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J Thorac Cardiovasc Surg 2000;119:233-241
© 2000 Mosby, Inc.
SURGERY FOR ACQUIRED CARDIOVASCULAR DISEASE |
From the University Hospital Munich-Grosshadern, Munich, Germany,a the Italian Hospital of Buenos Aires, Buenos Aires, Argentina,b Stanford University Medical Center, Stanford, Calif,c and Cornell University Medical College, New York, NY.d
Address for reprints: Hermann Reichenspurner, MD, PhD, Department of Cardiac Surgery, University Hospital Grosshadern, Marchioninistrasse 15, Munich, Germany D-81377 (E-mail: hcr{at}hch.med.uni-muenchen.de) .
| Abstract |
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| Introduction |
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The pathogenesis of these neurologic and neurobehavioral sequelae is multifactorial, with studies indicating hypoperfusion, anesthesia, cardiopulmonary bypass, and patient comorbidity among the potential predisposing factors.
2-8 Although the prevalence of each of these contributors is not well understood, recent studies have indicated that particulate embolization (atheromatous or other nature) during surgical manipulation of the aorta is significantly linked with neurologic complications.
9-12 Gold and colleagues
13 and Barbut and colleagues
14 assessed the timing and quantity of microemboli release during cardiac surgical procedures by means of transcranial Doppler scanning. They demonstrated that up to 60% of perioperative emboli are attributed to clamp manipulation, primarily clamp removal, during cardiopulmonary bypass. These emboli have the potential to cause widespread, devastating, cerebral and peripheral ischemic damage when released into the circulation.
These findings led to the assumption that providing a means of filtration during unclamping of the aorta may significantly reduce the incidence and severity of neurologic injury related to particulate embolization. The device and method of filtration were designed to eliminate a need for additional incisions into the aorta, as well as to be ideally situated in the aorta for optimal efficiency. Experimental studies of the device were performed in vitro and in vivo to evaluate safety and efficiency.
15 Results demonstrated that the device was atraumatic, had excellent thromboresistance, and was effective at capturing particulate matter.
The purpose of this study was to evaluate, in human subjects, the feasibility of a novel method of particulate emboli filtration during routine cardiopulmonary bypass, specifically during the period when the aorta is unclamped. Furthermore, the study was aimed at evaluating the nature of captured particulate emboli by means of histologic and scanning electron microscopy analysis in a core laboratory.
| Patients and methods |
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After routine anesthesia induction, the aorta was evaluated by palpation and transesophageal echocardiography (TEE) for assessment of size, integrity, and presence of calcification. An intra-aortic arterial filter (EMBOL-X, Inc, Mountain View, Calif) size (extra small, small, medium, large, or extra large) was selected on the basis of the TEE findings or external measurement estimating the internal diameter of the aorta.
Patients were then cannulated for cardiopulmonary bypass per usual routines. A modified 24F arterial return cannula (EMBOL-X, Inc) with a side port designed to house the filtration device was inserted into the ascending aorta with double purse-string sutures in accordance with standard surgical technique (Fig 1). Choice of venous return cannula was at the discretion of the surgeon.
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All filters were visually inspected on removal for captured material. Filters were collected in specimen tubes and fixed with formalin for analysis. Particulate emboli were analyzed, and filter analysis included gross visual examination at 10x magnification to identify the particulate matter (with 74/77 [96%] having particulate matter). Particulate matter was collected from 44 (59%) of 74 filters and sent to a central pathology laboratory (Stanford University) for histologic examination of the captured material. The histologic sections were stained with hematoxylin and eosin, trichrome, and elastica van Giesons stain. Histologic analysis included examination for presence of platelets and fibrin deposition, true thrombus, and/or blood clotting, grumous portion of plaque-cholesterol, fibrous atheroma, or fibrous cap, and the normal vessel wall.
Scanning electron microscopy was performed on a subset (n = 12 [16%]) of filters with the longest dwell times to assess thrombogenicity of the filter in the clinical application.
Clinical assessments included basic neurologic examinations preoperatively, first day postoperatively, and before discharge.
| Results |
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Deployment of the filter was facile, and no filter-related adverse events occurred. Two patients did not receive the filter device. One patient had a "porcelain" aorta detected intraoperatively, and the procedure was performed off-pump. In the other patient it was difficult to insert the filter. The latter case occurred very early in the study, and there were no further technical difficulties in filter deployment.
Clinical follow-up yielded no strokes that were observed in the perioperative or postoperative follow-up. Immediately after the operation, 4 (5%) patients had a short transient delirium ranging from 24 to 48 hours after surgery. At time of discharge, gross neurologic examination did not reveal any pathologic abnormalities, such as deficits in memory or any focal symptoms. There was one death unrelated to the filter in a high-risk patient unable to be weaned from bypass; this patient already had a preoperatively severely decreased left ventricular ejection fraction. One patient had a myocardial infarction after CABG.
Visual inspection after filter removal revealed hard granular particles, soft material, or both in 74 (96%) of the 77 filters (Fig 3). The average number of particulate emboli was 5 to 10 per filter, ranging from 1 to 20 per filter. The average particle size was 0.6 mm, ranging from 0.1 to 6 mm. The majority of filters (66 [85.7%]) were analyzed by either scanning electron microscopy (12 [18%]) to evaluate thrombogenicity of the device or by histology (44 [66%]) to evaluate the actual composition of the particles. A total of 12 (15.5%) filters did not undergo pathologic analysis for varied reasons, including risk related to blood-borne pathogens and loss of particles in processing.
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| Discussion |
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The described filter and cannula system is a first-generation device demonstrating the concept of intra-aortic filtration and is designed to address a potential source of complications, specifically particulate emboli generated during aortic manipulation. This clinical study demonstrates that this system is safe and easy to use and that the filter clearly captures particulate emboli, ranging from 0.1 to 6.0 mm, that are readily visible to the naked eye.
