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Eur J Cardiothorac Surg 2006;30:241-243
© 2006 Elsevier Science NL
Department of Cardiothoracic Surgery, University of California San Diego Medical Center, 200 West Arbor Drive, Mail Code 8892, San Diego, CA, USA
* Corresponding author. Tel.: +1 619 543 7777; fax: +1 619 543 2652. (Email: sjamieson{at}ucsd.edu).
Pulmonary endarterectomy is now an established therapy for the pulmonary hypertension caused by thromboembolic disease. It has had a painful acceptance, both in terms of clinical recognition and in the appreciation that this is a curable condition with surgery.
Means and Mallory [1] reviewed the entity of chronic thrombosis of the pulmonary arteries in 1931 and could find only six cases. Hollister and Cull [2] in 1956 stated, ‘it is probable that no more than 200 cases of the syndrome have been reported in the medical literature to date’. Much has changed. However, although chronic thromboembolic disease as a cause for pulmonary hypertension is now well recognized, many patients remain undiagnosed.
With regard to surgical treatment, there has also been increasing acceptance of the fact that thromboendarterectomy can cure this crippling and deadly condition. In 1984, Chitwood et al. [3] reviewed the world's literature to date and found a total of 85 cases managed surgically, with a mortality of 22%.
In 2006, perhaps less than 3000 of these operations have now been carried out worldwide, but it is gratifying that many centers are now starting to do this procedure. By far, the majority of operations (more than 2000) have been done at the University of California, San Diego, which has been promoting the operation for 35 years. The major experience at UCSD (1800 operations) has been gained over the last 15 years. During this time, the operation has been refined, and the last surgical report [4], analyzing in detail a cohort of 500 patients, demonstrated a mortality of 4.4%, with no cerebral complications.
There are, of course, many ways to perform any procedure, and there is no doubt that further modifications will result in better techniques and improved results. However, as it presently stands, results of new techniques have to be measured against those that are currently achieved. Over the years I have been asked to review many papers that advocate different techniques, but I have yet to see a paper that has demonstrated improved results or a simpler technique than currently used.
When I was asked to write an editorial comment assessing the article published in this edition of the journal, I at first refused. There were two reasons for this. First, the senior authors from each institution have been friends of mine for more than 25 years and I did not wish to be offensive. Second, I really did not believe that anybody would seriously advance the hypothesis that moderate hypothermia was as good for circulatory arrest as deeper hypothermia, and actually test this on patients.
However, it has been explained to me that the paper will be published anyway, and under those circumstances, I feel obligated to make some comments in order to prevent what, in my opinion, would result in substantial injury to many patients if the paper was taken seriously.
This is an article which describes pulmonary endarterectomy in 30 patients over a 13-month period. Twenty-four patients were from Hanover, and six from Barcelona. The basic premise of the article is that moderate hypothermia is sufficient for the circulatory arrest periods necessary to ensure complete removal of all obstructing material from the pulmonary vasculature in patients with thromboembolic pulmonary hypertension.
First, there seems to be some confusion in the paper as to what exactly constitutes the hypothermia used for circulatory arrest for endarterectomy in experienced hands. In the abstract, it states that the objective is to test whether deep hypothermia (<20 °C) is necessary for pulmonary endarterectomy. Yet, I am unaware of any group that cools to more than 20 °C. In the introduction, the paper then refers to the established protocol as <19 °C. Less than 19 °C is even more incorrect, but there should be some consistency of thought here. Let me clarify this and say that 20 °C is quite sufficient.
The introduction of the paper states that the established surgical therapy involves ‘intermittent periods of circulatory arrest (CA) of 35 min in average’. This is not true. I am unaware of any group that would deliberately exceed 20 min, even at 20 °C. The references the author refers to state 35 min as being the total time of accumulated arrest periods.
The premise of the article is that problems occur with current techniques. These problems are presented as a result of hypothermic arrest (‘deep hypothermic circulatory arrests (DHCA) are still associated with a relatively high mortality and a disturbing incidence of neurological complications’). Again, this is not true with regard to endarterectomy. The references given relate to operations on the aortic arch—a very different situation. The reference referring to endarterectomy [4], in a cohort of 500 patients, states that neurological side effects have been eliminated, i.e., a 0% incidence in 500 patients. The paper published here then goes on to demonstrate that a different technique in 30 patients, in whom there is one death, arguably as a result of poor protection, resulted in a 10% incidence of neurological complications. This is the first paper that I have been asked to review that seeks to advocate the benefits of a different technique by demonstrating worse results.
With regard to mortality, the paper is again incorrect. In the UCSD series there was 4.4% mortality in 500 patients, and it was demonstrated that this was related to failure to reduce completely the degree of pulmonary hypertension—it was not related to hypothermia or circulatory arrest times. It is now clearly established that mortality is related only to the postoperative pulmonary vascular resistance. Every effort should be made to completely clear the pulmonary vasculature of all occluding material. Our institution has now done more than 2000 of these operations, and is the most experienced in the world. Yet, none of the five surgeons involved in the series have ever felt they have been able to satisfactorily complete the operation without at least one circulatory arrest period on each side (not so in these 30 patients), and still, in a difficult case, the endarterectomy period may require at least 20 min, possibly repeated after reperfusion. Interestingly, as we have gained increased experience, our circulatory arrest times have increased, not decreased, as we have realized the extent of operability of this condition, and we have accepted more and more patients with distal disease for operation. We currently believe that there is no degree of thromboembolic disease that is inoperable, no disease that is ‘too distal’.
