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An introduction to aortic stenosis, the population health burden and the TAVI pathway

Aortic stenosis physiology

The heart is composed of four chambers (aorta and ventricles) and two valves: the mitral valve is between the left atrium and ventricle, and the tricuspid valve is between the right atrium and ventricle.1,2

There are a further two valves in the large blood vessels (the pulmonary artery and the aorta) that leave the heart: the aortic and pulmonic valves.1,2The heart valves ensure that blood flows through the heart in one direction and does not flow back into the heart once it has been pumped out.1 The heart pumps oxygenated blood through the aortic valve in the aorta to the rest of the body.3                                                                                   

                Figure adapted from New Heart Valve4

The aortic valve is comprised of thin leaflets that open and close to regulate blood flow.4 Over time, the valve leaflets can thicken, narrow and stiffen, resulting in the aortic valve failing to open and close properly. As the opening in the valve becomes smaller, the heart becomes less effective and pumps less blood out to the rest of the body. This is termed ‘aortic stenosis’ (AS),3,5,6and it is the most common valvular disease in developed countries among the elderly with a prevalence of 1-3% among those >70 years of age.7 If left untreated, aortic stenosis can lead to compromised heart function, heart failure and death.3,7

Aortic stenosis progession

Aortic stenosis is a progressive disease and is categorised as mild, moderate or severe, depending on how much damage there is to the aortic valve.7,8 During mild or moderate stages, patients may remain asymptomatic with no noticeable symptoms and may be told that they have a heart murmur during routine check-ups.7,8 Advice for patients with mild or moderate asymptomatic AS is watchful waiting and to maintain a healthy lifestyle.3,9

As stenosis worsens, there is an increase in pressure in the left ventricle, causing the muscle to enlarge as a compensatory mechanism (termed ventricular hypertrophy) to maintain cardiac output.5,7,9,10As the disease progresses, this compensatory mechanism becomes inadequate, leading to symptoms of pulmonary oedema or heart failure.7,9,10Once AS becomes severe, noticeable symptoms may appear such as fatigue, shortness of breath, chest pain, heart palpitations; dizziness, syncope, or oedema of the feet and ankles.3,5,7,11

                                                                Figure adapted from New Heart Valve4

Population health burden of aortic stenosis

Although the condition can be asymptomatic for years, when symptoms do appear, untreated patients with severe AS have high mortality (up to 50% within 2 years).12,13 Waiting for treatment for severe symptomatic AS (ssAS) has a 1-month mortality at 3.7% and a 6-month mortality at 11.6% (measured from the time intervention was recommended).14

With a growing and ageing population, the prevalence of valvular heart disease is expected to rise, further increasing the public health burden of the disease.15

TAVI: a cost-effective intervention

For severe symptomatic aortic stenosis, aortic valve replacement (AVR) should be recommended, which can include surgical repair or a less invasive procedure such as transcatheter aortic valve implantation (TAVI).3,7

TAVI is a minimally invasive interventional cardiology procedure catheter-based treatment that is performed under local rather than general anaesthetic.7,16The principle of TAVI is the insertion of a balloon-expandable valve inside the old valve, without the need to remove it.7 A catheter is inserted through a small incision in the groin (transfemoral TAVI) or via the left-hand side of the chest (transapical TAVI). The valve, which sits inside a stent is crimped onto the end of the catheter, and when in place, a small balloon is inflated, which allows the valve to expand.5,16Once expanded, the new valve displaces the native valve leaflets outward and takes over the regulation of blood flow across the aortic valve.7 TAVI significantly improves symptoms and potentially increases life expectancy and quality of life, without the need for open heart surgery.5,16

Clinical trial data have demonstrated that transcatheter AVR (TAVR) for inoperable patients extends median survival by approximately 19 months and significantly improves quality of life compared with medical therapy alone.12 In the same study, it has been suggested that substantial social value can be created as a result of TAVR treatment for these patients: up to $48.1 billion in value, roughly 80% of which accruing to patients (and 20% to device manufacturers).12 Using data from the PARTNER B trial,17 Reynolds and colleagues found that patients with ssAS considered to be at a high surgical risk who underwent TAVR experienced lifetime incremental cost-effectiveness ratios of $55,090 per quality-adjusted life year (QALY) gained and $43,114 per life-year gained.18 Such a perspective is useful for payers and policy makers because it extends the decision-making considerations concerning TAVR adoption beyond a narrow evaluation of short-term cost.


