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Eur J Cardiothorac Surg 2002;22:539-544
© 2002 Elsevier Science NL
a Department of Cardiothoracic Surgery and Anesthesiology, Karolinska Institutet, Huddinge University Hospital, SE-141 86 Stockholm, Sweden
b Department of Cardiothoracic Surgery, Glenfield University Hospital, Leicester, UK
Received 14 December 2001; received in revised form 1 April 2002; accepted 8 July 2002.
* Corresponding author. Tel.: +46-8-585-86296; fax: +46-8-585-86740
e-mail: jan.vanderlinden{at}thsurg.hs.sll.se
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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Key Words: Intraaortic filtration • Stroke • Atherosclerosis • Cardiopulmonary bypass • Coronary artery bypass surgery
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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The aim of this study was to (1) evaluate number and type of particulates captured in consecutive unselected patients undergoing CABG and (2) identify risk factors for particle embolization during CABG.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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Rite II, 9.0 MHz, Dymax Corporation, Pittsburg, USA). The probe's advantage is the approximately 6 cm long built-in hard shell standoff, which results in a good resolution even of the surface in contact with the probe. A film of sterile gel was applied on the tip of the probe and a sterile plastic bag was wrapped around. Two assessors, the surgeon and the anesthetist, interpreted the epiaortic ultrasound. In case of disagreement, a third assessor, blind to the conclusions of the first two, was asked for his opinion. Calcified plaques were identified by their almost total reflection of ultrasound, leaving an ultrasonic shadow (dark) distal to the plaque in the direction of the ultrasonic beam. Various minor procedural changes were adopted based on the findings of the epiaortic ultrasound. These included changes in the position of the aortic cross-clamp, the placing of the aortic and cardioplegia cannulas and the site of the proximal anastomoses. The ascending aorta was not evaluated with epiaortic ultrasound in two patients due to technical problems with the probe.
An intra-aortic arterial filter (EMBOL-X Inc, Mountain View, CA) size (extra small, small, medium, large, extra large) was selected on the basis of external measurements estimating the internal diameter of the aorta. A modified 24F arterial cannula (EMBOL-X, Inc) with a side-port designed to house the intra-aortic arterial filter was inserted into the ascending aorta in accordance with standard surgical techniques. The appropriate position of the arterial cannula in the lumen of the ascending aorta was confirmed by a back flow of blood through the cannula and the side-port. Before removal of the cross-clamp, the filter was inserted through the side-port of the arterial cannula and remained in the ascending aorta until and for a few minutes after end of cardiopulmonary bypass (CPB). The heparinized filter mesh has a pore size of 120 µm and it has been described in detail earlier [10, 11]. The filter was in the distal portion of the ascending aorta when the cross-clamp was removed and during placement and displacement of the partial occlusion clamp. Filters were removed from the ascending aorta through the side port. The filter was cut out from its metallic holder with an unused and sterile pair of scissors and new sterile non-starch surgical plastic gloves were used to avoid particulate contamination. Filters were collected in specimen tubes and fixed in formaline for analysis. Particulate emboli were analyzed and filter analysis included gross visual examination at 10x magnification to identify and count particulate matter. Particulate matter was collected and sent to a central laboratory (Stanford University, Stanford, CA) for histological examination. The histological sections were stained with hematoxyline and eosine, trichrome, and elastica van Gieson's stain. Histologic analysis included examination for presence of platelets and fibrin desposition, true trombus, and/or blood clotting, grumous portion of plaque cholesterol, fibrous atheroma, or fibrous cap, and the normal vessel wall. Clinical demographics were prospectively recorded. The presence and number of ascending aortic atheroma (intimal thickening
0.5 mm) as well as the maximal thickness were recorded. The grading of atheromatous disease in the ascending aorta was defined according the maximal thickness as follows: Class 0, normal aorta; Class 1, atheroma <1 mm; Class 2, 1<2 mm; Class 3, 2<3 mm; Class 4, 3<4 mm; and Class 5, 4 mm or mobile atheroma. Clinical assessment included basic neurological examinations preoperatively, first day postoperatively, and before discharge.
2.1. Statistical analysis
Logistic multiple regression analysis was used to identify the predictive value of various factors in the number of harvested particles. Results were expressed as percentages, mean±standard deviation, standard error and/or median and range. Differences were considered significant at a probability level of P less than 0.05. Data were analysed with SPSS version 8.0 statistical program.
