require the recipient to take anticoagulants to prevent stroke; and bioprosthetic (‘tissue’) valves that last ten to 15 years but do not require anticoagulation. AVR can restore a patient’s quality of life and life expectancy to close to that seen in the absence of AS. Standard surgical AVR involves open heart surgery, requiring cardiopulmonary bypass to replace the diseased aortic valve with a prosthetic valve. Transcatheter aortic valve implantation and sutureless aortic valve replacements (discussed below) are alternative to conventional surgical AVR.
Not all patients with aortic valve disease are candidates for surgical AVR; operations are complex and durability is limited. Other treatment options for AS, including surgical valve repair and balloon aortic valvuloplasty, have a very limited role in adults with aortic stenosis. Balloon aortic valvuloplasty may occasionally be used as a bridge to surgical AVR, to test if AVR is likely to be beneficial, or for palliative care.
A large proportion of patients with AS are elderly and while some elderly patients have good outcomes, others have complications and poor outcomes irrespective of the treatment received, due to frailty, cognitive impairment or poor general health. The majority of patients that do receive surgical valve replacement are over the age of 70.
Rates of aortic valve replacement were low 10-15 years ago, but now appear comparable with other developed countries
Ten to 15 years ago, intervention rates for cardiac surgery including aortic valve replacement were low in New Zealand compared with other developed countries. Consequently, a service development process for cardiac surgery services in New Zealand was requested by the Minister of Health and initiated in May 2008 by the Ministry of Health with the New Zealand Branch of the Cardiac Society of Australia and New Zealand. A Cardiac Surgery Service Development Working Group was established to lead the development process. In 2008, the working group released a report that recommended increasing cardiac surgery intervention rates, including for aortic valve replacement, by a third between 2007/08 and 2012/13. In 2009, the National Cardiac Surgery Network was established to lead the implementation of the working group’s recommendations. National cardiac surgical targets were introduced in 2009, and in conjunction with increased funding for elective surgery from 2006/07, have led to a substantial growth in the number of AVR operations undertaken.
The number of publicly-funded aortic valve replacements for aortic stenosis roughly doubled between 2006/07 and 2013/14 from about 300 to about 600 aortic valve replacements per annum (Figure ). While volumes of aortic valve replacement have increased, mortality from AS has declined significantly, from about four deaths per 100,000 New Zealanders in 2000 to about three deaths per 100,000 New Zealanders in 2011.
Figure : Publicly funded AVR for any diagnosis of aortic stenosis in New Zealand from 2002/03 to 2013/14
Source: NHC analysis of NMDS
It is not possible to precisely define the optimal rate of intervention for aortic valve replacement. However, New Zealand’s rate of aortic valve replacement appears to be in line with other developed countries. A 2013 meta analysis of European and US data found about 59% of elderly patients with severe symptomatic AS were receiving valve replacement, whereas the remaining 41% were considered inoperable. In New Zealand, a Waikato hospital study (2005-2009) found about half of patients with symptomatic severe AS in its region did not receive aortic valve replacement. With the approximate doubling of aortic valve replacements in New Zealand between 2006/07 and 2013/14, our expectation is that a significantly greater proportion of patients with severe AS now receive valve replacement. Indeed, using national records, it appears a similar proportion of elderly patients with severe AS receive AVR in New Zealand compared with the aforementioned meta analysis.
