A. Ross Naylor

Increased Matrix Metalloproteinase-9 Activity in Unstable Carotid Plaques A Potential Role in Acute Plaque Disruption

BACKGROUND AND PURPOSE Acute disruption of atherosclerotic plaques precedes the onset of clinical syndromes, and studies have implicated a role for matrix metalloproteinases (MMPs) in this process. The aim of this study was to establish the character, level, and expression of MMPs in carotid plaques and to correlate this with clinical status, cerebral embolization, and histology. METHODS Plaques were obtained from 75 consecutive patients undergoing carotid endarterectomy and divided into 4 groups according to symptomatology (group 1, asymptomatic; group 2, symptomatic >6 months before surgery; group 3, symptomatic within 1 to 6 months; group 4, symptomatic within 1 month). All patients underwent preoperative and intraoperative transcranial Doppler monitoring. Plaques were subjected to histological examination and quantification of MMPs by zymography and ELISA. RESULTS The level of MMP-9 was significantly higher in group 4 (median 125.7 ng/mL for group 4, median <32 ng/mL for all other groups; P=0.003), with no difference in the levels of MMPs 1, 2, or 3. Furthermore, the MMP-9 concentration was significantly higher in plaques undergoing spontaneous embolization (P=0.019) and those with histological evidence of plaque instability (P<0.03). In situ hybridization demonstrated increased MMP-9 expression in highly symptomatic plaques in areas of intense inflammatory infiltrate. CONCLUSIONS The concentration, production, and expression of MMP-9 is significantly higher in unstable carotid plaques. If this proves to be a causal relationship, MMP-9 may be a strong candidate for pharmacotherapy aimed at stabilizing plaques and preventing stroke.

Angiogenesis and the atherosclerotic carotid plaque: An association between symptomatology and plaque morphology

Purpose: Symptomatic carotid disease resulting from generation of thromboemboli has been associated with plaque instability and intraplaque hemorrhage. These features of the lesion could be influenced by the fragility and position of neovessels within the plaque. The purpose of this study was to determine whether any association exists between neovessel density, position, morphology, and thromboembolic sequelae. Methods: Carotid endarterectomy samples were collected from 15 asymptomatic patients with greater than 80% stenoses and from 13 highly symptomatic patients who had suffered ipsilateral carotid stenotic events within 1 month of surgery. Both groups were matched for gender, age, risk factors, degree of carotid artery stenosis, and plaque size. Samples were stained with hematoxylin/eosin and van Geison. Immunohistochemistry was performed by using an endothelial specific antibody to CD31. Plaques were assessed for histologic characteristics, and neovessels were counted and characterized by size, site, and shape. Results: There were significantly more neovessels in plaques (P < .00001) and fibrous caps (P < .0001) in symptomatic compared with asymptomatic plaques. Neovessels in symptomatic plaques were larger (P < .004) and more irregular. There was a significant increase in plaque necrosis and rupture in symptomatic plaques. Plaque hemorrhage and rupture were associated with more neovessels within the plaque (P < .017, P < .001) and within the fibrous cap (P < .046, P < .004). Patients with preoperative and intraoperative embolization had significantly more plaque and fibrous cap neovessels (P < .025, P < .001). Conclusion: Symptomatic carotid disease is associated with increased neovascularization within the atherosclerotic plaque and fibrous cap. These vessels are larger and more irregular and may contribute to plaque instability and the onset of thromboembolic sequelae. (J Vasc Surg 1999;30:261-8.)

Beneficial effects of clopidogrel combined with aspirin in reducing cerebral emboli in patients undergoing carotid endarterectomy.

