COST-EFFECTIVENESS OF STROKE PREVENTION THERAPIES IN ATRIAL FIBRILLATION PATIENTS: A NEW GENERATION OF DRUGS

Purpose: To evaluate the cost-effectiveness of pharmacologic stroke prevention therapies for atrial fibrillation (AF) patients at varying risks of stroke and bleeding.

Method: We used a Markov model to compare seven strategies for thromboprophylaxis in 65 year-old AF patients.  The strategies evaluated were: no treatment, aspirin, warfarin, dabigatran 110 mg, dabigatran 150 mg, apixaban, and rivaroxaban.  We risk-stratified potential patients using scores on the CHADS₂ index for stroke risk and the HAS-BLED index for bleeding risk. We identified six risk groups based on 3 stroke risk and 2 bleeding risk strata.  The analysis was undertaken from the Canadian healthcare payer perspective using a lifetime time horizon and a 5% discount rate.  Outcome measures were life years, Quality-Adjusted Life Years (QALYs), lifetime costs, and Incremental Cost-Effectiveness Ratios (ICERs).

Result: Cost-effectiveness and effectiveness of treatments varied significantly across risk groups.  Aspirin, dabigatran 110mg and rivaroxaban were not cost-effective strategies or the most effective strategies in any of the risk groups.  Additionally, warfarin was not the most effective strategy in any of the risk groups.  One-way and multi-way sensitivity analyses were run on key variables and probabilistic sensitivity analysis is underway.  The results were not sensitive to the quality of life associated with taking warfarin or to the rates of stroke and bleeding within each risk group.  The results were sensitive to the efficacy of the drugs and to the risk of bleeding while on them.    

Risk Group	CHADS2 Score	HAS-BLED Score	Most Effective Strategy	QALYs	Cost-Effective Strategies	ICER ($/QALY)
Low/Low	0	0-2	Apixaban	7.46	Warfarin	-
					Apixaban	1,733
Moderate/Low	1	0-2	Apixaban	7.41	Warfarin	-
					Apixaban	1,568
High/Low	2+	0-2	Dabigatran 150	7.26	Dabigatran 150	Dominant
Low/High	0	3+	No Treatment	7.17	No Treatment	Dominant
Moderate/High	1	3+	Apixaban	7.07	No Treatment	-
					Apixaban	15,520
High/High	2+	3+	Apixaban	6.90	Apixaban	Dominant

Conclusion: AF patients at high risk for bleeding should take apixaban, unless they are at low risk for stroke, whereby they should not take any thromboprophylactic therapy.  Patients at high risk for stroke should take apixaban or dabigatran 150 mg.  These recommendations are broadly consonant with the Canadian Cardiovascular Society Guidelines for AF, but guidance on how to combine a patient's specific stroke and bleeding risk scores in making prescribing and reimbursement decisions is limited.