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Biomedical subjects

A Selwyn

Publications and source records attributed to A Selwyn.

At least 19 recordsLinked to original sources

Simplified risk score models accurately predict the risk of major in-hospital complications following percutaneous coronary intervention.

The objectives of this analysis were to develop and validate simplified risk score models for predicting the risk of major in-hospital complications after percutaneous coronary intervention (PCI) in the era of widespread stenting and use of glycoprotein IIb/IIIa antagonists. We then sought to compare the performance of these simplified models with those of full logistic regression and neural network models. From January 1, 1997 to December 31, 1999, data were collected on 4,264 consecutive interventional procedures at a single center. Risk score models were derived from multiple logistic regression models using the first 2,804 cases and then validated on the final 1,460 cases. The area under the receiver operating characteristic (ROC) curve for the risk score model that predicted death was 0.86 compared with 0.85 for the multiple logistic model and 0.83 for the neural network model (validation set). For the combined end points of death, myocardial infarction, or bypass surgery, the corresponding areas under the ROC curves were 0.74, 0.78, and 0.81, respectively. Previously identified risk factors were confirmed in this analysis. The use of stents was associated with a decreased risk of in-hospital complications. Thus, risk score models can accurately predict the risk of major in-hospital complications after PCI. Their discriminatory power is comparable to those of logistic models and neural network models. Accurate bedside risk stratification may be achieved with these simple models.

Angioplasty, Balloon, Coronary↗

Usefulness of intravascular ultrasound in preventing stenting of hazy areas adjacent to coronary stents and its support of support spot-stenting.

The uncertain significance of hazy areas at the margins of coronary stents may lead to further, at times unnecessary, stenting. However, the risk of restenosis increases substantially when additional stents are deployed. We used intravascular ultrasound (IVUS) to identify the causes of hazy segments adjacent to stents. We identified 13 cases with hazy regions adjacent to coronary stents and 20 controls without hazy regions matched by age, gender, and vessel stented. Hazy regions were defined from the angiogram as reduced contrast density without a clearly defined intimal tear, dissection, thrombus, or stenosis (> 50%). IVUS images were obtained from the reference, stent, and hazy and control regions adjacent to the stent. Computerized planimetery was used to measure the vessel, lumen, and plaque cross-sectional areas (CSAs), the maximum arc of calcium, and the eccentricity ratio (minimum:maximum lumen diameter). There were no significant differences between hazy and control segments in the vessel, lumen, and plaque CSAs. All lumen CSAs were >4.0 mm2. Compared with control regions, the hazy regions had calcified plaque more often (69% vs 25%; odds ratio [OR] 6.75, 95% confidence intervals [CI] 1.82 to 25.0]) and more frequent intimal tears (23% vs 0%, OR 6.67, 95% CI 1.98 to 35.0). Haziness was particularly associated with calcified plaque and eccentric lumen (p = 0.037). Thus, haziness at the margins of coronary stents is often caused by calcified plaque. IVUS can differentiate calcified plaques from intimal tears and thereby obviate unnecessary stenting.

Adult↗

Lipid lowering improves endothelial functions.

The healthy endothelium usually provides an anticoagulant, vasodilatory and anti-inflammatory spectrum of functions that are central in vascular homeostasis. Dysfunction of the endothelium is a common feature of all phases of atherosclerosis. Hypercholesterolemia provokes many aspects of endothelial dysfunction before and during the development of atheroma. For example, a high cholesterol diet leads to the formation of a fatty streak and the recruitment and binding of blood leukocytes to the artery wall. This process requires expression by the endothelial cells of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1). In rabbits that are fed an atherogenic diet, the aortic endothelium, which usually expresses little VCAM-1, shows foci of VCAM-1 expression soon after initiating this diet. Furthermore, lowering plasma cholesterol by diet or drugs down-regulates the expression of VCAM-1 and reduces the density of inflammatory cells in the atherosclerotic plaque. Hypercholesterolemia also attenuates normal vasodilatation to several stimuli such as exercise and acetylcholine. In healthy subjects, the vascular endothelium produces the vasodilator nitric oxide. In atherosclerosis, however, nitric oxide bioavailability is impaired. As a result, atherosclerotic coronary arteries commonly display a vasoconstrictor response when challenged with acetylcholine. Lipid lowering appears to favorably influence endothelial vasomotor and inflammatory functions in ways that may benefit patients with coronary artery disease. Continued probing of the basic mechanisms of endothelial dysfunction and its treatment may lead to new therapies that offer clinical benefits in patients with atherosclerosis, including reductions in coronary events.

