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Biomedical subjects

Alan C Yeung

Publications and source records attributed to Alan C Yeung.

At least 19 recordsLinked to original sources
PubMed2007

Comparison of nonuniform rotational distortion between mechanical IVUS and OCT using a phantom model.

Optical coherence tomography (OCT) is an optical analog of mechanical intravascular ultrasound (M-IVUS) with much higher spatial resolution. However, no data exist regarding the nonuniform rotational distortion (NURD) with OCT. The aim of the study was to investigate whether OCT generates less NURD relative to M-IVUS. A coronary artery phantom model was constructed with a rubber ring (3.68 mm in diameter), located at the distal end of the phantom. This model was also composed of eight equally spaced steel wires and an additional marker-wire. Two types of vascular phantoms were used, mild curve (90 degrees ) and acute curve (near 180 degrees ). Subsequent M-IVUS (n = 6) and OCT (n = 6) imaging was performed. Eight angles between eight wires, except the marker-wire, were measured from each image. These angles, measured with M-IVUS and OCT, were compared with those of high-resolution optical photography as a gold standard. The average in angle differences was significantly smaller in OCT compared with M-IVUS in the mild curve model (3.2 +/- 1.0 degrees vs, 6.9 +/- 2.1 degrees , p < 0.01). Compared with the latter model, the average in angle differences was exaggerated in the acute curve model with M-IVUS (9.1 +/- 0.9 degrees vs. 6.9 +/- 2.1 degrees , p < 0.05) but not with OCT (3.5 +/- 0.8 degrees vs. 3.2 +/- 1.0 degrees , p= not significant). OCT generates significantly less NURD compared with M-IVUS, especially in tortuous situation.

Artifacts↗
PubMed2006

Arteriotomy closure device application following percutaneous coronary intervention may prevent bleeding complications in patients with acute myocardial infarction.

The current study was performed to determine whether application of arteriotomy closure devices (ACDs) affect bleeding complications as compared to manual compression in patients with ST-elevated acute myocardial infarction (STEMI) who undergo primary or rescue percutaneous intervention (PCI). 314 consecutive cases of STEMI treated with PCI were retrospectively evaluated. Overall, 82.8% of patients received ACDs with total bleeding rate of 4.2% vs. 11.1% in patients who had manual compression, p=0.042. This difference in bleeding rates did not correlate with any clinical characteristic or utilization of GPIIb/IIIa inhibitors. Accordingly, ACDs can improve the acute results of PCI in STEMI patients.

Aged↗
PubMed2006

Discordant changes in epicardial and microvascular coronary physiology after cardiac transplantation: Physiologic Investigation for Transplant Arteriopathy II (PITA II) study.

BACKGROUND: Investigating changes in coronary physiology that occur after cardiac transplantation has been challenging. Simultaneous and independent assessment of the epicardial artery by measuring fractional flow reserve (FFR) and of the microvasculature by calculating the index of microvascular resistance (IMR) with a single coronary pressure wire may be useful. METHODS: Twenty-five asymptomatic patients with normal coronary angiograms underwent FFR, thermodilution-derived IMR and coronary flow reserve (CFR) and intravascular ultrasound (IVUS) evaluation soon after cardiac transplantation and 1 year later. RESULTS: FFR significantly worsened (0.90 +/- 0.05 at baseline to 0.85 +/- 0.06 at 1 year, p = 0.004). FFR correlated strongly with percent plaque volume as measured by IVUS (r = -0.58, p < 0.0001). IMR improved significantly (29.2 +/- 15.9 at baseline to 19.3 +/- 7.6 units at 1 year, p = 0.007). CFR increased, but not significantly (2.6 +/- 1.4 at baseline to 3.2 +/- 1.2 at 1 year, p = not significant). Diabetes and donor heart ischemic time independently predicted baseline IMR. Treatment with rapamycin independently predicted FFR at 1 year. CONCLUSIONS: New coronary physiologic measures, FFR and IMR, show that epicardial artery physiology worsens and correlates with anatomic changes, whereas microvascular physiology improves during the first year after cardiac transplantation. CFR, the traditional method for evaluating coronary circulatory physiology, did not identify these changes.

