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Anesth Analg 2002;95:537-543 © 2002 International Anesthesia Research Society
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Abstract |
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Atrial arrhythmias are common after thoracic surgery, but the incidence and significance of ventricular arrhythmias early after such surgery are not well established. Our goal was to determine the incidence and outcome of this complication from a continuing prospective database in 412 patients who had lobectomy (n = 243) or pneumonectomy (n = 169) and were continuously monitored with Holter recorders for 72–96 h postoperatively. The primary end point of the study was the occurrence of ventricular tachycardia (VT) defined as three or more consecutive wide complexes. Sixty-one of 412 patients (15%) developed 1 or more episode of VT. There were no episodes of sustained (>30 s) VT and no patient required treatment for hemodynamic compromise associated with any VT episode. Patients with VT had a more frequent incidence of a preoperative left bundle branch block (P = 0.01) but did not differ in other clinical characteristics, operative data, or core temperature on arrival to the postanesthesia care unit, when compared with those without VT. Patients who developed VT had significantly more atrial premature contractions (P < 0.001), ventricular premature contractions (P < 0.001), ventricular couplets (P < 0.001), and postoperative atrial fibrillation, 21 of 61 (34%) versus 58 of 351 (17%), P = 0.001, than those without VT, respectively. Multivariate logistic regression analysis revealed that only postoperative atrial fibrillation occurrence was independently associated with VT (relative risk 2.6, 95% confidence intervals 1.4 to 4.8, P = 0.002). We conclude that nonsustained VT after noncardiac thoracic surgery occurs frequently but is not associated with poor outcome. The strong association of atrial and ventricular arrhythmogenesis with VT suggests that vagal withdrawal and/or adrenergic hyperactivity may have a role in precipitating these events in the early postoperative period.
IMPLICATIONS: In 412 patients, we determined that the incidence of nonsustained ventricular tachycardia after major thoracic surgery is 15% and is not associated with poor outcome.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Cardiac arrhythmias occur frequently after thoracic surgery and are most often supraventricular in origin (1,2). Few studies have reported on the incidence and clinical outcome of ventricular arrhythmias after noncardiac surgery (3–8). These studies varied in patient populations, methods, and length of continuous electrocardiogram (ECG) monitoring with few continuing the monitoring beyond 24 h. Furthermore, among the three studies that examined the incidence of nonsustained ventricular arrhythmias, there is controversy concerning whether these patients are more likely to have poor outcomes after surgery as a consequence of the arrhythmia or because of limited cardiovascular reserve (5,7,8). This information could help clinicians decide whether further electrophysiologic study or therapeutic actions are necessary. We therefore determined the incidence of ventricular arrhythmias and clinical outcome in a well defined population from a continuing prospective database of patients who had major thoracic surgery at a single institution and were continuously monitored with Holter recorders for 72–96 h. We also examined factors that may precipitate these arrhythmias, such as myocardial ischemia and modulation of autonomic influences on the heart, with the use of ST segment and heart rate variability (HRV) analyses, respectively.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The data used in this study were pooled from a continuing prospective database of patients undergoing major thoracic surgery who also had continuous postoperative ambulatory ECG monitoring for 72 h. With IRB approval and written informed consent, patients participated in consecutive trials focused on the study of postoperative atrial arrhythmias (9–11). All patients scheduled to undergo a lobectomy or pneumonectomy who met inclusion criteria (absence of a history of atrial fibrillation, presence of sinus rhythm before surgery, and not receiving class IC or III antiarrhythmic drugs) were approached to enroll in the above studies subject to the availability of research staff. Excluded were patients with a high-grade atrioventricular block and those who were hemodynamically unstable immediately after surgery. Of the 6 patients who had a perioperative myocardial infarction, 2 were excluded from this study because they required emergent cardiac catheterization and revascularization <6 h after surgery. Beginning in February 1994 until August 1999, there have been 412 patients who met the above study criteria. There were 203 of 412 patients who received prophylactic diltiazem immediately after surgery. Of the 209 of 412 patients who did not receive diltiazem, 35 received digoxin (9,11). The primary end point of the study was the occurrence of ventricular tachycardia (VT) defined as 3 or more consecutive wide (>120 ms) complexes with the ST-T vector pointing opposite to the major QRS deflection (12). Sustained VT was defined as lasting >30 s or requiring termination because of hemodynamic compromise.
