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Biomedical subjects

Ian T Meredith

Publications and source records attributed to Ian T Meredith.

At least 19 recordsLinked to original sources
PubMed2008

Profound hypoxaemia corrected by PFO closure device in carcinoid heart disease.

A 66-year-old man with known metastatic carcinoid tumor presented with increasing dyspnoea, right heart failure and marked hypoxaemia which did not correct with oxygen. Echocardiography demonstrated severe tricuspid regurgitation, moderate pulmonary regurgitation and marked right heart dilatation. The inter-atrial septum was aneurysmal, with a large patent foramen ovale (PFO) with continuous right to left shunting. Cardiac catheterization demonstrated oxygen saturations of 96% in the pulmonary veins and 74% in the left atrium with a significant right to left shunt. During percutaneous closure of the PFO, anaesthetic induction resulted in marked systemic hypotension and worsening hypoxia related to systemic vasodilatation and increased shunting. PFO flow was temporarily obstructed with a sizing balloon resulting in a rapid increase in arterial oxygen saturation from 60% to >90%, but marked systemic hypotension due to acute left ventricular preload reduction, requiring volume replacement and adrenaline. Following deployment of a PFO occluder device, prominent pulsatile splaying of the right and left discs was noted due to the severe tricuspid regurgitation, resulting in some residual inter-atrial shunting. Arterial oxygen saturation was 83%, increasing to 92% at day 4 post-procedure as tissue organization occurred within the device, and the patient reported improvement in dyspnoea.

Aged↗
PubMed2006

Rotational atherectomy and simultaneous kissing stenting of a bifurcation stenosis of left anterior descending and anomalous right coronary arteries.

Intervention to anomalous coronaries can present specific challenges: non-standard guide catheters may be required to provide adequate access and support, the course of the arteries can be tortuous with sharp angulations, and they may subtend a critical area of myocardium. We present the first report of percutaneous coronary intervention to the bifurcation of an anomalous right coronary artery arising from the left anterior descending artery. This lesion contained a high burden of calcification, which required rotational atherectomy of the left anterior descending artery before kissing stenting of the bifurcation.

Aged↗
PubMed2006

Acute and chronic effects of flavanol-rich cocoa on vascular function in subjects with coronary artery disease: a randomized double-blind placebo-controlled study.

Evidence suggests that flavonoid-containing diets reduce cardiovascular risk, but the mechanisms responsible are unclear. In the present study, we sought to determine the effect of flavanol-rich cocoa on vascular function in individuals with CAD (coronary artery disease). Forty subjects (61+/-8 years; 30 male) with CAD were recruited to a 6-week randomized double-blind placebo-controlled study. Subjects consumed either a flavanol-rich chocolate bar and cocoa beverage daily (total flavanols, 444 mg/day) or matching isocaloric placebos daily (total flavanols, 19.6 mg/day) for 6 weeks. Brachial artery FMD (flow-mediated dilation) and SAC (systemic arterial compliance) were assessed at baseline, 90 min following the first beverage and after 3 and 6 weeks of daily consumption. Soluble cellular adhesion molecules and FBF (forearm blood flow) responses to ACh (acetylcholine chloride; 3-30 microg/min) and SNP (sodium nitroprusside; 0.3-3 microg/min) infusions, forearm ischaemia and isotonic forearm exercise were assessed at baseline and after 6 weeks. FMD, SAC and FBF responses did not differ between groups at baseline. No acute or chronic changes in FMD or SAC were seen in either group. No difference in soluble cellular adhesion molecules, FBF responses to ischaemia, exercise, SNP or ACh was seen in the group receiving flavanol-rich cocoa between baseline and 6 weeks. These data suggest that over a 6-week period, flavanol-rich cocoa does not modify vascular function in patients with established CAD.

Aged↗
PubMed2006

Arterial remodeling correlates positively with serological evidence of inflammation in patients with chronic stable angina pectoris.

