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J Thorac Cardiovasc Surg 2000;120:790-798
© 2000 The American Association for Thoracic Surgery
General Thoracic Surgery |
From the Departments of Anesthesiology and Critical Care Medicine,a Epidemiology and Biostatistics,b Medicine,c and Surgery,d Memorial Sloan-Kettering Cancer Center, New York, NY.
Supported in part by a grant from the International Anesthesia Research Society.
Address for reprints: David Amar, MD, Memorial Sloan-Kettering Cancer Center, 1275 York Ave, M-304, New York, NY 10021 (E-mail: amard{at}mskcc.org).
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Abstract |
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60 years) or pneumonectomy (18 years) and orally thereafter for 14 days. The primary end point with respect to efficacy was a sustained (15 minutes) or clinically significant atrial arrhythmia during treatment. |
Introduction |
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1-3 Patients with postoperative AF have an extended hospital stay with accompanying increased costs, as well as greater need for hospital readmission after discharge. The risk of stroke is greater in patients with postoperative AF. 1,2,4 The etiologic mechanisms of this complication are poorly understood. As in AF unrelated to operations, age of 60 years or older is consistently the only independent preoperative risk factor most strongly associated with postoperative AF. 1-5 Biochemical studies done in our laboratory have shown a persistent downregulation and desensitization of the lymphocyte ß-adrenergic receptor/adenyl cyclase system that corresponded to global reductions in measures of heart rate variability throughout the first postoperative week. 6 These and other data 7,8 support the presence of increased sympathetic activity, parasympathetic withdrawal, or both during this critical period. We hypothesized that postoperative AF may be mediated, in part, by calcium channel mechanisms in response to adrenergic hyperactivity. Recent investigations in animals 9 and human subjects 10-12 showed that ;L-type calcium channel blockers possess antiarrhythmic capability against AF. Favorable pilot data from our institution established that diltiazem is well tolerated after thoracotomy. 13 Thus, this study was designed to determine whether early L-type calcium channel blockade with diltiazem reduces the incidence and morbidity of postoperative atrial arrhythmia. |
Methods |
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A total of 503 patients with pulmonary or pleural malignant tumors were enrolled from February 1997 to August 1999. Patients who were found to have unresectable disease at the time of operation because of extensive spread of tumor (n = 32) or those who underwent a lesser operation (n = 135) were excluded from the study. Four patients were excluded from the study after randomization but before the study medication was given: two patients had acute myocardial ischemia or infarction during or immediately after the operations; one patient had persistent hypotension (systolic blood pressure < 80 mm Hg) requiring vasopressor therapy for greater than 12 hours; and one patient had a persistent sinus bradycardia (heart rate < 50 beats/min). In addition, two patients were wrongly enrolled into the study: one patient was being treated with a class III antiarrhythmic drug for paroxysmal AF, and the other had poorly controlled hyperthyroidism and paroxysmal AF. These 6 patients were not included in the intention-to-treat analysis. The 330 consecutive patients who underwent lobectomy (n = 232), pneumonectomy (n = 63), or extrapleural pneumonectomy (n = 35) were randomly allocated in a double-blind fashion in the immediate postoperative period to receive diltiazem or placebo (see below).
