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Ann Thorac Surg 1999;67:1927-1930
© 1999 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, New York, New York, USA
Address reprint requests to Dr Griepp, Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
Presented at the Aortic Surgery Symposium VI, April 30May 1, 1998, New York, NY.
| Abstract |
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Methods. Changes in the aneurysms were followed with three-dimensional reconstructions of computed tomograph scans. Risk factors were compared in patients with dissecting and nondissecting aneurysms who experienced rupture, in whom operation was recommended during the course of follow-up, and in those without rupture or operation.
Results. Nondimensional variables associated with an enhanced risk of rupture include age, the presence of chronic obstructive pulmonary disease, and even uncharacteristic continued pain. Patients with rupture of dissections had significantly higher blood pressures than survivors, and significantly smaller maximal descending thoracic aortic diameters (median 5.4 cm) than patients with rupture of degenerative aneurysms (median 5.8 cm). The extent of the aneurysm, as reflected by the maximal abdominal aortic diameter, was a significant risk factor for rupture only in nondissecting aneurysms. Mortality from rupture was significantly higher in patients with chronic dissections than in patients with nondissecting aneurysms: 9/10 vs 26/34 (p = 0.004).
Conclusions. Almost 20% of patients followed nonoperatively succumbed to rupture, suggesting that a more aggressive surgical approach toward patients with chronic aneurysms of the descending thoracic and thoracoabdominal aorta is warranted. An individualized risk of rupture within 1 year can now be calculated, and patients whose operative risk is lower than their calculated risk should be offered elective surgery.
| Introduction |
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It has been difficult to extract information relevant for future patient care from studies of the natural history of aneurysms for several reasons. Most studies have included a mixture of different proportions of patients with aneurysms with different etiologies, different locations within the thorax, at varying intervals from acute onset, classified by several conflicting and overlapping systems of nomenclature. The completeness and accuracy of follow-up is also variable, so that is often difficult to be sure whether deaths occurred from rupture or from other causes. Recent improvements in the results of surgery and in the ability to image aneurysms accurately have resulted in the withdrawal of increasing numbers of patients for elective surgery, even in the most careful, rigorous studies. The removal of these patients weakens our ability to assess the possible contribution to rupture risk of factors that are frequent indications for surgery, such as aneurysm size, extent, growth rate, and the presence of pain. Thus, the conclusions of recent natural history studies must be viewed in context: they are most applicable to relatively asymptomatic patients with moderate-size or small aneurysms. Fortunately, these are the patients for whom the decision whether or not to operate is most often a dilemma.
| Risk factors for rupture: dimensional variables |
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Growth rate
Most studies have demonstrated that the rate of expansion of aneurysms is exponential, as might be predicted from physiological principles: enlargement accelerates as aneurysms get bigger [7]. Recently, the widely held belief that a faster growth rate is an independent risk factor for thoracic aneurysm rupture has been confirmed in a study by Lobato and Puech-Leao [4].
| Risk factors for rupture: nondimensional variables |
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Smoking/chronic obstructive pulmonary disease
The presence of chronic obstructive pulmonary disease (COPD) is surprisingly powerful predictor of aneurysm rupture, as first pointed out by Cronenwett and associates in relation to abdominal aneurysms [8]. In our multivariate analysis of nondissecting thoracic and thoracoabdominal aneurysms, a history of COPD increased the odds of rupture by a factor of 3.6 (p = 0.04) [6].
A history of smoking is found in the majority of patients with aortic aneurysms, and is also a risk factor for rupture, but COPD has eclipsed smoking in several studies in which the two are looked at in the same multivariate analysis [6, 7]. The greater predictive power of COPD may be related to individual differences in response to the toxic effects of smoking: the presence of COPD may be a sensitive indicator of intolerance of connective tissue to smoking-related toxicity both in the lung and in the aorta.
In a survey of abdominal aneurysms by Strachan, the risk of rupture was unequivocally increased by smoking, with an odds ratio of 6.5 [9]. The effect on abdominal aneurysm expansion of continued smoking was monitored in another study by measuring nicotine metabolites in blood. Significantly more rapid growth was seen in smokers, justifying continuing to recommend cessation of smoking in all patients with aneurysmal disease [10]. In one of our early studies, we documented more rapid expansion of thoracic aneurysms in patients with a history of smoking: 0.70 cm/year in smokers vs 0.35 cm/year in nonsmokers [7].
