I was taught that...

“I was taught that...”

Is a common phrase in medicine, and some other disciplines, which seems to suggest that the following statement is handed down with the wisdom of the years - a solid unchanging fact.

Yesterday, a friend told me that

“I was taught that coronary artery bypass grafting has no effect on mortality, but is only useful for pain relief.”

This sounded unlikely to me, but he's an anaesthetist with an interest in chronic pain management, so what do I know?

10 seconds on Google found what seemed to be an excellent counter example - a propensity matched study of more than 100,000 unselected patients who had coronary revascularisation on Medicare in the USA (full article at Annals of Internal Medicine) . At one year mortality was superior in the angioplasty group, whereas at 5 years it was superior in the CABG group - exactly as I'd expect. Admittedly this wasn't randomised, so there is potential here for confounding by indication.

30 seconds with Medline found a paper by Rezende et al (Ten-year outcomes of patients randomized to surgery, angioplasty, or medical treatment for stable multivessel coronary disease: Effect of age in the Medicine, Angioplasty, or Surgery Study II trial The Journal of Thoracic and Cardiovascular Surgery, Volume 146, Issue 5, pp1105-1112) which shows angioplasty as superior to CABG to no intervention - and this one is randomised.

The effect demonstrated and the number of patients involved seems to lead to two possible conclusions, either

  1. If CABG has no survival advantage over no intervention, then in the long term angioplasty has worse survival than no intervention.
  2. CABG shows a survival advantage over no intervention at 5 years.

Option 1 - that angioplasty is inferior to no intervention at 5 years (especially when it's superior to CABG at 1 year) - seems to be utterly implausible.

Therefore I have to conclude that what my friend “had been taught” was wrong.

And more generally, that 'I was taught...' is mearly an appeal to an undefined authority, and whatever follows should definitely not be accepted as truth uncritically.