The advent of cardioversion was not a human drama. In 1775 the French physician Abilgard used a Leyden jar to capture an electrical charge, then applied the charge to a chicken. The bird promptly fell dead. On a hunch, and the recommendation of folklore, Abilgard then applied a second charge to the carcass. It is said that the chicken jerked, blinked, and clucked off into the woods. No follow-up was obtained.
Abilgard was in contact with Benjamin Franklin who, in 1752, had taken his own approach to electricity. In an act of courageous inquiry, and breathtaking stupidity, Franklin ran through a Philadelphia rainfall while flying a kite. The episode ended expectedly: he was knocked senseless. (Admirers of Franklin hope that the tale is apocryphal.)
From these and other experiments medicine culled electrical cardioversion, a technique that has reversed countless ventricular arrhythmias. But the technique has also been used prolifically for atrial fibrillation (AF). In the 1950’s and 1960’s cardioversion of AF gained momentum and the medical literature was soon peppered with case series’ and observational reports. The mid-century consensus was that a 1-5% peri-procedural risk of embolism (an estimate from the small, early studies of cardioversion for chronic AF) compared favorably with the 30% long term risk of thromboembolism associated with remaining in AF. It was assumed that this risk was reversed by conversion to sinus rhythm.
The logic was reasonable, but the literature was not. After all, the plural of ‘anecdote’ is not ‘data,’ and early reports were indeed well-dressed anecdotes. The patients were also a highly selected group, and no controlled trials have been performed since these original reports. Remarkably, this ragged collection of case reports and series’ continues to be the evidence base that drives the American Heart Association’s recommendations. Despite this, the recommendations for cardioversion of AF are commonly invoked, rigidly followed, and can be summarized as follows: anticoagulate or image.
There are many pieces missing in this one-size-fits-all approach. Most conspicuously, the 30% vs. 1-5% comparison is misleading. We now know that diligent maintenance of sinus rhythm does not reliably lower the rate of thromboembolism (or death) for those in chronic AF. This is unfortunate, for if conversion to sinus rhythm doesn’t reduce events then the risks of cardioversion are simply an added short-term burden without long-term benefit. But this stumper is for cardiologists who deal with chronic AF, not emergency physicians.
Emergency physicians are in an enviable position, for the original reports of cardioversion risk that guide cardiologists who treat chronic and persistent AF are clearly irrelevant to acute, new AF. Cardioversions from the early case series’ were performed exclusively on patients with chronic and longstanding AF, and indeed most had chronic conditions such as rheumatic heart disease, valvular disease, and cardiomyopathy. These are structural abnormalities that made conversion difficult, and each is independently associated with increased thromboembolism. Moreover, many of the ‘embolism’ cases from early reports were of questionable etiology, and recovery was usually complete.
The older medical literature on cardioversion for AF is therefore not applicable to acute, new onset AF. This history has yet to be written, and the case series of Dr. Stiell and colleagues is a welcome start. While limited, it is already far superior to the evidence that drives the AHA guidelines. Therefore until high quality trials are published we will continue to use our most familiar tool: an educated guess based on the best available evidence. In the meantime, we should be careful not to commit the error of disproportionate confidence in thin, often irrelevant data. It is an error our cardiologic colleagues at the AHA have casually perfected. We might instead heed the words of a unique American who, in describing his own kite flying studies famously said, “If there is no other use discovered for electricity, this, however, is something considerable: that it may help make a vain man humble.”
David H. Newman, MD is the author of Hippocrates’ Shadow: Secrets from the House of Medicine (Scribner)
Don't miss Dr. Kevin Klauer's article Just Shock 'em