The Butterfly Effect Part II

... This is Chapter II in a multi-chapter series. If you happen to be coming to this tale in the middle, please begin here, with Part I.


In order to frame this story, we must play a game called walk in another man's shoes. For understanding this tragedy of the commons tale requires we look at the story from several different perspectives, or viewpoints, simultaneously.

The first perspective I want to share is the one which introduced me to our tale- my own. And to examine this tale from my perspective, e.g. that of a typical emergency physician, a small understanding of both the statistics of tPA's efficacy for stroke and the history of how we came to understand these statistics is in order. I will try to simplify as much as possible.

In 1995, the year I completed my residency, the state of our knowledge was such that seven studies, including three major studies with names like ECASS, ECASS2 and ATLANTIS, showed no benefit in using tPA for stroke when compared against placebo. However, as we all know, statistics are a rabbit hole with no end and the story of tPA in stroke proved no exception to this rule... Though it did validate another rule of mine which I have come to call Thai's Alice in Wonderland rule of medical advice which goes something like "if something is controversial it is also not important; for if it were important, it would not be controversial". However physicians may differ in opinion, we almost all desire similar outcomes for our patients.

Remember that in order to observe a small effect in a large group of people, you need to study a very large number of people. Studying a small number of people can easily miss a small effect. The 7 prior studies were performed on a reasonable number of patients, but the argument was always lingering in the background that the studies to date had simply not been "powered" enough (which is medical speak for enrolling enough patients) to see tPA's effect. And so, "powered" with enough power to overcome all prevailing studies, a 1995 study titled NINDS overturned all prevailing wisdom as it showed a benefit to tPA on select stroke patients.

This is where we come to the part of the story where the butterfly flaps its wings. For on the basis of NINDS, in 2000, the FDA approved tPA for use in stroke and things got very interesting.

We come to the end of Chapter II. When you are ready, please progress to Chapter III.