Recurrent stroke in decline
MedWire News: The rate of recurrent stroke has "substantially" declined over the past 50 years, researchers report.
The leading causes of the decline are improved control of blood pressure and increased use of antiplatelet agents, says the team, led by Jeffrey Saver (University of California, Los Angeles, USA).
The findings have implications for clinical trial design. "The problem of needing very large sample sizes to adequately power trials is greater now than ever," Saver et al write in the journal Circulation.
They predict that, in the 2010s, the control arm of a randomized controlled trial will require nearly 16,000 patients to demonstrate a 20% difference in efficacy between an experimental drug and its control - up from less than 5000 in the 1960s.
In an accompanying editorial, Ralph Sacco (University of Miami, Florida, USA) and colleagues pointed out that "as baseline risk declines, a 20% relative risk reduction yields proportionally diminishing absolute risk reductions and proportionately increasing numbers needed to treat."
They said: "Trialists need to consider whether powering studies against smaller and smaller absolute benefits is appropriate."
The research included data on 66,157 patients from the control arms of 59 randomized controlled trials of secondary stroke prevention conducted between 1960 and 2009.
The average annual rate of recurrent stroke was 8.71% for trials initiated in the 1960s, falling to 6.10% in the 1970s, 5.41% in the 1980s, and 4.04% and 4.98% in the 1990s and 2000s, respectively.
Likewise, the annual rate of fatal stroke fell from 2.87% in the 1960s to 0.36% in the 2000s, and that of major vascular events fell from 10.91% to 6.29%, respectively.
Increased antithrombotic use and reduced systolic and diastolic blood pressure were independently associated with the decline in recurrent stroke rates, whereas smoking status, transient ischemic attack as a qualifying event for trial enrollment, and the maximum allowed delay between stroke onset and enrollment were not.
Sacco et al said that the findings "provide encouragement" that established secondary prevention methods are effective.
However, they warned against complacency. "An invigorated focus on improving cardiovascular health across the lifespan should not only reduce the risk of a first stroke, but also the risk of a recurrence among our growing number of stroke survivors."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Eleanor McDermid