A randomized controlled trial is conducted to compare transcatheter aortic valve replacement (TAVR), using a self-expanding transcatheter aortic valve bioprosthesis, with surgical aortic valve replacement in patients with severe aortic stenosis. The objective is to determine the difference in risk of death from any cause. Seven hundred forty-seven patients with severe aortic stenosis who are at increased surgical risk are recruited and randomly assigned to groups for treatment with TAVR or surgical valve replacement. Follow-up assessments are performed at discharge and at 1 month, 6 months, and 1 year. The 1-year follow-up results are as follows: Which of the following best represents the absolute risk reduction for death from any cause in patients treated with TAVR compared to those treated with surgical replacement?

Question

A randomized controlled trial is conducted to compare transcatheter aortic valve replacement (TAVR), using a self-expanding transcatheter aortic valve bioprosthesis, with surgical aortic valve replacement in patients with severe aortic stenosis.  The objective is to determine the difference in risk of death from any cause.  Seven hundred forty-seven patients with severe aortic stenosis who are at increased surgical risk are recruited and randomly assigned to groups for treatment with TAVR or surgical valve replacement.  Follow-up assessments are performed at discharge and at 1 month, 6 months, and 1 year.  The 1-year follow-up results are as follows:  Which of the following best represents the absolute risk reduction for death from any cause in patients treated with TAVR compared to those treated with surgical replacement?

Quizplus · Accepted Answer

Absolute risk reduction (ARR) describes the difference in risk of an unfavorable outcome between the treatment group (eg, new treatment) and the control group (eg, standard treatment): ARR = (Risk_control − Risk_treatment) In this example, Risk_control is the risk of death from any cause in the group treated with surgical aortic valve replacement and is determined by dividing the number of deaths in that group (68) by the total number of patients in that group (357). Risk_treatment is the risk of death from any cause in the group treated with transcatheter aortic valve replacement (TAVR) and is determined by dividing 57 by 390. Therefore, the ARR for death from any cause in patients treated with TAVR compared to those treated with surgical replacement is calculated as follows: ARR = (68/357) − (57/390) = 0.044 ARR can be used to determine the number needed to treat (NNT), calculated as: NNT = 1 / ARR NNT is the number of patients who need to be treated with a treatment (eg, TAVR) to prevent 1 additional negative event (eg, death from any cause) when compared to a control group (eg, surgical replacement). A lower NNT indicates a more effective treatment because fewer patients need to be treated to prevent 1 additional negative outcome. In this example, the approximate NNT with TAVR to prevent 1 additional death from any cause is: NNT = 1 / [(68/357) − (57/390)] = 22.562 (Choice E) (Choice B) [(68/357) − (57/390)] / (68/357) = 0.233 represents the relative risk reduction (RRR) for death from any cause in the TAVR group compared to the surgical replacement group: RRR = (Risk_control − Risk_treatment) / Risk_control. Unlike ARR, which quantifies the absolute difference in risk between the groups, RRR describes the difference in risk between the groups as a proportion of baseline risk (ie, risk in the control group). (Choices C and D) Switching the numerator and denominator changes the interpretation of the relative risk (RR, the ratio of the probability of an event occuring in one group compared to the other group). In this example, (57/390) / (68/357) represents the RR of death from any cause in the TAVR group compared to the surgical replacement group; (68/357) / (57/390) represents the RR of death from any cause in the surgical replacement group compared to the TAVR group. Educational objective: Absolute risk reduction (ARR) describes the difference in risk between control and treatment groups. It is calculated as follows: ARR = (Risk_control − Risk_treatment). __________ References: Measures of effect in epidemiological research. (http://www.ncbi.nlm.nih.gov/pubmed/20407271) Measures of effect: relative risks, odds ratios, risk difference, and "number needed to treat." (http://www.ncbi.nlm.nih.gov/pubmed/17653136)

A Randomized Controlled Trial Is Conducted to Compare Transcatheter Aortic