We are told that a study of aspirin's ability to prevent heart attacks in humans yielded positive results and so researchers immediately submitted the results to a medical journal that published the results six weeks later. The conclusion is that had the results been published sooner, many of the heart attacks that occurred during the delay could have been prevented.
Answer choice (D) does nothing to the argument. Regardless of it being the official policy of the medical journal to publish articles only after an extensive review or not, that doesn't have an effect on whether publishing the results sooner would have prevented many of the heart attacks that occurred during the delay.
Answer choice (E) on the other hand gives us a reason as to why the conclusion is not necessarily true. If one's risk of suffering a heart attack drops only after they have been taking aspirin for two years, then those who died during the delay, which was a period of six weeks, would not have benefited, i.e. would not have been saved, from taking the aspirin for only six weeks.
Thus, answer choice (E) undermines the conclusion in the argument.
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