Initial Energy for Cardioversion of Atrial Fibrillation
Abstract & Commentary
Synopsis: Patients with persistent atrial fibrillation an initial 360J shock for elective cardioversion is safe, much more effective than lower energy levels, and results in less cumulative energy delivery to achieve sinus rhythm.
Source: Joglar JA, et al. Am J Cardiol 2000;86: 348-350.
Despite its widespread use, the initial energy setting for direct current cardioversion of atrial fibrillation is controversial. Thus, Joglar and associates studied 64 patients who had been in atrial fibrillation for more than 48 hours and were referred for elective cardioversion. Initial energy settings were randomized between 100, 200, and 360J and the electrodes were placed in an anteroposterior orientation. If the first shock was not successful, the next level was tried or 360J with pressure to the anterior pad or 360J with an anterior-apex electrode orientation. The limit was five shocks. Immediately after cardioversion and the following day, troponin I measurements were made in 15 patients in whom the 360J level was reached. The success rate for the initial shocks were: 100J, 14%; 200J, 39%; 360J, 95% (P < .001). The overall conversion rate was 94%. Of the 13 patients in whom the 360J initial shock was unsuccessful, six were successful with chest pressure and another three with switch to an apical pad. Because of multiple shocks in some patients, the total energy delivered was : 615J for the 100J group; 620J for the 200J group; and 414J for the 360J group. None of the 15 high-energy shock patients had troponin I levels greater than 0.4 ng/mL and there were no serious complications observed. Joglar and colleagues concluded that in patients with persistent atrial fibrillation an initial 360J shock for elective cardioversion is safe, much more effective than lower energy levels, and results in less cumulative energy delivery to achieve sinus rhythm.
Comment by Michael H. Crawford, MD
In the era of a more aggressive approach to atrial fibrillation, elective direct-current cardioversion is being performed more often. The American Heart Association Advanced Life Support document suggests an initial energy level of 100J. My own experience suggests that 200J is the minimally effective dose, so I was not surprised at the results of this study. This study is robust for several reasons. It is a randomized trial of different starting levels. Previous step-up trials, where all patients start at lower energy shocks first, favor the success rate of lower energy shocks because of chance, since the patients get more low-energy shocks. Such studies have suggested that 200J is a good starting energy. Also, they studied only patients in atrial fibrillation for more than 48 hours, which eliminates those that are more likely to spontaneously convert. Such patients probably convert with lower energies.
It is interesting that the editor of the American Journal of Cardiology must have thought this was an important paper since two editorials accompany it. Neither refutes the findings and both cautiously endorse the approach. The one caveat mentioned is that current external defibrillators use a monophasic damped sinusoidal waveform, whereas internal defibrillators use a biphasic waveform that is believed to be superior. Biphasic external defibrillators are now before the FDA for approval and may decrease the initial energy needs for atrial fibrillation conversion.
Another important feature of this study is that no myocardial injury was detected by troponin I in the high- dose shock group. Previous studies have suggested that troponin elevations will be occasionally detected with cumulative shocks greater than 600J. This supports the 360J start, since in this study it reduced total J delivered to an average of 400J. Another advantage of the 360J start is it allows for alternate strategies that in this study increased the success rate from 80% to 94%. One strategy was hand pressure on the sternal pad. This seems to fly in the face of the "clear!" concept, but is apparently safe for the operator since a colleague of mine routinely does this. I thought he was just trying to impress the medical students, so I was surprised to learn that this is an accepted strategy for successful cardioversion. The second strategy used was moving the pads to a sternum-apex position. I have observed that when the technician or residents place the electrodes, they often line them up in a way more conducive to ventricular defibrillation. I try to line them up so that the energy goes through the atria. Finally, only about one-third of the patients were on anti-arrhythmic drugs before cardioversion. This is consistent with clinical practice and suggests that drugs do not play a big role in conversion, but are probably more important for maintenance of sinus rhythm. In conclusion, my new approach is 360J (in a normal-sized person) and leaning on the sternal pad for initial cardioversion of chronic atrial fibrillation.
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