Animals↗

Development of the multidimensional index of life quality. A quality of life measure for cardiovascular disease.

OBJECTIVES: The purpose of this study was to design a multidimensional measure of health-related quality of life appropriate for patients with cardiovascular disease that was psychometrically sound, brief, and easy to administer. METHODS: Qualitative interviews conducted with healthy subjects and patients with cardiovascular diseases identified nine major quality of life domains. Based on the responses of 129 cardiovascular disease patients recruited from hospitals and clinics, a criterion-based approach was used to select 35 questionnaire items that best tapped these domains. Psychometric properties of the Multidimensional Index of Life Quality (MILQ) were tested with a sample of 348 patients with various cardiovascular diseases. RESULTS: Cronbach's alpha was 0.76 or higher for eight of the nine MILQ domains. Test-retest reliability coefficients were 0.73 or greater in all but two domains. Individual domain scores as well as a weighted overall quality of life index were correlated highly with self-assessed health and the number of heart-related symptoms. CONCLUSIONS: The Multidimensional Index of Life Quality is a psychometrically reliable and valid instrument for measuring quality of life in patients with cardiovascular diseases. The MILQ also may be a suitable measure for other types of chronic diseases.

Adult↗

Hemodynamic evaluation of arterial stenoses by computer simulation.

A new method to assess the hemodynamic severity of arterial stenoses was proposed and evaluated. It is based on a previously developed finite element computer simulation model for laminar-separated flow in arteries of axially varying cross-section; the present modification allows use of angiographic stenosis shapes acquired by automatic edge-detection algorithms. The method was validated by comparing its results with published experimental and theoretic results for ideal stenosis shapes. At moderate flowrates (Reynolds number = 500), poststenosis flow separation was predicted for moderately severe (75% area reduction) but not for mild (25%) stenoses. For high flowrates (Reynolds number = 900) in a severe stenosis (89%), stagnation and reversed flow were predicted and the experimental nondimensional pressure drop of 48.5 was correctly determined. Bernoulli's Equation, which neglects viscosity, predicted a drop of only 40. For a severe stenosis (89%), even at low Reynolds numbers (50), reversed flow agreeing with other theoretic solutions was predicted. Predictions are especially useful at low flow rates, where experiments are difficult to conduct. The height of the curve on the graph of nondimensional pressure gradient vs. Reynolds number reflects the hemodynamic severity of a particular stenosis; these curves were predicted for moderate and severe ideal stenoses and agree with experiments. A similar analysis is applied to an actual human coronary artery stenosis, and the results are demonstrated to have use in assessing interventions during angiography.

Arterial Occlusive Diseases↗

Detection of transient myocardial ischemia by computer analysis of standard and signal-averaged high-frequency electrocardiograms in patients undergoing percutaneous transluminal coronary angioplasty.

Electrocardiographic manifestations of transient myocardial ischemia were studied, in 11 patients undergoing angioplasty (PTCA) of a left anterior descending coronary artery stenosis, by the visual inspection of the standard surface electrocardiogram (S-ECG) and the intracoronary ECG (IC-ECG) as well as computer-assisted analysis of the S-ECG. Cross-correlation analysis (CCA) performed by computer was used to compare beat-to-beat variability in ST-T morphology of the S-ECG during different stages of PTCA. CCA was also applied to the signal-averaged high-frequency QRS (SA-HFQ). All patients developed angina during balloon inflation, accompanied by transient marked ST-T changes in IC-ECG in 10 of 11 patients (90%). Visual inspection of S-ECG revealed transient ST-T changes in only 6 of 11 (54%). In contrast, CCA of the S-ECG revealed transient ST-T changes in 9 of 11 (82%). Analysis of SA-HFQ revealed that balloon inflation was associated with a marked reduction in the calculated root-mean-square (RMS) voltage for such signals (2.31 +/- 1.04 microV) as compared with RMS values before (3.27 +/- 1.12 microV, p less than .05) PTCA or after conclusion of PTCA (3.79 +/- 1.39 microV, p less than .01). Balloon inflation was also accompanied by changes in waveform morphology of the SA-HFQ, including the development of new or more prominent time zones of reduced amplitude in 10 of 11 individuals (90%). Such zones may represent slow conduction in regions of the heart rendered ischemic during PTCA. CCA of the S-ECG and of SA-HFQ appears to detect evidence of transient ischemia with greater sensitivity than simple visual inspection of S-ECG, and may therefore prove to be of use in the evaluation of patients with chest pain of uncertain origin.