Age
The risk that a thoracic aneurysm will rupture increases quite dramatically with age. This is illustrated in Figure 1, constructed from a Swedish autopsy study of deaths from thoracic aneurysms [1]. The proportion of women with thoracic aneurysms also increases with age, almost equaling male incidence in the elderly. In our multivariate analysis of descending thoracic and thoracoabdominal aneurysms, the relative risk of rupture increased by a factor of 2.6 for every decade of age (p = 0.02) [6]. The recognition that there is a greater risk of aneurysm rupture in elderly patients should lead to a reexamination of the predilection of most surgeons to propose elective surgery more readily to younger patients.
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Hypertension
A history of hypertension is present in most patients with aneurysms, and it is widely recognized that hypertension, especially diastolic hypertension, is very highly correlated with the initial development of aneurysms [7]. Consequently, treatment of patients with aneurysms with beta-adrenergic blocking agents and other antihypertensive agents is almost universally recommended to minimize progression of their disease. Perhaps because such treatment is often effective, hypertension has only intermittently emerged as a risk factor for rupture in recent studies. In our own just-completed study of patients with chronic type B dissection, however, patients who experienced rupture had significantly higher diastolic and mean blood pressures during follow-up visits than patients who survived without rupture, even though a history of hypertension was equally prevalent in both groups [11]. This observation reinforces the need for vigorous treatment of hypertension, as well as consideration of elective surgery for those patients in whom hypertension cannot adequately be controlled.
Renal failure
The presence of renal failure has been identified as a risk factor for rupture of thoracic, abdominal, and thoracoabdominal aneurysms by Cambria and colleagues and Perko and colleagues, and Masuda and colleagues cite renal failure as a risk factor for rapid expansion of thoracic aneurysms [2, 5, 12]. In our own studies, however, renal failure has not emerged as a significant risk factor for aneurysm rupture.
Etiology: degenerative aneurysms vs chronic dissections
There are conflicting reports regarding whether or not the etiology of an aneurysm plays a decisive role in the likelihood of rupture. Certainly, there is a consensus that patients with known disorders of connective tissue, particularly those with Marfans syndrome, are likely to experience rupture more readily than other patients with aneurysms, and that patients with a family history of early dissection and rupture may be particularly at risk.
A number of studies over the years have also suggested that the presence of dissection is a risk factor predisposing to rupture even in patients without Marfans syndrome [13, 14]. Our recent natural history study of descending aortic and thoracoabdominal aortic aneurysms excluded chronic dissections from the initial analysis with the idea that they might behave differently; they were subsequently studied separately. Comparisons of patients who experienced rupture revealed that those with chronic type B dissection had smaller maximal diameters in the descending aorta before rupture than patients with degenerative aneurysms: a median of 5.4 cm in dissections vs 5.8 cm in patients with degenerative aneurysms (p = 0.05) [6, 11]. Furthermore, the extent of the aneurysm, as reflected by the presence of a large abdominal diameter, was not a significant risk factor for rupture in dissections, in contrast to its significant role in predicting rupture in degenerative aneurysms.
The contribution of nondimensional risk factors in predicting rupture is no different in patients with dissection than in patients with degenerative aneurysms, with a higher risk of rupture in older patients, and in those with COPD and/or continued pain [6, 11]. Continued hypertension was significantly more prevalent among patients with chronic dissection who experienced rupture than in those who remained alive; unfortunately, follow-up blood pressures were not available for comparison in patients with degenerative aneurysms [11]. The characteristics of patients with degenerative and dissecting aneurysms who underwent rupture during nonoperative follow-up are shown in Table 1.
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Our recent study of the natural history of descending aortic and thoracoabdominal aortic aneurysms has allowed us to generate an equation for the probability of rupture within 1 year for each patient [6]. The equation incorporates the patients age, history of COPD, presence of pain, and the maximal thoracic and abdominal diameters of the aneurysm (Fig 2). An individualized risk of death, paraplegia, or other serious complication of operation can also be calculated, based on some of the same factors, including the patients age and the extent of the aneurysm to be resected [15]. For patients with degenerative aneurysms, our current practice is to recommend operation if the calculated risk of rupture within 1 year exceeds the estimate of operative risk. In patients with chronic type B dissection, in whom death is overwhelmingly likely to be related to rupture, and in whom rupture tends to occur more readily in less dilated and perhaps less extensive aneurysms, we recommend adding 0.4 cm to the thoracic diameter before carrying out the calculation; this will result in a conservative but still individualized estimate of rupture risk.
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