Positive coronary artery remodeling is associated with unstable coronary syndromes. Serum inflammatory markers, including high-sensitivity CRP (hsCRP), can predict future risk of acute coronary events in patients with stable coronary artery disease. We sought to elucidate the relationship of specific serum inflammatory markers with intravascular ultrasound (IVUS) estimation of coronary artery remodeling in patients with stable coronary artery disease. Thirty-one sequential patients at our institution undergoing IVUS-assisted percutaneous coronary intervention (PCI) with stable coronary artery disease were enrolled. Automated IVUS pullback and offline analysis were performed in all patients. Images were analyzed for vessel wall area (VWA) and lumen area (LA), at the culprit lesion and at a proximal reference site, and the remodeling index (RI) was calculated. Positive and negative remodeling were defined as a RI of > 1.05 and < 0.95, respectively. ELISA essays were performed for soluble VCAM-1, ICAM-1 and E-selectin. The distribution of data followed a lognormal distribution. By defining arterial remodeling as simply positive or negative, significant differences were identified for log E-selectin only (1.80 +/- 0.04 versus 1.62 +/- 0.05, respectively; p = 0.02). The RI correlation coefficient was 0.38 (p = 0.04) for log sVCAM-1 and 0.42 (p = 0.02) for log sICAM-1. The log E-selection and RI correlation coefficient, although weaker at 0.32, showed a trend toward significance (p = 0.08). There was no significant correlation between log hsCRP and RI (p = 0.42). Using step-wise multivariate analysis, log sVCAM-1 only remained an independent predictor of the RI (p = 0.03). Positive coronary artery remodeling correlates with serological markers of inflammation in patients with stable coronary artery disease.

Aged↗
PubMed2005

Aortic stiffness affects the coronary blood flow response to percutaneous coronary intervention.

We examined the hypothesis that a stiff aorta is associated with reduced coronary blood flow (CBF) and CBF response to percutaneous coronary intervention (PCI). Aortic mechanical properties are thought to affect CBF, with increased stiffness associated with decreased coronary perfusion. Animal studies are conflicting, and human evidence is lacking. Even less is known about the effects of aortic stiffness on the CBF response to successful PCI. In 18 subjects undergoing elective PCI, a Doppler velocity guidewire was positioned proximal to a severe coronary stenosis to measure resting and adenosine-induced hyperemic CBF before and after PCI. Stenosis severity was assessed with Doppler velocity and pressure guidewires. Aortic mechanical indexes measured included central pulse-wave velocity (cPWV) and central pulse pressure (cPP). PCI was successful in all subjects (diameter stenosis: 88 +/- 9% to 2 +/- 7%; coronary flow velocity reserve: 1.8 +/- 0.6 to 3.0 +/- 0.8; fractional flow reserve: 0.57 +/- 0.19 to 0.92 +/- 0.06; all P < 0.001). With the adjustment for age and gender, resting and hyperemic CBF were inversely related to cPWV irrespective of the presence of stenosis (resting: before PCI, r2 = 0.452, P < 0.01; after PCI, r2 = 0.261, P = 0.043; hyperemic: before PCI r2 = 0.503, P = 0.005; after PCI r2 = 0.500, P = 0.002), whereas they were related to cPP in absence of stenosis (resting: r2 = 0.368, P = 0.022; hyperemic: r2 = 0.370, P = 0.016). Hyperemic CBF response (P = 0.005) and hyperemic CBF improvement from PCI (P = 0.025) were less marked in a stiff aorta than a compliant aorta. A stiff aorta is associated with a reduction in CBF, a lower hyperemic CBF response, and may reduce the improvement in hyperemic CBF after successful PCI.

Adenosine↗
PubMed2005

Waveform dispersion, not reflection, may be the major determinant of aortic pressure wave morphology.

The objective of this study was to investigate the determinants of aortic pressure waveform morphology in the thoracoabdominal aorta with specific reference to features of potential prognostic value for cardiovascular disease. In particular, we aimed to determine the location of major pressure wave reflection sites within the aorta. Aortic pressure waveforms were acquired with 2-Fr Millar Mikro-tip catheter transducers in 40 subjects (26 men, 14 women), and repeated in 10 subjects, at five predetermined points within the aorta: aortic root, transverse arch, and at the levels of the diaphragm, renal arteries, and aortic bifurcation. Waveforms were analyzed for augmentation index (AI), time to inflection point (Ti), and pressure parameters. AI decreased progressively between the aortic root and bifurcation (P < 0.001), and Ti increased (P < 0.01). There was the expected progressive peripheral amplification of systolic and pulse pressures and fall in time to peak pressure (all P < 0.001). There was no difference on repeat pullback or between sexes. These data are at variance with the concept that central AI results solely from pressure wave reflection, when Ti would be expected to decrease and AI increase with distal progression. Pressure wave propagation phenomena may contribute, and the potential role of frequency dispersion merits investigation.

