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Ann Thorac Surg 2001;71:1239-1243
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Preoperative risk factors for hospital mortality in acute type A aortic dissection

^a Department of Cardiovascular Surgery, Omiya Medical Center, Jichi Medical School, Saitama, Japan

Accepted for publication November 19, 2000.

Address reprint requests to Dr Kawahito, Omiya Medical Center, Jichi Medical School, 1-847 Amanuma, Omiya, Saitama 330-8503, Japan
e-mail: kawahito{at}omiya.jichi.ac.jp

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Acute type A dissection is associated with postoperative complications and a high mortality rate. This study was performed to determine the perioperative risk factors leading to hospital mortality in patients with acute type A aortic dissection.

Methods. One hundred twenty-two patients with acute type A aortic dissection treated surgically within 48 hours after onset were enrolled in this study. Thirty-two perioperative risk factors were used in statistical analysis for prediction of mortality. Risk factors for hospital death were investigated with univariate and multiple logistic regression analysis.

Results. The in-hospital mortality rate including operative death was 12.3% (15 of 122 patients) and the actuarial survival rate (including in-hospital death) was 72% ± 6% at 5 years. Univariate analysis revealed 10 risk factors to be statistically significant predictors of hospital death: age, year of operation (1990 to 1995), Marfan syndrome, preoperative ST segment elevation, heart failure from aortic regurgitation, preoperative shock, preoperative coma, long operation time (> 6 hours), long cardiopulmonary bypass time (> 4 hours), and massive blood transfusion (> 20 units) (p < 0.05). Multiple logistic regression analysis confirmed preoperative ST-T segment elevation and massive blood transfusion to be statistically significant independent risk factors for hospital death (p < 0.05).

Conclusions. Preoperative ST-T elevation and massive blood transfusion during operation were identified as significant independent risk factors for hospital mortality after operation for acute type A aortic dissection. Our findings should contribute to estimation of operative risk in individual patients.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Recent reports have demonstrated improved surgical outcomes in patients with acute type A aortic dissection. However, acute type A dissection continues to be associated with postoperative complications and a high mortality rate [1–11]. Surgical mortality rates have been estimated to range from 9% to 36% [1–11] with 5-year survival rates of approximately 50% to 80% [1, 2, 4, 7, 10, 11]. To predict the surgical outcome of acute type A aortic dissection in individual patients, we must be able to evaluate accurately preoperative and perioperative risks. In this study, we retrospectively reviewed 122 consecutive surgical patients with acute type A dissection to explore perioperative risk factors for hospital death in such patients.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Patients
Between March 1990 and March 2000, 122 consecutive patients (72 men and 50 women) with acute type A dissection were treated surgically at Omiya Medical Center, Jichi Medical School. Patient age ranged from 25 to 92 years (mean, 63 ± 13 years). Emergency operations were performed within 48 hours of acute onset in all patients. Mortality was defined as death that occurred in the hospital after operation.

Surgical procedures
The surgical procedures performed are shown in Table 1. In 85 patients, the operation was limited to the ascending aorta (including eight ascending aorta replacements plus coronary artery bypass grafting). In 31 patients, it was necessary to partially or totally replace the aortic arch (including one ascending aorta and arch replacement plus coronary artery bypass grafting). Aortic root replacement with composite graft was performed in 4 patients. Other combined surgeries were performed in 2 patients.

Once cardiopulmonary bypass was established, systemic cooling was initiated. Retrograde femoral perfusion was used in 94 patients (77%); antegrade subclavian perfusion was performed in the other 28 patients (23%). After the onset of ventricular fibrillation, the aorta was clamped. Antegrade (selectively) or retrograde blood cardioplegia was performed after the ascending aorta was opened. The proximal stump was then trimmed and reinforced with a Teflon strip. The arch was explored under hypothermic circulatory arrest at a rectal temperature of 20°C. If intimal tear was found in the ascending aorta, we simply replaced it. Distal anastomosis was performed with the open aorta technique under circulatory arrest. Usually, distal anastomosis was finished within 30 minutes (the range of the circulatory arrest time was 1 to 46 minutes; mean 24.1 ± 10.9 minutes). After distal anastomosis was achieved, cardiopulmonary bypass was restarted, and proximal anastomosis was performed. In 48 patients (39%), the cannula was repositioned in the graft to reestablish antegrade flow on rewarming. The other 74 patients (61%) were rewarmed by retrograde femoral perfusion. The replacement technique always included the interpositioning of woven collagen-impregnated or albumin-sealed grafts with Teflon strip reinforcement of the aortic stumps. Gelatin-resorcin-formalin (GRF) adhesive was not routinely used. If an intimal tear was present or extended to the aortic arch, we partially or totally replaced the arch using a selective cerebral perfusion technique. If it was necessary to prolong circulatory arrest because of complex anatomy, we converted immediately to a selective cerebral perfusion technique.