The paper states that ‘profound hypothermia is associated with prolonged CPB times, activation of the inflammatory system, and coagulation disorders predisposing to postoperative bleeding and multisystem organ failure’. Yet our group, which has the largest series of hypothermic arrest in the world, does not associate hypothermic circulatory arrest with these problems; indeed, the majority of patients do not receive blood transfusion, and spend one day in the intensive care unit (as opposed to six days in this study). We do not use aprotinin, as described in this paper, and believe that to use this agent for pulmonary endarterectomy may be unwise.
The design of the study seeks as an endpoint an adverse neurological event. There was apparently no IRB permission needed ‘Because of our previous experience ...’. In my opinion, to design a study seeking an adverse neurological event when there are established techniques to prevent this does require IRB approval, which is unlikely to be given.
During the operation, the superior vena cava ‘was fully transected’. I find this puzzling. To mobilize the superior vena cava sufficiently to move it completely out of the way takes less than a minute. No repair is required. How can it be a ‘technical advantage’ to actually transect the superior vena cava and then have to repair it? Perfect visibility of every sub-segmental branch can be obtained without dividing the superior vena cava.
The paper states that periods of circulatory arrest were limited to 10 min maximally. To achieve complete clearing of obstructing material often takes considerably more than that, even in the most experienced hands in the world. I believe it would be very damaging to many patients to propagate the idea that 10 min arrest periods would always be sufficient to achieve the vital objective—complete resolution of all occluding material.
The patients were given inhaled nitric oxide postoperatively. This is interesting. Thromboembolic pulmonary hypertension is the mechanical occlusion of the pulmonary vasculature by clot or scar tissue. The operation is designed to remove this. If the operation has been successfully and completely carried out, inhaled nitric oxide should have no effect. It is not used in our patients postoperatively—it would have no benefit.
In the results section, it is described that the mean core temperature was 30.1 °C at the time of circulatory arrest, and the total duration of arrest was maximally 19 min. Now, of course, it is possible to perform an endarterectomy within this period. But I will categorically state that it is not possible to perform a complete endarterectomy. The pressures may come down, and the majority of the occluding material may be removed, particularly in a Type 1 patient (as shown in the figure). But there is a difference between removal and complete removal, and I doubt that the authors of this paper are so technically superior to surgeons that have done hundreds of these cases that they can achieve complete resolution in a third of the time. I would imagine that the need to use nitric oxide reinforces this.
One patient died in this series of liver and renal impairment. This is not explained. Why should a patient die of hepatic and renal impairment? I would imagine that this is related to inadequate organ protection. Three patients suffered from neurological dysfunction. In my opinion, this is unacceptable. There is no discussion of postoperative echocardiography, exercise studies, or lung scans. Without these, it is impossible to state that the thromboembolic material was completely removed.
In the discussion, the case is made that in rats and dogs, there is some evidence that deep hypothermia is not necessary. However, it is well established, and beyond dispute, that metabolic rate is directly inversely proportional to temperature. The cooler the temperature, the lower the metabolic rate, and the better protection of the organs. I find it hard to believe that this paper is actually challenging this established theory, yet this seems to be the case.
The authors state that we and others require longer arrest times and cite some technical differences that in their opinion must improve exposure. Yet it is unlikely that experienced surgeons from a major University center would not be able to use any technical advance that would improve exposure, when doing three or four cases a week. I think it is far more likely that this paper represents early results in a small number of patients by surgeons who are not accustomed to seeing the full range of disease, and either have operated on patients with proximal disease or provided incomplete resolution of disease, or both.
The last paragraph, ‘this study provides definitive evidence ... safely performed ... without the need of profound hypothermia’ is, in my opinion, a dangerous conclusion. How safe is safe? A 10% incidence of cerebral impairment and a death from renal and hepatic failure? In patients who required nitric oxide postoperatively, and who on average required a week in the intensive care unit? In my opinion, this is not acceptable as the standard of care. Although I am gratified that other centers are now performing this operation, it is vital that the message be sent that cerebral side effects are a thing of the past, and should not be tolerated, and every effort should be made to clear the occluding material completely. Arrest times are no longer an issue.
Pulmonary endarterectomy in 2006 is a safe and established procedure. Circulatory arrest as currently applied does not result in cerebral complications. Mortality is only related to residual pulmonary hypertension. Every effort should be made to clear completely all occluding material from the pulmonary vasculature. The currently established techniques have been worked out over 20 years in 2000 patients. No doubt modifications of existing techniques will be made. But the bar is high—a 4.4% mortality taking all comers, including those presenting to the operating room on ventilators or in cardiac arrest, those with very distal disease, in whom it has been established that not all the pulmonary hypertension is a result of thromboembolic disease, and results that demonstrate no residual cerebral effects from operation. There is nothing in this paper, which in my opinion presents mediocre results in a very small series of 30 patients, which should cause anyone to change the presently described techniques.
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  B. Thomson, S. S.L. Tsui, J. Dunning, A. Goodwin, A. Vuylsteke, R. Latimer, J. Pepke-Zaba, and D. P. Jenkins Pulmonary endarterectomy is possible and effective without the use of complete circulatory arrest--the UK experience in over 150 patients Eur. J. Cardiothorac. Surg., February 1, 2008; 33(2): 157 - 163. [Abstract] [Full Text] [PDF]
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