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Ann Thorac Surg 2001;72:2065-2069
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Risk stratification in acute type A dissection: proposition for a new scoring system

^a Department of Cardiothoracic Surgery, St. Antonius Hospital, Nieuwegein, The Netherlands
^b Department of Cardiology Research and Statistical Analysis, St. Antonius Hospital, Nieuwegein, The Netherlands

Accepted for publication August 7, 2001.

* Address reprint requests to Dr Tan, Department of Cardiothoracic Surgery, St. Antonius Hospital, Koekoekslaan 1, 3435 CM Nieuwegein, The Netherlands
e-mail: erwin.tan{at}tiscali.nl

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The aim of this study was to develop a scoring system for operative mortality of patients with acute type A aortic dissection.

Methods. Between 1974 and 1999, a total of 252 patients were operated on for an acute type A aortic dissection. We reviewed retrospectively preoperative and intraoperative records to conduct an analysis of risk factors associated with surgery. Multivariate analysis was used to predict operative mortality and to provide a preoperative risk profile of each individual patient that could be used for future patients.

Results. Operative mortality was 25.0% (n = 63). A logistic regression model with three explanatory variables to predict operative death showed a good fit: the risk factors associated with operative mortality were preoperative cardiopulmonary resuscitation (p = 0.0013, odds ratio = 15.7) and iatrogenic dissection (p = 0.0014, odds ratio = 9.8). Drained pericardial tamponade (p = 0.0386, odds ratio = 0.12) appeared to be a protective factor associated with decreased mortality.

Conclusions. Because existing scoring systems do not fit this pathologic condition, we propose the use of this Antonius Dissection Scoring System, based on the logistic regression model, to predict the chances of operative mortality for each patient before operation. The survival of patients with concomittant pericardial tamponade may benefit from pericardial drainage.

	Introduction

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In acute type A aortic dissection, emergency surgery is required to prevent fatal rupture into the pericardium and to avoid pericardial tamponade. Improved surgical techniques and perioperative care have resulted in a reduction of the operative risk over the last decades [1–6]. However, the surgical treatment of an acutely dissected ascending aorta still carries a considerable operative mortality, ranging from 21% to 30% [1–11]. We assessed the relationship between preoperative risk factors and operative mortality. We retrospectively reviewed the charts of patients who underwent operation in our institution, and conducted a detailed preoperative risk analysis. Based on this model, we aimed to define a new scoring system to predict operative mortality.

	Material and methods

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Patient population
Between November 1974 and September 1999, a total of 252 patients with acute type A aortic dissection were admitted for emergency surgery to the St. Antonius Hospital (Nieuwegein, The Netherlands). There were 163 men and 89 women with a mean age of 58 years (range 16 to 82 years). We obtained all clinical data by retrospective review of the patient records. The diagnosis of acute type A aortic dissection, according to the Stanford classification [12], was made mainly by transesophageal echocardiography (63%, n = 160), which is our current diagnostic method of choice; computed tomography (26%, n = 66), or magnetic resonance imaging. In the early years, diagnosis was confirmed by aortography. The interval between onset of acute symptoms and operation was within 14 days. Eleven patients (4.4%) had Marfan’s syndrome. In 2 patients, dissection occurred during pregnancy. Twelve patients had an iatrogenic dissection after cardiac surgery (coronary bypass grafting in 6, aortic valve replacement in 4, combined coronary bypass grafting and aortic valve replacement in 1, and mitral valve plasty in 1) with a median interval of 2 days before the onset of the diagnosis of dissection. In 4 of these patients, type A dissection originated intraoperatively. A total of 31 patients (12%) had signs of neurologic dysfunction before surgery. This included 3 patients with peripheral neurologic dysfunction and 28 with central neurologic dysfunction. In 11 patients (4.4%), adequate circulation was preoperatively restored by draining pericardial tamponade; this was done by puncture in all cases. Cardiopulmonary resuscitation was performed in 12 patients (4.8%). Operative mortality was defined as death occurring within 30 days after the operation or during initial hospitalization. No patients were lost to follow-up during this period.

