Ann Thorac Surg 2001;72:694-697
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Predictors of conversion of atrial fibrillation after cardiac operation in the absence of class I or III antiarrhythmic medications
Richard J. Soucier, MDa,
Saema Mirza, MBBSa,
Melecio G. Abordo, MDa,
Ellison Berns, MDa,
Honora C. Dalamagas, RN, MSa,
Anis Hanna, MDa,
David I. Silverman, MDb
a The Hoffman Heart Institute, St. Francis Hospital and Medical Center, Hartford, Connecticut, USA
b Division of Cardiology, University of Connecticut Health Center, Farmington, Connecticut, USA
Accepted for publication May 3, 2001.
Address reprint requests to Dr Soucier, The Hoffman Heart Institute of Connecticut, St. Francis Hospital and Medical Center, 114 Woodland St, Hartford, CT 06105
e-mail: rsoucier{at}stfranciscare.org
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Abstract
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Background. Although risk factors for the development of atrial fibrillation (AF) after cardiac operations have been studied extensively, predictors of conversion to sinus rhythm within 24 hours of onset have not been examined.
Methods. Eleven hundred consecutive adults undergoing cardiovascular operations from July 1997 to June 1998 were screened for new onset AF after operation. Patients with chronic persistent preoperative AF or those who died within 48 hours of the operation were excluded.
Results. Three hundred fifty-three patients developed AF after operation; of these, 163 received therapy only for control of ventricular response, and 131 of the 163 (80%) converted to sinus rhythm within 24 hours. Logistic regression analysis determined that postoperative ß-blocker use before the onset of AF, and the absence of severe LV dysfunction or diabetes, predicted reversion to sinus rhythm. Patients who converted had a shorter hospital stay and were more likely to be discharged in sinus rhythm.
Conclusions. Atrial fibrillation resolves in most patients and it is possible to predict in which patients resolution is most likely, based on clinical data.
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Introduction
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Atrial fibrillation (AF) after cardiac operations is a common, troublesome arrhythmia that occurs in up to one-third of patients after coronary artery bypass grafting (CABG) and in as many as 50% of patients after valvular heart operations [1–4]. Time of presentation of postoperative AF is variable, but this arrhythmia is most frequently observed within the first 3 days postoperatively [5]. Although rarely fatal, AF in this setting is associated with a number of postoperative complications, including congestive heart failure, hypotension, cardiac ischemia, and stroke. Despite these complications, most patients revert rapidly to sinus rhythm without treatment with class I or III antiarrhythmic medications [6], although the patients who develop postoperative AF experience longer and more costly hospital stays [1–3, 7].
Multiple risk factors for the development of AF after cardiac operations have been well documented, and include advanced age, mitral valve disease, left atrial enlargement, male gender, intraaortic balloon counterpulsation, postoperative pneumonia, prolonged intubation, previous history of AF, hypertension, congestive heart failure, or pulmonary disease [2–4, 8]. Although such risk factors have been extensively catalogued, to our knowledge, factors that predict conversion to sinus rhythm in the absence of Vaughn Williams class I or III antiarrhythmic drugs have not yet been examined. Accordingly, we examined a large, consecutive cohort of patients presenting with AF after cardiac operations who were treated with agents to control ventricular response only (either ß blockers, calcium blockers, digoxin, or a combination), to determine what factors, if any, might predict conversion to sinus rhythm within 24 hours of the onset of their arrhythmia.
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Material and methods
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Patients
One thousand one hundred consecutive adult patients (older than 18 years) who underwent either CABG and or valvular heart operation at St. Francis Hospital and Medical Center from July 1997 to June 1998 were included in the analysis. Data were obtained by complete review of each patient’s medical record. Patients were included in this analysis if they developed new onset AF after open heart surgical procedures and their physicians elected to treat them with ß blockers, calcium blockers, or digoxin but not a class I or III antiarrhythmic drug for at least the initial 24 hours of the arrhythmia. Atrial fibrillation was identified by direct inspection of an electrocardiogram (ECG) or rhythm strip. In more than 95% of cases, the onset and duration of AF was determined directly from the telemetry record. Patients were excluded from the study if they had chronic persistent AF before the operation that continued through the perioperative period or if they died within 48 hours postoperatively. Timing and duration of AF were determined from the treating physician’s notes in the remainder of cases. A minimum of 3 hours of continuous AF was required for patient inclusion. Conversion to sinus rhythm after AF was defined as any period of sinus rhythm sufficiently long enough to be documented by telemetry or ECG, and was typically longer than 5 minutes.
Clinical characteristics that we hypothesized may predict increased likelihood of spontaneous conversion were prospectively selected for testing by univariate analysis (Table 1); converters were initially compared with nonconverters using these variables. Logistic regression was then performed using a stepwise regression model that included those variables found to be significant by univariate analysis.
Data analysis
All data are presented as mean ± standard deviation unless otherwise noted. Differences in continuous variables were computed using an unpaired t test. Categorical variables were compared using a 
2 or Fisher’s exact test where appropriate. The p value for statistical significance was predetermined to be less than 0.05. Univariate analysis and logistic regression were performed as described above. Statistical calculations were performed using SPSS software (SPSS Inc, Chicago, IL).
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Results
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Atrial fibrillation was noted in 425 patients (38.6%) after their operations but before discharge (Fig 1). Seventy-two patients meeting at least one of the exclusion criteria were disqualified from the analysis. Of the remaining 353 patients, 190 received a class I or III antiarrhythmic agent within 24 hours of arrhythmia onset at the discretion of the primary cardiologist or cardiovascular surgeon and 163 received therapy for control of ventricular response alone. The latter patients formed the data set for this study. As previously published, the clinical characteristics were similar in the antiarrhythmic and rate control only groups [6]. Of these 163 patients, 96% were white, 2% were African American, and 2% belonged to other ethnic groups. Sixty-nine percent (113 of 163 patients) were men.
