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Biomedical subjects

K A Fox

Publications and source records attributed to K A Fox.

At least 73 records · Page 4Linked to original sources
PubMed1998

Prospective use of platelet glycoprotein IIb/IIIa receptor blockers in the emergency department setting.

Platelets play a pivotal role in the pathophysiology of acute coronary syndromes (ACS) and thus are logical therapeutic targets for treatment of this disease process. Platelet glycoprotein (GP IIb/IIIa receptor antagonists, which interrupt the final common pathway of platelet aggregation, have been proven to reduce the 30-day incidence of death, acute myocardial infarction (MI), and urgent revascularization in both high-risk and low-risk patients undergoing percutaneous intervention procedures. Three-year follow-up has indicated that these benefits appear durable. Recent large-scale randomized trials have demonstrated the value of GP IIb/IIIa receptor inhibitors in reducing the risk of death and MI in unstable angina/non-Q-wave MI patients receiving pharmacologic management. And, emerging evidence suggests a future role for GP IIb/IIIa receptor inhibitors as an adjunct to low-dose fibrinolytic therapy in patients with acute MI. As the list of indications for GP IIb/IIIa receptor antagonists expands to encompass the full spectrum of ACS, there is increasing interest in the potential use of these agents in the emergency department setting. The integration of GP IIb/IIIa receptor inhibitors into emergency department protocols will ultimately depend largely on whether these drugs prove to be safe and effective regardless of the direction of ST-segment deviation, and irrespective of whether definitive therapy will be invasive or conservative.

Algorithms↗
PubMed1997

A comparison of low-molecular-weight heparin with unfractionated heparin for unstable coronary artery disease. Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events Study Group.

BACKGROUND: Antithrombotic therapy with heparin plus aspirin reduces the rate of ischemic events in patients with unstable coronary artery disease. Low-molecular-weight heparin has a more predictable anticoagulant effect than standard unfractionated heparin, is easier to administer, and does not require monitoring. METHODS: In a double-blind, placebo-controlled study, we randomly assigned 3171 patients with angina at rest or non-Q-wave myocardial infarction to receive either 1 mg of enoxaparin (low-molecular-weight heparin) per kilogram of body weight, administered subcutaneously twice daily, or continuous intravenous unfractionated heparin. Therapy was continued for a minimum of 48 hours to a maximum of 8 days, and we collected data on important coronary end points over a period of 30 days. RESULTS: At 14 days the risk of death, myocardial infarction, or recurrent angina was significantly lower in the patients assigned to enoxaparin than in those assigned to unfractionated heparin (16.6 percent vs. 19.8 percent, P=0.019). At 30 days, the risk of this composite end point remained significantly lower in the enoxaparin group (19.8 percent vs. 23.3 percent, P=0.016). The need for revascularization procedures at 30 days was also significantly less frequent in the patients assigned to enoxaparin (27.1 percent vs. 32.2 percent, P=0.001). The 30-day incidence of major bleeding complications was 6.5 percent in the enoxaparin group and 7.0 percent in the unfractionated-heparin group, but the incidence of bleeding overall was significantly higher in the enoxaparin group (18.4 percent vs. 14.2 percent, P=0.001), primarily because of ecchymoses at injection sites. CONCLUSIONS: Antithrombotic therapy with enoxaparin plus aspirin was more effective than unfractionated heparin plus aspirin in reducing the incidence of ischemic events in patients with unstable angina or non-Q-wave myocardial infarction in the early phase. This benefit of enoxaparin was achieved with an increase in minor but not in major bleeding.

Aged↗
PubMed1997

Doppler myocardial imaging vs. B-mode grey-scale imaging: a comparative in vitro and in vivo study into their relative efficacy in endocardial boundary detection.

