- Email: [email protected]
New-onset sustained ventricular tachycardia and fibrillation early after cardiac operations
John A. Yeung-Lai-Wah, MBChB, Anzhen Qi, MD, Elizabeth McNeill, MB ChB, James G. Abel, MD, Stanley Tung, MD, Karin H. Humphries, DS, and Charles R. Kerr, MD Division of Cardiology and Cardiovascular Surgery, St. Paul’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada
Background. Malignant ventricular tachyarrhythmia early after cardiac surgery is an uncommon arrhythmic complication but has a negative impact on mortality. The purpose of this study was to evaluate the incidence of new-onset sustained postoperative ventricular tachycardia-ventricular fibrillation and to identify risk factors for the dysrhythmia. Methods. Demographic, clinical, operative, and postoperative data, including a variable of postoperative ventricular tachycardia, were prospectively obtained from 4,748 patients undergoing nonemergency coronary artery bypass graft and(or) valve replacement with no history of sustained ventricular tachycardia or sudden death. A detailed analysis was performed to define the risk factors for the ventricular tachycardia and the prognostic impact of the arrhythmia on 30-day mortality was evaluated. Results. Forty-five patients (0.95%) had sustained ventricular tachycardia or ventricular fibrillation and the initial episode occurred 3.9 ⴞ 5.2 days (mean ⴞ standard
deviation) after surgery. By multivariate analysis, female sex (odds ratio, 1.982), left ventricular ejection fraction (< 35%: > 50%, 4.771), the presence of pulmonary hypertension (3.066), the presence of systemic hypertension (2.391), and pump time (per 10 minutes, 1.085) were independently associated with the dysrhythmias. Early mortality of patients with the arrhythmia was 28.9%, strikingly higher than that of patients without ventricular tachycardia/ventricular fibrillation (1.9%). Conclusions. Left ventricular ejection fraction is the strongest risk factor for new-onset postoperative sustained ventricular tachycardia-ventricular fibrillation; female sex, pump time, pulmonary and systemic hypertension are independent predictors of the dysrhythmias; the arrhythmia is associated with increased 30-day mortality after cardiac surgery.
T
several case reports and small series describing sustained ventricular tachycardia after cardiac surgery, but a detailed risk factor analysis has not been performed in a large study population [14 –17]. The present study evaluated the incidence of newonset sustained postoperative ventricular tachycardiafibrillation (SPOVT) in patients undergoing CABG, valvular surgery, and concomitant CABG, and valvular surgery and identified risk factors associated with the development of the tachyarrhythmias from the detailed prospectively collected data in a large series.
achyarrhythmias occur as early complications in the recovery period after coronary artery bypass grafting (CABG) and valvular surgery [1]. Postoperative atrial tachyarrhythmias, mainly atrial fibrillation and atrial flutter, develop in up to 40% of patients after CABG and in more than 50% of patients after valvular surgery [2]. This type of postoperative tachyarrhythmia has been widely investigated, and is usually transient and benign [3– 6]. Nonsustained ventricular tachycardias, as a short run of three or more consecutive ventricular complexes terminating spontaneously, are common with an incidence up to 36% [1]. This type of ventricular dysarrhythmia is often asymptomatic and may not be associated with increased morbidity or mortality after cardiac surgery [7]. In contrast, postoperative sustained ventricular tachyarrhythmias, such as monomorphic or polymorphic ventricular tachycardia and ventricular fibrillation, are uncommon but are life threatening [8 –10]. Partly because of its low incidence, the prevalence, mortality, and mechanisms have not been well defined [11–13]. There are Accepted for publication Dec 10, 2003. Address reprint requests to Dr Qi, Division of Cardiology, St. Paul’s Hospital, 1081 Burrard St, Vancouver BC, Canada V6Z 1Y6; e-mail: [email protected].
© 2004 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2004;77:2083– 8) © 2004 by The Society of Thoracic Surgeons
Patients and Methods Study Population The British Columbia Cardiac Registries [18] were created in 1991 and collect demographic, clinical, and operative data on all patients who undergo cardiac surgery procedures. At the time of cardiac surgery, the surgeon completes a 16-page form with detailed clinical and surgical information. The hospital Discharge Summary data form was first introduced in 1994. A trained researcher was responsible for completing the Discharge Data Form, which 0003-4975/04/$30.00 doi:10.1016/j.athoracsur.2003.12.020
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includes postoperative variables: patients’ outcome, major hospital events such as renal failure, myocardial infarction, and congestive heart failure, as well as ventricular tachycardia (VT). The present study reviewed data in the registries of all patients who underwent CABG, valve, and both operations between 1994 to 1999 in St. Paul’s Hospital. Patients who had emergent surgery or had a history of sustained VT or cardiac arrest before operation were excluded from the study. Therefore, 4,748 patients formed the subset for the study. The study protocol was approved by the Research Ethics Board of St. Paul’s Hospital, a teaching hospital of the University of British Columbia.
Surgical Procedures and Perioperative Management All patients were placed on cardiopulmonary bypass. Coronary artery bypass grafting was performed in 3,316 patients (69.8%), valvular surgery in 813 patients (17.1%), and both procedures in 619 patients (13.0%) using a standardized technique. There were six surgeons to perform the operations. One surgeon completed 245 procedures in this series (5.2%) and the remaining surgeons carried out 719 to 1,059 procedures (15.1% to 22.3%). Myocardial protection was provided by intermittent blood cardioplegia in all patients. After surgery, all patients were monitored in intensive care units and later in a monitored unit with a median interval of 6 days. Ventricular tachycardia (any episode with consecutive ventricular beats ⱖ 3) was identified and recorded in the Discharge Data Form. Of 224 identified with VT, further retrospective chart review confirmed new-onset SPOVT (n ⫽ 45), which was defined as VT ( ⬎ 100 beats/min), or ventricular fibrillation within 30 days of cardiac surgery, lasting more than 30 seconds unless terminated earlier because of hemodynamic collapse. At the time of the initial episode, there was no indication of hemodynamic compromise, absence of an electrolyte, or metabolic abnormality. Patient charts were reviewed thoroughly to assess SPOVT characteristics and management of the dysrhythmia. The primary physician and consultants managed ventricular tachycardia according to general clinical principles. The remaining 179 patients had nonsustained POVT, which was defined as a run of 3 or more consecutive ventricular beats at a rate more than 100 beats/min, terminating spontaneously within 30 seconds. Left ventricular (LV) ejection fraction was evaluated by cardioangiography (79.0%), echocardiography (14.6%), and radionuclide ventriculography (6.4%) before operation. Left ventricular ejection fraction collected in the registries was grouped as the following: (1) less than 35%; (2) 35% to 50%; (3) more than 50%.
