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Biomedical subjects

A C Yeung

Publications and source records attributed to A C Yeung.

At least 19 recordsLinked to original sources
PubMed2002

Predictors and outcomes of stent thrombosis: an intravascular ultrasound registry.

AIMS: To investigate whether intravascular ultrasound provides additional information regarding the prediction of stent thrombosis, a retrospective multicentre registry was designed to enrol patients with stent thrombosis following stent deployment under ultrasound guidance. METHODS AND RESULTS: A total of 53 patients were enrolled (mean age 61+/-9 years) with stable angina (43%), unstable angina (36%), and post-infarct angina (21%) who underwent intracoronary stenting. The majority had balloon angioplasty alone prior to stenting (94%) with 6% also undergoing rotational atherectomy. The indication for stenting was elective (53%), suboptimal result (32%) and bailout (15%). There were 1.6+/-0.8 stents/artery with 87% undergoing high-pressure dilatation (> or =14 atmospheres). The minimum stent area was 7.7+/-2.8 mm(2)with a mean stent expansion of 81.5+/-21.9%. Overall, 94% of cases demonstrated one abnormal ultrasound finding (stent under-expansion, malapposition, inflow/outflow disease, dissection, or thrombus). Angiography demonstrated an abnormality in only 32% of cases (chi-square=30.0, P<0.001). Stent thrombosis occurred at 132+/-125 h after deployment. Myocardial infarction occurred in 67% and there was an overall mortality of 15%. CONCLUSION: On comparison with angiography, the vast majority of stents associated with subsequent thrombosis have at least one abnormal feature by intravascular ultrasound at the time of stent deployment.

Humans↗
PubMed2001

Prevention of distal embolization during coronary angioplasty in saphenous vein grafts and native vessels using porous filter protection.

BACKGROUND: Although distal embolization and the "no-reflow" phenomenon are well described in saphenous vein graft (SVG) interventions, the frequency, magnitude, and characterization of embolized debris have not been evaluated in routine coronary interventions. A unique embolus protection device described herein provides a means of containing and retrieving plaque material dislodged during percutaneous coronary interventions. This report details the first clinical experience of the effectiveness and safety of an emboli protection system in 11 SVG lesions and 15 native coronary artery lesions. METHODS AND RESULTS: The AngioGuard Emboli Capture Guidewire (Cordis) consists of a PTCA wire with an expandable filter at the distal tip. The porous membrane permits normal distal blood flow, while trapping potential emboli by filtration. After crossing the lesion, the filter is expanded, and routine angioplasty is performed over the same wire. Emboli retrieval is achieved by collapsing the filter and retracting the emboli capture wire (ECW). In 26 patients, standard angioplasty was performed over the ECW; 20 of these 26 patients received a stent. Collected debris was sent for histopathological analysis. Plaque debris was retrieved after native coronary and SVG interventions in all cases. The ECW was positioned and retrieved without complications. No major adverse events occurred. Myocardial infarctions and no-reflow were not observed. CONCLUSIONS: The embolization of plaque fragments frequently occurs during coronary and SVG intervention. Distal embolization leading to microvascular obstruction and no-reflow could be successfully minimized by using the ECW.

Adult↗
PubMed2001

Fractional flow reserve compared with intravascular ultrasound guidance for optimizing stent deployment.

BACKGROUND: Determination of fractional flow reserve (FFR) has been proposed as a means to assess stent deployment. In this prospective, multicenter trial, we evaluate the use of FFR to optimize stenting by comparing it with standard intravascular ultrasound (IVUS) criteria. METHODS AND RESULTS: Eighty-four stable patients with isolated coronary lesions underwent coronary stent deployment starting at 10 atm and increased serially by 2 atm until the FFR was >/=0.94 or 16 atm was achieved. IVUS was then performed. FFR was measured with a coronary pressure wire with intracoronary adenosine to induce hyperemia. The diagnostic characteristics of an FFR <0.94 to predict suboptimal stent expansion by IVUS, defined in both absolute and relative terms, were calculated. Over a range of IVUS criteria, the highest sensitivity, specificity, and predictive accuracy of FFR were 80%, 30%, and 42%, respectively. Receiver operator characteristic analysis defined an optimal FFR cut point at >/=0.96; at this threshold, the sensitivity, specificity, and predictive accuracy of FFR were 75%, 58%, and 62%, respectively (P=0.03 for comparison of predictive accuracy, P=0.01 for concordance between FFR and IVUS). The negative predictive value was 88%. Significantly better diagnostic performance was achieved in a subgroup that received higher doses (>30 microgram) of intracoronary adenosine during pressure measurements, suggesting that FFR might be overestimated in the other group. CONCLUSIONS: A fractional flow reserve <0.96, measured after stent deployment, predicts a suboptimal result based on validated intravascular ultrasound criteria; however, an FFR >/=0.96 does not reliably predict an optimal stent result. Higher doses of intracoronary adenosine than previously used to measure FFR improve these results.

