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Ann Thorac Surg 2003;75:1185-1188
© 2003 The Society of Thoracic Surgeons
a Department for Cardiac Surgery, University Hospital Luebeck, Luebeck, Germany
Accepted for publication October 29, 2002.
* Address reprint requests to Prof Sievers, Klinik fuer Herzchirurgie, Universitaetsklinikum Luebeck, Ratzeburger Allee 160, 23538 Luebeck, Germany
e-mail: sievers{at}medinf.mu-luebeck.de
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Abstract |
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METHODS: Sixteen patients (mean ± SD, 66.4 ± 5.4 years) were randomized to LEC and 32 patients (66.3 ± 5.0 years) to standarized medical treatment in the event of postoperative AF. Age, comorbidity, and surgical variables did not differ significantly between the groups.
RESULTS: After cardiac surgery, AF occurred in 6 patients (38%) assigned to LEC and in 11 patients assigned to medical treatment (34%; p = NS). Low-energy cardioversion restored sinus rhythm in all but 1 patient, and 1 patient in the LEC group had early recurrence of AF. All other patients in the LEC group had prompt and stable restoration of sinus rhythm. Medical treatment was associated with the restoration of sinus rhythm in all patients. Although the total time in AF was decreased significantly by LEC (median 5 minutes versus 22 hours; p = 0.037), the length of postoperative hospitalization was not (5.1 ± 1.4 days for the LEC group compared with 5.3 ± 1.6 days for controls).
CONCLUSIONS: Low-energy cardioversion significantly decreased the amount of time cardiac surgery patients spent in AF after the operation. Larger studies are needed to determine whether this new treatment modality has the ability to decrease morbidity associated with postoperative AF and is cost-effective.
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Introduction |
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Many placebo-controlled trials of pharmacologic agents have been published that have reported significant reductions in the incidence of postoperative AF [4–6]. Biatrial overdrive pacing appears to be another means of reducing the incidence of postoperative AF [7–9]. However, no strategy has completely suppressed the occurrence of postoperative AF, and all means of AF prophylaxis put patients at risk for side effects.
The transthoracic, R-wave-triggered application of a direct current shock appears to most reliably result in prompt restoration of sinus rhythm, but because of the high recurrence rate of AF and because conventional electrical cardioversion requires additional anesthesia, such treatment is usually reserved for patients with hemodynamic compromise [10–12]. Liebold and associates [13], however, reported on the feasibility of low-energy cardioversion (LEC) by means of biatrial epicardial wire electrodes implanted during surgery. We prospectively compared this new treatment modality with standard medical treatment (targeted primarily at ventricular rate control) to determine whether LEC offers benefit in terms of the time spent in AF and the duration of hospitalization.
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Material and methods |
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Surgery was performed through a median sternotomy using cardiopulmonary bypass with moderate systemic hypothermia. Coronary anastomoses were made during cardioplegic arrest achieved by cold-blood cardioplegia. Myocardial revascularization was complete in all patients; both groups received a median of one arterial and two venous bypass grafts.
The biatrial epicardial wire electrodes were stainless steel and polyurethane coated, except for the distal 10 cm (defibrillation electrode). Approximately 5 mm before the beginning of the defibrillation electrode, the wire contained an additional small electrode allowing bipolar atrial sensing and pacing (pacing electrode). The wire electrodes were placed epicardially to both atria as described previously [13]; care was taken to encircle as much muscle of both atria with the defibrillation electrode as possible. In the control group, an epicardial pacing electrode (Medtronic 6492; Medtronic, Minneapolis, MN) was sutured to the lateral wall of the right atrium. In all patients, an epicardial pacing electrode (Medtronic 6500) was sutured to the anterior wall of the right ventricle. All electrodes were brought out through the skin and secured with a suture.
After surgery, all patients were continuously monitored using a three-channel electrocardiogram (Sirecust 1281 and SC 6000; Siemens, Danvers, MA) for the first 72 hours. Thereafter, the patients were checked for the presence of arrhythmias by pulse palpation every 4 hours, and continuous monitoring restarted in the event of AF. Oral ß-blocking therapy was restarted on the first postoperative morning. In the event of AF, all patients received intravenous heparin and bed rest was prescribed. In the control group, ventricular rate control was the target. Medical treatment was not strictly standarized, but sotalol was recommended as the primary drug to be used. In the LEC group, patients were immediately connected to an external defibrillator (Life Pak 10; PhysioControl, Redmond, WA) through a defibrillation interface module (TADpole 2250, InControl), which reduces the energy of the defibrillator to about 3%. R-wave synchronous monophasic shocks were then delivered starting with an effective dose of 3 J; if AF was not converted to sinus rhythm at this starting dose, the dose was increased in 3-J increments up to a maximal dose of 9 J. The treatment was termed primarily successful if AF was converted to sinus rhythm. Early recurrent AF was defined as the recurrence of AF within the first minute after primarily successful LEC [13]. With any recurrence of AF, a second attempt of LEC was made; if conversion to sinus rhythm was unsuccessful, pharmacologic rate control was the primary target. All patients received analgesic therapy with piritramide (3.8 mg intravenously) before LEC; on request, sedatives (midazolam, 2 to 5 mg intravenously) were given.
