Paclitaxel stent coating inhibits neointimal hyperplasia at 4 weeks in a porcine model of coronary restenosis.

BACKGROUND: Despite limiting elastic recoil and late vascular remodeling after angioplasty, coronary stents remain vulnerable to restenosis, caused primarily by neointimal hyperplasia. Paclitaxel, a microtubule-stabilizing drug, has been shown to inhibit vascular smooth muscle cell migration and proliferation contributing to neointimal hyperplasia. We tested whether paclitaxel-coated coronary stents are effective at preventing neointimal proliferation in a porcine model of restenosis. METHODS AND RESULTS: Palmaz-Schatz stents were dip-coated with paclitaxel (0, 0.2, 15, or 187 microgram/stent) by immersion in ethanolic paclitaxel and evaporation of the solvent. Stents were deployed with mild oversizing in the left anterior descending coronary artery (LAD) of 41 minipigs. The treatment effect was assessed 4 weeks after stent implantation. The angiographic late loss index (mean luminal diameter) decreased with increasing paclitaxel dose (P<0.0028 by ANOVA), declining by 84.3% (from 0.352 to 0.055, P<0.05) at the highest level tested (187 microgram/stent versus control). Accompanying this change, the neointimal area decreased (by 39.5%, high-dose versus control; P<0.05) with increasing dose (P<0.040 by ANOVA), whereas the luminal area increased (by 90.4%, high-dose versus control; P<0.05) with escalating dose (P<0.0004 by ANOVA). Inflammatory cells were seen infrequently, and there were no cases of aneurysm or thrombosis. CONCLUSIONS: Paclitaxel-coated coronary stents produced a significant dose-dependent inhibition of neointimal hyperplasia and luminal encroachment in the pig LAD 28 days after implantation; later effects require further study. These results demonstrate the potential therapeutic benefit of paclitaxel-coated coronary stents in the prevention and treatment of human coronary restenosis.

Focal modification of electrical conduction in the heart by viral gene transfer.

Modern treatment of cardiac arrhythmias is limited to pharmacotherapy, radiofrequency ablation, or implantable devices. Antiarrhythmic medications suppress arrhythmias, but their systemic effects are often poorly tolerated and their proarrhythmic tendencies increase mortality. Radiofrequency ablation can cure only a limited number of arrhythmias. Implantable devices can be curative for bradyarrhythmias and lifesaving for tachyarrhythmias, but require a lifetime commitment to repeated procedures, are a significant expense, and may lead to severe complications. One possibility is the use of gene therapy as an antiarrhythmic strategy. As an initial attempt to explore this option, we focused on genetic modification of the atrioventricular node. First, we developed an intracoronary perfusion model for gene delivery, building on our previous work in isolated cardiac myocytes and hearts perfused ex vivo. Using this method, we infected porcine hearts with Adbetagal (recombinant adenovirus expressing Escherichia coli beta-galactosidase) or with AdGi (adenovirus encoding the Galphai2 subunit). We hypothesized that excess Galphai2 would mimic the effects of beta-adreneric antagonists, in effect creating a localized beta-blockade. Galphai2 overexpression suppressed baseline atrioventricular conduction and slowed the heart rate during atrial fibrillation without producing complete heart block. In contrast, expression of the reporter gene beta-galactosidase had no electrophysiological effects. Our results demonstrate the feasibility of using myocardial gene transfer strategies to treat common arrhythmias.

Real-time projection MR angiography: feasibility study.

Intraarterial injections of small doses of gadopentetate dimeglumine were combined with a fast spoiled-gradient-echo magnetic resonance (MR) sequence to obtain real-time projection angiographic images of the rabbit aorta and canine coronary arteries. Arterial filling and washout, as well as venous and perfusion phases, were clearly displayed, demonstrating that arterial fluoroscopy in which an MR technique is used is feasible.

A minimally invasive method for creating coronary stenosis in a swine model for MRI and SPECT imaging.

RATIONALE AND OBJECTIVES: To develop a less-invasive method for creating coronary stenosis in an animal model for the study of myocardial perfusion defects by using magnetic resonance imaging (MRI) and single-photon-emission computed tomography (SPECT). METHODS: Eleven farm pigs were instrumented with an MR-compatible coronary flow-reduction fitting in the left anterior descending coronary artery (LAD). These fittings were turned from a nylon rod, tapered from a maximum outer diameter of 3 mm, and drilled to a specified inner diameter (depending on the degree of coronary stenosis desired). The flow-reducing fittings were delivered over a coronary guidewire and advanced to a wedge position in the proximal LAD with an angioplasty catheter via a carotid artery approach. Perfusion determined by contrast-enhanced MRI at peak dipyridamole stress was compared with that obtained by 99mTc sestamibi SPECT. Radiolabeled microspheres were injected at rest, after stenosis implantation, and at peak pharmacological stress to establish the severity of the coronary lesion. RESULTS: Coronary stenosis was successfully created in seven animals. Mild coronary stenoses (<60%) were created in four animals. Significant coronary stenoses (80%-90%) were created in three animals. Thrombosis of the coronary flow-reducing fittings was observed in four animals, leading to sudden death in three animals and myocardial infarction in one animal. CONCLUSIONS: This method of angioplasty-guided, LAD coronary stenosis creation in a swine model presents a less-invasive alternative to open-chest techniques such as hydraulic occluders and ameroid constrictors.