The operations were performed by using standard thoracotomy approaches 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 the continuous administration of either epidural opioid (usually fentanyl) infusion (n = 220) or IV opioid (usually morphine) patient-controlled analgesia (n = 192). Central venous catheters were not routinely placed and chest tube location was routinely examined and corrected with the help of chest radiography. Tympanic membrane temperature was measured on admission to the postanesthesia care unit. After an overnight stay in the postanesthesia care unit, patients were transferred to the thoracic surgical floor on the first postoperative day. Patients had routine assessment and correction of potassium and magnesium. Magnesium levels on postoperative day 3 were also available in a subset of 318 of 412 patients (77%). Patients underwent routine postoperative oxygen saturation monitoring at rest and with ambulation and were given oxygen to maintain an SpO2 >90%. Major postoperative cardiac (unstable angina defined as recurrent or persistent ischemic cardiac pain at rest with ECG changes, myocardial infarction documented by new Q waves of at least 0.04-s duration and a minimum of 1-mm depth on 12-lead ECG or increase of CK-MB or troponin I levels, congestive heart failure defined as a clinical diagnosis based on the presence of rales, increased pulmonary capillary wedge pressure, classic chest radiographic findings and requiring treatment with inotropes or vasodilators) or pulmonary (pulmonary embolism, pneumonia requiring antibiotic therapy, or respiratory failure requiring mechanical ventilation) complications were recorded throughout the hospital stay. A research nurse monitored all patients for cardiac or pulmonary complications as outpatients for 30 days and queried patients about intercurrent hospitalizations or emergency room visits. An investigator reviewed these medical records.
Continuous dual-lead ECG recordings (leads CM2 and CM1 or CM5) were made on Marquette 8500 Holter recorders (Marquette Electronics, Milwaukee, WI) for 72–96 h after surgery in 412 patients. The Holter tapes were digitized on a Marquette series 8000 scanner. The signal was sampled at 128 Hz. Sampling was triggered by the timing track on the tape to correct for flutter and wow of the recording or playback tape transport. QRS complex recognition and arrhythmia detection were done automatically by template matching. This system generates a beat-by-beat annotation of the ECG with a consistent and accurate time stamp for each QRS complex and classifies each complex as normal sinus, atrial or ventricular premature complex, or noise. The decisions made automatically by the computer were reviewed and corrected by an experienced technician and then by a cardiologist. When calculating the HRV variables, only normal R-to-R (RR) intervals were used. Each interval that was to be excluded because of ectopic beats or artifacts was replaced by holding the previous coupling interval level throughout the time interval to the next valid coupling interval. HRV indices measured were: mean RR interval (ms), and its standard deviation (SD; ms); root mean square of difference of successive RRs (rMSSD; ms); proportion of adjacent RRs >50 ms different (pNN50; %); low (LF; 0.04–0.15 Hz) and high frequency (HF; 0.15–0.40 Hz) power (ms2). The LF/HF ratio has been proposed to be an index of sympathovagal balance. Fast Fourier transformation was used to compute the power within the defined frequency limits for each 2-min interval (256 samples). Using the Marquette automated ST analysis program, the ST segment was measured 60 ms after the J point. An episode of ischemia was defined as ST horizontal or down sloping of 0.1 mV or more or increase of 0.2 mV or more lasting 1 min or longer in 1 or more leads.
Statistical analysis was performed with the software SPSS version 10.1 (Chicago, IL). To determine the difference of patient and operative characteristics between patients with and without VT, all variables were examined by using univariate analysis (Student’s t-tests and Fisher’s exact test). Those variables showing a univariate association (P < 0.10) with VT occurrence were entered into a stepwise logistic regression model. The final model showed the variables with independent influence on the incidence of VT. To examine the correlation of changes in time or frequency domain variables of HRV, a repeated-measures analysis of variance was performed. A P value < 0.05 was considered significant. Data were presented as mean value ± SD unless otherwise indicated.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Patient characteristics and surgical data are presented in Table 1. Sixty-one of 412 patients (15%) developed 1 or more episodes of nonsustained VT within 72–96 h of operation. Preoperatively, patients with VT had a more frequent incidence of left bundle branch block than patients without VT, P = 0.01 (Table 1). The timing of VT onset was as follows: 0–24 h, n = 31, median (range, mean ± SD) episodes 1 (0–42, 2 ± 7); 25–48 h, n = 28, 0 (0–40, 5 ± 16); 49–72 h, n = 30, 1 (0–96, 9 ± 19), respectively. No patient required treatment for hemodynamic compromise associated with any VT episode. The longest recorded episode of VT was 42 beats lasting 15 s and did not require treatment. Four patients had a perioperative myocardial infarction but none had developed VT. Patients who received diltiazem had fewer episodes of VT compared with those who did not (12 of 203 [6%] versus 49 of 209 [24%], P < 0.0001, respectively). On arrival to the postanesthesia care unit, the core temperature of patients with VT did not differ from patients without VT (35.6° ± 0.7°C versus 35.4° ± 0.9°C, respectively, P = 0.53). Plasma magnesium concentrations taken on postoperative day 3 were identical in patients with (n = 37) or without VT (n = 281), 1.6 ± 0.2 mEq/L, P = 0.89; normal range, 1.4–2.2 mEq/L. The use of postoperative epidural analgesia did not differ among patients with or without VT (31 of 61 [51%] versus 189 of 351 [54%], P = 0.89). One patient died suddenly 90 h after an extrapleural pneumonectomy for mesothelioma without evidence of ventricular arrhythmias during the first 72 h after surgery as determined by Holter recordings. A postmortem examination in this patient failed to show evidence of significant coronary thrombosis or pulmonary embolism.