Cardiac Catheterization↗
PubMed2006

Invasive assessment of the coronary microcirculation: superior reproducibility and less hemodynamic dependence of index of microcirculatory resistance compared with coronary flow reserve.

BACKGROUND: A simple, reproducible invasive method for assessing the coronary microcirculation is lacking. A novel index of microcirculatory resistance (IMR) has been shown in animals to correlate with true microvascular resistance and, unlike coronary flow reserve (CFR), to be independent of the epicardial artery. We sought to compare the reproducibility and hemodynamic dependence of IMR with CFR in humans. METHODS AND RESULTS: Using a pressure-temperature sensor-tipped coronary wire, thermodilution-derived CFR and IMR were measured, along with fractional flow reserve (FFR), in 15 coronary arteries (15 patients) under the following hemodynamic conditions: (1) twice at baseline; (2) during right ventricular pacing at 110 bpm; (3) during intravenous infusion of nitroprusside; and (4) during intravenous dobutamine infusion. Mean CFR did not change during baseline measurements or during nitroprusside infusion but decreased during pacing (from 3.1+/-1.1 at baseline to 2.3+/-1.2 during pacing, P<0.05) and during dobutamine infusion (from 3.0+/-1.0 to 1.7+/-0.6 with dobutamine, P<0.0001). By comparison, mean values for IMR and FFR remained similar throughout all hemodynamic conditions. The mean coefficient of variation between 2 baseline measurements was significantly lower for IMR (6.9+/-6.5%) and FFR (1.6+/-1.6%) than for CFR (18.6+/-9.6%; P<0.01). Mean correlation between baseline measurements and each hemodynamic intervention was superior for IMR (r=0.90+/-0.05) and FFR (r=0.86+/-0.12) compared with CFR (r=0.70+/-0.05; P<0.05). CONCLUSIONS: Compared with CFR, IMR provides a more reproducible assessment of the microcirculation, which is independent of hemodynamic perturbations. Simultaneous measurement of FFR and IMR may provide a comprehensive and specific assessment of coronary physiology at both epicardial and microvascular levels, respectively.

Adult↗
PubMed2006

Acute and long-term outcomes of the novel side access (SLK-View) stent for bifurcation coronary lesions: a multicenter nonrandomized feasibility study.

OBJECTIVE: To evaluate technical feasibility and procedural safety of SLK-View stent for treating bifurcation lesions. BACKGROUND: Percutaneous treatment of coronary bifurcation lesions represents a technical challenge. Several stenting techniques and dedicated devices have proven unsuccessful, with high rates of side branch occlusion at index procedure and follow-up. METHODS: Eighty one patients with 84 de novo coronary artery lesions involving a major side branch underwent SLK-View (Advanced Stent Technologies, Inc., Pleasanton, CA) stent implantation with subsequent kissing balloon post dilatation. SLK-View stent is a new scaffolding device incorporating a side aperture that allows access to the side-branch of a bifurcation after deployment of the stent in main vessel. All patients underwent angiographic follow-up at 6 months. Procedural, in-hospital, and 6-month follow-up outcomes were examined. RESULTS: The lesions were located in left main (n = 11), left anterior descending (n = 50), left circumflex (n = 8), right coronary artery (n = 7), and 1 ramus intermedius. The most frequent lesions (44.1%) were true bifurcations. Successful stent delivery to bifurcation was accomplished in 82/84 of the cases (97.6%). Technical success was obtained in 99 and 94% of main vessel and side branches, respectively. Stenting in side-branch was performed in 21 lesions (25%). Side-branches were accessed effectively in 100% of bifurcations postprocedurally. Binary restenosis rate at 6-month follow-up was 28.3% and 37.7% for main vessel and side-branch, respectively. TLR rate at 6-month follow-up was 21% and CABG rate of 6%. CONCLUSION: In this consecutive multicenter series of patients with coronary bifurcation lesions, this novel side-branch access stent proved feasible, with a high procedural success rate, while maintaining side-branch access.