Adenosine↗
PubMed2001

Stent-based delivery of sirolimus reduces neointimal formation in a porcine coronary model.

BACKGROUND: The purpose of this study was to determine the efficacy of stent-based delivery of sirolimus (SRL) alone or in combination with dexamethasone (DEX) to reduce in-stent neointimal hyperplasia. SRL is a potent immunosuppressive agent that inhibits SMC proliferation by blocking cell cycle progression. METHODS AND RESULTS: Stents were coated with a nonerodable polymer containing 185 microgram SRL, 350 microgram DEX, or 185 microgram SRL and 350 microgram DEX. Polymer biocompatibility studies in the porcine and canine models showed acceptable tissue response at 60 days. Forty-seven stents (metal, n=13; SRL, n=13; DEX, n=13; SRL and DEX, n=8) were implanted in the coronary arteries of 16 pigs. The tissue level of SRL was 97+/-13 ng/artery, with a stent content of 71+/-10 microgram at 3 days. At 7 days, proliferating cell nuclear antigen and retinoblastoma protein expression were reduced 60% and 50%, respectively, by the SRL stents. After 28 days, the mean neointimal area was 2.47+/-1.04 mm(2) for the SRL alone and 2.42+/-1.04 mm(2) for the combination of SRL and DEX compared with the metal (5.06+/-1.88 mm(2), P<0.0001) or DEX-coated stents (4.31+/-3.21 mm(2), P<0.001), resulting in a 50% reduction of percent in-stent stenosis. CONCLUSIONS: Stent-based delivery of SRL via a nonerodable polymer matrix is feasible and effectively reduces in-stent neointimal hyperplasia by inhibiting cellular proliferation.

Animals↗
PubMed2001

Percutaneous in situ coronary venous arterialization: report of the first human catheter-based coronary artery bypass.

Diffuse coronary artery disease is frequently untreatable by coronary artery bypass or angioplasty. Many such "no-option" patients have been subjects for trials of angiogenesis using growth factor manipulation or laser injury. We think these novel revascularization strategies are limited by insufficient inflow to putative areas of new microvasculature and thus seek a more mechanical solution. We report the use of a catheter-based system for arterializing the adjacent anterior cardiac vein in a patient with chronic total occlusion of the left anterior descending coronary artery. A composite catheter system (phased-array ultrasound imaging system mounted on a catheter with extendable nitinol needle) was used to deliver an exchange-length intracoronary guidewire from the proximal left anterior descending coronary artery into the parallel anterior interventricular vein. Using standard angioplasty techniques, a fistula was then constructed from the proximal artery to the coronary vein using a self-expanding connector. The proximal vein was blocked with a novel self-expanding "blocker," thus precluding "steal" through the coronary sinus and forcing retroperfusion of the anterior wall. The procedure was completed without complication, and a follow-up angiogram at 3 months confirmed continued patency of the arteriovenous connection. This patient, who had severe angina before the procedure, has been asymptomatic for 12 months. Percutaneous in situ venous arterialization may be an effective therapy for diffuse, "untreatable" coronary disease by supplying a robust inflow of arterialized blood via retroperfusion to severely ischemic myocardium.

Catheterization↗
PubMed2001

Utility of mechanical rheolysis as an adjunct to rescue angioplasty and platelet inhibition in acute myocardial infarction and cardiogenic shock: a case report.

We describe the value of mechanical rheolysis as an adjunct to rescue angioplasty and platelet glycoprotein IIb/IIIa receptor inhibition in a patient with acute myocardial infarction and cardiogenic shock in whom the severity of the intracoronary thrombus burden precluded restoration of antegrade coronary flow by conventional balloon angioplasty and stenting.

Aged↗
PubMed2001

Evaluation of the percutaneous intramyocardial injection for local myocardial treatment.