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The average 24-h heart rate increased significantly for all patients between postoperative days 1 to 3 (P < 0.01, repeated-measures analysis of variance) (Table 2). In 12 of 61 patients (26%) who developed VT, heart rate was increased (>110 bpm, n = 5) or increased by
20% (n = 7) during the 30 min preceding the onset of VT. However, HRV analysis performed during the hour preceding VT onset showed no significant changes in time or frequency domain variables (Table 3). Similarly, no patient with VT had evidence of myocardial ischemia on Holter monitoring. Holter data showed that patients who developed VT had significantly more atrial premature contractions (P < 0.001), ventricular premature contractions (P < 0.001), and ventricular couplets (P < 0.001) than patients without VT (Table 2).
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Seventy-nine of 412 patients (19%) developed sustained postoperative atrial fibrillation. The incidence of postoperative atrial fibrillation was more frequent among patients with VT compared with those without VT (21 of 61 [34%] versus 58 of 351 [17%], P = 0.001, respectively) (Table 1). Because some patients received prophylactic diltiazem immediately after surgery to reduce the incidence of postoperative atrial fibrillation (9,11), we repeated this analysis omitting such patients and the results remained similar in patients who did or did not develop VT, respectively (15 of 49 [31%] versus 19 of 160 [12%], P = 0.002). Episodes of VT preceded atrial fibrillation onset in 17 patients, occurred simultaneously with atrial fibrillation onset in 2 patients, and during atrial fibrillation in 2 patients. Multivariate logistic regression analysis showed that postoperative atrial fibrillation occurrence was the only independent characteristic associated with VT (relative risk 2.6, 95% confidence intervals 1.4 to 4.8, P = 0.002).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The main findings of this study are that the incidence of nonsustained VT after noncardiac thoracic surgery is 15% and is not associated with poor outcome within 30 days of surgery. The only preoperative characteristic associated with postoperative VT was the presence of left bundle branch block. In addition to the observation that all patients had a significant increase in average heart rate over the first 3 days after surgery, 26% of patients with VT showed further increases in heart rate during the hour preceding VT onset. We did not find any significant changes in time or frequency domain variables of HRV before VT onset. This may be explained, in part, by the relative tachycardia of the postoperative state and wide inter-patient variability. Postoperative atrial fibrillation occurred in 19% of patients and was the only clinical characteristic independently associated with VT. The association of postoperative VT and atrial fibrillation has been previously reported in patients recovering from cardiac, but not thoracic, surgery (13). Unlike postoperative atrial fibrillation (1,11), however, postoperative VT was not age-dependent in our patients. Although some patients received prophylactic diltiazem in an effort to reduce the incidence of postoperative atrial fibrillation, the proportion of patients developing atrial fibrillation among patients with or without VT did not change when diltiazem-treated patients were excluded from the analysis. Diltiazem use, however, was associated with a significant reduction in the incidence of VT. These results suggest that calcium channel blockade attenuates atrial and ventricular arrhythmias in a state of presumed adrenergic predominance such as after surgery.
Our results and conclusions regarding VT incidence and outcome are comparable to those from other studies in which Holter recorders were used for 12–72 h after intraabdominal, thoracic, or vascular surgery (Table 4) (5–8,14–16). Although patient demographics in the current study differed in the incidence of known structural heart disease and other risk factors from those in the above studies, this did not impact on the incidence or outcome of postoperative VT (Table 4) (5–8,14–16). Frequent atrial ectopy has been proposed as one mechanism contributing to postoperative arrhythmias in the setting of autonomic imbalance (16–18). Older age, a faster preoperative heart rate, and postoperative adrenergic hyperactivity and/or vagal withdrawal have been implicated in the pathogenesis of postoperative atrial arrhythmias (10,19,20). The strong association of atrial and ventricular arrhythmias and an increased postoperative heart rate in the current study suggest that similar mechanisms also have a role in precipitating VT in the early postoperative period (13). In a small study of patients undergoing thoracic surgery, the use of postoperative epidural bupivacaine attenuated the incidence of supraventricular tachyarrhythmias (21). These authors, however, did not report the incidence of ventricular arrhythmias between the groups. We recently found preliminary evidence linking focal inflammatory mechanisms such as myocarditis, but not pericarditis, to postoperative supraventricular arrhythmias in an experimental model of thoracic surgery (22). Whether similar changes occur in humans remains unproved.
