Atrial Fibrillation

afindexDr Thomas Tape wrote an article “Coherence and correspondence in medicine” that appeared in the March 2009 edition of Judgment and Decision Making.  As you might expect, Dr Tape is applying some of the ideas of Kenneth Hammond to medicine.  Tape notes that the distinction between coherence (making logical sense) and correspondence (being empirically correct) seldom appears in the medical literature.

Tape suggests that the field of medicine began with coherence approaches and has only recently adopted correspondence approaches at all. The original rationale for bloodletting was based on the idea that disease comes from an imbalance of humors.  This coherent argument was around for hundreds of years before being dispelled.  It seems surprising that patient outcome was not the indicator of choice, but even today with medical progress and sophisticated statistics, it is not so easy to tell what works.

Tape provides the example of atrial fibrillation as the current controversy between coherence and correspondence in medicine.  Atrial fibrillation was first treated nearly one hundred years ago with rest and digitalis which slowed the heart, but did not correct the underlying rhythm disturbance. This was a correspondence strategy. Later by means of electric shock and/or anti-arrhythmia drugs, a new approach sought rhythm control.

Rhythm control is a coherent strategy  because a slow, regular rhythm moves blood more efficiently by allowing more filling time and avoids clot formation caused by dislodged clots. The rate control proponents say that rate control is good enough and avoids side effects of the anti-arrhythmia drugs.

Numerous studies have tried to determine which approach is best. At the time of Tape’s paper, rate control seemed to have the clear edge. In one previous meta-analysis, rate and rhythm control strategies were not significantly different in terms of mortality but a trend towards rate control was observed in patient survival (odds ratio 0.87 [95% CI: 0.74—1.02]; P = 0.09) Statistically significant results favoring rate control with regard to a mortality-stroke composite were  reported in another meta-analysis (odds ratio 0.84 [95% CI: 0.73—0.98]; P = 0.02).  A meta-analysis published in 2012, found an all cause mortality odds ratio of .95 (95% CI: 0.86-1.05).  The 2010 Canadian Cardiovascular Society Guidelines suggest that certain patient factors favor rate control over rhythm control (Table 3 below)

All in all it appears that rate control maintains a slight edge over rhythm control over the 4 years after Tape’s paper. Tape mentions the editorial published in the New England Journal of Medicine in 2002  that accompanied some trial results.  In essence, Tape notes, the editorial questions the newly published correspondence data, and using coherence arguments suggests that rhythm control strategy may be preferable.  Another editorial in the New England Journal of Medicine in 2008 accompanying more results stated:  “Nature has equipped the human heart with a complex electrical system for the purpose of coordinated propulsion of blood under a variety of physiologic conditions….Cardiac electrophysiologists …. are frustrated by the conundrum that atrial fibrillation  is associated with increased morbidity and mortality, yet attempts to prove that a strategy to maintain nature’s rhythm has a favorable effect on patients have been met with one setback after another.”

Tape reminds us that coherence based research to control blood pressure resulted in the drug Viagra only after the correspondence based clinical trials showed a marketable side effect and further coherence study explained why.

Tape explains that the move toward evidence based medicine’s correspondence approach using clinical trials does not signal the coherence approach is unscientific. Tape suggests that both means of evaluating truth are necessary. Teaching physicians about the value of each of the two approaches could reduce controversy and improve research.  The historic tendency to discount the correspondence data in favor of prevailing coherent theory should be replaced by a search guided by both philosophical traditions.

I have been concerned that evidence based medicine  and its correspondence basis would lead to rules that soon get out of date. Although such rules have been better than experts over the short run, I have wondered about the long run.  Tape gives me reassurance that this can be overcome.

 

 

 

 

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