Study end points
The primary end point of the study was the new onset of sustained (15 minutes) or clinically significant (requiring intervention) AF or supraventricular tachyarrhythmia (SVT) during the first 14 days after the operation. AF was defined by an irregular cardiac rhythm, other than sinus rhythm, confirmed by either ambulatory electrocardiography (ECG) or 12-lead ECG. SVT was defined as the new onset of paroxysmal supraventricular tachycardia or multifocal atrial tachycardia necessitating treatment. Once the primary end point was reached, the assignment code was unblinded, and the primary physician was allowed to cross over to diltiazem from placebo or administer additional diltiazem or other medications as clinically indicated. Patients in whom the heartbeat failed to convert to sinus rhythm within 24 to 48 hours of AF onset were given heparin followed by warfarin. The incidence of late (>14 days) AF was recorded during hospitalization or if documented as outpatients within 30 days of operation. Need for intensive care unit (ICU) admission for any reason during the 14-day treatment period was also recorded. Data on total hospitalization costs for the study population were provided through the use of a commercially available decision-support information software system (Financial Management System; Shared Medical Systems, Malvern, Pa) used by the patient account office at our institution. Professional service fees were not included in these charges. The 3M APR-DRG (All Patient Refined-Diagnostic Related Groups; 3M Health Information Systems, Salt Lake City, Utah) severity adjustment model was used in adjusting for age, sex, comorbidity, operation, and the interactions thereof. These adjustments were based on the 1996 northeast normative data file. A relative resource weight was established for each patient. These weights were summed for each group and divided by the total patients in the group, yielding a group case mix index. The average cost per group was then divided by the case mix index to develop a neutral cost per case. This neutralized cost was then multiplied by the case mix index for all patients analyzed (2.78) to yield an adjusted average cost.
Anesthesia, operation, and postoperative care
All patients were premedicated with midazolam and glycopyrrolate (INN: glycopyrronium bromide) and received standard anesthetic management that consisted of isoflurane and nitrous oxide supplemented by intravenous fentanyl and morphine as needed. Intentional crystalloid restriction (<25 mL/kg) during the operation was attempted in all patients. The operations were performed by experienced thoracic surgeons using standard thoracotomy approaches. Entry into the pericardial space or resection of the pericardium was recorded. Resection was carried out in a manner designed to completely remove all neoplastic disease along with an ipsilateral mediastinal lymph node dissection. Intraoperative estimated blood loss was recorded. Postoperative pain relief was provided to all patients by continuous administration of either epidural opioid (usually fentanyl) administration (n = 195) or intravenous opioid (usually morphine) patient-controlled analgesia (n = 135). After an overnight stay in the postanesthesia care unit, patients were transferred to the thoracic surgical floor on the first postoperative day. Postoperative complications were recorded throughout the hospital stay. A research nurse monitored patients for complications as outpatients for 30 days and queried patients about intercurrent hospitalizations or emergency department visits. An investigator reviewed these medical records.
Ambulatory ECG
Continuous dual-lead ECG recordings (leads CM2 and CM1 or CM5) were made on Marquette 8500 Holter recorders for 72 to 96 hours after the operation. QRS complex recognition and arrhythmia detection were done automatically by template matching. The decisions made automatically by the computer were reviewed and corrected by an experienced technician and then by a cardiologist.
Antiarrhythmic prophylaxis
Patients were randomly assigned to receive either diltiazem or placebo with stratification on the basis of the type of operation (ie, lobectomy, pneumonectomy, or extrapleural pneumonectomy). Randomization of patients in permuted blocks was done between the epidemiology and biostatistics departments and the hospital pharmacy with sealed, opaque, treatment-code envelopes. All clinical and study personnel were blinded to the study group assignments throughout the trial. On admission to the postanesthesia care unit, treated patients (n = 167) received an intravenous loading dose of diltiazem (0.25 mg/kg [50 mL]) given over 30 minutes, followed by 0.1 mg · kg–1 · h–1 (constituted as 1 mg/mL) intravenously for 18 to 24 hours. Diltiazem was temporarily discontinued for systolic hypotension (<80 mm Hg) or marked bradycardia (<50 beats/min). Similarly, control patients (n = 163) received intravenous placebo loading doses of 50 mL given over 30 minutes, followed by a placebo infusion at 0.1 mL · kg–1 · h–1 given over the first 18 to 24 hours. Starting in the morning of postoperative day 1, patients received either diltiazem SR 120 mg or placebo orally twice daily for a total of 14 days. Patients who could not take oral medication during the treatment period were temporarily switched to the intravenous route. Adjustments in the oral dose were made for patients weighing less than 50 kg, those who had a systolic blood pressure of less than 90 mm Hg, or those showing other adverse effects to diltiazem. Venous blood was drawn to determine plasma diltiazem and magnesium levels on the morning of postoperative day 3 before receiving the morning dose. Plasma diltiazem concentration was determined by high-performance liquid chromatography with ultraviolet detection by Bioassay Laboratory (Houston, Tex).