Statistical Analysis Patients were divided into two groups: (1) patients experiencing SPOVT within 30 days of surgery; and (2) patients who did not experience SPOVT. Continuous variables are expressed as mean ⫾ standard deviation or median and interquartile range, as appropriate. Student’s t test or Wilcoxon Sign Rank test were applied to compare continuous variables and the 2 test was per-
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Table 1. Characteristics of Patients and Incidence of SPOVT by Surgery Type
Age (yr) Male, n (%) LV ejection fraction ⬍35% Urgent operation Graft number ⱖ3 Artery conduit ⱖ 1 ⱖ 2 valve replaced SPOVT a
CABG (n ⫽ 3316)
Valve (n ⫽ 813)
CABG ⫹ Valve (n ⫽ 619)
64.6 ⫾ 9.8 2639 (79.6) 254 (7.7)
63.2 ⫾ 13.3 458 (56.3) 46 (5.7)
70.5 ⫾ 8.6a 454 (73.3)a 139 (22.5)a
1449 (43.7) 3.0 ⫾ 0.8 2516 (75.9) 2304 (69.5) (N/A) 23 (0.69%)
157 (19.3) (N/A)
222 (35.9)a 2.1 ⫾ 0.9 244 (39.4) 81 (13.1) 74 (12.0) 16 (2.58%)a
(N/A) 157 (19.3) 6 (0.74%)
p ⱕ 0.001.
Values are n (%) or as mean ⫾ standard deviation. CABG ⫽ coronary artery bypass grafting; LV ⫽ left ventricle; N/A ⫽ not applicable; SPOVT ⫽ sustained postoperative ventricular tachycardia.
formed to assess categorical variables. A p value less than 0.05 (two-tailed) was considered to be statistically significant. Incidence of SPOVT was calculated. Univariate logistic regression was used to identify factors associated with SPOVT. All factors univariately associated with SPOVT at the p less than 0.10 level were selected for the multivariable model. Stepwise, conditional forward and backward variable entry techniques were used to identify the factors independently associated with SPOVT. Goodness of fit of the final model was assessed using the Hosmer-Lemeshow statistic and collinearity. For example, systemic hypertension and ejection fraction was assessed by examining the correlation matrix. The following variables were tested in the multivariable model: (1) clinical and demographic variables were age, gender, systemic hypertension, pulmonary hypertension, diabetes, chronic obstructive pulmonary disease, Canadian Cardiovascular Society angina class, New York Heart Association congestive heart failure class, LV ejection fraction, previous cardiovascular surgery, and urgent surgery; (2) operative variables included surgeon, warm or cold cardioplegia, number of bypass grafts, placement of arterial conduit, left main disease (stenosis ⬎ 50%), number of implanted valves, location of implanted valves, type of surgery, pump time, and aortic cross-clamp time.
Results Incidence of SPOVT Among 4,748 study patients, 45 patients suffered from SPOVT after CABG, and/or valvular surgery. The overall incidence of SPOVT was 0.95%. Patients undergoing both procedures had the highest rate, 2.58% compared to 0.69% and 0.74% in isolated CABG and isolated valvular surgery, respectively (Table 1). However, patients undergoing CABG plus valve surgery were older and often had reduced LV function and urgent surgery. Of note, su-
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Table 2. Clinical and Surgical Characteristics of Patients
Fig 1. Time of initial episode of postoperative ventricular tachycardia in the 45 study patients.
praventricular tachycardia and(or) atrial fibrillation occurred in 2,070 patients (43.6%).
