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Biomedical subjects

K M Kent

Publications and source records attributed to K M Kent.

306 records · Page 17Linked to original sources
PubMed1972

Potentiation of the contractile effects of norepinephrine by hypoxia.

Hypoxia has been found to depress the concentration response curve of norepinephrine (NE) in isoalted cat papillary muscles. To investigate the effects of hypoxia in intact hearts, a heart-lung preparation was developed and maximum left ventricular dp/dt (max dp/dt) was measured at constant heart rate, preload, and after load. Left main coronary arterial flow (Q(e)) was measured with an electromagnetic flow probe. As arterial P(O2) decreased from 90 mm Hg (96% saturation) to 20-25 mm Hg (40% saturation) at constant P(CO2) and pH, no change in max dp/dt occurred and Q(e) increased 298%. In contrast to cat papillary muscles, the contractile responses to NE were augmented in hypoxia. The NE dose-response curves shifted to the left. No deterioration of contractility occurred after exposure to NE. In contrast, the chronotropic response was unaltered in hypoxia. Dose-response curves to isoproterenol also were shifted to the left in hypoxia, but responses to paired pacing were unchanged. The responses to NE under oxygenated conditions were unaltered by mechanically increased coronary flow or by increased coronary flow with nitroglycerin. Although the mechanisms responsible for these effects are unknown, the results suggest that hypoxia may open previously nonfunctioning vascular channels and thereby allow more extensive exposure of beta adrenergic receptors to circulating catecholamines.

Animals↗
PubMedDate not supplied

Three-dimensional intravascular ultrasonography: reconstruction of endovascular stents in vitro and in vivo.

BACKGROUND: Intravascular ultrasonography displays an artery in loosely related cross-sectional images with limited axial information. However, intravascular ultrasound images are suited to three-dimensional reconstruction. METHODS: A comprehensive intravascular ultrasound imaging system was used to reconstruct planar images in three-dimensions. This system consisted of a 25MHz transducer-tipped rigid probe (for in vitro studies) or a 25MHz transducer-tipped catheter within a 3.9F monorail imaging sheath (for in vivo studies), a motorized catheter pullback device that withdraws the transducer at 0.5mm/s, and an image processing computer that stacks 15 cross-sectional images/mm of stent axial length and then performs thresholding-based three-dimensional image rendering. We imaged 10 stents (4 Palmaz-Schatz, 3 Wiktor, 2 Strecker, and 1 Medinvent) in vitro after implantation in freshly harvested saphenous veins and 37 Palmaz-Schatz stents in vivo, 10 in native coronary arteries and 27 in vein grafts, 21 acutely and 18 on follow-up. RESULTS: Three-dimensional reconstruction of images obtained with this system reproduced the geometry of each stent design. In vitro, images of the Palmaz-Schatz stents showed the expanded diamonds, the central articulation, and flaring of both ends of both halves of the stents. Images of the Wiktor stents showed the sinusoidal wave-shaped coils in their helical configuration. Images of the Strecker stents showed the interlocking-loop design with gaps between the terminal loops at either end of the stent. Images of the Medivent stent reproduced the woven texture formed by braiding the stent wires. Three-dimensional reconstruction of images obtained in vivo also reproduced the spatial geometry of the Palmaz-Schatz stent. However, reconstruction of in vivo images was limited by cardiac-cycle-linked vessel motion and torsion and the presence of echo-dense tissue that could not be separated completely from the stent itself. CONCLUSIONS: Properly acquired intravascular ultrasound images can be used to reconstruct the spatial geometry of endovascular stents. Because stent spatial geometry is known and unambiguous, reconstruction of endovascular stents should be one of the tests of imaging systems designed to perform three-dimensional reconstruction of ultrasound images.

Adult↗
PubMedDate not supplied

Intracoronary radiation for patients with refractory in-stent restenosis: an analysis from the WRIST-Crossover Trial. Washington Radiation for In-stent Restenosis Trial.