Statistical analysis
We estimated that the overall incidence of postoperative AF in this group would be 15%. 3 To detect an absolute reduction of 10% in the incidence of early AF with a 2-tailed test at an 
level of 5% with 80% power, a sample size of 330 patients (165 per arm) would be required. The sample size was adjusted for one interim analysis with monitoring boundaries in the spirit of the O'Brien-Fleming rule but with early rejection of either the null or the alternative hypothesis. 14 An interim analysis was performed after 189 patients were enrolled. Atrial arrhythmias occurred in 21 (22%) of 95 control subjects and 15 (16%) of 94 treated patients (P = not significant). The overall incidence of AF with or without SVT was tested among all 3 subgroups (lobectomy, pneumonectomy, and extrapleural pneumonectomy) with the Mantel-Haenszel test for differences in proportions. All analyses were performed on an intention-to-treat basis, and all P values are 2-tailed. Statistical analysis was performed with the software SAS version 6.12 (SAS Institute, Inc, Cary, NC). To determine the difference of patient and operative characteristics between the 2 treatment groups, we examined all variables by univariate analysis (Student t test and Fisher exact test). Data are presented as mean value ± SD unless otherwise indicated.
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Results |
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Length of hospital stay and total costs
Length of hospital stay did not differ between patients assigned to diltiazem in comparison with control subjects (8.9 ± 7.9 vs 8.7 ± 7.8 days, P = .82). The median length of hospital stay was 7 days for both groups. The mean total hospitalization costs for the diltiazem group were $23,773 ± $19,443 compared with $23,515 ± $18,152 for the placebo group (P = .90). Patients with a clinically significant arrhythmia (n = 48) had a longer length of hospital stay (14.4 ± 13.0 vs 7.9 ± 6.1 days, P = .001) when compared with patients who did not have an arrhythmia (n = 282) and were more frequently 60 years or older (47/290 vs 1/40, P = .02). Mean hospitalization costs for patients who had a clinically significant arrhythmia were $26,013 ± $21,636 versus $23,070 ± $16,730 in those patients who did not (P = .28). There was a trend for patients who had clinically significant arrhythmias and received diltiazem (n = 17) to have lower hospitalization costs than similar control subjects (n = 31; $22,498 ± $15,378 vs $28,508 ± $26,144, P = .16). Nonbillable services associated with every symptomatic arrhythmia included more intense nursing coverage, additional monitoring, and more frequent house staff visits.
Subgroup analyses
Diltiazem therapy reduced the incidence of early postoperative AF in patients undergoing lobectomy when compared with placebo (16/117 vs 29/115, P = .03), as well as in patients 60 years or older (all 3 subgroups; P = .05;Table II
). In the diltiazem group the incidence of AF was 24% (4/17 patients) among the patients receiving ß-blockers and 13% (20/150 patients) among those not receiving ß-blockers. In the placebo group the incidence of AF was also 24% (4/17 patients) among the patients receiving ß-blockers and 22% (32/146 patients) among those not receiving ß-blockers. The use of ß-blockers did not influence the incidence of AF in either study group (P = .40, Fisher exact test).
When all patients were combined, those in whom AF developed were found to be older than those in whom AF did not develop (71 ± 7 vs 66 ± 10 years, P < .01). Patients with AF had a longer length of hospital stay (12.9 ± 12.1 vs 7.9 ± 6.2 days, P = .002). More patients with AF had ICU admission (9/60) compared with patients without AF (6/270, P < .01). The use of ß-blockers did not differentiate patients who did or did not have AF (8/60 [13%] vs 26/270 [10%], P = .36). Side of operation and presence of pericardiotomy did not differentiate patients in whom AF did or did not develop (data not shown).