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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50%. The mean duration of CPB and aortic cross-clamping was 103.8 min (±27 min, 53–180 min) and 61.5 min (±20 min, 23–129 min), respectively. Patients received in average 3.8 distal anastomoses (±0.9, 2–5), 2.2 proximal anastomoses (±0.6, 1–3), and 3.1 grafts (±0.6, 2–4). The aortic cross-clamp was used once in 38 patients and twice in two patients. A partial aortic cross-clamp was used in 83% (33/40) of the patients 1.13 times (±0.5, 1–4). The partial cross-clamp was not used in seven patients, due to the routine use of single clamp technique by one of the surgeons. Patients were extubated 7.8 h (±3.6 h, 3.5–25 h) after arrival to the intensive care unit and left the hospital 7.6 days (±4.5, 3–24) postoperatively.
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Only the three largest sizes of the filters were used, medium 33%, large 35%, and extra large 33%. Filter deployment was uneventful in all patients, with no adverse events such as aortic dissection. None of the patients had ventricular aneurysms and none of the patients had a history of atrial fibrillation. None of the patients were found to have potentially important sources described in methods for aortic emboli according to TEE. There were no adverse neurological events during the hospital stay, except that one patient with unstable angina experienced a slight visual impairment after waking up in the intensive care unit. This patient had a normal ascending aorta, a normal aortic arch and a normal descending aorta, according to both epiaortic ultrasound and TEE. The carotid arteries of this patient were also normal. A following computerized tomogrophy of the brain showed a small occipital infarction of the right hemisphere.
The mean filter dwell time was 43.9 min (±16 min, 23–99 min). Hard granular or soft material upon visual examination was seen in all 40 filters. Mean number of particles per filter was 10.5 (±5.4, 2–23) with a mean surface area of 8.1 mm2 (9.3 mm, 0.3–51.1 mm). Histologic examination differentiated the captured particulate into the presence or absence of platelet/fibrin deposition, true red blood cell thrombus, grumous atheroma, fibrous atheroma or fibrous cap (with and without calcification or grumous/cholesterol), and medial tissue. Fibroatheromatous material, including needle-shaped cholesterol fragments and atheroma, was the type of particulate commonly found in the 40 filters. Fibrous atheroma or fibrous cap was found in 85% of the filters. Fibrin, with or without the obvious presence of platelets, was present in 30% of the filters, and true thrombus (including clot rich with erythrocytes) was present in 13% of the filters. Medial tissue was not present in any of the filters and grumous portion of the atheromatous plaque was found in one filter (3%). Mature hyaline cartilage, suture material and/or fat was not found in any of the filters (Table 2). Smokers (8/40) were found to have significantly more calcified fibrous atheroma than non-smokers (32/40), 25% vs. 0% (P<0.05), respectively. However, there was no difference in particulate mean surface area between smokers and non-smokers.
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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Filter deployment was successful and uneventful in all patients. One patient experienced visual disturbances postoperatively. The cause of this is unclear, considering that this patient did not have atheromatous changes in the thoracic aorta, according to epiaortic ultrasound and TEE.
All our filters contained particulates and this is in accordance with the other two filter studies, where the capture rate was 99 and 96%, respectively. Thus, our study provide direct evidence of particulate embolization in all patients undergoing CABG, indirectly supporting evidence from transcranial Doppler (TCD) studies of the middle cerebral artery. An association between TCD detected emboli and specific surgical events such as aortic cannulation, onset of CPB [12] and the release of the aortic clamp [2,5,13,14] has been reported earlier. Barbut et al. utilizing TCD and TEE, have demonstrated that most emboli (60%) during CABG are released during clamp manipulation of the ascending aorta, primarily following cross-clamp removal [2–5,14]. Accordingly, we inserted the intra-aortic filter before unclamping the cross-clamp and they were not removed before the end of CPB. However, since the filter in this study was inserted just before release of the cross-clamp, it could not have harvested possible particles, that could have embolized into the aorta prior to the insertion of the filter.
Using TEE and TCD, to determine emboli size, Barbut et al. [4], reported that 72% of emboli measured more than 0.6 mm in diameter (28% more than 1 mm and 44% between 0.6 and 1 mm) and 27% measured 0.6 mm or less. The filters pore size of 0.12 mm should thus be adequate to capture most medium-sized and large particles released proximal to the filter. The number of TCD detected emboli during cardiac surgery [15] including coronary surgery [16,17] has been shown to correlate with postoperative neuropsycological dysfunction. The possible protective effect of intra-aortic filters on neuropsycological function has not yet been studied.
Severe neurologic complications after cardiac surgery are related to the severity of aortic atheroma [1,6–8] as well as to the number of TCD detected emboli [3], despite the fact that the severity of aortic atheroma and the number of TCD detected emboli have been reported to be unrelated [5]. This lack of correlation is most likely due to diagnostic weaknesses. Neither TCD nor TEE can reliably discriminate between gaseous and particulate emboli and both TEE and palpation underestimate the incidence and extent of aortic atheroma. In this study, the presence of aortic atheroma in the ascending aorta was diagnosed with epiaortic ultrasound, the current gold standard.