Aorta↗
PubMed2005

Systemic inflammatory markers in acute coronary syndrome: association with cardiovascular risk factors and effect of early lipid lowering.

BACKGROUND: Evidence for statin therapy in prevention of coronary artery disease is overwhelming. In spite of theoretical benefits, any additional advantage of its early introduction in the management of acute coronary syndrome is, however, uncertain. We therefore investigated differences between plasma levels of the systemic inflammatory markers intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, C-reactive protein and interleukin-6 in patients presenting with unstable angina or acute myocardial infarction, and assessed whether the 30-day levels of these markers are influenced by early instigation of the HMG-CoA reductase inhibitor pravastatin. MATERIALS AND METHODS: 170 (134 male) patients presenting with acute coronary syndrome, but without previous statin therapy, participated. Blood was taken within 24 h of onset of ischaemic pain and again at 30 days. In all, 87 (71 male) participants were treated with pravastatin (20-40 mg daily) and 83 (63 male) with a matched placebo. RESULTS: At presentation, interleukin-6 was higher in males than in females (P=0.008) and lower in those with a pre-existing history of myocardial infarction (P=0.038). C-reactive protein and interleukin-6 were greater in myocardial infarction, but this difference was lost at 30 days. Thirty-day changes in all parameters were inversely related to level at presentation but not to treatment with pravastatin. Hypertension (P=0.011) and smoking (P=0.042) were associated with elevation of C-reactive protein with no difference between unstable angina or acute myocardial infarction. The effect of these individual factors was cumulative. CONCLUSIONS: Interleukin-6 was greater in acute myocardial infarction than in unstable angina; E-selectin was positively associated with a previous myocardial infarction and inversely related to age. We found no effect of early introduction of pravastatin on systemic inflammatory markers 30 days after acute coronary syndrome.

Aged↗
PubMed2004

Coronary flow velocity reserve does not correlate with TIMI frame count in patients undergoing non-emergency percutaneous coronary intervention.

OBJECTIVES: The purpose of this research was to compare the Thrombolysis In Myocardial Infarction (TIMI) frame count (CTFC) with coronary flow velocity reserve (CFVR) in patients undergoing percutaneous coronary intervention (PCI). BACKGROUND: The relationship between CTFC and CFVR has not been adequately assessed in patients with coronary artery disease. METHODS: We studied 62 patients who underwent successful non-emergent PCI. All patients had Doppler evaluation of CFVR, CTFC, and quantitative coronary angiography. In an additional 17 patients, a frame count reserve was calculated as baseline CTFC/CTFC at peak hyperemia, induced by intracoronary adenosine after PCI. RESULTS: The CTFC decreased from 27 +/- 13 to 18 +/- 8, and CFVR increased from 1.5 +/- 0.4 to 2.6 +/- 0.7 (both p < 0.0001). The pre-PCI CTFC and the CFVR were closely related to minimal lumen diameter (p < 0.0001). After PCI, there was no correlation between CFVR and CTFC. In addition, no relationship was observed between CFVR and the frame count reserve. CONCLUSIONS: There was no significant correlation between CFVR and CTFC in patients undergoing coronary intervention. The relative utility of these measures in predicting outcomes in this setting requires further evaluation, but CTFC (or frame count reserve) does not appear to be an adequate surrogate measure of Doppler-derived CFVR.

Adenosine↗
PubMed2004

Effect of ATP-sensitive potassium channel inhibition on coronary metabolic vasodilation in humans.

