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Eur J Cardiothorac Surg 2001;19:606-610
© 2001 Elsevier Science NL
a Division of Cardiac Surgery, University Hospital Zürich, Zurich, Switzerland,
b Division of Echocardiography, University Hospital Zürich, Zurich, Switzerland
c Department of Biostatistics ISPM, University of Zürich, Zurich, Switzerland
Received 10 October 2000; received in revised form 27 February 2001; accepted 1 March 2001.
Corresponding author. Department of Heart Surgery, Triemli City Hospital, Birmensdorferstr 397, 8063 Zurich, Switzerland. Tel.: +41-1-466-1185; fax: +41-1-466-2745
e-mail: michele.genoni{at}triemli.stzh.ch
| Abstract |
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Key Words: Aortic dissection Antihypertensive agent Beta-blocker Cost of treatment
| 1. Introduction |
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| 2. Materials and methods |
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In the absence of rupture or complications of the dissections, 78/130 patients received medical treatment alone; 71/78 of the medically treated patients were discharged alive. Of these, 51 received treatment with ß-blockers and 20 were treated with other antihypertensive drugs. The mean age of the medically treated patients was 64 years (61.8±8.9 years for patients who received ß-blockers and 65.2±12.6 years for patients who received other antihypertensive medication).
The records of all patients who were treated for type B aortic dissection were reviewed. There were no statistically significant differences between the group given ß-blockers and the group given other antihypertensive medication with respect to the incidence of smoking (25 and 21%, respectively) and the incidence of obstructive airways disease (8.9 and 7.1%, respectively). The diameter of the aorta at the time of diagnosis also did not differ significantly between the group given ß-blockers (<4.5 cm: 41 (80%); 4.55.5 cm: six (12%); >5.5 cm: four (8%)) and those given other antihypertensive medications (<4.5 cm: 15 (75%); 4.55.5 cm: three (15%); >5.5 cm: two (10%)). All patients who were still alive were contacted and asked to complete a questionnaire with the help of their doctor, in particular, CT-scan data was collected. The total follow-up period encompassed 194 years, with a mean observation time of 4.2 years (3.9±3.2 years for the group given ß-blockers and 4.3±2.5 years for the group given other antihypertensive medications). A total of 19/130 (14.6%) patients died during the first hospitalization, and of the remaining 111 patients, follow-up was completed in 105 patients (95%); 37 patients died during follow-up.
The costs of treatment correspond to the those of the University Hospital, Zurich. The prices cover all hospital costs as follows: 1 day's stay in hospital, 1044 euros; 1 day's stay in an intensive care unit, 2680 euros; major aortic surgery, 9375 euros; 100 mg atenolol, 0.55 euros.
2.1. Statistical analysis
Variables are reported either as percentages or as means±standard deviation. Statistical analyses were performed using SPSS 6.1 software. The effects on nominal variables were evaluated with the Chi-quadrant test and effects on independent variables were evaluated with the MannWhitney and KruskalWallis tests; continuous variables were univariately evaluated with the Wilcoxon-signed rank test. Differences between groups were analyzed using the log-rank test. Significance was assumed at a P level of <0.05.
| 3. Results |
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| 4. Discussion |
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It has been generally advocated that patients who have type B acute aortic dissection without complications, such as rupture, potential risk of rupture or organ ischaemia, should be treated with hypotensive drugs during the acute phase and that surgical treatment be carried out if the aortic diameter becomes enlarged during the chronic phase [8]. The goals of early medical treatment in the acute phase are to reduce blood pressure and heart rate, and to treat congestive heart failure [9]. Nevertheless, 11% of all patients treated in our institution for acute type B aortic dissection needed surgery after the acute phase but before discharge, most frequently because of an increase in aortic diameter.
The pharmacological approach is aimed primarily at the forces that influence dissection propagation, namely the pulsatile load (dP/dt) and blood pressure. Where luminal dilatation of the aorta occurs, shear stresses on the wall are greatly increased, according to the law of LaPlace, in which wall tension at a constant arterial pressure, increases with increasing luminal diameter [10]. Yin et al. have shown that dP/dt, which is also affected by wave reflections (conditions of increased peripheral vascular resistance), is greatest in areas of dilatation [11]. In cases of type B dissections, the portion of the aorta just distal to the left subclavian artery is subject to a significant degree of torsion and flexion during each cardiac circle. Experimental models of aortic dissection have shown that two interrelated forces of dP/dt and blood pressure play a part, not only in intimal tear formation, but also in the propagation of aortic dissection [1]. Studies using artificial aortas indicate that dissection propagation occurs when the dP/dt is high and the flow is pulsatile, not laminar or non-turbulent. Studies in hypertensive turkeys found that ß-blockers, at doses that do not decrease the dP/dt, afford protection from aortic dissection [12]. Additional experimental evidence from dog models supports the role of blood pressure in the propagation of the aortic dissection; Carney et al. showed that the depression of myocardial contractility alone does not prevent progression of dissection, but that the inhibition of propagation can be achieved by controlled hypotension plus myocardial depression [13].
