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Ann Thorac Surg 1999;67:182-186
© 1999 The Society of Thoracic Surgeons
a Department of Pharmacy Services, London Health Sciences Centre, London, Ontario, Canada
b Department of Surgery, London Health Sciences Centre, London, Ontario, Canada
c Medicine, London Health Sciences Centre, London, Ontario, Canada
Address reprint requests to Dr Inculet, London Health Sciences Centre, 375 South St, London, Ontario, N6A 4G5, Canada
Presented at the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 2628, 1998.
| Abstract |
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Methods. A randomized, double-blind, placebo controlled trial of propranolol (10 mg every 6 hours) for 5 days was undertaken in patients undergoing major thoracic operations to determine whether arrhythmias requiring treatment could be reduced. Secondary outcomes included overall arrhythmia rate, adverse events, and length of stay. Arrhythmias were assessed by 72-hour Holter monitoring. Patients with a history of heart failure, asthma, advanced heart block, preexisting arrhythmias, sensitivity to propranolol, or use of antiarrhythmic drugs were excluded.
Results. Using the intention-to-treat principle there was a 70% relative risk reduction from 20% to 6% in the rate of treated arrhythmias with propranolol (p = 0.071, 95% confidence interval 0.6% to 27.2%). Overall arrhythmias were common but usually benign. Adverse effects were common, although generally mild with hypotension and bradycardia being reported more often in the propranolol group. Length of stay was not different.
Conclusions. There was a trend to a reduction in the risk of perioperative arrhythmias with propranolol. Moreover, propranolol was well tolerated showing a slight increase in minor adverse events.
| Introduction |
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Several antiarrhythmic agents have been used to treat and prevent these arrhythmias including digoxin, calcium channel blockers, and ß-blockers [6]. Most often these agents have been studied in patients undergoing cardiac operations, although small trials of patients undergoing general thoracic operations have been performed. Digoxin has not proven useful in patients undergoing general thoracic procedures whether given to treat arrhythmias or to prevent their occurrence [2, 3]. Calcium channel blockers are often used in the treatment of acute arrhythmias, but are not particularly useful in their prevention [7]. In one study of patients undergoing general thoracic operations, a nonsignificant decrease in the frequency of atrial fibrillation was noted and adverse events were common in the active treatment (verapamil) arm [8]. Amiodarone has also been studied in this population but was found to be associated with a high incidence of serious pulmonary toxicity [9]. Flecainide was studied in one small, single-blinded series and was found to be superior to digoxin administered prophylactically [10]. Given the lack of efficacy, and indeed the potential for digoxin to cause or aggravate arrhythmias in this setting, it is difficult to determine whether flecainide is useful [3].
ß-Blockers are used both in the treatment of these arrhythmias and in their prevention [11]. Extensive experience with low-dose ß-blocker therapy, using doses of propranolol as low as 5 mg every 6 hours, in patients who have undergone cardiac operations support this as a viable option for preventing these arrhythmias [11]. However, the efficacy of these drugs in patients undergoing general thoracic operations has not been studied, likely due to concerns of bronchospasm in a patient population with chronic obstructive pulmonary disease secondary to an extensive smoking history.
The primary objective of the study was to determine whether low-dose prophylactic propranolol reduced the need for treatment of postoperative arrhythmias in patients undergoing major general thoracic operations. Secondary end points included the overall incidence of arrhythmias, the tolerability and safety of propranolol in this setting, and the duration of hospital stays between the two groups.
| Material and methods |
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The following criteria were used for toxicity. Hypotension was defined as a recorded systolic blood pressure of <100 mm Hg that required the administration of intravenous fluids. Congestive heart failure was defined as the appearance of pulmonary edema on chest roentgenogram as determined by a radiologist who was blinded to the treatment received. Chest roentgenograms were routinely performed daily for at least the first 5 days. Bradycardia was defined as heart rate of
60 beats/min from Holter monitor or as noted by nursing staff. Bronchospasm was determined by the need for bronchodilator therapy (ie, ipratropium or salbutamol). Other adverse effects that were identified in the patients chart were recorded.
Statistical analysis
A review of the literature suggested that the rate of postoperative arrhythmias was likely to be 40% [2, 3]. We anticipated that ß-blocker therapy would reduce the need for treatment by 63%. A trial of 49 patients per group would have 80% power to detect a 63% reduction in the primary outcome event in the treatment group as compared to controls (40% to 15%) at 5% (two-tailed) significance.
Baseline patient demographics of the two groups were compared using descriptive statistics. For dichotomous outcomes the two groups were compared using the
-squared statistic or Fishers exact test as appropriate. Continuous variables were compared using the Students t test or Wilcoxon two-sample test where appropriate. Analyses were performed according to the intention-to-treat principle. A two-sided p value less than 0.05 was considered as statistically significant.
The statistical analysis was performed using the SAS statistical program [13]. Written informed consent was obtained from all patients. The protocol was approved by the University of Western Ontario Review Board for Health Sciences Research involving human subjects.
| Results |
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Of the remaining 100 patients, 99 were included in the analysis. One patient, who was scheduled for a lobectomy underwent a wedge resection and was excluded. Baseline demographic data from the 50 patients randomized to placebo and the 49 patients randomized to propranolol are shown in Table 1. Baseline demographic data were comparable between the groups.