Therapeutic angiogenesis requires the induction of new blood vessel formation for the treatment of peripheral vascular and coronary artery disease. Efficacious application of this new therapy requires optimizing multiple factors, including the therapeutic agent, dosing, frequency of administration, and delivery modality. In this study, a helical needle drug infusion catheter was applied for optimal application of percutaneous intramyocardial delivery (PIMD). (125)Iodine-labeled albumin was injected by PIMD into the left ventricle myocardium in eight swine. After 1 hr, PIMD resulted in a high concentration of radiolabel at the treatment site; 16.4% +/- 2.1% of delivered and 81.4% +/- 2.6% of the total cardiac activity was concentrated at the site of delivery. The depth of needle penetration correlated with the myocardial retention of delivered protein. The myocardial retention of radiolabel in animals with shallow injections was 10.1% +/- 0.8%, compared to 18.9% +/- 3.3% retention after deep injections. The specific activity at the treatment site (radioactive counts per gram of tissue) was 115 +/- 36, 226 +/- 55, and 47 +/- 10 times higher compared to liver, lung, and kidney, respectively. Continuous coronary sinus and aortic blood sampling indicates that within 15 min following intramyocardial injection, a significant amount of nonretained protein is found within the coronary sinus. This study defines some of the parameters that can affect optimal application of PIMD and demonstrates that PIMD is a safe and efficient method for local drug delivery.

Animals↗
PubMed2001

Initial results of the Quanam drug eluting stent (QuaDS-QP-2) Registry (BARDDS) in human subjects.

Thirty-two patients presenting with varied coronary syndromes and anatomy were treated with a new coronary multisleeve drug delivery coronary stent (QuaDS-QP-2) containing up to 4,000 microg of a taxol-derived lipophilic microtubule inhibitor (QP2). The device was successfully implanted in 32 patients who have been followed for up to 2 years. Twenty-five patients have undergone stress ECHO or SPECT Thallium and all are currently asymptomatic. Thirteen patients have already been restudied angiographically, by IVUS and/or by SPECT Thallium testing and are detailed in this report. Angiographic, IVUS, and SPECT Thallium have been controlled at a mean of 11.2 months (range, 6-15 months) in this 13-patient cohort. Although all 13 QuaDS-QP-2 (QDES) stents were angiographically and IVUS patent, two reinterventions have been required in the 32-patient study group thus far, both relate to either new disease or to distal, small-vessel disease beyond the stent. There was no evidence of significant proliferation in the QDES devices. On the basis of this preliminary data and a European pilot study, a controlled randomized trial (SCORE) is currently in progress in western Europe.

Adult↗
PubMed2001

Coronary artery distensibility and compensatory vessel enlargement--a novel parameter influencing vascular remodeling?

Vascular remodeling implies the concept of compensatory vessel enlargement to preserve luminal dimensions during atheromatous plaque development. However, negative remodeling, i.e. vessel shrinkage in response to plaque accumulation has also been described. So far, the factors influencing positive or negative remodeling are uncertain. We hypothesized that vascular distensibility, a measure of vessel compliance, is related to compensatory enlargement. In 58 patients undergoing intravascular ultrasound interrogation of a de novo lesion prior to coronary intervention, the cross-sectional vessel area (VA), lumen area (LA) and plaque area (PA = VA minus LA) were measured at end diastole and end systole at the lesion site and at the proximal and distal reference segments. Positive remodeling was defined to be present when the VA at the lesion was > 1.05 times larger than that at the proximal reference (group A), negative remodeling when the VA at the lesion was < 0.95 of the reference site (group C) and in-between was considered to be intermediate (group B). Vessel compliance was measured by calculating vascular distensibility. Results showed a similar LA at the lesion site in all groups (4.18+/-2.18 vs. 4.36+/-1.19 vs. 3.74+/-1.81 mm2, NS) while VA and PA were significantly larger in group A (17.19+/-5.08 vs. 14.22+/-3.66 and 12.45+/-4.82 mm2, p = 0.005 and 13+/-4.55 vs. 9.95+/-3.58 and 8.7+/-3.83, p = 0.003, respectively). Vascular distensibility at the proximal reference segment was significantly greater in group A (3.55+/-2.67 vs. 1.25+/-1.03 and 0.85+/-0.73 mmHg(-1), p < 0.001) with a positive correlation between remodeling and distensibility (R = 0.52, p < 0.001). In a multiple regression model including clinical and lesional factors, distensibility was the only predictor of remodeling. In conclusion, these results suggest that compensatory vessel enlargement occurs to a greater degree in patients with increased coronary artery distensibility, which appears to be a predictor for positive remodeling.

Adaptation, Physiological↗
PubMed2001

The influence of plaque orientation (pericardial or myocardial) on coronary arterial remodeling.

