The CVD Model, and its Scenarios

The CVD Model

This document describes the CVD state-transition model, and the scenarios which are run using it.

Model Structure

CVD Models creates several scenarios: cvd_null, CV1, CV2a, CV2b, CV3, CV4a, CV4b, CV6 and CV7

The CVD Model refers to a "Model architecture": A structure of states and transitions, which can be used to run different scenarios. A scenario is when the structure has a different set of transition rates between the states.

The CVD model is used to run several scenarios of treatment coverage: CV1, CV2a, CV2b, CV3, CV4a, CV4b, CV6 and CV7. NOTE - CV5a and CV5b relate to Rheumatic Heart Disease, and rely on a separate disease model. In addition, the CVD model is also used to run a "Null Scenario": Called cvd_null. We will explain the Null Scenario later.

Structure of the CVD Model

CVD has several key states, DsFreeSus, IHDAcute, StrokeAcute, IHDPostAcute, StrokePostAcute, StrokeIHDPostAcute and Deceased DsFreeSus means "Disease free, susceptible", and this refers to the majority of the population. IHD refers to Ischaemic Heart Disease, and is generally referring to the process of an acute myocardial infarction (AMI) Deceased refers to the people in the model who have died, either through background mortality (DsFreeSus -> Deceased) or through the CVD episode (cvdEpsd -> Deceased).

In general, people are Disease Free, but may have an Acute Myocardial Infarction (IHDAcute) or a stroke (StrokeAcute). After these events, people move to being PostAcute and end in the state StrokeIHDPostAcute, which collects both groups of persons. There is no recovery from any of these states, so once someone has had an AMI or Stroke, they will progress irreversibly to StrokeIHDPostAcute.

Treatments (described below) work by reducing the mortality of IHDAcute or StrokeAcute. For example, if someone has a stroke (i.e. moves to StrokeAcute), and they receive aspirin (TreatStrokeAcuteAspirin), this may reduce their mortality. If they survive, they will move to StrokePostAcute

In addition to these states, there are other "states" which are used to perform calculations, or collect useful statistics about the model. This is something we have chosen to do in our model structure, so it's visible to users, but it is not strictly necessary. For example, we have states for Disability, which collects information about the stock of key states and multiplies them against some disability weight. We also have states to calculate births, migration, and the effects of interventions on disability and mortality. Once again, we made these design decisions so that users can see how these work, but they aren't strictly necessary. They can be done elsewhere, and simply rendered as a transition rate.

The Model has two key components

The main component moves people between states

The main component has the states we've introduced: DsFreeSus, IHDAcute, IHDPostAcute, StrokeAcute, StrokePostAcute, StrokeIHDPostAcute, Deceased, Disability, Births. Importantly there are some other states which sit between states:

• DsFreeSus Disability sits between DsFreeSus and Disability
• IHDAcute Disability sits between IHDAcute and Disability
• IHDPostAcute Disability sits between IHDPostAcute and Disability
• StrokeAcute Disability sits between StrokeAcute and Disability
• StrokePostAcute Disability sits between StrokePostAcute and Disability
• StrokeIHDPostAcute Disability sits between StrokeIHDPostAcute and Disability
• IHDAcute Mortality sits between IHDAcute and Mortality
• IHDPostAcute Mortality sits between IHDPostAcute and Mortality
• StrokeAcute Mortality sits between StrokeAcute and Mortality
• StrokePostAcute Mortality sits between StrokePostAcute and Mortality
• StrokeIHDPostAcute Mortality sits between StrokeIHDPostAcute and Mortality

These states aren't really states in a true sense. Rather, these states set the value of the transition rates around them. So, for example, DsFreeSus Disability is really the transition rate for DsFreeSus -> Disability. In the nomenclature of the Botech protocol, we call this a "Surrogate node". This is a structural decision we have made, but it doesn't change the results. Rather, we do this, so we can show how the calculations work to determine the disability and mortality effects.

The calculation component sets the transition rates

The "Surrogate Nodes" mentioned above, are set by a series of calculations in the model. These calculations follow the common order of operations described in the introduction.

Order of Operations

The CVD model follows the common order of operations used by all disease models. The key CVD-specific variations are:

Treatment Effect Calculations (Steps 4-7)

CVD has eight acute treatments for stroke and myocardial infarction events, each with specific mortality impacts.

Step 4 example: TreatAMIAcuteAspirin_PIN × TreatAMIAcuteAspirin_Mortality_Impact × TreatAMIAcuteAspirin_Calculated_Coverage

Step 6: Blended disability calculated for multiple states: StrokeAcute, StrokePostAcute, IHDAcute, IHDPostAcute, and StrokeIHDPostAcute

Main State Transitions (Step 10)

CVD has a more complex state progression:

• DsFreeSus → StrokeAcute or IHDAcute (acute events)
• StrokeAcute → StrokePostAcute and IHDAcute → IHDPostAcute (survival)
• StrokePostAcute, IHDPostAcute → StrokeIHDPostAcute (combined post-acute state)
• Various mortality pathways throughout the progression

Interventions

Intervention Overview Table

The modelled treatments and their assumptions

For CVD, there are eight treatments, which are referenced in the table below. This table also lists the reference name in the model, and in which scenario the treatment is scaled up. Furthermore, the PIN (population in need) and the impact is listed.

CV1

CV2a

CV2b

CV3a

CV3b

CV3c

CV3d

CV4a

CV4b

CV6

CV7