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The smallest reported incidence of postoperative VT at 5% by Frank et al. (7) in patients undergoing thoracic, vascular, or abdominal surgery, is likely attributable to their definition of VT as 5 or more consecutive beats. When we examined our data by using a similar definition as Frank et al. (7), the incidence of VT was nearly identical at 6% (Table 4, legend). These investigators also reported that patients whose temperature was colder on arrival to the postanesthesia care unit were more likely to have nonsustained VT. We did not observe an association between the incidence of ventricular arrhythmias and postoperative temperature. More recently, Mahla et al. (8) reported on 60 patients with, or at risk for, structural heart disease undergoing noncardiac surgery. The incidence of nonsustained VT was frequent and similar to that reported by O’Kelly et al. (5) who studied 230 men with, or at risk for, coronary artery disease undergoing noncardiac surgery. VT was not associated with poor short-term outcome in either of these studies. Data from the Multicenter Study of General Anesthesia whose patients were enrolled in the mid 1980s, suggest an incidence of
0.6% of life-threatening ventricular arrhythmias after noncardiac surgery in healthy patients (Table 4) (3,18). These data are limited by nonspecification of the definition of a "serious" arrhythmia and what the criteria were for initiating treatment. More recent data from Baron et al. (6), obtained from a cohort of 468 high-risk patients undergoing abdominal aortic surgery, showed that 2 patients (0.4%) developed severe ventricular tachyarrhythmias defined as VT or fibrillation with hemodynamic compromise that were successfully treated. Few data are available on whether repeated or frequent ventricular ectopy after noncardiac surgery is associated with poor long-term cardiovascular outcome. Only one study evaluated the relationship of the development of VT in patients without ischemia during hospitalization after noncardiac surgery, and it showed that VT was not associated with adverse long-term outcome (23). The incidence of sustained VT or fibrillation after cardiac surgery has been reported to be 0.5%–1% from large observational studies of patients who were monitored postoperatively (14,15). Attempts to prophylactically suppress nonsustained ventricular arrhythmias after cardiac surgery with lidocaine failed to show that such a strategy improves outcome (24). In the general population or after an acute myocardial infarction, electrophysiologic testing in patients with no symptoms, or only mild ones related to frequent ventricular ectopy or nonsustained VT, is now believed to be inappropriate because of the lack of evidence that therapeutic strategies for such events have improved outcome (25). Exceptions to these guidelines may be applied to patients with low ejection fraction or to those who have positive signal-averaged ECG and who are highly symptomatic. However, there is controversy about the short- and long-term prognosis of persons with exercise-induced premature ventricular depolarizations, which has been primarily linked to stress-induced ischemia (26). A larger study of 6101 asymptomatic middle-aged men showed an association between the occurrence of frequent ventricular ectopy during exercise and a long-term increase in the risk of death from cardiovascular causes (27). The link between frequent ventricular ectopy and enhanced cardiovascular morbidity was independent of exercise-induced ischemia, and suggests that early intervention to reduce or modify known cardiac risk factors should be used in such patients (27). Because exercise and perioperative stress have often been compared physiologically, these findings may have some implications in the preoperative evaluation of patients with multiple risk factors and exercise-induced ventricular ectopy. The abnormal physiologic conditions of surgical intervention may cause these arrhythmias to become manifest (18). Supraventricular ectopy may be one form of trigger. Vagal irritation or withdrawal, increased sympathetic tone, or respiratory distress may likewise act alone or in combination to provide the milieu for arrhythmia generation (16–18).
The limitations of this study are that it is a post hoc analysis of prospectively collected data with limited power to assess the true outcome of rare events such as sustained ventricular arrhythmias after thoracic surgery. Our conclusions are limited to the postoperative period because preoperative Holter recordings were not performed. Although we provided magnesium data obtained on postoperative day 3 only, routine postoperative care at our institution included measurement and correction of electrolyte abnormalities.
We conclude that nonsustained VT after noncardiac thoracic surgery occurs frequently. In the cohort of patients studied, there was no association of worsened perioperative outcome with transient ventricular arrhythmias.
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Acknowledgments |
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Supported in part by an International Anesthesia Research Society Clinical Scholar Research Grant.
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References |
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