Doppler myocardial imaging (DMI) is a new ultrasound imaging modality in which colour Doppler algorithms are adapted to visualise the myocardium. It allows measurement of regional intramyocardial velocities and quantification of intramural left ventricular function. However promising the technique is, to date the accuracy of endocardial boundary detection by DMI has not been validated. As Doppler velocity estimation is based on measurement of phase shift rather than signal strength, the technique is relatively independent of chest wall attenuation. In the current study, a series of in vitro and in vivo studies was performed to compare standard B-mode grey-scale imaging (GSI) and DMI techniques in endocardial boundary detection. In vitro, the minimum and maximum volumes of a single-chamber tissue-mimicking phantom were calculated using both imaging techniques. In vivo, left ventricular end-diastolic (ED) volume and end-systolic (ES) volume indices were measured from GSI and DMI images in a group of 40 volunteers. All images were obtained in the freeze-frame mode with the Doppler display turned on and off so that simultaneous DMI and GSI information was obtained. In vitro, the limits of agreement between the minimum volume of the phantom and the minimum volume measured by GSI and DMI was 4% and 3%, respectively. For maximum volumes, limits of agreement were 3% for GSI and 2% for DMI. In vivo, the limits of agreement between the two imaging techniques in volume measurements were 6 mL (9%) for ED and 4 mL (11%) for ES. The comparison of the endocardial boundary detection by GSI vs. DMI showed DMI to be significantly superior: ED (72 +/- 16% vs. 85 +/- 8%, respectively; p < 0.05) and ES (71 +/- 13% vs. 88 +/- 7%, respectively; p < 0.05). The results of the study show that: (1) in vitro, based on two-dimensional algorithms, DMI provides as accurate volume measurements as GSI; and (2) in vivo, there is a very good agreement of left ventricular volume measurements between GSI and DMI. However, the endocardial boundary is more reliably displayed and visually easier to detect using DMI than GSI.

Adult↗
PubMed1997

Characterisation of atherosclerotic plaque by spectral analysis of intravascular ultrasound: an in vitro methodology.

Raw 30-MHz intravascular ultrasound data have been captured from postmortem coronary arteries (n = 4) to develop radio frequency analysis techniques for the characterisation of atherosclerotic plaque. Digitised data acquired from positions (n = 8) within diseased sections of artery were compared with the corresponding histology and radiology. Scan-converted images were used to locate regions of interest (ROI = 33) within areas of tissue composition: loose fibrotic tissue (LFT), dense fibrotic tissue (DFT) and calcium (CA). A range of parameters was extracted from the normalised power spectrum of each ROI within the bandwidth 17-42 MHz. Significant discrimination between LFT/DFT and between LFT/CA was provided by maximum power and spectral slope (dBMHz-1). However, the greatest discriminative power was given by the y-axis (0 Hz) intercept of the spectral slope: LFT/DFT (p = 0.001); LFT/CA (p = 0.0001); and DFT/CA (p = 0.089).

Coronary Artery Disease↗
PubMed1997

Characterisation of red and white thrombus by intravascular ultrasound using radiofrequency and videodensitometric data-based texture analysis.

Visual assessment of intravascular ultrasound (IVUS) video images cannot reliably identify thrombus. We examined if texture analysis of radiofrequency (r.f.) data or videodensitometric data (VD) could distinguish thrombi of different ages and cell compositions. Whole human blood (red clot = RC), platelet-rich plasma (white clot = WC) and plasma (n = 6/group) were imaged at 4 and 24 h with 30 MHz IVUS transducers. At 4 h, VD- and r.f.-based analyses revealed significant differences between RC and WC with variance (VD red 26.4 +/- 2.5, white 33.9 +/- 7.8; r.f. red 1.4 +/- 0.5, white 4.9 +/- 1.3), kurtosis (VD red 0.29 +/- 0.9, white 0.23 +/- 0.3) and skewness (VD red 0.23 +/- 0.13, white 0.35 +/- 0.52; r.f. red 0.06 +/- 0.01, white -0.06 +/- 0.05). Also mean grey-level from both data sets was higher in RC (VD 134.8 +/- 18.0; r.f. -13.3 +/- 1.2) than in WC (VD 105.3 +/- 17.4, r.f. 16.5 +/- 2.2) (p < 0.01). With increasing time, variance increased in WC (5.5 +/- 1.5 at 24 h) and decreased in RC (0.9 +/- 0.3.3 at 24 h). The more heterogeneous structure of WC may be distinguished from that of RC using texture analysis of either VD or r.f.-signals.

Blood Coagulation↗
PubMed1997

Differences in myocardial velocity gradient measured throughout the cardiac cycle in patients with hypertrophic cardiomyopathy, athletes and patients with left ventricular hypertrophy due to hypertension.