Characteristics of SPOVT and Clinical Course The day of the initial episode of SPOVT was 3.9 ⫾ 5.2 days after operations and Figure 1 shows a histogram presenting the day of onset. The first episode presented in a monomorphic form in 24 patients (53.3%) or polymorphic form in 8 patients (17.8%) and the rate was 180.0 ⫾ 28.3 beat/min. The remaining 13 patients (28.9%) had an initial episode of ventricular fibrillation (VF) or flutter. In 43 of these 45 patients (95.5%), additional episodes of VT or VF occurred. Sustained postoperative ventricular tachycardia required direct current cardioversion to restore normal sinus rhythm in 30 patients (62.5%). All patients were given antiarrhythmic agents: intravenous amiodarone in 16 patients, and/or lidocaine in 25, procainamide in 6, -blocker in 5, sotalol in 4 [19 –23]. In 7 SPOVT patients, perioperative myocardial infarction, diagnosed according to electrocardiographic and enzymes evidence, occurred postoperatively. One patient was found to have a low serum potassium level 6 days after the surgery. In another patient, prolonged QT interval was observed and proarrhythmia induced by sotalol was suspected. Cardiac echocardiography was frequently performed postoperation to examine ventricular function, and the results showed deterioration of LV systolic function in 3 patients. Coronary angiography was performed in one patient, revealing patent grafts. One patient had stress myocardial perfusion imaging and a small ischemic zone was detected. The length of postoperative hospital stay differed among patients without and with SPOVT: 11.1 ⫾ 9.0 days and 15.6 ⫾ 11.4 days (p ⫽ 0.013). There were thirteen deaths in this subgroup within 30 days after operation. Among 32 survivors, 5 patients underwent electrophysiological study before discharge and 3 patients received implantable cardioverter defibrillators [24] due to induction of sustained VT similar to clinical VT. A total of 27 patients received chronic therapy
Group 2 (n ⫽ 4703)
Age (year) 69.3 ⫾ 8.9 65.1 ⫾ 10.6 Female sex 18 (40.0) 1179 (25.1) Systemic hypertension 22 (48.9) 1255 (26.7) Pulmonary hypertension 20 (44.4) 537 (11.4) CCS angina class ⱖ3 31 (68.9) 3277 (69.7) CHF NYHA class ⱖ3 19 (42.2) 1058 (22.5) LV ejection fraction ⬍35% 14 (31.1) 425 (9.0) 35–50% 20 (44.4) 1405 (29.9) ⬎50% 11 (24.4) 2873 (61.1) Previous cardiovascular 5 (11.1) 227 (4.8) surgery Urgent surgery 25 (55.6) 1803 (38.3) Type of operations CABG 23 (51.5) 3292 (70.0) Valve 6 (13.3) 807 (17.2) CABG ⫹ valve 16 (35.6) 603 (12.8) Cold cardioplegia 23 (51.4) 2002 (42.7) Bypass grafts, n 2.3 ⫾ 1.3 2.2 ⫾ 1.3 Arterial conduit placed 11 (24.4) 2374 (50.5) Pump time (min) 120.0 ⫾ 43.5a 93.0 ⫾ 45.0a Cross-clamp time (min) 75.0 ⫾ 43.0a 65.0 ⫾ 43.0a Left main disease 6 (13.3) 654 (13.9) Mitral valve replacement 16 (35.6) 733 (15.6) Aortic valve replacement 8 (17.8) 812 (17.3) Tricuspid valve replacement 5 (11.1) 80 (1.7) Death 13 (28.9) 90 (1.9)
p 0.008 0.022 0.001 ⱕ0.001 0.909 0.002 ⱕ0.001
0.052 0.018 ⬍0.001
0.249 0.558 0.001 0.005 0.069 0.912 ⱕ0.001 0.928 ⱕ0.001 ⱕ0.001
Categorical variables are counts and (%); continuous variables mean ⫾ standard deviation or a median ⫾ interquartile range. CCS ⫽ Canadian Cardiovascular Society; CHF ⫽ congestive heart failure; NYHA ⫽ New York Heart Association.
with amiodarone in 20 patients and -blocker in 8 patients. Amiodarone appeared to suppress SPOVT effectively. Two patients were discharged without antiarrhythmic agents and SPOVT in them was considered due to transient or reversible disorder, such as proarrhythmia due to sotalol. Over a mean follow-up of 18.1 ⫾ 11.2 months, late death occurred in 6 patients between 1.0 year and 5.1 years after cardiac surgery. Two of them had cardiac operations at ages of 81 years and 87 years. Recurrence of sustained VT was found in 5 patients, including one patient with a defibrillator.
Clinical and Operative Characteristics of Study Population Table 2 demonstrates clinical characteristics of patients in the two study groups. Patients of group 1 experienced SPOVT and were significantly older than those of group 2. Sustained postoperative ventricular tachycardia/ fibrillation was associated with female sex, systemic and pulmonary hypertension but not related to diabetes, chronic obstructive pulmonary disease, or Canadian Cardiovascular Society angina class. Severe congestive heart failure and low LV ejection fraction were more frequent in group1. Urgent surgery was more common in group 1, as was previous cardiovascular surgery.
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Table 3. Independent Risk Factors for SPOVT Odds ratio (95% CI)
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Sex (female:male) Ejection fraction ⬍35% : ⬎50% 35–50% : ⬎50% Pulmonary hypertension Systemic hypertension Pump time (10 minutes) CI ⫽ confidence interval; ular tachycardia.
1.982 (1.068 –3.680) 4.771 (2.015–11.298) 3.017 (1.424 – 6.393) 3.066 (1.602–5.869) 2.391 (1.312– 4.359) 1.085 (1.037–1.135)
p 0.030 0.001 ⱕ0.001 0.004 0.001 0.004 ⱕ0.001
SPOVT ⫽ sustained postoperative ventric-
Concomitant CABG and valvular procedures were performed more often in group 1. There were no significant differences in the number of bypass grafts, crossclamp time, use of cold(warm) cardioplegia, left anterior descending coronary artery, or left main artery disease between the two study groups (Table 2). Arterial conduits were placed more frequently in group 2 patients. Pump time was significantly longer in group 1 patients compared to group 2 patients. Mitral valve and tricuspid valve replacement were performed more frequently in group 1. Incidence of SPOVT was not associated with individual surgeons (range, 0.4% to 1.4%; p ⫽ 0.548). Early mortality was 28.9% (n ⫽ 13) among patients with SPOVT, whereas it was 1.9% (n ⫽ 90) in patients without SPOVT. The overall 30-day mortality was 2.2% in this study cohort (103 of 4,748). The highest mortality was observed in CABG plus valve replacement, 6.6%, followed by 2.2% in valve surgery and 1.3% in CABG.
Risk Factors for SPOVT Clinical and surgical variables with p less than 0.10 from univariate analysis were entered into the stepwise multivariate logistic regression analysis to define independent risk factors for SPOVT. Ejection fraction was one of the major predictors for the arrhythmia (Table 3). Ejection fraction less than 35% was associated with a fivefold increase in risk of SPOVT compared to ejection fraction more than 50%. Females were twice as likely to develop SPOVT. The risk of SPOVT was higher if pump time was prolonged. Other independent risk factors were the presence of systemic and pulmonary hypertension. Of note, operation type is not an independent predictor of SPOVT despite its significant relationship in univariate analysis.