BACKGROUND: In-stent restenosis (ISR) is a limitation of intracoronary stent implantation. In animal models and clinical trials, ionizing radiation has been shown to decrease in-stent neointimal formation. METHODS AND MATERIALS: In the Washington Radiation for In-stent Restenosis Trial (WRIST), patients with in-stent restenosis were first treated with conventional catheter-based techniques and then randomized to gamma irradiation (l92Ir, 15 Gy at 2 mm from the source) or placebo. Patients randomized to placebo that developed recurrent ISR and presented with anginal symptoms were crossed-over to active therapy. We compared the clinical and angiographic outcomes of 39 patients in the crossover group with 65 patients treated primarily with radiation. The primary clinical endpoints were mortality, morbidity, and repeat target lesion revascularization (TLR) at 6 months. RESULTS: Procedural success was 100%. In-hospital and 30-day complications were minimal. At 6 months, the rate for any multiple adverse cardiac events (MACE: death, MI, or TLR) was 25.6% in the crossover group vs. 29.2% in the primary treatment group (p = 0.86). Three patients in the crossover group and four in the primary treatment group died (p = NS). There were no Q-wave myocardial infarction. Ten (9.6%) of the patients presented with late thrombosis and total occlusion: 6.2% (4/65) in the primary treatment group vs. 15.4% (6/39) in the crossover group (p = 0.13). CONCLUSIONS: Patients who fail conventional catheter-based intervention without radiation can be treated with 192Ir with results similar to those who initially receive brachytherapy. This is of specific importance with respect to patients initially assigned to the placebo arm of randomized clinical trials.

Brachytherapy↗
PubMedDate not supplied

Excimer laser coronary angioplasty and intracoronary radiation for in-stent restenosis: six-month angiographic and clinical outcomes.

BACKGROUND: The purpose of this study was to evaluate 6-month clinical and angiographic outcomes in patients treated with excimer laser coronary angioplasty (ELCA) and intracoronary radiation (ICR) for in-stent restenosis (ISR). METHODS: A consecutive series of 175 patients with ISR treated with ELCA+ICR (gamma and beta emitters) were compared to 33 patients with ISR treated with ELCA alone. Baseline characteristics were similar between groups. ELCA+ICR and ELCA-alone patients had similar lesion lengths (25.0+/-12.0 vs. 24.0+/-16.8 mm, P=NS) in predominantly saphenous vein grafts (SVG, 38% vs. 42%, P=NS). RESULTS: Procedural success was high (ELCA+ICR, 97.0% vs. ELCA alone, 98.5%, P=NS), with no perforations or acute vessel closures. ELCA+ICR therapy reduced target vessel revascularization (TVR; 27% vs. 64%, P<.0001) and major adverse cardiac events [MACE: death, myocardial infarction (MI), or TVR; 30% vs. 64%, P<.0001] compared to ELCA alone. Late loss was 0.66+/-0.90 mm in ELCA+ICR patients and 0.85+/-0.60 mm in ELCA-alone patients (P=NS). Angiographic binary restenosis (>50%) was significantly reduced with adjunctive ICR (28% vs. 54%, P=.014). CONCLUSION: Radiation therapy with ELCA significantly reduces angiographic binary restenosis at 6 months in patients with diffuse ISR, driven predominantly by reduced percutaneous TVR.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Three-year follow-up after intracoronary gamma radiation therapy for in-stent restenosis. Original WRIST. Washington Radiation for In-Stent Restenosis Trial.

BACKGROUND: The Washington Radiation for In-Stent Restenosis Trial (WRIST) is a double-blinded randomized study evaluating the effects of intracoronary radiation therapy (IRT) in patients with in-stent restenosis (ISR). METHODS: One hundred and thirty patients with ISR (100 native coronary and 30 vein grafts) underwent PTCA, laser ablation, rotational atherectomy, and/or additional stenting (36% of lesions). Patients were randomized to either Iridium-192 IRT or placebo, with a prescribed dose of 15 Gy to a 2-mm radial distance from the center of the source. RESULTS: Angiographic restenosis (27% vs. 56%, P=.002) and target vessel revascularization (TVR; 26% vs. 66%, P<.001) were dramatically reduced at 6 months in IRT patients. Between 6 and 36 months, IRT compared to placebo patients had more target lesion revascularization (TLR; IRT=17% vs. placebo=2%, P=.002) and TVR (IRT=17% vs. placebo=3%, P=.009). At 3 years, the major adverse cardiac event (MACE) rate was significantly reduced with IRT (39% vs. 65%, P=.003). CONCLUSIONS: In WRIST, patients with ISR treated with IRT using 192Ir had a marked reduction in the need for repeat target lesion and vessel revascularization at 6 months, with the clinical benefit maintained at 3 years.

Brachytherapy↗