BACKGROUND: Many systemic, regional and lesion factors have been identified which may influence arterial remodeling, but little is known about the importance of extravascular resistance to vessel enlargement. As myocardial systolic splinting may significantly affect vessel expansion the effect of plaque orientation on arterial remodeling in eccentric coronary atherosclerotic lesions was examined. METHODS: Using intravascular ultrasound imaging to obtain cross-sectional vessel area (VA), plaque area (PA) and lumen area (LA), remodeling in eccentric left anterior descending coronary artery lesions was compared which predominantly involved the pericardial or free arc (P, n=25) and the myocardial side (M, n=40) of the vessel wall. Normalized vessel area (NVA, VA(lesion)/VA(reference)) was compared as a continuous and categorical variable (positive>1.05, intermediate 0.95-1.05, negative<0.95) as well as remodeling index (RI, VA(lesion)-VA(reference)/PA(lesion)-PA(reference)). RESULTS: The two groups were well matched for clinical and lesion characteristics known to affect remodeling. Reference segments areas were similar in the two groups; while lesion LA was also similar, in the pericardial group there was significantly greater lesion PA (P 12.78+/-0.72, M 10.26+/-0.50 mm(2), P<0.05) and VA (P 15.71+/-0.90, M 12.82+/-0.57 mm(2), P<0.05) demonstrating enhanced compensatory remodeling. Outward remodeling was significantly greater in P than in M by both NVA (P 1.03+/-0.03, M 0.86+/-0.03, P<0.01) and RI (P 0.02+/-0.07, M -1.10+/-0.32, P<0.01). Positive, intermediate and negative remodeling occurred in nine, nine and seven lesions in P and in four, ten and 26 lesions in M (P<0.01). CONCLUSIONS: Remodeling compensates more for plaque growth in eccentric coronary lesions which are surrounded by the pericardium than those surrounded by the myocardium. Extravascular resistance appears to influence arterial remodeling.

Aged↗
PubMed2001

Impact of coronary artery remodeling on clinical presentation of coronary artery disease: an intravascular ultrasound study.

OBJECTIVES: We examined the association between the features of the culprit lesion in coronary artery disease (CAD) and clinical presentation as shown by intravascular ultrasound (IVUS). BACKGROUND: The association between coronary remodeling pattern and clinical presentation of CAD is unclear. METHODS: We analyzed 125 selected patients who underwent preintervention IVUS. Acute myocardial infarction (AMI) and unstable angina pectoris (UAP) were categorized as an acute coronary syndrome (ACS), and stable angina pectoris (SAP) and old myocardial infarction (OMI) as stable CAD. Coronary remodeling patterns and plaque morphology of the culprit lesion obtained by IVUS were analyzed in terms of their association with clinical presentation or angiographic morphology. RESULTS: Angiographically complex lesions were associated with ACS and OMI. In patients with a complex lesion, positive remodeling was observed more frequently than in those with a simple lesion. In AMI and UAP, positive remodeling was observed more frequently than in SAP and OMI (82% vs. 78% vs. 33% vs. 40%, respectively, p < 0.0001). The remodeling ratio was greater in AMI and UAP than in SAP and OMI (1.26 +/- 0.15 vs. 1.11 +/- 0.10 vs. 0.94 +/- 0.11 vs. 0.96 +/- 0.13, respectively, p < 0.0001). Furthermore, within ACS, the remodeling ratio was greater in AMI than in UAP (1.26 +/- 0.15 vs. 1.11 +/- 0.10, respectively, p < 0.05), whereas the frequency of positive remodeling was not different. CONCLUSIONS: Positive remodeling was more frequently observed in ACS than in stable CAD. Moreover, the degree of positive remodeling was greater in AMI than in UAP. These results may reflect the impact of remodeling types and its degree in the culprit lesion of CAD on clinical presentation.

Adult↗
PubMed2001

Role of vascular remodeling in the pathogenesis of early transplant coronary artery disease: a multicenter prospective intravascular ultrasound study.

BACKGROUND: Luminal narrowing in transplant coronary artery disease is thought to be primarily caused by intimal proliferation, and the role of vascular remodeling is less certain. METHODS AND RESULTS: We studied cardiac allografts from 83 prospectively recruited patients immediately and 1 year after transplant using intravascular ultrasound in a multicenter study. We measured coronary artery dimensions in 310 angiographically matched segments (175 were also fully matched by ultrasound criteria). At 1 year, lumen area changed by -1.8 +/- 3.7 mm(2) (p < 0.0001, 14% of baseline lumen area). Thirty-three percent of this luminal loss was due to intimal thickening and 67% to vessel shrinkage. Shrinkage also occurred (-0.9 +/- 3.2 mm(2), 7% of baseline total area) in segments free of detectable intimal disease at baseline and at 1 year. Using the mean baseline total vessel area (13.9 mm(2)) as the cutoff, we divided the cohort into the large and the small coronary-segment groups. The large-segment group (n = 176) shrank more (-2.6 +/- 4.4 vs. -0.03 +/- 2.8 mm(2), p < 0.0001), but intimal growth was similar in both groups (0.8 +/- 2.2 vs. 0.4 +/- 1.3 mm(2), p = not significant). Analysis of the 175 fully ultrasound matched sub-cohort showed similar results. Changes in intimal area, total vessel area, and lumen area were similar in segments with (n = 132) and segments without (n = 178) pre-existing donor disease. Despite overall shrinkage, change in total vessel area positively correlated with change in intimal area (r = 0.29, p < 0.0001). CONCLUSION: In large coronary segments, coronary artery shrinkage plays an important role in the loss of luminal diameter early after cardiac transplantation, whereas new intimal growth occurs in both large and small segments. Pre-existent donor disease does not aggravate these processes. Compensatory remodeling with increasing intimal growth retards the rate of lumen loss. As is intimal thickening, shrinkage and compensatory remodeling are important pathogenic mechanisms in transplant coronary artery disease.