Angioplasty, Balloon↗
PubMed2006

Successful removal of a paradoxical coronary embolus using an aspiration catheter.

BACKGROUND: A 28-year-old man presented at hospital with persistent pain in his chest and left arm, a paced rhythm on electrocardiography and elevated levels of cardiac enzymes. He was known to have patent foramen ovale and a dual-chamber pacemaker, which had been implanted following electrophysiological ablation to treat supraventricular tachycardia 3 years previously. The patient did not have a history of cardiovascular risk factors, recent travel, immobilization or clinical features of infection, and he was not taking any medication. INVESTIGATIONS: Electrocardiography, cardiac enzyme studies, coronary angiography and transthoracic echocardiography. DIAGNOSIS: Acute myocardial infarction, paradoxical coronary embolus and patent foramen ovale. MANAGEMENT: Coronary aspiration embolectomy and systemic anticoagulation.

Adult↗
PubMed2006

Drug-eluting stent strut distribution: a comparison between Cypher and Taxus by optical coherence tomography.

OBJECTIVES: The purpose of this study is to compare the stent strut distribution between Cypher and Taxus stents by using optical coherence tomography (OCT) in a phantom model. BACKGROUND: Previous studies demonstrated that the distribution of stent struts might affect amount of neointima proliferation after drug-eluting stent (DES) implantation. METHODS: We developed experimental models made of silicon tubing angled at 0 degrees, 30 degrees, and 60 degrees. Testing was performed on two types of stents, Cypher and Taxus, which represent current FDA-approved DES. After deployment, OCT was performed and measurements were obtained as follows at two cross sections; maximum and minimum numbers of visualized stent strut sites: (1) number of visualized stent struts; (2) angle between stent struts (interstrut angle); (3) mean interstrut angle; (4) the delta mean angle was defined as the margin between each value of the interstrut angle and mean interstrut angle. RESULTS: In the Cypher stent, both the interstrut angle and the delta mean angle were significantly better than all other stents evaluated (all comparisons between stents; p < 0.05, respectively). CONCLUSIONS: The present study found that the stent strut distribution of two stents, Cypher and Taxus, which represent current FDA-approved drug-eluting systems, were significantly different and suggested that the Cypher stent maintained a more regular strut distribution despite expansion in various anatomical situations, and therefore would provide the most regular and predictable drug delivery.

Equipment Design↗
PubMed2005

The conversion in application of percutaneous coronary intervention following the introduction of drug eluting stents.

In order to determine the changes in the pattern of techniques applied during elective coronary intervention, data from 688 patients prior to Sirolimus. Drug-Eluting Stents (DES) approval was compared to 438 patients who underwent coronary intervention after DES approval. There was increased intervention to higher risk lesions, including smaller vessels and re-stenotic lesions after DES approval. Total number of stents per patient significantly decreased, despite longer stent length per patient or per lesion after DES approval. No significant difference was found in multivessel interventions.

Aged↗
PubMed2005

Radiolabeled cell distribution after intramyocardial, intracoronary, and interstitial retrograde coronary venous delivery: implications for current clinical trials.