Theoretically, the use of ß-blockers offers many potential benefits. The ability of ß-adrenergic blockade to reduce pulsatile force (or dP/dt) has been demonstrated in animal models [14] and in patients with malignant hypertension [15]. Oral ß-blockade was also found to reduce the rate of enlargement of abdominal aortic aneurysms in humans [16]. Furthermore, ß-blockers decrease the sympathetic tone and increase the parasympathetic tone, thus improving autonomic imbalance. In our series, the positive influence of ß-blocker therapy is reflected in a significantly lower increase of aortic diameter and a significantly lower incidence of dissection-related surgical intervention in chronic type B aortic dissection. Therefore, the presumptive benefits of ß-blockers derive not only from their impact on blood pressure, but also from their negative inotropic and chronotropic properties. This is why some authorities do not recommend vasodilators without concomitant administration of a drug with negative inotropic and chronotropic effects. However, such an approach may actually increase the velocity of left ventricular contraction (dP/dt) and make the dissection worse. For the same reason, sublingual use of nifedipine is controversial; it reduces blood pressure in an uncontrolled fashion, potentially causing a reflex increase in heart rate and contractility, and thus, increasing the dP/dt [9].
Since serious early complications of type B dissection are not uncommon and unexpected late rupture (which is almost invariably fatal) cannot reliably be predicted, there has been an increasing tendency to operate on acute and subacute type B dissections [17]. The indication for emergency surgery after the acute phase of a type B aortic dissection must be balanced against the not inconsiderable morbidity and mortality rates carried by emergency surgery (Fig. 1). Although surgery is steadily improving, the risk is still quite substantial and there are few guidelines to suggest patients could justifiably be exposed to these surgical risks, apart from those with very large aneurysms or pronounced symptoms. Furthermore, it is known that age and chronic obstructive pulmonary disease are powerful predictors of rupture of chronic type B dissection [18,19]. It has been speculated that there must be a common, possibly smoking-related defect in connective tissue metabolism that predisposes towards both lung and aortic pathology in susceptible persons. On the other hand, our series shows a good survival rate and a good rate of freedom from any event. The low hospitalization rate of patients treated strictly with ß-blockers and the low treatment cost/patient per year are further reasons to encourage a positive view of a medical approach to type B aortic dissection which includes frequent treatment review, as well as regular determination of aortic diameter.
| Footnotes |
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| Appendix A. Conference discussion |
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Dr Genoni: We had only one patient with severe peripheral arterial disease who had contraindications to ß-blockers. All other patients did not show signs of contraindication. And it's important to say that this is a retrospective study, so we had no chance to change their medical treatment in the follow-up time.
Dr Alhan: My second question is, did you look at the initial aortic diameter at the time of dissection? Was there a difference between the two groups?
Dr Genoni: No. The diameter is comparable for the two groups. The univariate analysis of our patients revealed that a diameter larger than 4.5 cm is a predictor for surgery in the follow-up and also for death. Based on these observations, the indications for surgery is a diameter of 4.5 cm.
Dr R. Ascione (Bristol, UK): I have a few questions to ask. First, did you actually control the blood pressure during your follow-up period?
Dr Genoni: Yes. The values of blood pressure are comparable for both groups.
Dr Ascione: Was the blood pressure controlled? I mean was it in the right range?
Dr Genoni: Yes, retrospectively with the questionnaire we sent to the patients.
Dr Ascione: If that's the case, I would like to ask you which is the underlying mechanism allowing the ß-blockers to achieve this advantage?
Dr Genoni: Theoretically, the use of ß-blockers offers many potential benefits: firstly a decrease of the blood pressure; then reduction of the pulsatile force (dP/dt); and finally, decreasing of the sympathetic tone. Around that, I think that the benefit of ß-blockers derives not only from the direct impact of the blood pressure, but also from the negative inotropic and chronotropic properties.
Dr Ascione: So, we should then conclude that the most important thing is not controlling blood pressure. I mean this is the message we are getting.
Dr Genoni: I think both are very important. So, if you cannot control the blood pressure with ß-blockers only, you need additional medication.
Dr A. Arbulu (Detroit, MI, USA): Your work confirms the suggestion of Dr Myron Wheat over 30 years ago.
Our experience is very similar to yours, and although those patients had antihypertensive therapy, you show that some of those came to surgery. In a very small series, we found that the control of the hypertension at home was not the same as it used to be while they were in the hospital. We were able to obtain this information from a group of visiting nurses. I wonder if you had, in your experience, any out-of-hospital follow-up?
Dr R. Griepp (New York, NY, USA): To the best of my knowledge, this is the first published account that ß-blockers actually have a beneficial effect on the natural history of aortic disease in patients other than those with Marfan's syndrome. My first question is, whether you are aware of any other published accounts that show a beneficial effect of ß-blockers per se?
My second question relates to your graph of freedom from adverse events after acute dissection; it appears that most of the benefit of the ß-blockers occurs in the first year and that thereafter, the lines are parallel. Do you think that this phenomenon is real, does it mean we only need to use ß-blockers in the first year or is this apparent concentration of the benefits in the first year an artefact of the study for which you have another explanation?
Dr Genoni: I don't know. Our results call for a very strict follow-up examination of the diameter of the aorta. Furthermore, it is mandatory for all patients to take ß-blockers for the rest of their lives.
Dr M. Turina (Zurich, Switzerland): If I may add, that's the second consequence of this paper. Probably the equally important one is the need for very strict follow-up in the first 24 years. Our incidence of adverse events, after 4 years, becomes flat, but in the first 4 years, this patient needs very careful follow-up, otherwise you will have a substantial mortality in this period, and this is the second message which Dr Genoni is bringing to you.
Dr R. Martinez (Tenerife, Spain): Do you use ß-blockers in chronic bronchial disease?
Dr Genoni: If the patient tolerates the medication, we'll prescribe it. It depends on the patient.
Dr Turina: The question really is, do we know how many patients were put on ß-blockers and had to be taken off? Do you have this data?
Dr Genoni: We had only one patient with a contraindication to ß-blockers.
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