The pore size of the filtration system of 120 µm enables this device to capture particles greater than 120 µm. In the 1997 study by Barbut and associates,
10 which characterized emboli size by using TEE and transcranial Doppler studies, 72% of the particles were seen to be greater than 0.6 mm in size, with 28% of the particles greater than 1.0 mm, 44% between 0.6 and 1.0 mm in size, and 27% being 0.6 mm or less in diameter. This is well above the 0.12-mm diameter filter pore size of the device. On the basis of these data, the filter device is well designed to capture a majority of particulate emboli that may be generated during the course of the cardiac operation.
The scanning electron microscopy findings confirmed device safety relating to thromboresistance of the filter mesh, as demonstrated by the insignificant degree of platelet adhesion on the surface of the filter. In one patient in whom thrombus was detected, the procedure involved excising thrombus directly from the left atrium. Thus although the origin of the thrombus could not be determined from the specimen, it is plausible that the thrombus originated from the left atrium. There did not appear to be a correlation in filter dwell time and the microscopy findings of thrombus. Because 5% or less of the total filter mesh area was obstructed in all cases, these findings were not considered to be of clinical significance.
The histologic findings raise questions with regard to the incidence, quantity, and type of surgical debris released into the central circulation that have been heretofore undocumented in the surgical literature. The remarkable predominance of particles of fibroatheromatous origin (66%) must give us pause as to the amount of debris typically released into the circulation because of routine surgical procedures. Moreover, these preliminary findings beg a mandate for management of such surgical debris, which intuitively must be minimized or eliminated if possible. Theoretically, prevention of the embolization of these particles to the brain would reduce the risk of neurologic deficit. Furthermore, although cerebral injury relating to emboli generation is considered to be one of the most devastating results, other complications relating to systemic injury (eg, renal, pulmonary, and peripheral vasculature) that may be due to emboli generation during cardiac operations remain problematic as well.
The postoperative gross neurologic follow-up in the examined patients was completely uneventful, except for a brief period of fully reversible postoperative delirium in 5% of the patients. This low incidence of neurologic events was present despite the fact that complex cardiac surgical procedures were included.
Clearly, further research and clinical studies are needed to fully evaluate and quantify these preliminary findings. Specific efforts must be undertaken to understand the origin and the clinical significance of the capture of particulate debris during routine and complex cardiac operations. Clinical studies are underway (International Council on Emboli Management) to more fully explore the efficacy of emboli management with intra-aortic filtration. International Council on Emboli Management is planned as a prospective, consecutive observational study to evaluate the potential benefits of intra-aortic filtration by means of collection of clinical data related to preoperative disposition, surgical and procedural details, evaluation of the aorta with the degree of aortic manipulation, and postoperative clinical outcomes.
| Conclusion |
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| Appendix: Discussion |
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Second, for the material that you recovered, did you correlate that with your echocardiographic findings in terms of the nature of the aortic wall in relation to the amount and the nature of the material you recovered?
Dr Reichenspurner. To address your first question, in most of the patients I used a side-biting clamp to do the proximal anastomosis. However, 20% of the procedures were done with the proximal procedures done on the clamped aorta. As you saw before, over 90% of the filters did have material in them independent of whether we used the partial crossclamping.
We are so far not able to correlate the amount of material captured according to the degree of the condition of the aorta as verified by TEE.
Dr Mohamed Emara (Cairo, Egypt). I have a question and a comment. Do you think that you have to put this filter in earlier than bypass, especially for valve cases, where you can embolize things during manipulation of the heart?
Your results are perfect. What about the air embolism especially in valve cases?
Dr Reichenspurner. At the beginning, we were concerned whether if you leave the filter in too long, there may be evidence of thrombosis that might obstruct quite a bit of the area of the filter, leading to a higher resistance and an increased afterload for the heart. That is why we started off with relatively short dwell times, which were gradually increased. However, even in filters that stayed in for about an hour, we did not see an obstruction of more than 5% of the mesh area. Therefore it is probably safe to leave it in longer. When you clamp the aorta, there is already the possibility of generation of particulate emboli, and therefore it would be justified to put it in earlier.
Air embolism is certainly a concern with transcranial Doppler studies. It is always hard to differentiate on transcranial Doppler scanning between particulate and gaseous emboli. I think that you might be able to catch gaseous emboli, but I do not think you will actually get them out because once you pull the filter back, you squeeze the filter through the side port, and that will probably squeeze the air out again. Therefore I do not think you will get rid of all the air, but you will definitely get rid of the particulate material, which is probably the more dangerous material.
Dr Hazim J. Safi (Houston, Tex). Have you mapped the ascending aorta by using TEE? Without the hand-held probe, we have had little luck in detecting atheromatous debris or plaque in the ascending aorta.
Dr Reichenspurner. You are fully right. It is a challenge to assess the atheromatous, diseased ascending aorta because it is not easily accessible, but we did use TEE before, and in about half of the patients we used epiaortic scanning during the surgical procedures, which is probably the best way to verify aortic disease. But as mentioned before, we did not find a correlation of the degree of the aortic disease and the amount of captured material.
Dr Paul Kurlansky (Miami Beach, Fla). I congratulate you on a potentially extremely useful addition to the cardiac surgical armamentarium. I would like to recommend that in your future studies you assess not only neurologic function but renal function as well because I suspect that you will cause a significant decrease in postoperative renal complications.
Dr Reichenspurner. Thank you very much.
| Footnotes |
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Read at the Seventy-ninth Annual Meeting of The American Association for Thoracic Surgery, New Orleans, La, April 18-21, 1999.
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