OBJECTIVE: Experimental evidence indicates that ATP-sensitive potassium (K(ATP)) channels regulate coronary blood flow (CBF). However, their contribution to human coronary metabolic vasodilation is unknown. METHODS AND RESULTS: Seventeen patients (12 male, age 58+/-10 years) were studied. Coronary hemodynamics were assessed before and after K(ATP) channel inhibition with subselective intracoronary glibenclamide infused at 40 microg/min in an angiographically smooth coronary artery after successful percutaneous coronary intervention to another vessel. Metabolic vasodilation was induced by 2 minutes of rapid right ventricular pacing. Coronary blood velocity was measured with a Doppler guidewire and CBF calculated. The time course of hyperemia was recorded for 2 minutes after pacing, and hyperemic volume was estimated from the area under the flow-versus-time curve (AUC). Compared with vehicle infusion (0.9% saline), glibenclamide reduced resting CBF by 9% (P=0.04) and increased resting coronary vascular resistance (CVR) by 15% (P=0.03). Glibenclamide reduced pacing-induced peak CBF (50.8+/-6.8 versus 42.0+/-5.4 mL/min, P=0.001), peak CBF corrected for baseline flow (25.1+/-4.6 versus 17.6+/-3.1 mL/min, P=0.01), and increased minimum CVR (2.6+/-0.3 versus 3.1+/-0.3 mm Hg/mL per minute, P=0.002). Compared with vehicle, glibenclamide reduced total AUC at 2 minutes (3535+/-397 versus 3027+/-326 mL, P=0.001). CONCLUSIONS: Vascular K(ATP) channels appear to be involved in functional coronary hyperemia after metabolic stimulation.

Adenosine Triphosphate↗
PubMed2004

Transcatheter coil occlusion of coronary artery to right ventricular fistulae in pulmonary atresia with intact ventricular septum.

We describe a young adult with an underlying diagnosis of pulmonary atresia with intact ventricular septum and Fontan physiology who presented with extreme dyspnoea on exertion. Coronary artery to right ventricular fistulae and reversible myocardial ischaemia secondary to a right ventricular steal phenomenon were present. The right coronary artery to right ventricular fistula was completely occluded with coils, by a transcoronary approach, with amelioration of symptoms. However, one coil embolised and lodged uneventfully in the left atrium during the procedure. This case demonstrates that a transcatheter approach may be successfully employed not only in patients with isolated coronary artery fistulae, but also in patients with coexistent complex congenital heart disease.

Journal Article↗
PubMed2004

Effect of non-invasive calibration of radial waveforms on error in transfer-function-derived central aortic waveform characteristics.

Transfer function techniques are increasingly used for non-invasive estimation of central aortic waveform characteristics. Non-invasive radial waveforms must be calibrated for this purpose. Most validation studies have used invasive pressures for calibration, with little data on the impact of non-invasive calibration on transfer-function-derived aortic waveform characteristics. In the present study, simultaneous invasive central aortic (Millar Mikro-tip catheter transducer) and non-invasive radial (Millar Mikro-tip tonometer) pressure waveforms and non-invasive brachial pressures (Dinamap) were measured in 42 subjects. In this cohort, radial waveforms were calibrated to both invasive and non-invasive mean and diastolic pressures. From each of these, central waveforms were reconstructed using a generalized transfer function obtained by us from a previous cohort [Hope, Tay, Meredith and Cameron (2002) Am. J. Physiol. Heart Circ. Physiol. 283, H1150-H1156]. Waveforms were analysed for parameters of potential clinical interest. For calibrated radial and reconstructed central waveforms, different methods of calibration were associated with differences in pressure (P<0.001), but not time parameters or augmentation index. Whereas invasive calibration resulted in little error in transfer function estimation of central systolic pressure (difference -1+/-8 mmHg; P=not significant), non-invasive calibration resulted in significant underestimation (7+/-12 mmHg; P<0.001). Errors in estimated aortic parameters differed with non-invasively calibrated untransformed radial and transfer-function-derived aortic waveforms (all P<0.01), with smaller absolute errors with untransformed radial waveforms for most pressure parameters [systolic pressure, 5+/-16 and 7+/-12 mmHg; pulse pressure, 0+/-16 and 4+/-12 mmHg (radial and derived aortic respectively)]. When only non-invasive pressures are accessible, analysis of untransformed radial waveforms apparently produces smaller errors in the estimation of central aortic systolic pressure, and other waveform parameters, than using a generalized transfer function.