Morbidity and mortality in the hospital
There was no significant difference in the incidence of postoperative complications between the two groups(Table IV). Among patients who had a clinically significant arrhythmia, other major postoperative complications occurred in 4 (24%) of 17 patients assigned to diltiazem and in 8 (26%) of 31 assigned to placebo (P = .99). One patient who was treated with diltiazem had a cerebrovascular accident attributed to new-onset AF within 24 hours of its onset. In this patient the first 12 hours of AF were asymptomatic. The length of stay in the ICU did not differ between patients assigned to diltiazem (8.0 ± 4.7 days, n = 7) compared with patients assigned to placebo (8.4 ± 4.8 days, n = 8; P = .88). The reasons for ICU admission were pneumonia (n = 8), acute respiratory distress syndrome (n = 3), AF (n = 2), and pulmonary embolism (n = 2). Death within 30 days of the operation occurred in 3 patients assigned to placebo and in 1 patient assigned to diltiazem (P = .37,Table IV).
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15 In a subset of 17 of 24 patients in whom AF developed during diltiazem treatment, the plasma diltiazem levels did not differ from levels found in those without AF (n = 121; 294 ± 150 vs 312 ± 167 ng/mL, P = .67). |
Discussion |
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3,13 the observed incidence of AF was lower than expected in patients undergoing pneumonectomy who were assigned to placebo. This is likely a result of the sample size and relatively younger age of patients undergoing pneumonectomy compared with that of the lobectomy subgroup.
Diltiazem therapy did not alter the overall length of hospital stay despite reducing the number of clinically significant episodes of AF and SVT. This may be due to the relatively early onset of AF when compared with the median length of hospital stay of 1 week in both groups and our practice of discharging patients after early anticoagulation. AF has recently been shown to be the single most important cause for hospital readmission after fast-track cardiac operations. 16 Unlike patients undergoing cardiac operations who are fast-tracked, it is possible that our patient's postoperative comorbidities, such as pneumonia or a prolonged air leak, masked the effect of diltiazem on the overall length of hospital stay. The significantly higher length of hospital stay in our patients with an arrhythmia is consistent with findings in other studies. 1-4 The burden of AF after cardiac operations on hospital costs is well documented. 1,2,4 In our study the mean hospitalization cost attributed to a clinically significant arrhythmia was close to $3000. Our results demonstrated that a 14-day course of intravenous and oral diltiazem ($120 hospital cost, n = 167) was responsible for a 45% (14 patients) risk reduction of clinically significant atrial arrhythmias. Assuming that these 14 patients were to have an arrhythmia and that their total costs would exceed that of patients without an arrhythmia by $3000, this would translate into cost savings after the cost of diltiazem is deducted. Because extended monitoring, intensity of nursing care, and house staff interventions were not billed for at our institution, our cost savings with diltiazem are probably underestimated. Strategies that can further maximize the cost effectiveness of diltiazem could include beginning oral therapy before the operation, shortening the course of intravenous diltiazem therapy after the operation, and reducing the duration of postoperative therapy to 10 days because the majority of arrhythmias occurred before this time in our study.