In both groups, the total time spent in AF (primary event plus recurrence, if appropriate) was calculated. Before hospital discharge, all temporary electrodes were removed by transcutaneous retraction and checked for completeness.
Data are presented as absolute numbers and percentages or mean ± standard deviation, except where otherwise stated. Continuous data were compared using the Mann-Whitney U-test, dichotomous variables were compared using Fisher’s exact test. All analyses were completed with SPSS for Windows 8.0 (SPSS, Chicago, IL).
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Results |
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In the control group, medical treatment (sotalol, n = 7; digoxin, n = 3; amiodarone, n = 1) was associated with the restoration of sinus rhythm in all patients. Two patients had temporary recurrences of AF (18%, p = NS as compared with LEC). The total amount of time spent in AF was decreased significantly by the use of LEC (Fig 1; median 5 minutes [range 4 minutes to 28 hours] versus 22 hours [range 4 to 56 hours; p = 0.034]). However, the length of postoperative hospitalization was not significantly different (5.1 ± 1.4 days versus 5.3 ± 1.6 days; p = NS). No complications related to the extraction of the wires were observed. All patients were discharged in sinus rhythm.
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Comment |
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The reported incidence of postoperative AF varies widely, but most recent large studies report a frequency at around 30% [1, 3, 14]. Therefore, AF can be considered to be the most common complication after cardiac surgery. Although the condition generally carries a favorable prognosis, AF after cardiac surgery can cause considerable morbidity, among which cerebral infarctions are most worrisome [1, 2]. Furthermore, postoperative AF increases resource utilization, length of stay, and, ultimately, costs [1, 3].
Many risk factors for the development of postoperative AF have been described (such as increasing age, increasing P-wave duration, increased left atrial size, valvular surgery, increasing aortic cross-clamp duration, electrolyte abnormalities, autonomic imbalance with elevated adrenergic tone, pericardial inflammation), but the pathogenesis of postoperative AF is not well understood (for reviews see [10–12]) and is most likely multifactorial. Whether any prophylactic strategy can completely eliminate its occurrence, therefore, is doubtful.
The primary goal of treatment of postoperative AF is ventricular rate control and prevention of complications, especially embolism [12]. Theoretically, decreasing the time spent in AF decreases the time during which thrombus formation can occur as well as the likelihood of postcardioversion atrial stunning causing late embolism [15, 16]. Therefore, early restoration of sinus rhythm is potentially advantageous. Electrical cardioversion appears to result in prompt cardioversion, but because of the high energy applied, the procedure requires anesthesia. Thus, electrical cardioversion is usually not the initial approach to postoperative AF [10–12].
Temporary epicardial wire electrodes have been used safely and effectively for decades for pacing and diagnostic purposes after cardiac surgery. The technique of LEC using epicardial wire electrodes was developed in animals [17, 18] and has been tested safely in patients since then. Liebold and coworkers [13] and Kleine and colleagues [19] reported high primary success rates, but high recurrence rates, especially early after LEC, occurred in one study [13]. Liebold and coworkers [13] provided no details on the total time spent in AF, whereas that time appeared to be long in the other study (a waiting period of 337 minutes before the first shock was delivered to reduce the risk of early recurrence [19]). Furthermore, whether LEC is more efficient than standard care has not yet been determined.
Our data indicate that LEC is more effective than standard medical treatment in reducing the time spent in AF. However, as we did not observe any major complications in any of the patients, we were unable to detect any clinical benefit from the reduced time spent in AF. In our department, as in many German cardiac surgery units, almost all patients are discharged directly into a rehabilitation facility rather than home. Therefore, subtle differences in the degree of early postoperative mobility may be missed.
Low-energy cardioversion did not result in the termination of AF in all patients, whereas medical treatment was associated with eventual restoration of sinus rhythm without exception. Sotalol was recommended and used most frequently for AF in the control group because the medication has no pharmacodynamic drug–drug interactions, is associated with ready achievement of ventricular rate control, and has a known ability to stabilize sinus rhythm after an episode of AF [20, 21].
The observed rate of recurrence of AF after LEC was comparable to that reported by Kleine and coworkers [19] and was no different from that observed in the control group, a result that may be related to the consequent continuation of ß-blocking therapy after surgery [22]. The energy needed for cardioversion as well as the safety and ease of retraction are comparable to data reported earlier [13, 19].
The main limitation of our study is its small size. The inclusion criteria for the study were chosen in such a way that a homogenous patient sample with moderate risk for the development of postoperative AF was to be expected [3, 23], but the generalizability of our results is therefore limited. Other limitations of our study are the nonstandardized medical treatment in the control group (although treatment was uniform in most patients) and the absence of continuous electrocardiographic monitoring after the first 3 postoperative days. However, although short episodes of asymptomatic AF may have been missed, this possibility is unlikely for sustained or symptomatic episodes, because patients were checked for the presence of arrhythmias by pulse palpation every 4 hours and asked to report any palpitations.
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This article has been cited by other articles:
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  C. A. Palin, R. Kailasam, and C. W. Hogue Jr Atrial Fibrillation After Cardiac Surgery: Pathophysiology and Treatment Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2004; 8(3): 175 - 183. [Abstract] [PDF]
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