Aorta↗
PubMed2004

Use of arterial transfer functions for the derivation of central aortic waveform characteristics in subjects with type 2 diabetes and cardiovascular disease.

OBJECTIVE: Optimal blood pressure control in subjects with diabetes reduces cardiovascular complications. There is theoretical benefit in the assessment of central aortic waveforms including the augmentation index, which is taken as a putative index of stiffness. Transfer functions may be used to reconstruct aortic from radial pressure waveforms; however, a single generalized transfer function may not be appropriate for all patients. We aimed to evaluate the technique in subjects with diabetes. RESEARCH DESIGN AND METHODS: Simultaneous invasive central aortic and noninvasive radial waveforms were acquired in 19 subjects with type 2 diabetes, and a diabetes-specific transfer function was derived. Similar data were acquired from 38 age- and sex-matched subjects without diabetes. Central waveforms were reconstructed using a generalized transfer function in all patients and the diabetes-specific transfer function in individuals with diabetes. RESULTS: There was no difference between groups in measured central pressures. The error in generalized transfer function-derived systolic pressure was greater in individuals with diabetes (6 +/- 7 mmHg) (mean +/- SD) than without diabetes (2 +/- 8 mmHg) (P<0.05). Errors in other parameters were no different. The diabetes-specific transfer function reduced the error in derived systolic pressure to 0 +/- 7 mmHg in individuals with diabetes--no different than that with the generalized transfer function in individuals without diabetes. The central augmentation index reconstructed by either transfer function was unrelated to that directly measured. CONCLUSIONS: A generalized transfer function is inappropriate for the derivation of central waveforms in subjects with type 2 diabetes. Errors in subjects with diabetes might be reduced with a diabetes-specific transfer function.

Aged↗
PubMed2003

Relative contribution of vasodilator prostanoids, NO, and KATP channels to human forearm metabolic vasodilation.

Isolated ATP-sensitive K(+) (K(ATP)) channel inhibition with glibenclamide does not alter exercise-induced forearm metabolic vasodilation. Whether forearm metabolic vasodilation would be influenced by K(ATP) channel inhibition in the setting of impaired nitric oxide (NO)- and prostanoid-mediated vasodilation is unknown. Thirty-seven healthy subjects were recruited. Forearm blood flow (FBF) was assessed using venous occlusion plethysmography, and functional hyperemic blood flow (FHBF) was induced by isotonic wrist exercise. Infusion of N(G)-monomethyl-l-arginine (l-NMMA), aspirin, or the combination reduced resting FBF compared with vehicle (P < 0.05). Addition of glibenclamide to l-NMMA, aspirin, or the combination did not further reduce resting FBF. l-NMMA decreased peak FHBF by 26%, and volume was restored after 5 min (P < 0.05). Aspirin reduced peak FHBF by 13%, and volume repaid after 5 min (P < 0.05). Coinfusion of l-NMMA and aspirin reduced peak FHBF by 21% (P < 0.01), and volume was restored after 5 min (P < 0.05). Addition of glibenclamide to l-NMMA and aspirin did not further decrease FHBF. Vascular K(ATP) channel blockade with glibenclamide does not affect resting FBF or FHBF in the setting of NO and vasodilator prostanoid inhibition.

ATP-Binding Cassette Transporters↗
PubMed2003

Vessel caliber and restenosis: a prospective clinical and angiographic study of NIR stent deployment in small and large coronary arteries in the same patient.