Adult↗
PubMed2001

The topography of intimal thickening and associated remodeling pattern of early transplant coronary disease: influence of pre-existent donor atherosclerosis.

BACKGROUND: With native coronary disease, intimal plaque initially accumulates at focal areas in the artery, often accompanied by compensatory vessel enlargement. With transplant coronary disease, the topography of intimal thickening and associated remodeling pattern are less studied. METHODS: We studied 72 prospectively recruited transplant patients with serial intravascular ultrasound using 4.3F catheters at baseline and at 1-year follow up. We considered 175 ultrasound-recorded segments (mean, 2.4 +/- 1.1 segments per patient) exactly matched on the serial studies by both angiographic criteria and ultrasound criteria, using arterial and venous branch points, pericardium, and sinuses as anatomic landmarks. RESULTS: Eighty-eight segments had no donor disease, and 87 had donor disease (80 eccentric and 7 concentric intimal thickening). Progressive intimal thickening occurred in 48 segments without (55%) and 43 segments with donor disease (48%, p = NS). Thickening from segments without donor disease was mainly eccentric (81%). Thickening from segments with donor eccentric plaque was also mainly eccentric (67%, p = NS compared with segments without donor disease), with further thickening superimposed on the original plaque. Concentric intimal thickening was uncommon. Of the 58 patients who had >1 segment matched, intimal changes were discordant in 34 (59%), with progression in some and lack of progression in other segments. Total vessel area change correlated with intimal area change (r = 0.37 with a slope of 0.79, p < 0.001), including segments with (r = 0.39; slope, 0.69) and segments without (r = 0.37; slope, 1.16) donor disease. CONCLUSION: The intimal thickening of early transplant coronary disease is mainly eccentric and often discordant within each individual patient. Donor eccentric plaque often serves as a nidus for further intimal growth. The topography of intimal thickening in transplant coronary disease resembles that of native coronary disease, but the presence of a pre-existent donor plaque may impede compensatory remodeling as further intimal thickening occurs after transplantation.

Adult↗
PubMed2001

Mild hyperhomocysteinemia is not associated with cardiac allograft coronary disease.

BACKGROUND: Hyperhomocysteinemia is an independent risk factor for coronary disease and elevated plasma homocysteine levels have been documented in heart transplant recipients. The aim of this study was to test the hypothesis that homocysteine levels are associated with presence or absence of transplant coronary artery disease. METHODS: Forty-three non-smoking adults were recruited, all of whom had received a heart transplant between 2 and 7 yr previously. All 43 had blood drawn for fasting homocysteine level on the day of presentation. All patients had undergone diagnostic coronary angiography within the past 6 months. RESULTS: For all patients, the average fasting plasma homocysteine level was 17.0+/-SD 6.6 micromol/L with a range from 6.0 to 36.9 micromol/L. Twenty-six patients (60%) had fasting plasma homocysteine levels above 15.0 micromol/L. On the basis of arteriography, patients were categorized as those with angiographically normal (n=22) or abnormal (n=21) coronary arteries. There was no difference in the mean plasma homocysteine level comparing patients with angiographically normal (17.2+/-SD 7.0 micromol/L) to those with abnormal (16.8+/-SD 6.2 micromol/L) coronary arteries. Plasma homocysteine levels increased with increasing plasma creatinine levels (r=0.63, p<0.0001) and with decreasing vitamin B6 levels (r=-0.56, p<0.0001). CONCLUSIONS: Mild hyperhomocysteinemia is a consistent finding among heart transplant recipients. This finding was not associated with transplant coronary artery disease in our patients. The combination of renal dysfunction and vitamin B6 deficiency may explain the unusual prevalence of hyperhomocysteinemia in heart transplant recipients.

Adult↗