Adult↗

Significance of exercise induced ST segment elevation in patients with previous myocardial infarction.

In order to determine the significance of exercise induced ST segment elevation in patients with previous myocardial infarction, we have studied 156 patients, 26 months (mean) after myocardial infarction. Each patient underwent 16 lead precordial electrocardiographic mapping before, during, and after exercise and in addition coronary arteriography was performed. There was no significant difference in the extent of coronary disease or abnormalities of left ventricular function between patients with exercise induced ST segment elevation that was noted to occur in leads with Q waves and those with ST segment elevation plus depression or those with ST segment depression alone. Patients without exercise induced ST segment changes had fewer coronary arteries involved than those who developed ST segment changes. Nineteen patients with exercise induced ST segment elevation alone underwent coronary artery bypass surgery; in 11 this resulted in complete abolition of the exercise induced ST segment elevation and was associated with symptomatic relief and patent grafts without alteration of left ventricular function. Thus, exercise induced ST segment elevation in patients with previous myocardial infarction should be considered as important as ST segment depression in terms of underlying myocardial ischaemia, coronary anatomy, and left ventricular function.

Adult↗

Nuclear magnetic resonance imaging of the heart. Current status and future prospects.

The basic principles and current status of proton nuclear magnetic resonance imaging are outlined. Nuclear magnetic resonance images of the heart have improved in quality with advances in technique and better gating but clinical experience remains very limited. Myocardial infarction has been shown in animals and man, and plaques of atheroma have been seen with nuclear magnetic resonance flow studies. Further improvements in image quality, faster examination times, 23Na imaging, and the use of paramagnetic contrast agents are advances that are anticipated in the near future.

Animals↗

Inability of exercise-induced R wave changes to predict coronary artery disease.

To determine the value of exercise-induced R wave changes in diagnosing coronary disease 200 patients undergoing coronary angiography were studied with 16 lead precordial exercise mapping. R wave amplitude was calculated before and immediately after exercise as the sum of R in all 16 leads, the sum of the R waves in the left plus the S waves in the right precordial leads, as well as the sum of the R waves only in those leads that manifested S-T depression. Coronary artery disease was found in 154 patients, S-T depression developed in 122 (sensitivity 79 percent); the sum of R increased or remained unchanged in 61 and decreased in 93 (sensitivity 40 percent). Forty-six patients did not have coronary artery disease; S-T depression developed in 5 (specificity 89 percent); the sum of R increased or was unchanged in 30 and decreased in 16 (specificity 35 percent). Similar results were obtained using the other criteria for calculating R wave amplitude. Exercise-induced S-T depression was identified in 5. 1 +/- 2.6 (mean +/- standard deviation) of the 16 precordial leads and in 2.0 +/- 1. 1 of the chest leads of the standard electrocardiogram (p less than 0.01). Thus, electrocardiographic alterations found in the standard chest leads represent only a small variable proportion of the total projection. When the whole precordial area was analyzed, R wave changes were so unpredictable that they could not be used in the diagnosis of coronary disease.

Adult↗

Treatment of angina pectoris with propranolol: the harmful effects of cigarette smoking.

The effects of smoking on the treatment of angina has been studied in 10 patients. Each patient underwent 4 randomized 1-week treatments consisting of on and off smoking, and on and off propranolol (360 mg/day). At the end of each treatment a maximal exercise test was performed using 16 praecordial leads. Smoking was associated with a significantly higher heart rate, blood pressure, area and severity of ST-segment depression. This was not abolished by propranolol. Thus, smoking aggravates the simple haemodynamic variables used to assess myocardial oxygen requirements and the electrocardiographic signs of ischaemia; this is true even after treatment with propranolol.