Background—Postoperative thromboembolic stroke affects 2% to 3% of patients undergoing carotid endarterectomy (CEA) and is preceded by 1 to 2 hours of increasing cerebral embolization. Previous work has demonstrated that high rates of postoperative embolization are associated with increased platelet reactivity to adenosine 5′-diphosphate (ADP). Our hypothesis was that preoperative administration of the platelet ADP antagonist clopidogrel could reduce postoperative embolization. Methods and Results—One hundred CEA patients on routine aspirin therapy (150 mg) were randomized to 75 mg clopidogrel (n=46) or placebo (n=54) the night before surgery. Platelet response to ADP was assessed by whole-blood flow cytometry. The number of emboli detected by transcranial Doppler within 3 hours of CEA was independently quantified. Time taken from flow restoration to skin closure was used as an indirect measure of the time to secure hemostasis. In comparison with placebo, clopidogrel produced a small (8.8%) but significant reduction in the platelet response to ADP (P <0.05) while conferring a 10-fold reduction in the relative risk of those patients having >20 emboli in the postoperative period (odds ratio, 10.23; 95% CI, 1.3 to 83.3; P =0.01, Fisher’s exact test). However, in the clopidogrel-treated patients, the time from flow restoration to skin closure (an indirect marker of hemostasis) was significantly increased (P =0.04, Fisher’s exact test), although there was no increase in bleeding complications or blood transfusions. Conclusions—This is the first study to show that a CEA patient’s postoperative thromboembolic potential can be significantly reduced by targeted preoperative antiplatelet therapy without increasing the risk of bleeding complications.

Prevention of postoperative thrombotic stroke after carotid endarterectomy: The role of transcranial Doppler ultrasound

PURPOSE To determine the incidence of particulate embolization after carotid endarterectomy (CEA), the effect of dextran-40 infusion in patients with sustained postoperative embolization, and the impact of transcranial Doppler (TCD) monitoring plus adjuvant dextran therapy on the rate of postoperative carotid thrombosis. METHODS Prospective study in 100 patients who underwent CEA with 6-hour postoperative monitoring using a TCD that was modified to allow automatic, intermittent recording from the ipsilateral middle cerebral artery waveform (10 minute sample every 30 minutes). An incremental dextran-40 infusion was commenced if 25 or more emboli were detected in any 10-minute period. RESULTS Overall, 48% of patients had one or more emboli detected in the postoperative period, particularly in the first 2 hours. However, sustained embolization that required Dextran therapy developed in only five patients. In each case, the rate of embolization rapidly diminished. CONCLUSIONS A small proportion of patients have sustained embolization after CEA, which in previous studies has been shown to be highly predictive of thrombotic stroke. Intervention with dextran reduced and subsequently stopped all the emboli in those in whom it was used and contributed to a 0% perioperative morbidity and mortality rate in this series.

The role of risk and benefit perception in informed consent for surgery.

Background. Informed consent relies on patients’ ability to understand risk information. Evidence suggests that people may extract the gist of any risk information to make medical decisions. Existing evidence also suggests that there is an inverse relationship between the perception of risk and the perception of benefit. Method. Seventy-one patients on the waiting list for carotid endarterectomy (CEA) were surveyed regarding their understanding and recall of the risk and benefit to health of undergoing CEA. Patients were surveyed 1 month after their initial consultation, and a subgroup was surveyed again on the day before their operation. Results. Patients’ estimates of their baseline risk of stroke without surgery were significantly different from what they had been told by the surgeon. Patients’ estimates of stroke risk due to surgery ranged from 0% to 65% (actual local risk 2%). Patients also had unreasonable expectations about the benefit of the operation for their health. Estimates of stroke risk correlated positively with the degree of expected benefit from the operation (r = 0.29, P = 0.05). When resurveyed the day before the operation, patients’ perceptions of both risk and benefit had increased significantly. The risk perception data from some patients appeared to contradict some of the predictions of the fuzzy-trace theory. Conclusions. Most patients failed to understand the risks and benefits associated with CEA. Some patients’ estimates of stroke risk were actually greater than the perceived potential benefit of surgery in terms of risk reduction. The data also suggested a positive correlation between the degree of perceived benefit and the degree of perceived risk.

Prospective, randomized, double-blind trial investigating the effect of doxycycline on matrix metalloproteinase expression within atherosclerotic carotid plaques.

