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Chen Wang, MD, PhD, FCCP; for the China Venous Thromboembolism (VTE) Study Group
Author and Funding Information

From the Beijing Key Laboratory of Respiratory and Pulmonary Circulation, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital, Capital Medical University.

Correspondence to: Chen Wang, MD, PhD, FCCP, Beijing Key Laboratory of Respiratory and Pulmonary Circulation, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital, Capital Medical University, No. 8 Gongren Tiyuchang S Rd, Chaoyang District, Beijing 100020, China; e-mail: cyh-birm@263.net


Financial/nonfinancial disclosures: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;138(6):1520-1521. doi:10.1378/chest.10-1916
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To the Editor:

We appreciate Dr Pena’s comments on our article in CHEST (February 2010).1 Indeed, bleeding complication is one of the main concerns that limit the use of thrombolytic therapy for pulmonary thromboembolism (PTE).2 We appreciate Dr Pena’s calculations using attributable risk percentage (AR%) (the percentage of bleeding complications that could be prevented among patients receiving a regular dose of recombinant tissue-type plasminogen activator [rt-PA] if they received a low dose rt-PA) and population attributable risk percentage (the percentage of bleeding complications in the population with PTE given thrombolytics that is due to receiving the regular dose of rt-PA and could be eliminated by using a lower dose of rt-PA, as described in Dr Pena’s letter), which provide a better and clearer illustration for the benefit of 50 mg rt-PA in reducing bleeding complications. Without accurate data of the bleeding complications in PTE thrombolytic therapy in China, we are currently unable to provide AR% for the Chinese population.

Inspired by Dr Pena’s calculation, we performed additional analyses of the relative risk (RR) (I50mg/I100mg, the ratio of the bleeding incidences of the 50-mg rt-PA and 100-mg rt-PA groups), the absolute risk reduction (ARR) (I100mg − I50mg, the difference between the bleeding incidences of the 100-mg rt-PA and 50-mg rt-PA groups), and the number of patients needed to treated (NNT) (the number of patients needing to be treated with 50 mg rt-PA to reduce one bleeding incidence,3 which is the reciprocal of the absolute risk difference, or 1/ARR(1/[I100mg − I50mg])(Table 1).

Table Graphic Jump Location
Table 1 —Assessment of the Effect of 50 mg vs 100 mg Recombinant Tissue-Type Plasminogen Activator Treatment on Bleeding Complications

AR% = attributable risk percentage; ARR = absolute risk reduction; I = incidence; NNT = number needed to treat; RR = relative risk; rt-PA = recombinant tissue-type plasminogen activator.

In our study, the overall AR% is 47% and NNT is seven, indicating that seven patients need to be treated with 50 mg rt-PA to prevent one patient from bleeding complications. Importantly, the degree of benefits differs among patients with different body weights. AR% is relatively lower (26%) and NNT is higher (20) in patients with body weight ≥ 75 kg, AR% is increased (33%) and NNT is decreased (eight) in patients with body weight of 65 to 74 kg, and the AR% is highest (63%) and NNT is lowest (four) in patients with body weight < 65 kg. The similar trend is also observed in patients with different BMIs: the AR% is largest and NNT is smallest in patients with the lowest BMI. These data suggest that patients with PTE with lower body weight or BMI will benefit more with 50 mg rt-PA treatment than patients with higher body weight or BMI.

Finally, we thank Dr Pena again for his evaluation of our study. We look forward to more studies that validate our data in terms of therapeutic efficacy and bleeding complication reduction.

Wang C, Zhai Z, Yang Y, et al; for the China Venous Thromboembolism (VTE) Study Group for the China Venous Thromboembolism (VTE) Study Group Efficacy and safety of low dose recombinant tissue-type plasminogen activator for the treatment of acute pulmonary thromboembolism: a randomized, multicenter, controlled trial. Chest. 2010;1372:254-262. [CrossRef] [PubMed]
 
Lankeit M, Konstantinides S. Thrombolysis for pulmonary embolism: past, present and future. Thromb Haemost. 2010;1035:877-883. [CrossRef] [PubMed]
 
Altman DG. Confidence intervals for the number needed to treat. BMJ. 1998;3177168:1309-1312. [CrossRef] [PubMed]
 

Figures

Tables

Table Graphic Jump Location
Table 1 —Assessment of the Effect of 50 mg vs 100 mg Recombinant Tissue-Type Plasminogen Activator Treatment on Bleeding Complications

AR% = attributable risk percentage; ARR = absolute risk reduction; I = incidence; NNT = number needed to treat; RR = relative risk; rt-PA = recombinant tissue-type plasminogen activator.

References

Wang C, Zhai Z, Yang Y, et al; for the China Venous Thromboembolism (VTE) Study Group for the China Venous Thromboembolism (VTE) Study Group Efficacy and safety of low dose recombinant tissue-type plasminogen activator for the treatment of acute pulmonary thromboembolism: a randomized, multicenter, controlled trial. Chest. 2010;1372:254-262. [CrossRef] [PubMed]
 
Lankeit M, Konstantinides S. Thrombolysis for pulmonary embolism: past, present and future. Thromb Haemost. 2010;1035:877-883. [CrossRef] [PubMed]
 
Altman DG. Confidence intervals for the number needed to treat. BMJ. 1998;3177168:1309-1312. [CrossRef] [PubMed]
 
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