OBJECTIVES: We sought to compare the myocardial velocity gradient (MVG) measured across the left ventricular (LV) posterior wall during the cardiac cycle between patients with hypertrophic cardiomyopathy (HCM), athletes and patients with LV hypertrophy due to systemic hypertension and to determine whether it might be used to discriminate these groups. BACKGROUND: The MVG is a new ultrasound variable, based on the color Doppler technique, that quantifies the spatial distribution of transmyocardial velocities. METHODS: A cohort of 158 subjects was subdivided by age into two groups: Group I (mean [+/-SD] 30 +/- 7 years) and Group II (58 +/- 8 years). Within each group there were three categories of subjects: Group Ia consisted of patients with HCM (n = 25), Group Ib consisted of athletes (n = 21), and Group Ic consisted of normal subjects; Group IIa consisted of patients with HCM (n = 19), Group IIb consisted of hypertensive patients (n = 27), and Group IIc consisted of normal subjects (n = 33). RESULTS: The MVG (mean [+/-SD] s-1) measured in systole was lower (p < 0.01) in patients with HCM (Group Ia 3.2 +/- 1.1; Group IIa 2.9 +/- 1.2) compared with athletes (Group Ib 4.6 +/- 1.1), hypertensive patients (Group IIb 4.2 +/- 1.8) and normal subjects (Group Ic 4.4 +/- 0.8; Group IIc 4.8 +/- 0.8). In early diastole, the MVG was lower (p < 0.05) in patients with HCM (Group Ia 3.7 +/- 1.5; Group IIa 2.6 +/- 0.9) than in athletes (Group Ib 9.9 +/- 1.9) and normal subjects (Group Ic 9.2 +/- 2.0; Group IIc 3.6 +/- 1.5), but not hypertensive patients (Group IIb 3.3 +/- 1.3). In late diastole, the MVG in patients with HCM (Group Ia 1.3 +/- 0.8; Group IIa 1.4 +/- 0.8) was lower (p < 0.01) than that in hypertensive patients (Group IIb 4.3 +/- 1.7) and normal subjects (Group IIc 3.8 +/- 0.9). An MVG < or = 7 s-1, as a single diagnostic approach, differentiated accurately (0.96 positive and 0.94 negative predictive value) between patients with HCM and athletes when the measurements were taken during early diastole. CONCLUSIONS: In both age groups, the MVG was lower in both systole and diastole in patients with HCM than in athletes, hypertensive patients or normal subjects. The MVG measured in early diastole in a group of subjects 18 to 45 years old would appear to be an accurate variable used to discriminate between HCM and hypertrophy in athletes.

Adult↗
PubMed1997

Can a hospital be like a supermarket? Better data will provide cost controls, efficiencies, and income streams.

Electronic bar coding, scanning, and the data generated are an inevitable part of a health care provider's future. Initially, it will probably be implemented in hospitals, where the diversity of products and scrutiny to reduce costs are greatest. Many lessons can be learned from the introduction of electronic scanning in the grocery or supermarket industry. The transformation to scanning in the grocery industry met with initial resistance and problems, but generated creative solutions, best practices, and a rich database.

Cost Allocation↗
PubMed1997

Preoperative detection of sporadic parathyroid adenomas using technetium-99m-sestamibi: what role in clinical practice?

Preoperative localization of pathologic parathyroid glands remains controversial. Because experienced parathyroid surgeons can identify and cure parathyroid pathology in sporadic primary hyperparathyroidism in better than 95 per cent of first-time explorations, few consider preoperative localization studies cost effective in this population. However, the primary reason for failure at the initial exploration is the inability of the surgeon to identify an adenoma in a normal anatomical location. Recent reports have indicated that operative time can be reduced and initial success improved with preoperative localization of adenomas using the highly sensitive technetium-99m (Tc)-sestamibi scan. We evaluated 16 consecutive patients with sporadic primary hyperparathyroidism using a double-phase Tc-sestamibi scan with delayed images, hypothesizing that 90 per cent of adenomas would be accurately detected, and furthermore that a negative scan would predict multigland disease. Of the 16 scans, 13 showed a focal delayed washout of the tracer, constituting a positive scan. Eleven of 13 were true positive (85%), with two false positive scans (15%), both of which also had nodular thyroid disease. The three negative scans were indeed hyperplastic multigland disease, determined at exploration. The mean operative time for a bilateral exploration for the true positive cases was 109 minutes, compared to 148 minutes for a small cohort group without imaging (not significant). In conclusion, 85 per cent of adenomas can be successfully localized with the Tc-sestamibi delayed-image technique, and may decrease operative time. Additionally, a negative scan is a likely predictor of multigland disease, which allows for improved preoperative patient education and preparation for cryopreservation. These data suggest that preoperative Tc-sestamibi scanning may improve the success rate for the occasional parathyroid surgeon, and that an extended prospective trial is warranted.

Adenoma↗
PubMed1997

An in vivo model for the assessment of acute fibrinolytic capacity of the endothelium.