When the site of the intimal tear could not be identified, we simply replaced the ascending aorta. Aortic root replacement with composite prosthesis and reimplantation of the coronary arteries by the modified Bentall or Cabrol technique was performed in 4 patients with conspicuous dilatation of the aortic root. From 1990 to 1993, we used sutureless ringed intraluminal grafts when the intimal tear could not be clearly identified in the arch.

Follow-up
Outcome data was obtained through patient follow-up. We either examined patients at our outpatient clinic or contacted them by telephone or mail. All patients were followed up. The time between operation and examination or other contact ranged from 0 to 117 months (mean, 29.8 ± 30.4 months).

Statistical analysis
A set of preoperative and operative variables was retrospectively gathered from clinical records, and 32 perioperative variables were selected for the determination of statistically significant risk factors for death (Tables 2 and 3). A search for risk factors of in-hospital mortality was then carried out. Univariate analysis between survivors (n = 107) and nonsurvivors (n = 15) was performed using ² analysis and Student’s t test. A p value less than 0.05 was used to select variables for possible inclusion in a multiple logistic regression model for mortality prediction. Statistical analysis was performed with StatView 5.0 (SAS Institute Inc, Cary, NC). Late survival was estimated by the Kaplan-Meier method. p values less than 0.05 were considered statistically significant. Data are expressed as mean ± standard deviation.

	Results

Top Abstract Introduction Patients and methods Results Comment References

View larger version (22K): [in this window] [in a new window]   Fig 1. Kaplan-Meier curves for long-term survival in patients undergoing operation for acute type A dissection.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

The intraoperative factors of long perfusion time (cardiopulmonary bypass time > 4 hours), prolonged operation time (> 6 hours), and massive blood transfusion (> 20 units) were found to be statistically significant risk factors for hospital death including operative death. In particular, multivariate analysis confirmed massive blood transfusion to be a statistically significant independent risk factor for hospital death. Although hemorrhage has been a frequent and serious complication, it has recently been better controlled with the use of new materials such as sealed grafts and hemostatics. Massive blood transfusion during operation can mean technical difficulties, unfavorable anatomy, or intraoperative complications, and these factors can contribute to prolonged operation or cardiopulmonary bypass time and, therefore, affect surgical outcome. The strong association between prolonged operation time, prolonged cardiopulmonary bypass time, and operative death has been observed by other investigators as well [14, 15]. In this study, one of the main reasons for massive transfusion or prolonged operation time was preexisting bleeding tendency caused by extensive consumption by the false lumen. Neither complex pathology nor imperfect surgical technique was a main reason for massive transfusion.

Contrary to previously reported findings [3, 4, 7, 8], we found age less than 50 years to be a preoperative risk factor. Our study group included 5 patients with Marfan syndrome, which was also found to be a risk factor (Marfan patients comprised 60% of the patients who died). Generally, aortic dissection frequently occurs in Marfan patients at a relatively younger age and sometimes requires complicated operation. Accordingly, operative results and prognosis in Marfan syndrome patients are worse than in other patients [14]. This partially explains our data. Despite the significant p value in ² analysis, no meaningful conclusion can be drawn from multivariate analysis for Marfan patients. This may result from the small sample size of this variable (only 4% of the patient population). As we reported previously, older age (> 75 years) was itself not a risk factor for early death [16].