Comment In this study, prospectively collected data on clinical characteristics of 4,748 patients as well as perioperative variables provide more accurate assessment of prevalence of SPOVT and the risk factors for the tachyarrhythmia following CABG, valve, and both procedures. The study reveals that the incidence of SPOVT is 0.95%. A significantly higher rate (2.58%) is observed in concomitant CABG and valvular surgery compared to either CABG or valvular surgery alone (0.69% to 0.74%). There
are several retrospective studies in which the observed rates range from 0.4% to 1.4% [8, 11, 14] but selection bias inherent in retrospective studies limits the accuracy of these results. Comparisons between studies are also limited because the definition of SPOVT varies, such that some investigators include SPOVT 5 months after the operation. Ducceschi and colleagues [17] report an incidence of 8.5% (n ⫽ 13) out of 152 patients. However, the study includes patients with a history of cardiac arrest and with LV aneurysmectomy. One prospectively designed study [25] reveals that the incidence of new-onset SPOVT within 30 days of surgery is 3.1% among 382 patients undergoing cardiac operations. Nevertheless, the prevalence of SPOVT is definitely low compared to postoperative atrial arrhythmias. Few studies have assessed the risk factors for SPOVT. In a case control study of 136 patients [15], there are 17 subjects with new-onset SPOVT. Univariate analysis shows that acute myocardial infarction, ejection fraction, and bypass graft to infarct zone are associated with SPOVT. In another study of 382 patients by Steinberg and colleagues [25], univariate analysis reveals that ejection fraction, previous myocardial infarction, and congestive heart failure increase the risk of SPOVT. However, placement of a bypass graft across a noncollateralized occluded vessel is the only independent predictor from multivariate analysis. The present study delineates potential risk factors from a multivariate analysis using a rich data set of variables. Ejection fraction is one of the strongest independent predictors of SPOVT, consistent with previous findings. Female gender generates a twofold increase in the risk of SPOVT. Prolonged pump time significantly influences the development of SPOVT. Previous studies report mortality rates of patients with SPOVT from 16.7% to 44.4%. Despite medical advances in pharmacological and nonpharmacological antiarrhythmic therapy, mortality in our study cohort remains high, 28.9% among patients with SPOVT compared to 1.9% in patients without the dysrhythmia. Surgical revascularization and valve surgery may present an antiarrhythmic function in selected patients because the procedures improve coronary circulation in patients with coronary artery disease, and improve ventricular performance by removing volume overload or relieving mechanical obstruction in patients with valve disease [26, 27]. However, the surgical procedure may trigger ventricular arrhythmias in a specific subset of patients. The underlying mechanism of POVT is less known and elevated levels of catecholamines and autonomic imbalance during early recovery period of surgery may be involved in the initiation of the dysrhythmias [1]. The autonomic nervous system has been widely implicated in the genesis of life-threatening arrhythmias in humans [28]. The present study suggests that selected patients with impaired LV function, prolonged pump time, and female gender are at increased risk of SPOVT. Multiple studies have demonstrated that impaired LV function is associated with complex ventricular arrhythmias and arrhythmic sudden death is common in patients with severe heart failure [29]. In respect to pro-
longed pump time, the presence of less optimal myocardial protection results in myocardial cellular damage [30], subsequently generating abnormal cellular electrophysiology, leading to significant ventricular arrhythmias. Female gender has been reported to have higher 30-day mortality and operative complications than male after CABG. Multiple factors contribute to this phenomenon. One of them is smaller body surface area in women, which is associated with coronary artery luminal diameter [31, 32] and greater difficulty in revascularization. In this study, women were older (67.3 years vs 64.4 y of men, p ⱕ 0.001) and the absence of artery grafting was more frequent in women (55.0% vs 35.0%, p ⱕ 0.001). The optimal management of SPOVT has not been well established, partly because SPOVT is uncommon and the mechanism has not been defined. Correction of any reversible causes of SPOVT, such as acute ischemia, should be routine. The SPOVT should be treated with intravenous antiarrhythmic medication and lidocaine is generally the first drug of choice in our institution. Amiodarone, developed as a coronary vasodilator, has complex electropharmacologic properties [33]. It slows intraventricular conduction by blocking sodium channel, slows the heart rate and impedes atrioventricular node conduction by blocking -adrenergic receptors and calcium channels, and prolongs atrial and ventricular repolarization by inhibiting potassium channels. Amiodarone has emerged as an important drug for the treatment of VT because of a low probability of VT/VF recurrence compared to other class I antiarrhythmic agents. Moreover, it rarely causes proarrhythmia (arrhythmia aggravation), which is not uncommon in class I antiarrhythmic agents and sotalol. In this series, patients with SPOVT frequently received intravenous and/or oral amiodarone and the medication appeared to be effective in a subgroup. Although conclusions cannot be drawn from this study, amiodarone is a choice to manage SPOVT. In summary, SPOVT is an uncommon arrhythmic complication in the early recovery period following cardiac surgery, but is associated with high 30-day mortality. The results of this study suggest that low LV ejection fraction, female gender, and prolonged pump time are strongly related to the development of SPOVT.
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Southern Thoracic Surgical Association: Fifty-first Annual Meeting The Fifty-first Annual Meeting of the Southern Thoracic Surgical Association (STSA) will be held November 4 – 6, 2004, in Cancun, Mexico. The Postgraduate Course will be held the morning of Thursday, November 4, 2004, and will provide in-depth coverage of thoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. Manuscripts accepted for the Resident Competition need to be submitted to the STSA headquarters office no later than September 17, 2004. The Resident Award will be based on abstract, presentation, and manuscript. Applications for membership should be completed by September 15, 2004, and forwarded to John P. Marbarger,
MD, Membership Committee Chairman, Southern Thoracic Surgical Association, 633 N Saint Clair St, Suite 2320, Chicago, IL 60611-3658. John H. Calhoon, MD Secretary/Treasurer Southern Thoracic Surgical Association 633 N Saint Clair St, Suite 2320 Chicago, IL 60611-3658 (800) 685-STSA or (312) 202-5892 fax: (312) 202-5801 e-mail: [email protected]; website: http://www.stsa.org.
Please visit the STSA (http://www.stsa.org) or CTSNet (http://www.ctsnet.org) websites for detailed information on submitting abstracts. All abstracts must be submitted electronically for consideration.