Retrospective analyses of patient cohorts undergoing stent deployment have shown that small vessel diameter and long lesion length are two angiographic predictors of increased restenosis. We determined the effects of these factors in patients with lesions treated in both small- and large-diameter coronary arteries. This multicenter prospective quantitative angiographic study evaluated patients with de novo coronary disease undergoing intervention who had at least two lesions < or = 16 mm length, one in a vessel < or = 2.75 mm diameter (9 or 16 mm length seven-cell NIR stent) and the other in a vessel > or = 3.0 mm diameter (9 or 16 mm nine-cell NIR stent). Of 94 patients enrolled, 76% were male, mean age was 62 years (range, 40-85), 41% were hypertensive, 18% had diabetes, 15% were current smokers, and 64% had hypercholesterolemia. Additional lesions were treated in 23% of patients. The procedural success rate was 99%. Six months postprocedure, there were no deaths or late stent occlusions. One patient suffered a Q-wave myocardial infarction, one a non-Q-wave infarction, eight underwent percutaneous reintervention, two coronary artery bypass graft surgery operations, and five stenting of other nonstudy lesions. The mean reference diameter for the small vessel was 2.35 mm and the large vessel 3.22 mm. Six-month angiography was performed in 87 patients (92% of those eligible). The overall restenosis rate was 24% in the small vessel (9 mm length stent, 17%; 16 mm length stent, 30%) and 15% in the large vessel (9 mm length stent, 3%; 16 mm length stent, 22%), respectively. Multivessel stenting including treatment of lesions in small-caliber vessels can be performed with a good clinical and angiographic outcome. When the patient, operator, technique, and stent type are the same, vessel caliber and stent length both appear to influence the restenosis rate.

Adult↗
PubMed2003

Use of arterial transfer functions for the derivation of aortic waveform characteristics.

OBJECTIVE: To investigate the utility and accuracy of radial-aortic arterial transfer functions for the derivation of central blood pressure waveforms. DESIGN Prospective measurement of central and peripheral waveforms in patients undergoing coronary angiography or percutaneous coronary intervention. METHODS: Simultaneous invasive central aortic and non-invasive radial pressure waveforms were recorded in 78 subjects (61 male : 17 female). Data were applied to a single-input/single-output model for the calculation of a transfer function (TF). Individual TFs were derived by two methods and ensemble averaged TFs obtained for the group. Reverse transformation was performed using each averaged TF applied to the radial data of each subject. RESULTS: There was close linear correlation between measured aortic parameters and both radial and TF-derived aortic systolic and diastolic pressures (P < 0.001) and most other waveform parameters. However, despite small mean differences between measured and most TF-derived aortic parameters (systolic pressure 0.8-2.9 mmHg, augmentation index 4.3-5.6%), individual scatter was marked, with 95% limits of agreement of +/- 14.6 mmHg (systolic pressure) and +/- 24.4% [augmentation index (AI)]. Indeed, scatter for AI was so marked that measured and derived values were not statistically significantly correlated. CONCLUSIONS: Transfer functions may be valid for the derivation of some central aortic waveform characteristics. However, in providing neither improved reproducibility nor data on parameters not obtainable from the radial waveform, transfer function techniques may offer no additional clinical benefit. The absence of correlation between measured and TF-derived aortic AI and wide limits of agreement of other parameters should be considered if this technique is utilized in clinical practice.

Aged↗
PubMed2002

Inhibition of vascular ATP-sensitive K+ channels does not affect reactive hyperemia in human forearm.

The extent to which ATP-sensitive K(+) channels contribute to reactive hyperemia in humans is unresolved. We examined the role of ATP-sensitive K(+) channels in regulating reactive hyperemia induced by 5 min of forearm ischemia. Thirty-one healthy subjects had forearm blood flow measured with venous occlusion plethysmography. Reactive hyperemia could be reproducibly induced (n = 9). The contribution of vascular ATP-sensitive K(+) channels to reactive hyperemia was determined by measuring forearm blood flow before and during brachial artery infusion of glibenclamide, an ATP-sensitive K(+) channel inhibitor (n = 12). To document ATP-sensitive K(+) channel inhibition with glibenclamide, coinfusion with diazoxide, an ATP-sensitive K(+) channel opener, was undertaken (n = 10). Glibenclamide did not significantly alter resting forearm blood flow or the initial and sustained phases of reactive hyperemia. However, glibenclamide attenuated the hyperemic response induced by diazoxide. These data suggest that ATP-sensitive K(+) channels do not play an important role in controlling forearm reactive hyperemia and that other mechanisms are active in this adaptive response.

Adenosine Triphosphate↗