Transesophageal magnetic resonance imaging.

The purpose of this study was to develop a non-invasive method of imaging the thoracic aorta that would provide both morphological detail within the aortic wall and information about regional aortic wall motion. An esophageal probe is described that allows transesophageal MR imaging (TEMRI) of the thoracic aorta and has several potential advantages over the competing non-vasculoinvasive techniques of transesophageal echocardiography (TEE) or standard MRI. The probe consists of a loopless antenna housed inside a modified Levin gastric tube, with external matching and tuning circuitry. Using this probe, the thoracic aorta has been imaged in longitudinal and cross-sectional views. Details of the aortic wall were readily seen. Tissue tagging for measurement of focal stress/strain relationships was demonstrated to be feasible. TEMRI avoids the risks inherent in intravascular MRI yet provides comparable image quality. Potential applications of the device are discussed.

Methylation of the estrogen receptor gene is associated with aging and atherosclerosis in the cardiovascular system.

OBJECTIVE: Methylation of the promoter region of the estrogen receptor gene alpha (ER alpha) occurs as a function of age in human colon, and results in inactivation of gene transcription. In this study, we sought to determine whether such age-related methylation occurs in the cardiovascular system, and whether it is associated with atherosclerotic disease. METHODS: We used Southern blot analysis to determine the methylation state of the ER alpha gene in human right atrium, aorta, internal mammary artery, saphenous vein, coronary atherectomy samples, as well as cultured aortic endothelial cells and smooth muscle cells. RESULTS: An age related increase in ER alpha gene methylation occurs in the right atrium (range 6 to 19%, R = 0.36, P < 0.05). Significant levels of ER alpha methylation were detected in both veins and arteries. In addition, ER alpha gene methylation appears to be increased in coronary atherosclerotic plaques when compared to normal proximal aorta (10 +/- 2% versus 4 +/- 1%, P < 0.01). In endothelial cells explanted from human aorta and grown in vitro, ER alpha gene methylation remains low. In contrast, cultured aortic smooth muscle cells contain a high level of ER alpha gene methylation (19-99%). CONCLUSIONS: Methylation associated inactivation of the ER alpha gene in vascular tissue may play a role in atherogenesis and aging of the vascular system. This potentially reversible defect may provide a new target for intervention in heart disease.

Acute effects of conjugated estrogens on coronary blood flow response to acetylcholine in men.

Estrogen therapy is associated with a 50% reduction in the clinical manifestations of coronary artery disease in postmenopausal women. Attenuation of coronary vasomotor dysfunction may contribute to estrogen's cardioprotective effects. We hypothesized that conjugated estrogens, which contain several vasoactive estrogenic compounds, may favorably influence the vasomotor response to acetylcholine in men. Twenty men, 56 +/- 5 years of age, referred for clinically indicated coronary angiography, participated in this study. Acetylcholine-induced changes in coronary flow were measured by quantitative coronary angiography and intracoronary Doppler ultrasonography before and 15 minutes after intravenous administration of conjugated estrogens (0.625 mg) in 12 men and placebo in 8 men. Initial acetylcholine infusion resulted in no significant increase in coronary blood flow. However, 15 minutes after estrogen administration repeat acetylcholine infusion caused a mean 32% increase in coronary blood flow from 41 +/- 5 to 54 +/- 8 ml/min (p = 0.02). Acetylcholine-induced change in flow after estrogen was significantly different from that before estrogen (p = 0.03). Placebo administration did not affect acetylcholine-induced changes in coronary flow. Thus, intravenous conjugated estrogens favorably modulate acetylcholine-induced changes in coronary hemodynamics in men. This suggests that novel nonfeminizing estrogenic compounds may have anti-ischemic effects in men.

Clinical evaluation of a microsample coagulation analyzer, and comparison with existing techniques.

A new microsample coagulation analyzer (Hemochron Jr.) has recently been developed which performs a modified activated clotting time (ACT+) and an aPTT by using different reagents. The Hemochron Jr. measures the clotting time of a 5-microliter whole-blood sample by an optical detector and extrapolates the results to the activated clotting time (ACT+) or the plasma-activated partial thromboplastin time by using a validated regression analysis. We compared 124 simultaneous ACT+ and Hemochron ACTs, and 53 paired Hemochron Jr. aPTTs and hospital laboratory aPTTs, in 44 patients during coronary intervention. The Hemochron Jr. aPTT closely correlated with the lab aPTT (r = .79, P < .0001), and the test results were available much more rapidly than the lab aPTT (3.5 +/- 1.1 vs. 56.3 +/- 25.5 min, P = 0.0029). A comparison of duplicate ACT+ measurements did not identify a significant difference in the means (292 +/- 115 sec vs. 293 +/- 112 sec, P = 0.72). The ACT+ closely correlated with the Hemochron ACTs (r = .85, P < .0001). At baseline, the mean ACT+ (175 +/- 43 sec) exceeded the Hemochron ACT (144 +/- 36 sec) by 22% (P < .001). After heparin administration, the mean ACT+ (378 +/- 74 sec) exceeded the Hemochron ACT (332 +/- 65) by 12% (P < .001). The Hemochron Jr. provides a fast and reproducible methodology for measuring ACT and aPTT, using a small blood volume. Further studies are required to determine the optimal anticoagulation range when using the Hemochron Jr. during or after interventional procedures.