Background and Purpose— Elevated levels of matrix metalloproteinases (MMPs), particularly MMP-1 and MMP-9, have been implicated in plaque rupture. It has been suggested that inhibition of MMPs may stabilize vulnerable atherosclerotic plaques and improve clinical outcome. The aim of the study was to investigate the ability of doxycycline, a nonspecific MMP inhibitor, to reduce MMP concentration in carotid atheroma. Methods— The study design was a prospective, double-blind randomized trial. One hundred patients requiring carotid endarterectomy were randomized to receive 200 mg/d doxycycline or placebo for 2 to 8 weeks before surgery. During endarterectomy, carotid plaques were retrieved. The concentrations of MMPs and doxycycline were determined in the atherosclerotic tissue by enzyme-linked immunosorbent assay and high-performance liquid chromatography, respectively. Clinical events were recorded, as was the rate of preoperative embolization (transcranial Doppler). Results— Analysis of endarterectomized specimens demonstrated a mean doxycycline concentration of 6.0 &mgr;g/g wet weight in treated patients. Administration of doxycycline significantly reduced the concentration of MMP-1 in carotid plaques from a mean of 14.8 to 10.3 ng/100g wet weight (P =0.038). This difference was due to decreased MMP-1 transcript (P <0.001). There was no difference in any other MMP (MMP-2, -3, or -9) or tissue inhibitor of matrix metalloproteinases–1 or –2. Conclusions— Doxycycline penetrated atherosclerotic plaques with acceptable tissue levels. This resulted in a reduction in MMP-1 concentration because of decreased expression.

Interpretation of Embolic Phenomena During Carotid Endarterectomy

BACKGROUND AND PURPOSE Air and particulate emboli are a major source of morbidity during carotid endarterectomy (CEA); however, amplitude overload and poor time resolution have restricted the ability of transcranial Doppler ultrasound to differentiate between the two. METHODS We have now overcome these two limitations by (1) rerouting embolic signals away from the audio frequency amplifier to avoid amplitude overload and (2) substituting the Wigner distribution function for the fast Fourier transform to improve time and frequency resolution. Thus, we can now accurately determine embolic duration and embolic velocity, the product of which is the sample volume length (SVL). This measurement represents the physical distance over which an embolic signal can be detected. The underlying hypothesis was that air reflected more ultrasound and would therefore be detected over a greater SVL. RESULTS The median SVL (interquartile range) for 75 in vitro air emboli was 1.97 cm (range, 1.70 to 2.35) compared with 0.27 cm (range, 0.16 to 0.43) for 185 particulate emboli detected during the dissection phase of CEA. Off-line analysis on an additional 560 embolic signals detected during different phases of CEA suggested that 46 of 143 (32%) of emboli immediately after shunt insertion were particulate, as were 19 of 33 (58%) occurring during shunting, 28 of 78 (36%) after restoration of flow in the external carotid artery, 23 of 251 (9%) after restoration of flow in the internal carotid artery, and 55 of 55 (100%) of those emboli detected during the early recovery phase. CONCLUSIONS This development provides objective physical criteria upon which embolus characterization (particulate/air) can be based. This could have major implications for future patient monitoring with respect to modification of surgical technique and pharmacological intervention.

Time is brain

Carotid endarterectomy (CEA) is a proven treatment in the prevention of stroke, but its overall effectiveness is reduced by excessive delays from symptom to surgery. Specifically, delaying surgery in symptomatic patients with 50-99% NASCET stenoses (70-99% ECST) for >12 weeks prevents only eight strokes per 1000 CEAs in the long term. This is a very depressing observation as the 2004 Sentinel Audit observed that only 50% of stroke patients in the UK will have undergone a Duplex scan by 12 weeks. Excessive delays prior to surgery not only undermine professional confidence in the role of CEA, but they effectively mean that while every patient is exposed to the risks of surgery, many may gain little in the way of long-term stroke prevention. Many of the issues debated in this review will only be resolved by a paradigm shift in political emphasis, but surgeons too have a responsibility to recognise and correct important deficiencies within their own practice.