The effects on blood flow and plasma fibrinolytic and coagulation parameters of intraarterial substance P, an endothelium dependent vasodilator, and sodium nitroprusside, a control endothelium independent vasodilator, were studied in the human forearm circulation. At subsystemic locally active doses, both substance P (2-8 pmol/min) and sodium nitroprusside (2-8 microg/min) caused dose-dependent vasodilatation (p <0.001 for both) without affecting plasma concentrations of PAI-1, von Willebrand factor antigen or factor VIII:C activity. Substance P caused local increases in t-PA antigen and activity (p <0.001) in the infused arm while sodium nitroprusside did not. At higher doses, substance P increased blood flow and t-PA concentrations in the noninfused arm. We conclude that brief, locally active and subsystemic infusions of intraarterial substance P cause a rapid and substantial local release of t-PA which appear to act via a flow and nitric oxide independent mechanism. This model should provide a useful and selective method of assessing the in vivo capacity of the forearm endothelium to release t-PA acutely.

Adult↗
PubMed1996

Chronic memory impairment after cardiac arrest outside hospital.

OBJECTIVES: To evaluate the nature, prevalence, and severity of chronic memory deficit in patients resuscitated after cardiac arrest outside hospital and to determine whether such deficits are related to duration of cardiac arrest. DESIGN: Case-control study. SUBJECTS: 35 survivors of cardiac arrest outside hospital and 35 controls matched for age and sex who had had acute myocardial infarction without cardiac arrest. MAIN OUTCOME MEASURES: Subjects assessed at least two months after index event for affective state (hospital anxiety and depression scale), premorbid intelligence (national adult reading test), short term recall (digit recall test), and episodic long term memory (Rivermead behavioural memory test). RESULTS: Cases and controls showed no difference in short term recall. Cases scored lower on Rivermead test than controls (mean (SD) score out of 24 points: 17.4 (5.4) v 21.8 (2.0), P < 0.001), particularly in subtests relating to verbal and spatial memory. Moderate or severe impairment was found in 37% of cases and in no controls. Severity of impairment of memory correlated significantly with measures of duration of cardiac arrest. This deficit was not significantly associated with subjects' age, interval from index event to assessment, occupation, measures of comorbidity, social deprivation, anxiety or depression scores, or estimated premorbid intelligence. CONCLUSIONS: Clinically important impairment of memory was common after cardiac arrest outside hospital. Improvement in response times of emergency services could reduce the severity of such deficits. With an increasing numbers of people expected to survive cardiac arrest outside hospital, rehabilitation of those with memory deficit merits specific attention.

Aged↗
PubMed1996

Resuscitation from out-of-hospital cardiac arrest: implications for cardiac enzyme estimation.

BACKGROUND: diagnosis of precipitating myocardial infarction is essential for management of victims of out-of-hospital cardiac arrest, since investigations and treatment are determined by the underlying cause. Skeletal muscle and myocardial damage from external cardiac massage and defibrillation may complicate biochemical diagnosis of myocardial infarction. OBJECTIVES: (a) to examine the relationship between cumulative defibrillation energy and serum levels of cardiac troponin T and MB creatine kinase (MB-CK) mass in out-of-hospital cardiac arrest survivors without electrocardiographic evidence of myocardial infarction; (b) to reassess diagnostic thresholds for myocardial infarction using MB-CK mass and troponin T in this setting. METHODS: 77 victims of out-of-hospital cardiac arrest were studied. Serum was obtained for MB-CK mass, CK and troponin T estimation on the first 4 days of admission. Patients were divided into three groups using electrocardiographic criteria: group 1, myocardial infarction; group 2, no evidence of infarction; and group 3, equivocal electrocardiograms. Correlation coefficients were calculated for highest recorded levels of the biochemical markers versus defibrillation energy. Receiver-operating characteristic plots were used to determine optimum biochemical diagnostic thresholds for subjects in groups 1 and 2. RESULTS: using predefined criteria, 27 patients had myocardial infarction, 34 did not have myocardial infarction and 16 had equivocal electrocardiograms. Significant correlations were found for defibrillation energy versus log troponin T (r = 0.42, P < 0.05), log MB-CK mass (r = 0.51, P < 0.01) and total CK (r = 0.68, P < 0.001) in group 2. Within groups 1 and 2, MB-CK mass and troponin T provided additional diagnostic value over MB-CK fraction (P < 0.001). Diagnostic accuracy was not improved by adjusting for shock energy. The optimum threshold value was 4 ng/ml for troponin T (sensitivity 88%, specificity 95%), 60 ng/ml for MB-CK mass (sensitivity 88%, specificity 88%) and 8% of total CK for MB-CK fraction (sensitivity 74%, specificity 82%). These values should be interpreted with caution, since this study is limited by the exclusion of patients with uncertain electrocardiographic diagnoses into group 3. CONCLUSIONS: skeletal muscle and myocardial damage occurs in survivors of out-of-hospital cardiac arrest and is related to the duration of resuscitation. This complicates biochemical diagnosis of underlying myocardial infarction. Specific high diagnostic threshold values for MB-CK and troponin T are needed to optimise diagnostic accuracy. The use of MB-CK fraction leads to greater diagnostic error because of the variability of muscle CK release after resuscitation.