© 2004 by The Society of Thoracic Surgeons Published by Elsevier Inc
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Background. Malignant ventricular tachyarrhythmia early after cardiac surgery is an uncommon arrhythmic complication but has a negative impact on mortality. The purpose of this study was to evaluate the incidence of new-onset sustained postoperative ventricular tachycardia-ventricular fibrillation and to identify risk factors for the dysrhythmia. Methods. Demographic, clinical, operative, and postoperative data, including a variable of postoperative ventricular tachycardia, were prospectively obtained from 4,748 patients undergoing nonemergency coronary artery bypass graft and(or) valve replacement with no history of sustained ventricular tachycardia or sudden death. A detailed analysis was performed to define the risk factors for the ventricular tachycardia and the prognostic impact of the arrhythmia on 30-day mortality was evaluated. Results. Forty-five patients (0.95%) had sustained ventricular tachycardia or ventricular fibrillation and the initial episode occurred 3.9 ⴞ 5.2 days (mean ⴞ standard
deviation) after surgery. By multivariate analysis, female sex (odds ratio, 1.982), left ventricular ejection fraction (< 35%: > 50%, 4.771), the presence of pulmonary hypertension (3.066), the presence of systemic hypertension (2.391), and pump time (per 10 minutes, 1.085) were independently associated with the dysrhythmias. Early mortality of patients with the arrhythmia was 28.9%, strikingly higher than that of patients without ventricular tachycardia/ventricular fibrillation (1.9%). Conclusions. Left ventricular ejection fraction is the strongest risk factor for new-onset postoperative sustained ventricular tachycardia-ventricular fibrillation; female sex, pump time, pulmonary and systemic hypertension are independent predictors of the dysrhythmias; the arrhythmia is associated with increased 30-day mortality after cardiac surgery.
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several case reports and small series describing sustained ventricular tachycardia after cardiac surgery, but a detailed risk factor analysis has not been performed in a large study population [14 –17]. The present study evaluated the incidence of newonset sustained postoperative ventricular tachycardiafibrillation (SPOVT) in patients undergoing CABG, valvular surgery, and concomitant CABG, and valvular surgery and identified risk factors associated with the development of the tachyarrhythmias from the detailed prospectively collected data in a large series.
achyarrhythmias occur as early complications in the recovery period after coronary artery bypass grafting (CABG) and valvular surgery [1]. Postoperative atrial tachyarrhythmias, mainly atrial fibrillation and atrial flutter, develop in up to 40% of patients after CABG and in more than 50% of patients after valvular surgery [2]. This type of postoperative tachyarrhythmia has been widely investigated, and is usually transient and benign [3– 6]. Nonsustained ventricular tachycardias, as a short run of three or more consecutive ventricular complexes terminating spontaneously, are common with an incidence up to 36% [1]. This type of ventricular dysarrhythmia is often asymptomatic and may not be associated with increased morbidity or mortality after cardiac surgery [7]. In contrast, postoperative sustained ventricular tachyarrhythmias, such as monomorphic or polymorphic ventricular tachycardia and ventricular fibrillation, are uncommon but are life threatening [8 –10]. Partly because of its low incidence, the prevalence, mortality, and mechanisms have not been well defined [11–13]. There are Accepted for publication Dec 10, 2003. Address reprint requests to Dr Qi, Division of Cardiology, St. Paul’s Hospital, 1081 Burrard St, Vancouver BC, Canada V6Z 1Y6; e-mail: [email protected].
© 2004 by The Society of Thoracic Surgeons Published by Elsevier Inc
(Ann Thorac Surg 2004;77:2083– 8) © 2004 by The Society of Thoracic Surgeons
Patients and Methods Study Population The British Columbia Cardiac Registries [18] were created in 1991 and collect demographic, clinical, and operative data on all patients who undergo cardiac surgery procedures. At the time of cardiac surgery, the surgeon completes a 16-page form with detailed clinical and surgical information. The hospital Discharge Summary data form was first introduced in 1994. A trained researcher was responsible for completing the Discharge Data Form, which 0003-4975/04/$30.00 doi:10.1016/j.athoracsur.2003.12.020
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includes postoperative variables: patients’ outcome, major hospital events such as renal failure, myocardial infarction, and congestive heart failure, as well as ventricular tachycardia (VT). The present study reviewed data in the registries of all patients who underwent CABG, valve, and both operations between 1994 to 1999 in St. Paul’s Hospital. Patients who had emergent surgery or had a history of sustained VT or cardiac arrest before operation were excluded from the study. Therefore, 4,748 patients formed the subset for the study. The study protocol was approved by the Research Ethics Board of St. Paul’s Hospital, a teaching hospital of the University of British Columbia.
Surgical Procedures and Perioperative Management All patients were placed on cardiopulmonary bypass. Coronary artery bypass grafting was performed in 3,316 patients (69.8%), valvular surgery in 813 patients (17.1%), and both procedures in 619 patients (13.0%) using a standardized technique. There were six surgeons to perform the operations. One surgeon completed 245 procedures in this series (5.2%) and the remaining surgeons carried out 719 to 1,059 procedures (15.1% to 22.3%). Myocardial protection was provided by intermittent blood cardioplegia in all patients. After surgery, all patients were monitored in intensive care units and later in a monitored unit with a median interval of 6 days. Ventricular tachycardia (any episode with consecutive ventricular beats ⱖ 3) was identified and recorded in the Discharge Data Form. Of 224 identified with VT, further retrospective chart review confirmed new-onset SPOVT (n ⫽ 45), which was defined as VT ( ⬎ 100 beats/min), or ventricular fibrillation within 30 days of cardiac surgery, lasting more than 30 seconds unless terminated earlier because of hemodynamic collapse. At the time of the initial episode, there was no indication of hemodynamic compromise, absence of an electrolyte, or metabolic abnormality. Patient charts were reviewed thoroughly to assess SPOVT characteristics and management of the dysrhythmia. The primary physician and consultants managed ventricular tachycardia according to general clinical principles. The remaining 179 patients had nonsustained POVT, which was defined as a run of 3 or more consecutive ventricular beats at a rate more than 100 beats/min, terminating spontaneously within 30 seconds. Left ventricular (LV) ejection fraction was evaluated by cardioangiography (79.0%), echocardiography (14.6%), and radionuclide ventriculography (6.4%) before operation. Left ventricular ejection fraction collected in the registries was grouped as the following: (1) less than 35%; (2) 35% to 50%; (3) more than 50%.