Angina Pectoris↗

The dose-response effects of nifedipine of ST-segment changes in exercise testing: preliminary studies.

This study examines the effects of increasing doses of nifedipine on exercise-induced ST-segment depression in patients with severe typical stable angina pectoris. 10 patients underwent four 1-week treatment periods in a single-blind clinical trial. These were nifedipine 0, 30, 60, and 90 mg in divided doses daily. At the end of each week a maximum exercise test was performed using 16 precordial electrocardiographic leads and the ST-segment changes measured immediately after exercise. In 4 patients nifedipine produced no effects on these electrocardiographic parameters; 4 patients improved and 2 deteriorated. Thus, a dose of nifedipine, effective in 1 patient, can have opposite effects in another.

Angina Pectoris↗

Interaction between cigarettes and propranolol in treatment of angina pectoris.

To determine whether cigarette smoking interferes with the medical management of angina pectoris, 10 patients with angina pectoris who smoked at least 10 cigarettes a day were studied before, during, and after a standardised maximal exercise test. This was done at the end of four randomly allocated one-week treatment periods during which the patients took glyceryl trinitrate while not smoking, took glyceryl trinitrate while smoking, took glycerly trinitrate and propranolol (380 mg/day) while not smoking, and took glyceryl trinitrate and propranolol while smoking. Carboxyhaemoglobin was measured to ensure compliance. Smoking was associated with a significantly higher heart rate, blood pressure, number of positions with ST-segment depression, and total ST-segment depression after exercise than non-smoking (p < 0.01) whether or not the patients were taking propranolol. These results suggest that smoking aggravates the simple haemodynamic variables used to assess myocardial oxygen requirements and the exercise-induced precordial electrocardiographic signs of myocardial ischaemia. These effects were still evident after treatment with propranolol and represent a hindrance to the effective medical treatment of angina pectoris.

Adult↗

Myocardial infarction in the dog: effects of intravenous propranolol.

The effects of propranolol on myocardial perfusion and metabolism during acute myocardial infarction were studied in 18 mongrel dogs. A reversible snare was placed on the left anterior descending coronary artery; regional myocardial perfusion was continuously measured using the short-lived isotope krypton-81m, and myocardial metabolism was assessed using the epicardial electrocardiogram and measurement of release of creatine kinase activity from the affected segment of myocardium. Six dogs with no arterial occlusion acted as "sham operated" dogs; six others in which the snare was occluded acted as a control group and a third group of six were given propranolol, 0.5 mg/kg, 30 minutes after coronary occlusion. All variables were recorded before and for 5 hours after coronary occlusion. Dogs treated with propranolol showed a significant improvement in regional myocardial perfusion to the affected segment, decreased loss of electrically active myocardium at the end of each experiment for any given degree of early S-T segment elevation and a delay in the local release of creatine kinase activity compared with that in the control dogs. These results suggest that propranolol exerts a beneficial effect on the progress of ischemic myocardial damage when given shortly after the onset of infarction.

Animals↗

Praecordial surface mapping after exercise in evaluation of propranolol for angina pectoris.

The effect of propranolol on ST depression in the praecordial 16 lead electrocardiogram was observed in 52 patients before and after treatment, both at rest and after exercise. In a further 20 patients exercise tests repeated on separate days two months apart showed that the technique gave reproducible results. A variable relation between symptomatic relief and praecordial exercise-induced ST segment depression was noted. Use of a single fixed-position chest lead (V5) was shown to be less accurate. The relief of symptoms alone is probably an inadequate guide to the success of medical treatment, which should control not only angina but also the manifestations of ischaemia on the praecordial electrocardiogram.

Angina Pectoris↗

Precordial electrocardiographic mapping after exercise in the diagnosis of coronary artery disease.

A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (68 percent) or a single chest lead (64 percent) (P less than 0.01). The specificity of the three techniques did not differ significantly (P greater than 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.

Adult↗