An exploratory cost-effectiveness analysis of a novel tissue valve compared with mechanical valves for surgical aortic valve replacement in subgroups of people aged 55–64 and 65+ with aortic stenosis in the UK

Figures & data

Figure 1. Model structure.

*Those entering either Functioning heart valve or Disabling stroke in the partitioned survival model are still at risk of the events listed. People within these states are also attributed to a NYHA class (independent of having a stroke or not). Anticoagulation events only occur in the first 6 weeks in the model. This therefore means that they occur either in the decision tree or the first cycle of the partitioned survival model.

Table 1. Costs used in the model.

Parameter	Value	Source/comment
One off event costs
Procedural costs
Procedure cost: novel tissue valve	£11,134	Micro-costed. See supplementary information for more detail.
Procedure cost: mechanical valve	£10,136	Micro-costed. See supplementary information for more detail.
Event costs
Reoperation	£10,310	Micro-costed. See supplementary information for more detail.
Bleeding	£9,364	Luengo-Fernandez et al [41]
Thromboembolic event	£2,068	NHS cost collection 2018–19 [39], Weighted average for stroke with CC score of under 10 (AA35D-AA35F)
Endocarditis	£809	NHS cost collection 2018–19 [39], Weighted average of total HRG for endocarditis EB02A-EB02C. Non-elective short stay
Disabling stroke (first month cost)	£24,229	Xu et al [42] Mean total health and social care costs per patient. 1 year cost taken. Assumed that the majority will stem from the initial stroke.
Monitoring costs
Re-admission to treat subtherapeutic INR	£704	NHS cost collection 2018–19 [39], Rehabilitation, Admitted Patient Care, Rehabilitation for Acute Myocardial Infarction or Other Cardiac Disorders, currency code: VC38Z. £352.17 Lopez et al [38], Impact of Mechanical Aortic Prostheses in hospital stay and anticoagulation related complications. suggests this required at least 2 days in hospital.
INR check and anticoagulation dosage adjustment	£330	NHS cost collection 2018–19 [39], Cardiac rehabilitation Service code 327. £94.32 per attendance. Lopez et al [38], Impact of Mechanical Aortic Prostheses in hospital stay and anticoagulation related complications. suggests 1–7 attendances required over the 6 weeks.
Health state and recurring monthly costs
Functioning heart valve (year 1)	£65	NHS cost collection 2018–19 [39], Total outpatient attendance (code 172 cardiac surgery). Assumed a follow up consultation is required at month 1, 6 and 12. £259 per appointment, £777 per year, £64.75 per month
Functioning heart valve (year 1+)	£22	NHS cost collection 2018–19 [39], Total outpatient attendance (code 172 cardiac surgery). Assumed a follow up consultation is required annually. £259 per appointment, £21.58 per month
Pacemaker complication	£145	Fox et al [43]. 5-year cost minus insertion cost averaged across both pacemaker types, then converted to a monthly cost.
Disabling stroke (post month 1 costs)	£829	Xu et al [42]. Mean total health and social care costs per patient. 5-year cost taken and converted to a monthly cost.
NYHA I (medication and outpatient care)	£41	Cost per month calculated by taking the unit costs associated with outpatient care (Cardiology consultation [39] and GP visits [40]) and the disease related visits per year associated with each NYHA class [44]. Medication costs per month were calculated using BNF [45] costs and dosages to calculate costs per month for each NYHA class.
NYHA II (medication and outpatient care)	£53
NYHA III (medication and outpatient care)	£59
NYHA IV (medication and outpatient care)	£69
Echocardiogram (monthly monitoring costs applied from year 3)	£7	NHS cost collection 2018–19 [39], Complex Echocardiogram EY50Z. = £85. Divided by 12 for a monthly cost.
Warfarin (monthly medication and monitoring costs)	£14.29	Medication costs per month £1.21 (BNF [45]) Monitoring costs per month £13.08 (BNF [45], monitored every 3 months for their INR levels. This is assumed the cost of a GP appointment. Cost taken from PSSRU 2020. Cost=£39.23. Divided by 3 for monthly cost

Table 2. Utilities used in the model.