Statistical Analysis Patients were divided into two groups: (1) patients experiencing SPOVT within 30 days of surgery; and (2) patients who did not experience SPOVT. Continuous variables are expressed as mean ⫾ standard deviation or median and interquartile range, as appropriate. Student’s t test or Wilcoxon Sign Rank test were applied to compare continuous variables and the 2 test was per-
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Table 1. Characteristics of Patients and Incidence of SPOVT by Surgery Type
Age (yr) Male, n (%) LV ejection fraction ⬍35% Urgent operation Graft number ⱖ3 Artery conduit ⱖ 1 ⱖ 2 valve replaced SPOVT a
CABG (n ⫽ 3316)
Valve (n ⫽ 813)
CABG ⫹ Valve (n ⫽ 619)
64.6 ⫾ 9.8 2639 (79.6) 254 (7.7)
63.2 ⫾ 13.3 458 (56.3) 46 (5.7)
70.5 ⫾ 8.6a 454 (73.3)a 139 (22.5)a
1449 (43.7) 3.0 ⫾ 0.8 2516 (75.9) 2304 (69.5) (N/A) 23 (0.69%)
157 (19.3) (N/A)
222 (35.9)a 2.1 ⫾ 0.9 244 (39.4) 81 (13.1) 74 (12.0) 16 (2.58%)a
(N/A) 157 (19.3) 6 (0.74%)
p ⱕ 0.001.
Values are n (%) or as mean ⫾ standard deviation. CABG ⫽ coronary artery bypass grafting; LV ⫽ left ventricle; N/A ⫽ not applicable; SPOVT ⫽ sustained postoperative ventricular tachycardia.
formed to assess categorical variables. A p value less than 0.05 (two-tailed) was considered to be statistically significant. Incidence of SPOVT was calculated. Univariate logistic regression was used to identify factors associated with SPOVT. All factors univariately associated with SPOVT at the p less than 0.10 level were selected for the multivariable model. Stepwise, conditional forward and backward variable entry techniques were used to identify the factors independently associated with SPOVT. Goodness of fit of the final model was assessed using the Hosmer-Lemeshow statistic and collinearity. For example, systemic hypertension and ejection fraction was assessed by examining the correlation matrix. The following variables were tested in the multivariable model: (1) clinical and demographic variables were age, gender, systemic hypertension, pulmonary hypertension, diabetes, chronic obstructive pulmonary disease, Canadian Cardiovascular Society angina class, New York Heart Association congestive heart failure class, LV ejection fraction, previous cardiovascular surgery, and urgent surgery; (2) operative variables included surgeon, warm or cold cardioplegia, number of bypass grafts, placement of arterial conduit, left main disease (stenosis ⬎ 50%), number of implanted valves, location of implanted valves, type of surgery, pump time, and aortic cross-clamp time.
Results Incidence of SPOVT Among 4,748 study patients, 45 patients suffered from SPOVT after CABG, and/or valvular surgery. The overall incidence of SPOVT was 0.95%. Patients undergoing both procedures had the highest rate, 2.58% compared to 0.69% and 0.74% in isolated CABG and isolated valvular surgery, respectively (Table 1). However, patients undergoing CABG plus valve surgery were older and often had reduced LV function and urgent surgery. Of note, su-
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Table 2. Clinical and Surgical Characteristics of Patients
Fig 1. Time of initial episode of postoperative ventricular tachycardia in the 45 study patients.
praventricular tachycardia and(or) atrial fibrillation occurred in 2,070 patients (43.6%).
Characteristics of SPOVT and Clinical Course The day of the initial episode of SPOVT was 3.9 ⫾ 5.2 days after operations and Figure 1 shows a histogram presenting the day of onset. The first episode presented in a monomorphic form in 24 patients (53.3%) or polymorphic form in 8 patients (17.8%) and the rate was 180.0 ⫾ 28.3 beat/min. The remaining 13 patients (28.9%) had an initial episode of ventricular fibrillation (VF) or flutter. In 43 of these 45 patients (95.5%), additional episodes of VT or VF occurred. Sustained postoperative ventricular tachycardia required direct current cardioversion to restore normal sinus rhythm in 30 patients (62.5%). All patients were given antiarrhythmic agents: intravenous amiodarone in 16 patients, and/or lidocaine in 25, procainamide in 6, -blocker in 5, sotalol in 4 [19 –23]. In 7 SPOVT patients, perioperative myocardial infarction, diagnosed according to electrocardiographic and enzymes evidence, occurred postoperatively. One patient was found to have a low serum potassium level 6 days after the surgery. In another patient, prolonged QT interval was observed and proarrhythmia induced by sotalol was suspected. Cardiac echocardiography was frequently performed postoperation to examine ventricular function, and the results showed deterioration of LV systolic function in 3 patients. Coronary angiography was performed in one patient, revealing patent grafts. One patient had stress myocardial perfusion imaging and a small ischemic zone was detected. The length of postoperative hospital stay differed among patients without and with SPOVT: 11.1 ⫾ 9.0 days and 15.6 ⫾ 11.4 days (p ⫽ 0.013). There were thirteen deaths in this subgroup within 30 days after operation. Among 32 survivors, 5 patients underwent electrophysiological study before discharge and 3 patients received implantable cardioverter defibrillators [24] due to induction of sustained VT similar to clinical VT. A total of 27 patients received chronic therapy