BACKGROUND: Several clinical studies are evaluating the therapeutic potential of delivery of various progenitor cells for treatment of injured hearts. However, the actual fate of delivered cells has not been thoroughly assessed for any cell type. We evaluated the short-term fate of peripheral blood mononuclear cells (PBMNCs) after intramyocardial (IM), intracoronary (IC), and interstitial retrograde coronary venous (IRV) delivery in an ischemic swine model. METHODS AND RESULTS: Myocardial ischemia was created by 45 minutes of balloon occlusion of the left anterior descending coronary artery. Six days later, 10(7) 111indium-oxine-labeled human PBMNCs were delivered by IC (n=5), IM (n=6), or IRV (n=5) injection. The distribution of injected cells was assessed by gamma-emission counting of harvested organs. For each delivery method, a significant fraction of delivered cells exited the heart into the pulmonary circulation, with 26+/-3% (IM), 47+/-1% (IC), and 43+/-3% (IRV) of cells found localized in the lungs. Within the myocardium, significantly more cells were retained after IM injection (11+/-3%) compared with IC (2.6+/-0.3%) (P<0.05) delivery. IRV delivery efficiency (3.2+/-1%) trended lower than IM infusion for PBMNCs, but this difference did not reach significance. The IM technique displayed the greatest variability in delivery efficiency by comparison with the other techniques. CONCLUSIONS: The majority of delivered cells is not retained in the heart for each delivery modality. The clinical implications of these findings are potentially significant, because cells with proangiogenic or other therapeutic effects could conceivably have effects in other organs to which they are not primarily targeted but to which they are distributed. Also, we found that although IM injection was more efficient, it was less consistent in the delivery of PBMNCs compared with IC and IRV techniques.

Animals↗
PubMed2005

Multicenter intravascular ultrasound validation study among heart transplant recipients: outcomes after five years.

OBJECTIVES: We sought to assess the validity of first-year intravascular ultrasound (IVUS) data as a surrogate marker for long-term outcome after heart transplantation. BACKGROUND: Cardiac allograft vasculopathy (CAV) is a major impediment to long-term graft survival. Intravascular ultrasound is more sensitive than coronary angiography and detects intimal thickening (early CAV) in the coronary arteries of the donor heart. Single-center studies have suggested first-year IVUS results might be a surrogate marker for long-term outcome. METHODS: First-year IVUS results and subsequent five-year clinical follow-up data were reviewed in 125 heart transplant recipients from five institutions. The IVUS tapes (at baseline and one year) were re-analyzed at a core IVUS laboratory. The change in maximal intimal thickness (MIT) from baseline to one year was recorded for several matched sites in the same coronary artery. Patients were classified into two groups: those with >/=0.5 mm in the MIT in any matched site (group 1) and those with MIT <0.5 mm (group 2). RESULTS: Group 1 patients compared with group 2 patients had a higher incidence of death or graft loss (D/GL, 20.8% vs. 5.9%; p = 0.007), had more nonfatal major adverse cardiac events and/or D/GL (45.8% vs. 16.8%; p = 0.003), and had more findings of newly occurring angiographic luminal irregularities (65.2% vs. 32.6%, p = 0.004). CONCLUSIONS: This multicenter study suggests that progression of intimal thickening >/=0.5 mm in the first year after transplantation appears to be a reliable surrogate marker for subsequent mortality, nonfatal major adverse cardiac events, and development of angiographic CAV through five years after heart transplantation.

Adult↗
PubMed2005

Risk factors for the development of retroperitoneal hematoma after percutaneous coronary intervention in the era of glycoprotein IIb/IIIa inhibitors and vascular closure devices.

OBJECTIVES: We sought to determine the incidence, clinical features, and risk factors for retroperitoneal hematoma (RPH) after percutaneous coronary intervention (PCI). BACKGROUND: Little is known about the clinical features, outcomes, and determinants of this serious complication in the contemporary era of PCI. METHODS: A retrospective analysis yielded 26 cases of RPH out of 3,508 consecutive patients undergoing PCI between January 2000 and January 2004. Cases were compared with a randomly selected sample of 50 control subjects without RPH. RESULTS: The incidence of RPH was 0.74%. Features of RPH included abdominal pain (42%), groin pain (46%), back pain (23%), diaphoresis (58%), bradycardia (31%), and hypotension (92%). The mean systolic blood pressure nadir was 75 mm Hg. The hematocrit dropped by 11.5 +/- 5.1 points from baseline in RPH patients, as compared with 2.3 +/- 3.3 points in controls (p < 0.0001). The mean hospital stay was longer in RPH patients (2.9 +/- 3.8 days vs. 1.7 +/- 1.5 days, p = 0.06). The following variables were found to be independent predictors of RPH: female gender (odds ratio [OR] 5.4, p = 0.005), low body surface area (BSA <1.73 m(2); OR 7.1, p = 0.008), and higher femoral artery puncture (OR 5.3, p = 0.013). There was no association between RPH and arterial sheath size, use of glycoprotein IIb/IIIa inhibitors, or deployment of a vascular closure device. CONCLUSIONS: Female gender, low BSA, and higher femoral artery puncture are significant risk factors for RPH. Awareness of the determinants and clinical features of RPH may aid in prevention, early recognition, and prompt treatment.