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Adverse effects were common (see Table 3 ). Eight patients were withdrawn from the study for adverse effects. Three patients in the placebo group were withdrawn for shortness of breath attributed to the therapy. Those patients received bronchodilator therapy and furosemide. Five patients in the active arm were withdrawn because of shortness of breath. Two of those patients received bronchodilator and furosemide therapy, the other three received bronchodilator therapy alone. In 1 patient clearance of a mucus plug resulted in symptomatic improvement. One patient was withdrawn from the study by the team as he was deemed to be unstable. Three patients died during the study, 2 in the active group and 1 in the placebo group. Two deaths occurred in the operating room, one attributable to exsanguination and the other due to myocardial infarction. The third patient died on the second postoperative day from a pulmonary embolism. In none of the cases were the study medications implicated in the deaths.
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| Comment |
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Although arrhythmias were common, most of these were of little clinical importance and required no treatment. Atrial fibrillation/flutter requiring treatment occurred in 10% of placebo recipients and 6% of propranolol recipients. These rates are similar to the active treatment arm in a recent trial [7], but substantially less than the placebo arm in that trial. One of the reasons for this may be differences in the study designs. In the previously cited trial [7], aerosol ß-agonists (eg, salbutamol) were routinely administered, whereas in our trial these agents were discouraged. A previous study from our institution showed a trend toward increased digoxin use in an attempt to control atrial fibrillation when higher ß-agonist doses were used [14]. This is in agreement with recent data from cardiac surgical patients that atrial fibrillation after operation was associated with sympathetic activation [15] and hence, the administration of sympathomimetics could potentially increase the risk of dysrhythmia in a patient population already at risk.
Although the total number of episodes of arrhythmias were lower in the placebo than in the propranolol arm (2.42 ± 3.56 versus 4.96 ± 6.24, respectively), this is a misleading parameter. Although fewer in number, the duration of arrhythmias in the placebo group was substantially longer than in the propranolol group (42.9 ± 146.4 minutes versus 12.5 ± 65.0 minutes, respectively), although not statistically so.
Although the number of events was small, the only treatable arrhythmia in patients receiving propranolol was atrial fibrillation. A number of different arrhythmias required treatment in the placebo group. This is of interest in light of recent information on the benefits of ß-blocker therapy in patients undergoing noncardiac operations [16]. Ischemic events occurred in 3 of 50 patients receiving placebo versus 1 of 49 patients receiving propranolol. None of these progressed to acute myocardial infarction.
Adverse events were common but generally not serious. Only 8 patients were withdrawn from the study due to suspected toxicity. Particularly bothersome was the high and statistically significant rate of hypotension in patients who received propranolol. Most patients received thoracic epidural analgesia and it may be that even low doses of propranolol may potentiate hypotension in the presence of epidural analgesia. In most patients reducing epidural dose or withholding study drug resulted in improvement in blood pressure. Bradycardia was noted to a greater extent in the propranolol group but no patient was withdrawn because of this adverse effect. This side effect is peculiar given the relatively small dose of ß-blocker received. The incidence of bronchospasm was not different between the two groups and hence the reservations about using low-dose ß-blockers in patients who have a history of mild to moderate chronic obstructive pulmonary disease, or are at risk of same because of a smoking history, appear unfounded. Although several of our patients had either a history or indication of chronic obstructive pulmonary disease, those patients with severe obstructive disease were considered inoperable and hence not included. When bronchospasm did occur, it was generally easily managed by administration of ipratropium. Patients with a history of asthma were excluded from our trial. These patients are known to be at increased risk of bronchospasm from the administration of a ß-blocker.
Finally, although not an objective of our study, the mean length of stay of patients who had treated arrhythmias was 15.5±12.3 days versus 13.3±12.2 days for those who did not have treatable arrhythmias (p = 0.57). Hence, we were unable to confirm recent information that suggest these dysrhythmias were associated with a prolonged stay [17].
Our study had several limitations, the major one being a potential type II error. In addition, a number of patients screened for the study were not enrolled. Administration of other agents with antiarrhythmic properties was the most common single reason for excluding patients from the study. This was done to avoid the confounding effects of these agents on arrhythmias and to avoid potential differences between groups. The prophylactic role of ß-blockers in patients already receiving these therapies is unknown. In addition, although every attempt to minimize differences between the groups was taken, and indeed there were no statistical differences between the groups, there were more pneumonectomies in the placebo group and more esophagectomies in the propranolol group. Whereas esophagectomies are reported to have a comparable rate of arrhythmias as do pneumonectomies and higher than that of lobectomies, this may only be true for thoracic approach [35]. As some of our patients had their esophagectomy by way of the transhiatal approach, this may have altered the event rate in favor of the active treatment arm.
In conclusion, although propranolol did not statistically significantly reduce the need for treatment of arrhythmias in the perioperative setting of major thoracic operation, a trend was shown in favor of the active drug. The administration of propranolol in this setting is associated with an increased risk of hypotension and bradycardia, but these are not associated with clinical sequelae.
| Acknowledgments |
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