Cost–Effectiveness of Rivaroxaban Versus Heparins for Prevention of Venous Thromboembolism After Total Hip or Knee Surgery in Sweden

Lars Ryttberg; Alex Diamantopoulos; Fiona Forster; Michael Lees; Anina Fraschke; Ingela Björholt

Disclosures

Expert Rev Pharmacoeconomics Outcomes Res. 2011;11(5):601-615. 

In This Article

Chronic Phase

After 3 months post-surgery, it was assumed that the cohort is no longer at risk of an initial venous thromboembolic event. However, patients who experienced a symptomatic venous thromboembolic event in previous phases remain at risk of developing post-thrombotic syndrome (PTS) or chronic thromboembolic pulmonary hypertension (CTPH) (in patients who suffered a PE) or suffering a recurrent VTE.[16–19] The chronic phase was analyzed using a Markov process with 1-year cycles. The Markov model contains five health states:

  • No long-term complications

  • PTS

  • CTPH

  • CTPH and PTS

  • Death (absorbing state)

Figure 2 represents the possible transitions within the Markov model. The cohort starts the long-term complications module from the no-complications health state. Within that health state, the cohort could be divided into three parts:

  • Individuals without a venous thromboembolic event;

  • Individuals who experienced a DVT event in previous modules (prophylaxis or post-prophylaxis module);

  • Individuals who experienced a PE event in previous modules (prophylaxis or post-prophylaxis module).

Individuals who experienced a DVT event in previous modules (prophylaxis or post-prophylaxis module) remain at risk of developing PTS. Individuals who experienced a PE event in previous modules remain at risk of developing CTPH. In addition, approximately 37% of PE patients also had DVT,[17,18] so they are also at risk of PTS.

The annual probability of developing PTS falls from 18% in the first year following the DVT to 7.9% in the second year, and to an average of 2.3% in the third, fourth and fifth years following a DVT.[19] The probability of developing CTPH falls from 3.1% in the first year following a PE to 0.7% in the second and subsequent years.[17] The same risk of developing PTS is assumed for patients with a DVT and for patients with both a DVT and PE event. In the absence of clinical data, the analysis assumes that these patients would not develop CTPH and PTS in the same year. However, they can progress to the combined CTPH and PTS health state at a later stage from either complication – PTS or CTPH.

Moreover, all individuals who experienced a DVT or PE in previous modules (prophylaxis or post-prophylaxis module) are at risk of recurrent VTE. Using data from a large, Italian prospective cohort study,[19] the annual probability of recurrent VTE was estimated at 9% in the first 2 years after the initial VTE and 2.9% in the following 3 years. The incidence of recurrent VTE is modeled as a transitory event with a disutility and a relevant cost applied based on time-dependent transition probability. Similar to the post-prophylaxis module, in the absence of data indicating any difference in the long-term profile between the pharmacological methods of prophylaxis, the model applies the same risk of long-term complications to both comparators.

Background mortality, based on Swedish all-cause mortality data, was applied to the whole cohort regardless of health state membership.[101] The age of the evaluated model cohort was based on the average age of patients in the RECORD program (64 years).

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