Surgical considerations
A standard median sternotomy was performed and the patients were generally placed on total cardiopulmonary bypass with venous cannulation of the right atrium and right or left femoral arterial cannulation. Myocardial protection was obtained with cold crystalloid cardioplegic solution directly into the coronary ostia. The left heart was vented through a transmitral catheter. Depending on the operative findings, in most patients a Dacron tubegraft replacement of the ascending aorta was performed; if an intimal tear was found in the aortic arch, concomitant partial, total arch replacement or elephant trunk was performed in 30 patients (11.9%), 9 patients (3.6%), and 1 patient (0.4%), respectively. Teflon felt was frequently used. Deep hypothermic circulatory arrest was applied in 118 patients (46.8%) to allow for an open distal anastomosis or for arch replacement. Antegrade selective cerebral perfusion was used in 43 patients (17.1%) during circulatory arrest of the body [13]. We used retrograde cerebral perfusion on two occasions. The remaining 89 patients (35.3%) have been operated on with simple aortic cross-clamping without deep hypothermic circulatory arrest, antegrade selective cerebral perfusion, or retrograde cerebral perfusion. The aortic valve was examined and, if necessary, resuspended in 125 cases (49.6%) with commissural stitches or reconstructed with gelatin-resorcinol-formaldehyde (GRF) glue (Colle biologique, Fii, Saint Just Malmont, France) [14]. In 2 patients, to preserve the aortic valve leaflets, aortic root remodeling was performed by reimplantation of the aortic valve in a tubular Dacron graft according to David and Feindel [15]. When this procedure was deemed inappropriate or inadequate because of aortic valve disease or damage to the cusps, a mechanical bileaflet valve was inserted in 16 cases (6.3%) or an aortic root replacement with composite prosthesis and reimplantation of the coronary arteries (Bentall technique) in 30 cases (11.9%).

Statistical analysis
We evaluated the influence of 23 preoperative variables on operative mortality by univariate and multivariate analysis. The modeling process for risk stratification followed a standard equation and the probability of operative mortality was calculated for each patient.

The Statistical Analysis Software program (version 6.12 for Windows, SAS Institute, Cary, NC) was used to perform all analyses. Stepwise multivariate analysis was performed to determine patient characteristics independently associated with operative mortality. In univariate analysis discrete variables were analyzed by the ² or Fisher exact test. Statistical significance was associated with a p value of less than 0.05. Variables with a p value of less than 0.15 were entered into multivariate analysis by stepwise logistic regression to develop a risk equation of the form p = 1/[1 + exp (- x)]. In this equation, p is the probability of operative death, x = B0 X0 + B1 X1 + Bk Xk, each B value is a constant associated with a specific risk factor, and the X values denote the status of the risk factor for a given patient. The patient related variables are listed in Table 1.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Operative mortality among all 252 patients was 25.0% (63 of 252). Univariate significant predictors for operative mortality were preoperative cardiopulmonary resuscitation (p = 0.002) and its derivative emergency sternotomy (p = 0.002), iatrogenic dissection (p = 0.002), and acute pain at presentation (p = 0.003). Preoperative pericardial drainage by punction or subxyphoidal route did not reach significance at univariate analysis.

Independent significant risk factors for operative mortality determined by stepwise logistic regression were iatrogenic dissection and preoperative cardiopulmonary, as listed in Table 2. Preoperative pericardial drainage by punction or subxyphoidal route was a significant predictor for decreased operative mortality.

Based on this Antonius Dissection Scoring System, a patient who has his or her aorta dissected shortly after a cardiac intervention and who also needs to be resuscitated before the repair, has a risk of dying of: 1/[1+exp (-1.94 + 2.3 + 2.8 - 0)] = 1/(1+ exp -3.2) = 1/ [1 + 0.04] = 1/1.04 = 95.7%, whereas a patient without iatrogenic dissection, no need for cardiopulmonary resuscitation and no drained pericardial tamponade, has a chance of 87.4% to survive the repair. Possible permutations to determine a given patient’s operative risk are listed in Table 3.