Group 2 (n ⫽ 4703)
Age (year) 69.3 ⫾ 8.9 65.1 ⫾ 10.6 Female sex 18 (40.0) 1179 (25.1) Systemic hypertension 22 (48.9) 1255 (26.7) Pulmonary hypertension 20 (44.4) 537 (11.4) CCS angina class ⱖ3 31 (68.9) 3277 (69.7) CHF NYHA class ⱖ3 19 (42.2) 1058 (22.5) LV ejection fraction ⬍35% 14 (31.1) 425 (9.0) 35–50% 20 (44.4) 1405 (29.9) ⬎50% 11 (24.4) 2873 (61.1) Previous cardiovascular 5 (11.1) 227 (4.8) surgery Urgent surgery 25 (55.6) 1803 (38.3) Type of operations CABG 23 (51.5) 3292 (70.0) Valve 6 (13.3) 807 (17.2) CABG ⫹ valve 16 (35.6) 603 (12.8) Cold cardioplegia 23 (51.4) 2002 (42.7) Bypass grafts, n 2.3 ⫾ 1.3 2.2 ⫾ 1.3 Arterial conduit placed 11 (24.4) 2374 (50.5) Pump time (min) 120.0 ⫾ 43.5a 93.0 ⫾ 45.0a Cross-clamp time (min) 75.0 ⫾ 43.0a 65.0 ⫾ 43.0a Left main disease 6 (13.3) 654 (13.9) Mitral valve replacement 16 (35.6) 733 (15.6) Aortic valve replacement 8 (17.8) 812 (17.3) Tricuspid valve replacement 5 (11.1) 80 (1.7) Death 13 (28.9) 90 (1.9)
p 0.008 0.022 0.001 ⱕ0.001 0.909 0.002 ⱕ0.001
0.052 0.018 ⬍0.001
0.249 0.558 0.001 0.005 0.069 0.912 ⱕ0.001 0.928 ⱕ0.001 ⱕ0.001
Categorical variables are counts and (%); continuous variables mean ⫾ standard deviation or a median ⫾ interquartile range. CCS ⫽ Canadian Cardiovascular Society; CHF ⫽ congestive heart failure; NYHA ⫽ New York Heart Association.
with amiodarone in 20 patients and -blocker in 8 patients. Amiodarone appeared to suppress SPOVT effectively. Two patients were discharged without antiarrhythmic agents and SPOVT in them was considered due to transient or reversible disorder, such as proarrhythmia due to sotalol. Over a mean follow-up of 18.1 ⫾ 11.2 months, late death occurred in 6 patients between 1.0 year and 5.1 years after cardiac surgery. Two of them had cardiac operations at ages of 81 years and 87 years. Recurrence of sustained VT was found in 5 patients, including one patient with a defibrillator.
Clinical and Operative Characteristics of Study Population Table 2 demonstrates clinical characteristics of patients in the two study groups. Patients of group 1 experienced SPOVT and were significantly older than those of group 2. Sustained postoperative ventricular tachycardia/ fibrillation was associated with female sex, systemic and pulmonary hypertension but not related to diabetes, chronic obstructive pulmonary disease, or Canadian Cardiovascular Society angina class. Severe congestive heart failure and low LV ejection fraction were more frequent in group1. Urgent surgery was more common in group 1, as was previous cardiovascular surgery.
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Table 3. Independent Risk Factors for SPOVT Odds ratio (95% CI)
Risk factor CARDIOVASCULAR
Sex (female:male) Ejection fraction ⬍35% : ⬎50% 35–50% : ⬎50% Pulmonary hypertension Systemic hypertension Pump time (10 minutes) CI ⫽ confidence interval; ular tachycardia.
1.982 (1.068 –3.680) 4.771 (2.015–11.298) 3.017 (1.424 – 6.393) 3.066 (1.602–5.869) 2.391 (1.312– 4.359) 1.085 (1.037–1.135)
p 0.030 0.001 ⱕ0.001 0.004 0.001 0.004 ⱕ0.001
SPOVT ⫽ sustained postoperative ventric-
Concomitant CABG and valvular procedures were performed more often in group 1. There were no significant differences in the number of bypass grafts, crossclamp time, use of cold(warm) cardioplegia, left anterior descending coronary artery, or left main artery disease between the two study groups (Table 2). Arterial conduits were placed more frequently in group 2 patients. Pump time was significantly longer in group 1 patients compared to group 2 patients. Mitral valve and tricuspid valve replacement were performed more frequently in group 1. Incidence of SPOVT was not associated with individual surgeons (range, 0.4% to 1.4%; p ⫽ 0.548). Early mortality was 28.9% (n ⫽ 13) among patients with SPOVT, whereas it was 1.9% (n ⫽ 90) in patients without SPOVT. The overall 30-day mortality was 2.2% in this study cohort (103 of 4,748). The highest mortality was observed in CABG plus valve replacement, 6.6%, followed by 2.2% in valve surgery and 1.3% in CABG.
Risk Factors for SPOVT Clinical and surgical variables with p less than 0.10 from univariate analysis were entered into the stepwise multivariate logistic regression analysis to define independent risk factors for SPOVT. Ejection fraction was one of the major predictors for the arrhythmia (Table 3). Ejection fraction less than 35% was associated with a fivefold increase in risk of SPOVT compared to ejection fraction more than 50%. Females were twice as likely to develop SPOVT. The risk of SPOVT was higher if pump time was prolonged. Other independent risk factors were the presence of systemic and pulmonary hypertension. Of note, operation type is not an independent predictor of SPOVT despite its significant relationship in univariate analysis.
