Low-Energy Intracardiac Cardioversion After Failed External Cardioversion of Atr
January 1, 1997 3 minutes read
Low-Energy Intracardiac Cardioversion After Failed External Cardioversion of Atrial Fibrillation
ABSTRACT & COMMENTARY
Synopsis: Intra-atrial cardioversion can be useful in converting patients to sinus rhythm even if they failed to cardiovert with standard transthoracic shocks
Source: Schmitt, et al. J Am Coll Cardiol 1996;28: 994-999.
Schmitt et al evaluated the efficacy of low- energy intra-atrial cardioversion in patients who had failed standard transthoracic cardioversion for atrial fibrillation. The study group was relatively small, including only 25 patients. The mean age was 56 ± 9 years. The body mass index was 27 ± 3 kg/m2. The left atrial diameter was usually enlarged, with the mean diameter being 6.2 ± 0.8 cm. Atrial fibrillation had been present for between one and 26 months, with a mean of 11 ± 9 months. All patients had failed at least one trial of external cardioversion using synchronized direct current shocks of 200, 300, and 360 joules. Patients were eligible for entry into the study if they failed to convert with this three-shock standard protocol.
The protocol for internal cardioversion consisted of placing a custom built 6-French catheter with an active surface area of 2.5 cm positioned in the lower right atrium. The large surface area was achieved by placement of nine parallel stainless steel rings on the distal portion of the catheter. A second catheter of the same configuration was placed in either the coronary sinus or the left pulmonary artery. Atrial defibrillation thresholds were measured using biphasic shocks synchronized to the R wave. The initial shock delivery was a 60 V and the energy was increased in 40 V increments until cardioversion was achieved.
Cardioversion was successful in 22 of the 25 patients. The atrial defibrillation threshold was 6.5 ± 3.0 J. The right atrium to coronary sinus configuration was slightly more effective than the right atrium to pulmonary artery configuration. An additional two patients had sinus rhythm restored for a few seconds but then reverted to atrial fibrillation. These latter two patients were counted as failures. Only one patient could not be converted, even transiently, out of atrial fibrillation.
Long-term follow-up was also performed. Twelve of the 22 patients were still in sinus rhythm after a mean follow-up of 15 ± 12 months. Most of the recurrent episodes of atrial fibrillation occurred in the first three months of follow-up.
The authors conclude that intra-atrial cardioversion offers an opportunity to convert patients to sinus rhythm even if they cannot be cardioverted with standard transthoracic shocks. Since a significant portion of these patients will subsequently stay in sinus rhythm, this procedure may have substantial clinical value.
COMMENTS BY JOHN P. DIMARCO, MD
External transthoracic cardioversion of atrial fibrillation is successful in approximately 85% of the patients in whom it is attempted. If external cardioversion is not successful, there have been, until now, few alternatives for restoring sinus rhythm. Several years ago, Levy et al (Circulation 1992;86:1415-1420) described a procedure in which large high-energy shocks were delivered using a catheter placed in the right atrium as the cathode and a back skin electrode as the anode. More recently, it has been shown that truly internal cardioversions using electrodes placed in the right atrium and either coronary sinus or pulmonary artery with biphasic waveforms allows for conversion of recent onset or induced atrial fibrillation with very low atrial defibrillation thresholds (Alferness C, et al. PACE 1994;17:1043-1047). However, patients with long-standing atrial fibrillation who had failed cardioversion were not usually included in these studies.
The report by Schmitt et al shows that even patients who fail traditional external methods for cardioversion can be restored to sinus rhythm. If sinus rhythm can be restored, it may be possible for the atrium to recover its contractile function and for electrical remodeling to improve the stability of the atrium. This occurred in approximately 50% of the patients in this series. The best strategy for maintaining sinus rhythm during the early high risk period for recurrence however is uncertain. Most of the patients in this series were treated with sotalol at a mean dose of 194 ± 63 mg per day. Despite this, almost 50% of the patients reverted to atrial fibrillation within less than a year. However, all of the patients would have remained in atrial fibrillation if only transthoracic cardioversion had been available.
The technique of lower-energy internal cardioversion should be applicable in most electrophysiology laboratories. This approach gives us another tool for getting patients back into sinus rhythm. It still remains to be shown, however, that the majority of these patients can be effectively maintained long-term in stable rhythm without antiarrhythmic drug toxicity.
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