Aged↗
PubMed1996

Regional variations of ultrasonic integrated backscatter in normal and myopathic left ventricles. A new multi-view approach.

The purpose of the present study was to determine whether the cyclic variation of integrated backscatter is measurable and quantifiable in all left ventricular walls and whether the information obtained using both parasternal and apical transducer positions can be used to identify changes in myocardial structure and contractility. The cyclic variation of integrated backscatter was measured from the parasternal long-axis, apical four-chamber and two-chamber views in 26 patients with idiopathic dilated cardiomyopathy (mean age 58 +/- 9 years; ejection fraction 29 +/- 10%) and compared with information obtained from 30 aged-matched healthy volunteers. For each subject, the cyclic variation of integrated backscatter was calculated from 16 predetermined regions-of-interest located within the myocardium of the basal and mid-segments of the left ventricle imaged from the long-axis view and also the basal mid and apical left ventricular segments imaged from the two apical views. The cyclic variation of integrated backscatter was found to be present in 100% of the analysed regions-of-interest in healthy volunteers and in 87.5% of the analysed regions-of-interest in patients with idiopathic dilated cardiomyopathy. The mean value of cyclic variation of integrated backscatter, averaged from all regions-of-interest in the idiopathic dilated cardiomyopathy group, was significantly reduced compared to that in the healthy volunteers group (3.2 +/- 2.5 dB [mean +/- SD] vs 4.8 +/- 2.9 dB, P < 0.0001). Additionally, the healthy volunteers group demonstrated marked regional variability in the magnitude of cyclic variation of integrated backscatter which closely followed the regional changes in the contractile function of the normal heart. These regional differences in the magnitude of the cyclic variation of integrated backscatter were only partially retained in the idiopathic dilated cardiomyopathy group, and suggest that a multi-view approach of the recording of cyclic variation of integrated backscatter can be of value to differentiate normal from myopathic myocardium and to quantify regional differences in myocardial contractile performance throughout the left ventricular walls.

Adult↗
PubMed1996

Age-related transmural peak mean velocities and peak velocity gradients by Doppler myocardial imaging in normal subjects.

Doppler myocardial imaging is a new cardiac ultrasound technique based on the principles of colour Doppler imaging which can determine myocardial velocities by detecting the changes of phase-shift of the ultrasound signal returning directly from the myocardium. To determine the normal range of transmural velocities in healthy hearts a prospective study was carried out involving 42 normal subjects (age from 21 to 78, mean 47 +/- 16 years). Using M-mode Doppler myocardial imaging the peak values of the mean velocity and velocity gradient across the left ventricular posterior wall were measured during standardized phases of the cardiac cycle. Peak mean velocities had the following values during the cardiac cycle: isovolumic contraction - 1.3 +/- 1.2 cm. s-1, early ventricular ejection 4.2 +/- 1.2 cm. s-1, late ventricular ejection 1.8 +/- 1.1 cm. s-1, isovolumic relaxation -2.0 +/- 0.8 cm. s-1, rapid ventricular filling -6.6 +/- 2.2 cm. s-1, atrial contraction -2.8 +/- 1.8 cm. s-1, atrial relaxation 1.2 +/- 1.1 cm. s-1. Peak velocity gradients were: isovolumic contraction 1.3 +/- 1.9 s-1, early ventricular contraction 4.7 +/- 1.9 s-1, late ventricular contraction 1.1 +/- 1.0 s-1, isovolumic relaxation -0.6 +/- 0.5 s-1, rapid ventricular filling 6.1 +/- 3.4 s-1, atrial contraction 2.6 +/- 1.7 s-1, atrial relaxation 0.0 +/- 0.3 s-1. Linear regression analysis showed that with the increase of age, peak velocity gradient decreases during rapid ventricular filling (r = 0.83; P < 0.0001) and increases during atrial contraction (r = 0.86; P < 0.0001) while peak mean velocity increases only during atrial contraction (r = 0.80, P < 0.0001). Thus, there was no correlation between increasing age and systolic peak mean velocity and peak velocity gradient but both diastolic filling phases rapid ventricular filling and atrial contraction demonstrated age-related changes. In summary, this study has determined the age-related range of normal transmural myocardial velocities within the left ventricular posterior wall in healthy hearts during the cardiac cycle. We conclude that these measurements of peak mean velocities and peak velocity gradients, should form the baseline for subsequent Doppler myocardial imaging clinical studies on myocardial diseases processes.

Adult↗