References

  1. British Heart Foundation. Heart valve disease. Available from: www.bhf.org.uk/informationsupport/conditions/heart-valve-disease. Accessed April 1, 2021.
  2. Cleveland clinic. Heart Valves. 2018. Available from: https://my.clevelandclinic.org/health/articles/17067-heart-valves. Accessed April 1, 2021.
  3. American Heart Association. Aortic Stenosis. 2020. Available from: https://www.heart.org/-/media/files/health-topics/heart-valve-disease/aortic-stenosis-fact-sheet.pdf?la=en. Accessed April 1, 2021.
  4. New Heart Valve. What is aortic stenosis? 2021. Available from: https://newheartvalve.com/uk/understand-your-heart/what-is-aortic-stenosis/. Accessed April 1, 2021.
  5. NHS. Diagnosis and treatment: aortic stenosis. 2014. Available from: https://www.uhs.nhs.uk/OurServices/Bloodandcirculation/Transcatheter-aortic-valve-implantation/Diagnosis-and-treatment-TAVI/Diagnosis-and-treatment-TAVI.aspx. Accessed April 1, 2021.
  6. WebMD. What is Aortic Valve Stenosis? 2021. Available from: https://www.webmd.com/heart-disease/aortic-valve-stenosis. Accessed April 1, 2021.
  7. Zakkar M, Bryan A, Angelini G. Aortic stenosis: diagnosis and management. BMJ. 2016;355:i5425.
  8. WebMD. How severe is your aortic stenosis? 2019. Available from: https://www.webmd.com/heart-disease/aortic-stenosis-stages. Accessed April 1, 2021.
  9. Grimard B, Larson J. Aortic stenosis: diagnosis and treatment. Am Fam Physician. 2008;78(6):717-724.
  10. Kamperidis V, Delgado V, Van Mieghem N, Kappetein A, Leon M, Bax J. Diagnosis and management of aortic valve stenosis in patients with heart failure. European journal of heart failure. Eur J Heart Fail. 2016;18(5):469-481.
  11. Heart Valve Voice. Aortic Stenosis. Available from: https://heartvalvevoice.com/heart-valve-disease/the-condition/aortic-stenosis. Accessed April 1, 2021.
  12. Sussell J, Van Eijndhoven E, Schwartz T, et al. Economic Value of Transcatheter Valve Replacement for Inoperable Aortic Stenosis. Am J Manag Care. 2020;26(2):e50-e56.
  13. Otto C. Timing of Aortic Valve Surgery. Heart. 2000;84(2):211-218.
  14. Malaisrie S, McDonald E, Kruse J, et al. Mortality While Waiting for Aortic Valve Replacement. Ann Thorac Surg. 2014;98(5):1564-1571.
  15. Moore M, Chen J, Mallow P, Rizzo J. The direct health-care burden of valvular heart disease: evidence from US national survey data. Clin Outcomes Res. 2016;8:613-627.
  16. NHS. Transcatheter aortic valve implantation (TAVI) procedure. 2020. Available from: https://www.kch.nhs.uk/Doc/pl%20-%20859.3%20-%20transcatheter%20aortic%20valve%20implantation%20(tavi)%20procedure.pdf. Accessed April 1, 2021.
  17. Edwards Lifesciences. THE PARTNER TRIAL: Placement of Aortic Transcatheter Valve Trial (PARTNER). 2017. Available from: https://clinicaltrials.gov/ct2/show/NCT00530894. Accessed April 1, 2021.
  18. Reynolds M, Lei Y, Wang K, et al. Cost-effectiveness of Transcatheter Aortic Valve Repacement with a Self-Expanding Prosthesis Versus Surgical Aortic Valve Replacement. J Am Coll Cardiol. 2016;67:29-38.

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