Previous studies
Our early experience with the prophylactic use of diltiazem after pneumonectomy showed an overall reduction of AF or SVT by 50% when compared with that of patients treated with digoxin or with a comparison control group. 13 The sample size of that study was relatively small, and this difference only approached significance. The use of verapamil by other investigators immediately after thoracic operations for 72 hours was associated with similar reductions in the AF rate but with greater side effects related to a large loading dose. 17 In another study of patients undergoing coronary artery bypass grafting (CABG), short-term diltiazem therapy that was started during cardiopulmonary bypass and continued for 24 hours was shown to significantly reduce the AF incidence from 18% to 5%. 18 The limitations of that study, however, were the lack of arrhythmia definition and monitoring reported for only 24 hours. ß-Blockers have also been used for many years to prevent AF after cardiothoracic operations, but their efficacy for this purpose has been marginal. 1,2,19-21
In contrast to rate-control drugs, more recent reports have investigated the use of the class III antiarrhythmics amiodarone and ibutilide in patients undergoing cardiac operations. 22-24 The first report involved a relatively small group of patients given amiodarone for 1 week before CABG, valvular operation, or both and showed a significant effect of therapy on the incidence of AF (25% vs 53%), on hospital stay, and on cost when compared with placebo. 22 In a larger trial limited to patients undergoing CABG, amiodarone prophylaxis reduced the AF incidence from 47% to 35% but had no effect on hospital stay or cost. 23 Despite these reported reductions in AF rates with amiodarone, 22,23 the overall incidence of AF remained high, and when coupled with its significant cost and the potential for side effects, its routine use for prophylaxis against postoperative AF has been discouraged. 25 The concern of lung injury associated with amiodarone therapy in a small study of patients undergoing thoracic operations requires further confirmation. 26 Ibutilide has been shown to be effective in the conversion of acute AF after cardiac operations but was associated with a 1.8% risk of polymorphic ventricular tachycardia. 24 As in AF unrelated to an operation, it is not clear whether antiarrhythmics are superior to rate-control drugs in the management of postoperative AF. 25 In fact, a recent preliminary study of postoperative AF reported that the strategy of rhythm control is not superior to that of rate control for attainment of any clinical end point. 27
Limitations of the study
First, on the basis of our prior work, 3,13 we expected that younger age would not affect the incidence of AF after pneumonectomy. By study design, patients undergoing pneumonectomy were younger than patients undergoing lobectomy. We believe that this, combined with the smaller sample size in the pneumonectomy groups and the lower than expected AF occurrence, limited our ability to find a meaningful comparison between diltiazem-treated and control patients. Second, Holter recordings were made during the first 72 to 96 hours after the operation, a period when most arrhythmias are known to occur. Our conclusions beyond this monitoring period are limited to clinically evident episodes of AF. Third, our practice setting precluded doing a more exact cost analysis to assess the true burden of AF.
Potential mechanisms
Postoperative atrial arrhythmias and AF specifically may be seen in 2% to 4% of elderly patients undergoing noncardiothoracic operations. 28,29 The clinical presentation is identical whether a patient has had cardiac, thoracic, or other types of operations. What differs is the greater incidence of AF after cardiothoracic operations. 28 Although the etiologic mechanisms of postoperative AF are poorly understood, it has been shown that AF is generally initiated by an ectopic beat. 30 Whether the ectopic beat triggers AF depends on the vulnerability of the atrium. Atrial vulnerability is determined by a complex interaction of factors: dispersion of refractoriness, electrical remodeling, wavelength of the re-entrant impulse (product of the refractory period by the conduction velocity), and autonomic balance. 31 To date the only consistent clinical predictor of postoperative AF is older age. 1-5 It is widely known that aging causes degenerative changes in atrial anatomy 32,33 that are accompanied by shorter atrial effective refractoriness, longer sinoatrial and atrioventricular nodal conduction times, atrial stiffening, and splitting of the atrial excitation waveform caused by the pectinated trabeculae. 34 Experimental studies have shown that sympathetic stimulation by itself will not produce AF, whereas regional sympathetic denervation indirectly changed the vagal effects on atrial refractoriness to facilitate sustained AF. 34,35 We speculate that cardiac and thoracic operations provide a model of regionally denervated atria as a result of varying degrees of unavoidable trauma to sympathovagal fibers originating from the deep and superficial cardiac plexi to the atria. 13 Whether there is a yet undefined atrial denervation supersensitivity phenomenon to circulating plasma catecholamines in response to cardiothoracic operations is unknown, but this has been contemplated to explain atrial arrhythmias in a totally denervated transplanted heart. 36
The higher incidence of AF and other re-entry type atrial arrhythmias in the control group confirms the data from laboratory 9 and clinical studies 10-12 suggesting that intracellular calcium-lowering drugs mitigate some of the atrial electrophysiologic mechanisms that predispose to AF onset. The likely multifactorial composition of the substrate for postoperative AF partially explains why more than 60% of patients do not have this complication after cardiothoracic operations. 28 It also explains why clinical studies examining one mechanism, such as prolonged intra-atrial conduction (prolonged signal-averaged P-wave duration) as a predictor of postoperative AF, have provided conflicting results. 37-39
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Acknowledgments |
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