Eighty percent of patients (131 of 163) reverted to sinus rhythm within the first 24 hours of onset; 32 patients remained in AF for at least 1 day. The mean age was 70.9 ± 10.7 years and there was no difference in age between patients who did and did not convert. Although men were twice as likely to return to sinus rhythm as women, the difference did not reach significance (p = 0.07). Neither type of heart operation nor history of prior heart operation decreased the likelihood of conversion to sinus rhythm (Table 1). Similarly, there were no differences in the rates of hypertension, myocardial infarction, smoking history, pulmonary, renal, thyroid or cerebral vascular disease between the two groups. The presence or absence of left ventricular hypertrophy or left atrial enlargement (diagnosed by ECG) was also similar between the 2 groups (Table 1).
Patients with a prior history of paroxysmal AF were less likely to revert to sinus rhythm in the absence of class I or III antiarrhythmic medications. Significant differences between spontaneous converters and nonconverters were noted with regard to several other chronic disease states, including diabetes, peripheral vascular disease, and congestive heart failure (Table 2). Patients who had a shorter intraoperative cross-clamp time were also more likely to convert spontaneously. The percentage of patients receiving digoxin, ß-adrenergic receptor antagonists, calcium channel antagonists, or angiotensin-converting enzyme inhibitors preoperatively was similar in both groups, and there was also no difference in conversion rates in patients receiving digoxin or calcium channel antagonists after the development of AF (Table 1). By contrast, ß blockers administered after the onset of AF were given more frequently to spontaneous converters than to nonconverters (Table 1), and patients who received ß-blocker therapy after operation but prior to the development of AF were more likely to revert to sinus rhythm within 24 hours than those who did not (Table 3).
Independent factors that predicted reversion to sinus rhythm by logistic regression included the absence of diabetes, a left ventricular ejection fraction of more than 0.25, and postoperative prophylactic administration of ß-adrenergic receptor antagonists. These three factors combined to correctly discriminate 83% of patients as spontaneous converters or nonconverters. Among converters, 53 (40%) experienced at least one recurrent episode of AF. Thirty (57%) of these recurrences were again treated with rate control agents alone; all of these patients were discharged from the hospital in sinus rhythm. Twenty-three patients with recurrent AF (43%) ultimately received at least one antiarrhythmic medication, and 20 (87%) of those patients were discharged in sinus rhythm.
Among the 32 nonconverters, 15 (47%) eventually received a class I or III antiarrhythmic drug after the initial 24 hours of AF; 11 (73%) of these patients eventually converted to sinus rhythm. The remaining 17 nonconverters were treated with rate control agents alone; 10 of these patients eventually converted to and were ultimately discharged in sinus rhythm.
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Comment
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Our data confirm previous reports that substantial numbers of patients who develop AF after cardiac operation convert spontaneously to sinus rhythm. Furthermore, our data suggest that multiple comorbidities, including previous AF, diabetes, peripheral vascular disease, and heart failure, are significantly associated with a lower likelihood of spontaneous conversion to sinus rhythm, but that only relatively preserved left ventricular function and the absence of diabetes predict the likelihood of spontaneous conversion when all covariates are examined within a logistic regression model. Perhaps most importantly, our data demonstrate that ß-adrenergic receptor antagonists significantly increase the likelihood of conversion, especially when given prophylactically after operation. Other rate-controlling agents (digoxin and calcium channel antagonists) appear to have no effect on the return of sinus rhythm.
Several prior studies have reported that a significant proportion of patients convert to sinus rhythm within 24 hours with control of ventricular response alone [9–11]. Recurrent AF has also been commonly reported, but most recurrences resolve within 24 hours of appearance and an overwhelming majority of patients are discharged from the hospital in sinus rhythm without the use of class I or III antiarrhythmic agents [9]. Multiple antiarrhythmic agents, including quinidine, procainamide, dofetilide, sotalol, propafenone, and oral or intravenous amiodarone have been compared with rate control for both prophylaxis and treatment for postoperative AF [5, 12–20]. Results are mixed, with some trials reporting a modest positive benefit [9, 12], and others revealing no significant difference in the prevention or conversion of AF compared with placebo or ß blockers alone [13–18]. Previously we reported that the administration of antiarrhythmic medications within the first 24 hours after the onset of AF appears to confer no clear advantage over control of ventricular response alone [6]. The current study extends those observations to further risk-stratify patients in terms of likelihood of spontaneous conversion.
These findings suggest that most patients who develop AF after heart operations may be treated for control of ventricular response alone, at least for the first 24 hours after onset of their arrhythmia, especially if they are not diabetic and do not have severe left ventricular dysfunction. Also, our data, when combined with previous studies, strongly suggest that ß-adrenergic receptor antagonists should be the drugs of choice for control of ventricular response, and that prophylactic administration of ß blockers represents a sound strategy for preventing AF and limiting the duration of AF should it occur. Based on these data, one must consider those patients who have diabetes or severe left ventricular dysfunction to be significantly less likely to return to sinus rhythm without administration of antiarrhythmic agents, and therefore these are the patients who may require more aggressive treatment for arrhythmias.
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Acknowledgments
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Supported in part by the National Institutes of Health General Clinical Research Center, grant no. MO1RR06192. Doctor Silverman is the recipient of a grant from the Claude Pepper Center for Older Americans, grant no. 5P60-AG13631-03.
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Abstract
Introduction
