The JAMA authors looked at the strength of evidence multiple ACC/AHA guidelines and found:
Results: Among guidelines with at least 1 revision or update by September 2008, the number of recommendations increased from 1330 to 1973 (+48%) from the first to the current version, with the largest increase observed in use of class II recommendations. Considering the 16 current guidelines reporting levels of evidence, only 314 recommendations of 2711 total are classified as level of evidence A (median, 11%), whereas 1246 (median, 48%) are level of evidence C. Level of evidence significantly varies across categories of guidelines (disease, intervention, or diagnostic) and across individual guidelines. Recommendations with level of evidence A are mostly concentrated in class I, but only 245 of 1305 class I recommendations have level of evidence A (median, 19%).
Conclusions Recommendations issued in current ACC/AHA clinical practice guidelines are largely developed from lower levels of evidence or expert opinion. The proportion of recommendations for which there is no conclusive evidence is also growing. These findings highlight the need to improve the process of writing guidelines and to expand the evidence base from which clinical practice guidelines are derived.
OK, so there’s a problem with the guidelines, but what is it, exactly? Is it that the evidence available to the guideline writers was insufficient or that the writing process itself was faulty? I believe it was the former. The editorial writers seem to think it was both. They cite conflicts of interest and the bias of experts. These are valid concerns but are the problems more in perception than in fact? The guideline writers could do no better than align their recommendations with the best available evidence. In many cases the best available evidence is “low level.” To bolster their case the editorial writers might have given examples in which guidelines were not in accordance with best evidence or associated with negative consequences.
Do cardiology guidelines have negative consequences? Evidence suggests not. In fact, studies show that adherence to cardiology guidelines is associated with better patient outcomes.          The editorial writers do mention performance measures. But performance measures fail due to misappropriation of evidence, not true adherence to guidelines.