Parameter	Value	Source
Population norms (by age range)
55–64	0.80	Szende et al. [48]
65–74	0.78
over 75	0.73
Utility decrements
Functioning health state: NYHA class
NYHA I	0.00	Griffiths et al. [49]
NYHA II	0.05
NYHA III	0.15
NYHA IV	0.33
Disabling stroke health state
Disabling stroke	0.32	Rivero-Arias et al. [50]
Short-term events
Bleeding	0.07	Kaier et al. [51]
Operation/reoperation	0.05
Endocarditis	0.03	Sullivan et al. [52]
Thromboembolic event	0.07
Subtherapeutic INR	0.02
INR checks and dosage adjustments	0.02

Table 3. A summary of the base case results.

	Novel tissue valve	Generic mechanical valve	Difference
Age 55–64
Cost per patient	£28,156	£28,564	-£408
QALYs per patient	8.45	8.44	0.01
Life years per patient (discounted)	10.92	10.92	0.00
ICER per QALY	Dominant
NMB	£679
Age 65+
Cost per patient	£21,780	£21,833	-£53
QALYs per patient	5.73	5.73	0.01
Life years per patient (discounted)	7.62	7.62	0.00
ICER per QALY	Dominant
NMB	£181

NOTE: *Costs rounded to the nearest integer. QALYs rounded to two decimal places.

Figure 2. Deterministic sensitivity analysis.

*Where the figure refers to a ‘multiplier,’ this indicates a percentage change on the event rates, i.e. a value of 1.2 represents a 20% increase in rates at all time points for the specified event.

**Net monetary benefit (NMB) is a summary statistic that represents the value of an intervention in monetary terms when a willingness to pay a threshold for a unit of benefit (for example, a measure of health outcome or QALY) is known. A value above £0 indicates the treatment tissue valve is cost-effective at the specified cost-effectiveness threshold.

Table 4. Cost breakdown per patient.

Cost breakdown (per patient)	INSPIRIS RESILIA	Generic mechanical valve	Incremental
Age (55–64)
Cost of initial procedure	£11,134	£10,136	£998
Functioning heart valve cost	£3,334	£3,322	£11
NYHA medications and appointment costs	£5,613	£5,590	£23
Disabling stroke costs	£2,311	£2,963	-£652
Death costs	£0	£0	£0
Reoperation costs	£2,730	£1,460	£1,270
Bleeding costs	£1,086	£1,877	-£791
Endocarditis costs	£69	£69	£0
Thromboembolic event costs	£187	£239	-£52
Warfarin costs	£3	£1,872	-£1,869
Additional monitoring costs	£690	£0	£690
Anticoagulation complication costs	£0	£37	-£37
Pacemaker complication costs	£1,000	£1,000	£0
Total	£28,156	£28,564	-£408
Age 65 +
Cost of initial procedure	£11,134	£10,136	£998
Functioning heart valve cost	£2,488	£2,482	£5
NYHA medications and appointment costs	£3,929	£3,919	£10
Disabling stroke costs	£1,252	£1,605	-£353
Death costs	£0	£0	£0
Reoperation costs	£955	£540	£414
Bleeding costs	£632	£785	-£153
Endocarditis costs	£46	£46	£0
Thromboembolic event costs	£219	£280	-£61
Warfarin costs	£2	£1,306	-£1,304
Additional monitoring costs	£426	£0	£426
Anticoagulation complication costs	£0	£37	-£37
Pacemaker complication costs	£697	£697	£0
Total	£21,780	£21,833	-£53

Table 5. Scenario analysis- improvement in reoperation rate for novel tissue valve from the base case.

	Incremental cost per patient	Incremental QALY per patient	NMB
Age 55–64
Base case	-£408	0.01	£679
10% improvement in reoperation rate	-£670	0.01	£942
20% improvement in reoperation rate	-£931	0.01	£1,205
30% improvement in reoperation rate	-£1,192	0.01	£1,468
Age 65+
Base case	-£53	0.01	£181
10% improvement in reoperation rate	-£138	0.01	£266
20% improvement in reoperation rate	-£223	0.01	£352
30% improvement in reoperation rate	-£307	0.01	£437

Figure 3. Cost-effectiveness planes.

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