Comment In this study, prospectively collected data on clinical characteristics of 4,748 patients as well as perioperative variables provide more accurate assessment of prevalence of SPOVT and the risk factors for the tachyarrhythmia following CABG, valve, and both procedures. The study reveals that the incidence of SPOVT is 0.95%. A significantly higher rate (2.58%) is observed in concomitant CABG and valvular surgery compared to either CABG or valvular surgery alone (0.69% to 0.74%). There
are several retrospective studies in which the observed rates range from 0.4% to 1.4% [8, 11, 14] but selection bias inherent in retrospective studies limits the accuracy of these results. Comparisons between studies are also limited because the definition of SPOVT varies, such that some investigators include SPOVT 5 months after the operation. Ducceschi and colleagues [17] report an incidence of 8.5% (n ⫽ 13) out of 152 patients. However, the study includes patients with a history of cardiac arrest and with LV aneurysmectomy. One prospectively designed study [25] reveals that the incidence of new-onset SPOVT within 30 days of surgery is 3.1% among 382 patients undergoing cardiac operations. Nevertheless, the prevalence of SPOVT is definitely low compared to postoperative atrial arrhythmias. Few studies have assessed the risk factors for SPOVT. In a case control study of 136 patients [15], there are 17 subjects with new-onset SPOVT. Univariate analysis shows that acute myocardial infarction, ejection fraction, and bypass graft to infarct zone are associated with SPOVT. In another study of 382 patients by Steinberg and colleagues [25], univariate analysis reveals that ejection fraction, previous myocardial infarction, and congestive heart failure increase the risk of SPOVT. However, placement of a bypass graft across a noncollateralized occluded vessel is the only independent predictor from multivariate analysis. The present study delineates potential risk factors from a multivariate analysis using a rich data set of variables. Ejection fraction is one of the strongest independent predictors of SPOVT, consistent with previous findings. Female gender generates a twofold increase in the risk of SPOVT. Prolonged pump time significantly influences the development of SPOVT. Previous studies report mortality rates of patients with SPOVT from 16.7% to 44.4%. Despite medical advances in pharmacological and nonpharmacological antiarrhythmic therapy, mortality in our study cohort remains high, 28.9% among patients with SPOVT compared to 1.9% in patients without the dysrhythmia. Surgical revascularization and valve surgery may present an antiarrhythmic function in selected patients because the procedures improve coronary circulation in patients with coronary artery disease, and improve ventricular performance by removing volume overload or relieving mechanical obstruction in patients with valve disease [26, 27]. However, the surgical procedure may trigger ventricular arrhythmias in a specific subset of patients. The underlying mechanism of POVT is less known and elevated levels of catecholamines and autonomic imbalance during early recovery period of surgery may be involved in the initiation of the dysrhythmias [1]. The autonomic nervous system has been widely implicated in the genesis of life-threatening arrhythmias in humans [28]. The present study suggests that selected patients with impaired LV function, prolonged pump time, and female gender are at increased risk of SPOVT. Multiple studies have demonstrated that impaired LV function is associated with complex ventricular arrhythmias and arrhythmic sudden death is common in patients with severe heart failure [29]. In respect to pro-
longed pump time, the presence of less optimal myocardial protection results in myocardial cellular damage [30], subsequently generating abnormal cellular electrophysiology, leading to significant ventricular arrhythmias. Female gender has been reported to have higher 30-day mortality and operative complications than male after CABG. Multiple factors contribute to this phenomenon. One of them is smaller body surface area in women, which is associated with coronary artery luminal diameter [31, 32] and greater difficulty in revascularization. In this study, women were older (67.3 years vs 64.4 y of men, p ⱕ 0.001) and the absence of artery grafting was more frequent in women (55.0% vs 35.0%, p ⱕ 0.001). The optimal management of SPOVT has not been well established, partly because SPOVT is uncommon and the mechanism has not been defined. Correction of any reversible causes of SPOVT, such as acute ischemia, should be routine. The SPOVT should be treated with intravenous antiarrhythmic medication and lidocaine is generally the first drug of choice in our institution. Amiodarone, developed as a coronary vasodilator, has complex electropharmacologic properties [33]. It slows intraventricular conduction by blocking sodium channel, slows the heart rate and impedes atrioventricular node conduction by blocking -adrenergic receptors and calcium channels, and prolongs atrial and ventricular repolarization by inhibiting potassium channels. Amiodarone has emerged as an important drug for the treatment of VT because of a low probability of VT/VF recurrence compared to other class I antiarrhythmic agents. Moreover, it rarely causes proarrhythmia (arrhythmia aggravation), which is not uncommon in class I antiarrhythmic agents and sotalol. In this series, patients with SPOVT frequently received intravenous and/or oral amiodarone and the medication appeared to be effective in a subgroup. Although conclusions cannot be drawn from this study, amiodarone is a choice to manage SPOVT. In summary, SPOVT is an uncommon arrhythmic complication in the early recovery period following cardiac surgery, but is associated with high 30-day mortality. The results of this study suggest that low LV ejection fraction, female gender, and prolonged pump time are strongly related to the development of SPOVT.
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Southern Thoracic Surgical Association: Fifty-first Annual Meeting The Fifty-first Annual Meeting of the Southern Thoracic Surgical Association (STSA) will be held November 4 – 6, 2004, in Cancun, Mexico. The Postgraduate Course will be held the morning of Thursday, November 4, 2004, and will provide in-depth coverage of thoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. Manuscripts accepted for the Resident Competition need to be submitted to the STSA headquarters office no later than September 17, 2004. The Resident Award will be based on abstract, presentation, and manuscript. Applications for membership should be completed by September 15, 2004, and forwarded to John P. Marbarger,
MD, Membership Committee Chairman, Southern Thoracic Surgical Association, 633 N Saint Clair St, Suite 2320, Chicago, IL 60611-3658. John H. Calhoon, MD Secretary/Treasurer Southern Thoracic Surgical Association 633 N Saint Clair St, Suite 2320 Chicago, IL 60611-3658 (800) 685-STSA or (312) 202-5892 fax: (312) 202-5801 e-mail: [email protected]; website: http://www.stsa.org.
Please visit the STSA (http://www.stsa.org) or CTSNet (http://www.ctsnet.org) websites for detailed information on submitting abstracts. All abstracts must be submitted electronically for consideration.
© 2004 by The Society of Thoracic Surgeons Published by Elsevier Inc
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