	Comment

Top Abstract Introduction Material and methods Results Comment References

We reviewed 23 preoperative risk factors to construct a predictive model for operative mortality. Although we are aware of the fact that perioperative variables have been documented as independent predictors of operative mortality [1–6, 10], we did not include intraoperative and postoperative variables in our analysis because we believe that the risk stratification is supposed to be done before surgery and to help us to determine which patients have an unacceptable high operative risk.

Because surgery before 1990 was nearly significant as an operative risk factor (p = 0.087), we also assessed the operative date as a possible longitudinal risk factor of mortality in the analysis, which appeared not to be the case (p = 0.37, Relative Rate = 0.88 for each cumulative 5-year period, Confidence Interval = 0.67 to 1.16). This means that, although surgical treatment clearly evolved over the past 25 years, mortality remained comparatively stable. In the patient cohort operated before 1990, operative mortality was 32% (n = 26) versus 21% (n = 37) after 1990 (p = 0.08). Of course, we still need to consider the retrospective, nonrandomized nature of this study and the results of different surgeons using a variety of available techniques.

The predominant risk factors, which appeared to be associated with early death, were determined by multivariate analysis. The risk model that we developed uses statistical algorithms to calculate the probability of operative death. The presence or absence of any risk factor for any given patient was statistically manipulated to provide a risk-adjusted estimate of early mortality based on the total experience with all of our patients.

The operative mortality rates increased significantly for patients who had an iatrogenic dissection or who received cardiopulmonary resuscitation. In addition, preoperative pericardial drainage by punction decreased the mortality rate significantly for all patients.

Hemodynamic compromise or cardiogenic shock did not emerge as an independent risk factor for operative mortality. This is probably due to the fact that many of these patients required cardiopulmonary resuscitation, which was an independent risk factor for operative mortality.

In acute type A dissection, half of the strokes observed occurred in patients with severe hypotension, and much of the damage is considered to be done before the operation begins. Therefore, the stroke rate cannot be expected to respond to the generally beneficial effects of improvements and refinements in circulatory support adjuncts such as retrograde cerebral perfusion [20]. Neurologic dysfunction was included, even if present less than 24 hours before operation. Neurologic dysfunctioning was considered to be of central or peripheral origin, as with symptoms due to brain or myelum ischemia. Localized peripheral ischemia without focal brain or myelum symptoms was not included in this study as a relevant neurologic disorder.

In order to calculate a possible difference in catastrophic outcome, we have differentiated iatrogenic dissections occurring intraoperatively from those occurring postoperatively over the mid or long term. Twelve patients had an iatrogenic dissection, of which four originated intraoperatively. Three of these 4 patients (75.0%) died within 30 days, versus 5 of the remaining 8 patients with a history of cardiac surgery who died within 30 days (62.5%), p = 0.99. This means that the groups are not significantly different and therefore more or less comparable in terms of catastrophic outcome.

Preoperative hemodynamic compromise resulting from pericardial tamponade should be treated promptly. If emergency femoro-femoral bypass (the accepted treatment to restore adequate circulation) cannot be implemented quickly, it must be conceded that draining pericardial tamponade before operation could be faster and more effective. However, many referring physicians without facilities for open heart surgery may be reluctant to undertake this. We strongly believe that adequate circulation will improve survival, even if drainage of pericardial tamponade is required before transportation of the patient to a cardiothoracic center. Drainage by the subxyphoidal route is an option in the case of cardiac tamponade after cardiac surgery.

The Antonius Dissection Scoring System described above appears to be a reliable addition to estimate the risk of operative death before starting surgery for acute type A dissection. However, follow-up studies of this scoring system using prospective data will be required to validate the new model and its applicability to different cardiac units. It remains a matter of discussion whether patients with a high-risk profile and predicted operative mortality should undergo operation, and ethical issues will continue to play a major role in this decision.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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