Aged↗
PubMed2005

Impact of different definitions on the interpretation of coronary remodeling determined by intravascular ultrasound.

The objective of this study was to compare the categorizations and determinants related to remodeling by the three definitions commonly used. Several morphological and intravascular ultrasound (IVUS) studies have demonstrated the fundamental importance of arterial remodeling in atherosclerosis. However, lack of consensus on how to define remodeling has led to conflicting analyses of factors that influence this process. Analysis of pre-interventional IVUS images of 514 lesions in native coronary arteries was performed. Arterial remodeling was defined as outward by definition 1, when [cross-sectional area (CSA) of the external elastic membrane (EEM) at the lesion site (EEM(lesion))]/[EEM CSA either at the proximal (EEM(prox ref)) or distal (EEM(distal ref)) reference site with the least amount of plaque] was > 1.05, intermediate when this ratio was between 0.95 and 1.05, and inward when < 0.95. Remodeling was defined as outward by definition 2 when EEM(lesion) > both EEM(prox ref) and EEM(distal ref), inward when EEM(lesion) < both EEM(prox ref) and EEM(distal ref), and intermediate when EEM(lesion) was intermediate between EEM(prox ref) and EEM(distal ref). By definition 3, vessel remodeling was defined as outward when EEM(lesion) > (EEM(prox ref) + EEM(distal ref))/2 and intermediate/inward when EEM(lesion) < or = (EEM(prox ref) + EEM(distal ref))/2. The frequency of outward remodeling was significantly higher by definitions 1 and 3 than by definition 2, whereas a higher frequency of inward remodeling was observed in definition 1, resulting in significantly different remodeling distributions between the three definitions (P < 0.0001). By multivariate logistic analysis, the only clinical determinants related to outward remodeling was younger age, and only by definition 3. IVUS determinants varied significantly between the three definitions. The only consistent determinants among the three definitions were smaller lumen CSA at the reference site and larger plaque + media CSA at the lesion site. This study demonstrates the significant impact of different remodeling definitions on the incidence and determinants of remodeling patterns. The marked variability in categorization of remodeling underscores the importance of developing a standard methodology.

Aged↗
PubMed2005

Experience of percutaneous coronary intervention in the management of pediatric cardiac allograft vasculopathy.

In a retrospective study, we examined the procedural success rate and the short-, intermediate-, and long-term outcomes of coronary interventional procedures in children with cardiac allograft vasculopathy. Seven patients underwent 13 interventional procedures: balloon angioplasty alone (n = 3), angioplasty with stenting (n = 9), or angioplasty with brachytherapy (n = 1), with procedural success in all. Two major complications (cardiac arrest) and a single death occurred in the immediate postprocedural period. Five (83%) of the remaining 6 patients developed moderate to severe restenosis, diffuse disease, or progressive vasculopathy; 3 have been retransplanted, 1 died from progressive cardiac allograft vasculopathy, and 1 is awaiting retransplantation, 40 months after the procedure.

Adolescent↗
PubMed2005

Left main coronary artery disease: is CABG still the gold standard?

