Low-Energy Cardioversion After Open-Heart Surgery
Abstract & Commentary
Synopsis: Temporary epicardial atrial defibrillation electrodes placed at the time of surgery can facilitate management of postoperative atrial arrhythmias.
Source: Liebold A, et al. Circulation 1998;98:883-886.
Atrial fibrillation continues to be a problem after open-heart surgery. Thus, Liebold and associates tested the use of temporary epicardial wire electrodes in patients undergoing open-heart surgery. One hundred consecutive patients who were in sinus rhythm preoperatively and were scheduled for cardiac surgery with cardiopulmonary bypass were enrolled in the study. Eighty-nine patients underwent coronary artery bypass grafting alone or in combination with aortic valve replacement. Eight patients underwent isolated valve replacement, and three patients underwent various other procedures. With the patient on cardiopulmonary bypass, ring electrodes were sutured to the free right atrial wall and on the left atrial epicardium in the space between the AV groove and the upper and lower pulmonary veins. A temporary epicardial ventricular electrode was placed on the anterior right wall. The electrodes were connected to polyurethane-coated wires that were tunneled through the skin and used for temporary pacing. Once the patients arrived in the intensive care unit, pacing threshold and impedance as well as P- and R-wave amplitudes were measured with a standard pacing system analyzer. Biatrial monophasic and biphasic defibrillating shocks of 0.3 joules were delivered, and shock impedance was measured. After surgery, patients were continuously monitored for the development of atrial fibrillation. When atrial fibrillation was detected, the patient was connected to a standard external defibrillator with a special interface module that damped the defibrillator’s output to supply R-wave synchronous monophasic shocks with energies of 0.6-10.8 joules. The first shock delivered had an energy of 2 joules, and a step-up defibrillation protocol was used until sinus rhythm was restored. Sedatives or analgesics were given only if the patient requested them. The epicardial leads were left in place until just prior to hospital discharge. At that time, they were retracted transcutaneously.
It took 3.9 ± 7 minutes to place the epicardial defibrillation electrodes in the operating room. Early pacing thresholds were 2.1 ± 2 V in the right atrium and 1.9 ± 1.7 V in the left atrium. Right and left P-wave amplitudes were 2.3 ± 1.4 and 2.5 ± 1.6 mV, respectively. Monophasic test shocks revealed a mean lead impedance of 95 ± 12 ohms.
Twenty-three of 100 patients developed atrial fibrillation during their postoperative course—a mean of 2.1 ± 1.3 days after postop. Twenty of these patients were treated with internal atrial defibrillation, with 16 (80%) being converted successfully to sinus rhythm with a mean shock energy of 5.2 ± 3 joules. Eight patients developed early recurrence of atrial fibrillation. Four of these patients converted with medications, and four were treated with repeat atrial defibrillation. Five patients in the entire series had more than two episodes of atrial fibrillation. A total of 35 episodes of spontaneous atrial fibrillation were treated by internal atrial defibrillation, with an overall success rate of 31 of 35. Only six of the 20 patients required sedation or anesthesia for atrial defibrillation. General anesthesia was never required in the study. There were no complications associated with removal of the epicardial wire 5.7 ± 1.9 days postoperatively. Anticoagulation was not withheld in patients who had valve surgery.
Liebold et al conclude that temporary epicardial atrial defibrillation electrodes placed at the time of surgery can facilitate management of postoperative atrial arrhythmias. They argue that the rapid use of low energy defibrillation effectively and safely restores sinus rhythm and may be superior to approaches that use pharmacologic rate control and antiarrhythmic drugs for suppression as the primary approaches to therapy.
Comment by John P. DiMarco, MD, PhD
Atrial fibrillation is one of the most common complications encountered after cardiac surgery. In various series, it has been reported to occur in 20% to 50% of patients. Although atrial arrhythmias are not usually immediately life-threatening, they frequently prolong hospital stay and increase hospital costs. Prophylactic trials using amiodarone, several other antiarrhythmic drugs, and beta adrenergic blockers have been shown to decrease the frequency of post-operative atrial fibrillation, but it still remains a common clinical problem.
In the last several years, there has been a tremendous interest in the use of internal atrial defibrillation. First, internal atrial defibrillation was found to be effective for converting episodes in patients with atrial fibrillation that had been resistant to attempts at transthoracic cardioversion. Subsequently, an implantable atrial defibrillator was developed, and it is now undergoing clinical trials for the management of patients with recurrent arrhythmias. This use of temporary epicardial atrial pacing and defibrillation electrodes after cardiac surgery is still another application of this concept.
The use of temporary atrial and ventricular pacing wires has long been standard after cardiac surgery. The atrial electrograms they permitted could assist in the diagnosis of various arrhythmias, and rapid atrial pacing could be used to terminate episodes of atrial flutter. However, atrial fibrillation still usually required pharmacologic management. In this paper, Liebold et al demonstrate that epicardial electrodes with a special circular design can be safely attached to the left and right atria and used for defibrillation. This permits rapid and safe termination of each episode of atrial fibrillation and prevents the deterioration associated with the rapid rates seen during the episodes. This may prevent the electrical remodeling that occurs whenever a patient stays in atrial fibrillation and may greatly facilitate management.
Liebold et al did not use anesthesia and only rarely used sedation for their patients. It has been shown that even low-energy atrial defibrillation shocks are uncomfortable for the patient. However, many of these patients are probably already receiving analgesics, and most authors report that a single shock can be tolerated by most patients. It is only when multiple shocks are required that patients usually request sedation or analgesia.
Further experience with the use of these atrial defibrillation electrodes is required before they can be routinely recommended. However, this paper presents promising data, and it may be that these electrodes and the modules to adapt standard defibrillators will be part of every postoperative unit’s strategy.