The mean number of particulates captured during coronary surgery in our study was 10.5 per filter, which is similar to what has been reported in the other two filter studies [10,11], but much lower than reported with the TCD technique [3]. The histological examination of our filters revealed that 85% (34/40) contained atheromatous or fibrous cap, which is higher than the 62% (151/243, P<0.01) and 66% (29/44, P<0.05) reported by Harringer et al. [11] and Reichenspurner et al. [10], respectively. This is most likely explained by the more extensive manipulation of the ascending aorta and possibly the higher incidence of aortic atheroma in our study group. Patient selection may also explain the lower rate of thrombus and/or blood clot seen in our patients, since it cannot be explained by the longer filter dwell time of our patients.
Multiple regression analysis on the number of captured particles provided some interesting results. First, the number of particles captured by intra-aortic filtration during coronary surgery was strongly correlated with the number of plaques or atheroma grading of the ascending aorta. This rather expected relationship has not been documented in the other two filter studies, while TCD studies have failed to find an association [5], probably due to the inability of TCD to differentiate between gaseous and particulate emboli.
Second, hypertension and obesity were found to be independent risk factors for aortic embolization, implying that plaques in these patients may be more fragile. Third, the inverse correlation between the number of captured particles and the number of proximal anastomoses, although difficult to explain directly, may be due to diversion of particles away from the filters into the grafts.
Fourth, the lack of an association between duration of CPB or filter dwell time and number of captured particles may indicate that the filter per se may not produce particles if the heparinization is adequate. The fact that epiaortic ultrasound detected atheromas only in 47% of the patients may indicate that the current epiaortic ultrasound technique is not sensitive enough, despite being the gold standard for detection of atheroma of the ascending aorta.
4.1. Weaknesses of the study
This is a small study. More patients would have been needed to investigate if certain locations of atheromas in the ascending aorta are more prone to cause particulate embolization. Our failure to find risk factors for particulate surface areas per filter may also be due to a type II error, because of the large variation in particulate size. A multicenter study is currently being conducted in order to better evaluate the risk of atheromas in the ascending aorta in a larger group of patients undergoing coronary surgery. Almost all our patients had partial clamping and the risk of partial clamping in terms of particulate embolization could not adequately be investigated most probably due to a type II error. The study did not include a control group and neuropsychological tests were not undertaken. Still, it has shown some light to this difficult neurological area. A randomized study with the hypothesis that filters may change the incidence of Type 1 stroke would have needed far more than a thousand patients, due to the low incidence of overt postoperative stroke. However, randomized studies with intra-aortic filters are currently being conducted, but have so far not yet been published. The recent publication by Schmidt, Blackstone and the International Council of Emboli Management (ICEM) Study Group [17] indicates that the use of intra-aortic filters may lower adverse neurologic events in patients undergoing CABG. Out of 962 patients enrolled consecutively in a prospective, non-voluntary registry of intra-aortic filtration in 15 European centers, 447 underwent isolated CABG, the target population for applying the McSPI stroke risk index. Forty-five had incomplete data, yielding a study group of 402 patients. The stroke risk index was calculated for each patient, and the sum across patients yielded an expected number of neurologic events. Six neurologic events were observed (1.5%; 95% confidence limits 0.6–3.4%), roughly half the 13.7 predicted by the stroke risk index (3.4%; 95% confidence limits 2.0–5.8%), P=0.03. It was concluded that adverse neurologic events associated with coronary artery bypass grafting in which intra-aortic filtration was used were rare and fewer than expected on the basis of the stroke risk index.
4.2. Clinical implications
This study of coronary patients supports the results of two earlier studies that all or almost all patients undergoing cardiac surgery including coronary surgery have a significant amount of particulate embolization. It is the first study proving that number of captured particulates is related to number of plaques or degree of atheroma in the ascending aorta, confirming earlier studies of stroke rate [1,8,9]. Thus, a conservative approach is to use intra-aortic filters in all patients where epiaortic ultrasound detects atheromas in the ascending aorta and where the ascending aorta is clamped, considering the 8.7% risk of postoperative stroke in patients with epiaortic detected atheromas in the ascending aorta [9] and the up to 33% rate of cerebral dysfunction after CABG [1]. A more aggressive approach is to use filters in all patients undergoing cardiac surgery were aortic clamping is being used. Alternative techniques such as proximal anastomotic devices [19] or off pump coronary surgery without manipulation of the ascending aorta [18] may also prove to decrease the rate of cerebral complication. The current cost for the filter in Sweden is approximately 400 Euro. This has to be weighed against the possible decrease in the occurrence and costs of possible neuropsychologic impairment and of perioperative stroke. Although rare, the cost of a perioperative stroke has been estimated to between US $60,000 and 200,000.
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5. Conclusion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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Acknowledgments |
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References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. ConclusionReferences |
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