Severe stenosis of the left main coronary artery (LMCA) is a coronary artery-disease manifestation of critical prognostic importance. As a consequence of the survival advantage conferred by coronary artery bypass grafting (CABG) over medical therapy, lesions in the LMCA have been considered a standard indication for CABG for nearly 3 decades. Initial attempts to treat LMCA disease percutaneously by balloon angioplasty resulted in poor clinical outcomes, leading many to regard significant LMCA disease as a contraindication for percutaneous coronary intervention (PCI). However, the development and refinement of coronary stenting over the last 15 years, followed by the recent introduction of drug-eluting stents, has fueled renewed interest in percutaneous treatment of LMCA disease. Outcomes of recent studies using sirolimus- and/or paclitaxel-eluting stents for treatment of LMCA disease have yielded rates of in-hospital and 1-year mortality that compare favorably with those of surgery. This article will review the natural history of LMCA disease, the outcomes of CABG for LMCA disease, and the history and recent developments regarding PCI for LMCA disease.

Angioplasty, Balloon, Coronary↗
PubMed2004

Long-term effects of polymer-based, slow-release, sirolimus-eluting stents in a porcine coronary model.

BACKGROUND: Stent-based delivery of sirolimus (SRL) has shown reduction in neointimal hyperplasia and restenosis. The purpose of this study was to evaluate the chronic vascular response and the expression of cell cycle regulators after SRL-eluting stent implantation in a porcine coronary model. METHODS: Forty-nine pigs underwent placement of 109 oversized stents (control, n=54, SRL (140 microg/cm(2)), n=55) in the coronary arteries with histologic analysis and Western blot (PCNA, p27(kip1), CD45, MCP-1, IL-2, IL-6, TNF-beta) at 3, 30, 90 or 180 days. RESULTS: At 3 days, the mean thrombus area was similar for control (0.38+/-0.19 mm(2)) and SRL (0.29+/-0.09 mm(2)) stents. After 30 days, the mean neointimal area was significantly less for the SRL (1.40+/-0.35 mm(2)) versus the control stents (2.94+/-1.28 mm(2), p<0.001). At 90 and 180 days, the mean neointimal area was similar for the SRL (3.03+/-0.92 and 3.34+/-0.99 mm(2)) as compared with control stents (3.45+/-1.09 and 3.65+/-1.23 mm(2)). Western blot analysis demonstrated an increased expression of p27(kip1) in the vessel wall at 90 days for the SRL versus control stents (p=0.05) but with increased levels of PCNA in the SRL as compared with control stents (p=0.003). CONCLUSION: SRL-eluting stents favorably modulate neointimal formation for 30 days in the porcine coronary model. Long-term inhibition of neointimal hyperplasia is not sustained presumably due to delayed cellular proliferation despite increased levels of the cyclin-dependent kinase p27(kip1) in the vessel wall.

Animals↗
PubMed2004

Microvascular resistance is not influenced by epicardial coronary artery stenosis severity: experimental validation.

BACKGROUND: The effect of epicardial artery stenosis on myocardial microvascular resistance remains controversial. Recruitable collateral flow, which may affect resistance, was not incorporated into previous measurements. METHODS AND RESULTS: In an open-chest pig model, distal coronary pressure was measured with a pressure wire, and the apparent minimal microvascular resistance was calculated during peak hyperemia as pressure divided by flow, measured either with a flow probe around the coronary artery (R(micro app)) or with a novel thermodilution technique (apparent index of microcirculatory resistance [IMR(app)]). These apparent resistances were compared with the actual R(micro) and IMR after the coronary wedge pressure and collateral flow were incorporated into the calculation. Measurements were made at baseline (no stenosis) and after creation of moderate and severe epicardial artery stenoses. In 6 pigs, 189 measurements of R(micro) and IMR were made under the various epicardial artery conditions. Without consideration of collateral flow, R(micro app) (0.43+/-0.12 to 0.46+/-0.10 to 0.51+/-0.11 mm Hg/mL per minute) and IMR(app) (14+/-4 to 17+/-7 to 20+/-10 U) increased progressively and significantly with increasing epicardial artery stenosis (P<0.001 for both). With the incorporation of collateral flow, neither R(micro) nor IMR increased as a result of increasing epicardial artery stenosis. CONCLUSIONS: After collateral flow is taken into account, the minimum achievable microvascular resistance is not affected by increasing epicardial artery stenosis.

Animals↗