Multiple logistic regression analysis revealed ST segment elevation on the electrocardiogram before operation to be a strong predictor of operative death. ST elevation does not always indicate acute myocardial infarction, and it is difficult to obtain an early diagnosis of complicated acute myocardial infarction with aortic dissection by electrocardiogram alone. Associated acute myocardial infarction should be diagnosed based on clinical symptoms such as ventricular failure, myocardial enzyme elevation, and Q-wave appearance in the postoperative course. The echocardiogram is useful in supporting diagnosis in the emergent situation [17, 18]. We routinely perform echocardiography in patients with aortic dissection, and accordingly 7 of 12 patients were confirmed to have asymmetric left ventricle wall motion along with the dissection. Although we do not routinely perform angiography for acute type A dissection, 2 patients were diagnosed by coronary angiogram (these patients were initially misdiagnosed as primary acute myocardial infarction).

Chest or back pain, which is the typical presenting symptom of aortic dissection, may be present in patients with acute aortic dissection as a result of compression of the coronary arteries. Although the majority of early deaths from aortic dissection are because of aortic rupture, death may also occur from obstruction of the origins of the coronary arteries by the dissecting hematoma or by intussusception of the circumferentially disrupted inner layers of the aortic wall [5]. Acute myocardial infarction is not complicated frequently by acute dissection. The incidence of acute myocardial infarction along with acute aortic dissection is relatively rare at 2% to 5% [1, 4, 8]. Significant mortality can occur from heart failure because of coronary artery occlusion secondary to involvement of a coronary artery origin in the dissection process [12]. In our series, 10% of patients (12 of 122) demonstrated significant preoperative ST-T elevation on the electrocardiogram. Although significant ST-T elevation does not always confirm myocardial infarction, once an acute infarction occurs, it is one of the major causes of death after operation [5, 14]. To prevent this, immediate surgical repair including coronary reconstruction may be necessary when the myocardial damage is reversible. Hematoma removal and decompression of the false lumen may restore the coronary flow after graft replacement in some patients. When coronary disrupture or obstruction is obvious, however, we usually perform coronary artery bypass grafting using saphenous vein grafts during rewarming. Nine of 12 patients who had significant ST-T elevation required coronary artery reconstructions (seven coronary artery bypass grafts and two Cabrol procedures. For the seven coronary artery bypass grafts, bypass was to the right coronary artery in 6 patients and to the left coronary artery in 1. All of these cases resulted from extension of the dissection to the coronary arteries; severe atherosclerotic coronary arterial lesions were not observed in these patients.

Past history of ischemic heart disease had no influence on the development of postoperative low cardiac output. Kouchoukos and Dougenis [5] recommended that patients with symptoms or electrocardiographic changes indicative of myocardial ischemia undergo coronary angiography. We do not require routine coronary angiography, however, even if a coronary complication is suspected, because it is essential to reduce diagnostic time to a minimum and to perform the surgical repair as soon as possible. Rizzo and colleagues [3] suggested that a rapid noninvasive diagnostic technique such as transesophageal echocardiography and avoidance of routine angiography appear to improve survival by expediting surgical intervention and decreasing the risk of rupture.

Antegrade flow is essential in preventing malperfusion and in reducing the size of the false lumen on rewarming. Subclavian artery cannulation is widely used to prevent such complications [19], and it is reported that antegrade perfusion after completion of the distal anastomosis improves early and late outcomes of operation for acute type A aortic dissection [11]. Although univariate analysis did not indicate femoral cannulation or retrograde femoral perfusion on rewarming as risk factors in this study, all 4 patients who died of malperfusion underwent femoral cannulation and retrograde femoral perfusion on rewarming. To prevent this complication, in recent years we have used subclavian cannulation and antegrade perfusion through a repositioned cannula in the graft upon rewarming. Furthermore, we routinely monitor blood flow in the true lumen by transesophageal echocardiography during operation to prevent switching.

In conclusion, preoperative ST-T elevation and massive transfusion during operation are strong predictors of hospital death in acute type A aortic dissection. We recommended that aortic surgeons pay close attention to the problems of preoperative coronary artery injury by aortic dissection and massive bleeding during operation.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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