Percutaneous Transluminal Angioplasty in the Treatment of Critical Limb Ischemia

Purpose: To assess the role of percutaneous transluminal angioplasty (PTA) to treat critical limb ischemia (CLI) and to relate the changing experience with endovascular treatment of this condition in a major vascular unit. Methods: A prospective study was performed involving 110 consecutive patients (57 women; mean age 76 years, range 57–99) undergoing balloon angioplasty for critical limb ischemia in 133 limbs. Outcome at 1 year was examined by case note review or questionnaire to determine survival, amputation-free survival, limb salvage, and CLI recurrence. Results: Technical success was achieved in 105 (79%) of 133 limbs; the overall complication rate was 20% (3.8% major, 16.2% minor). The median follow-up was 15 months (minimum 12). The 12-month limb salvage rate by life-table analysis was 88%. Patients with an initially successful angioplasty had an extremely good outcome (95% 1-year limb salvage). In contrast, the 28 patients with failed angioplasty fared very poorly; a major amputation was required in 10, and death occurred in another 9, leaving only 9 survivors with limbs intact at 1 year. Conclusions: The results of this study justify the continuing use of PTA as first-line treatment for critical limb ischemia.

Predictors and clinical significance of progression or regression of asymptomatic carotid stenosis

OBJECTIVE To determine baseline clinical and ultrasonographic plaque factors predictive of progression or regression of asymptomatic carotid stenosis and the predictive value of changes in stenosis severity on risk of first ipsilateral cerebral or retinal ischemic events (including stroke). METHODS A total of 1121 patients with asymptomatic carotid stenosis of 50% to 99% in relation to the bulb diameter (European Carotid Surgery Trial [ECST] method) underwent six monthly clinical assessments and carotid duplexes for up to 8 years (mean follow-up, 4 years). Progression or regression was considered present if there was a change of at least one grade higher or lower, respectively, persisting for at least two consecutive examinations. RESULTS Regression occurred in 43 (3.8%), no change in 856 (76.4%), and progression in 222 (19.8%) patients. Younger age, high grades of stenosis, absence of discrete white areas in the plaque, and taking lipid lowering therapy were independent baseline predictors of increased incidence of regression. High serum creatinine, male gender, not taking lipid lowering therapy, low grades of stenosis, and increased plaque area were independent baseline predictors of progression. One hundred and thirty first ipsilateral cerebral or retinal ischemic events, including 59 strokes, occurred. Forty (67.8%) of the strokes occurred in patients whose stenosis was unchanged, 19 (32.2%) in those with progression, and zero in those with regression. For the entire cohort, the 8-year cumulative ipsilateral cerebral ischemic stroke rate was zero in patients with regression, 9% if the stenosis was unchanged, and 16% if there was progression (average annual stroke rates of 0%, 1.1%, and 2.0%, respectively; log-rank, P = .05; relative risk in patients with progression, 1.92; 95% confidence interval, 1.14-3.25). For patients with baseline stenosis 70% to 99% in relation to the distal internal carotid (North American Symptomatic Carotid Endarterectomy Trial [NASCET] method), in the absence of progression (n = 349), the 8-year cumulative ipsilateral cerebral ischemic stroke rate was 12%. In the presence of progression (n = 77), it was 21% (average annual stroke rates of 1.5% and 2.6%, respectively; log-rank, P = .34). Only nine (30%) of the 30 strokes occurred in the progression group. CONCLUSIONS Progressive asymptomatic carotid stenosis identified a subgroup with about twice the risk of ipsilateral stroke compared with those without progression. However, the clinical value of screening for progression simply for selecting patients for carotid procedures is limited because of the low frequency of progression and its relatively low associated stroke rate. The cost effectiveness of screening for change in stenosis severity to better direct current optimal medical treatment needs testing.