The electrocardiogram (ECG) as measured from healthy subjects shows a considerable interindividual variability. This variability is caused by geometrical as well as by physiological factors. In this study, the relative contribution of the geometrical factors is estimated. In addition a method aimed at correcting for these factors is described. First, a measure (RV) for quantifying the overall variability is presented, and for healthy individuals its value is estimated as 0.52. Next, based on a simulation study using the individual (heart-lung-torso) geometry of 25 subjects, the variability caused by geometrical factors is estimated as 0.40, indicating that in healthy subjects the RV for healthy individuals resulting from electrophysiology is of the order of 0.33. In an evaluation of the correction procedure, applied to realistic, simulated body surface potentials, it is shown that RV caused by geometrical factors can be reduced from 0.40 to 0.06. When applying the correction procedure to measured ECG data no reduction of the RV value could be demonstrated. These results indicate that the involved procedure of the inverse computation of a cardiac equivalent source, at the present time, is of insufficient quality to cash in on the substantial reduction of RV values from 0.52 down to 0.33 that might be obtainable.
Background Intensive lipid lowering may retard the pro gression of coronary atherosclerosis. LDL-apheresis has the potential to decrease LD L cholesterol to very low levels. To assess the effect of more aggressive lipid lowering with LDLapheresis, we set up a randomized study in men with hyper cholesterolemia and severe coronary atherosclerosis.Methods and Results For 2 years, 42 men were treated with either biweekly LDL-apheresis plus medication or medication alone. In both groups a dose of simvastatin of 40 mg per day was administered. Baseline (m ean±SD) LDL cholesterol was 7.8 ±1.9 mmol -L l and 7.9±2.3 mmol * L~! in the apheresis and medica tion groups, respectively. The mean reduction in LDL cholesterol was 63% (to 3.0 mmol * L" 1) and 47% (to 4.1 mmol • L_l), respectively. Primary quantitative coronary angiographic end points were changes in average mean segment diameter and minimal obstruction diameter. No differences between the apheresis and medication groups were found in mean segment diameter (-0.01 ±0.16 mm versus 0.03 ±0.16 mm, respectively)
The intrinsic limitations of coronary arteriography to predict the physiological effects of coronary obstructions are well known. Therefore, more direct assessments of the functional significance of coronary stenoses are becoming increasingly important. Study of contrast passage by electrocardiogram-triggered digital radiography has been proposed as a way of assessing changes in myocardial perfusion. The main problems in this approach are the limited time for motionless image acquisition, the potential alteration of vascular volume between different states, and the changing flow pattern induced by contrast agents. This has led to empiric substitution of mean transit time (Tmn) by other time parameters and to representation of vascular volume by maximal contrast intensity (D..). To avoid these problems, intact dogs were studied during almost motionless image acquisition of 20-25 consecutive paced heart beats obtained with synchronous radiographic pulses. In (weight, 26-36 kg) were anesthetized with sodium pentobarbital 25 mg/kg i.v., a left thoracotomy was performed, and epicardial pacing electrodes were sutured on the left atrium. The proximal part of the left circumflex artery (LCx) was gently dissected free, over a distance of 1.0-1.5 cm proximal of the origin of the first large obtuse marginal branch. A ring-mounted 20-MHz pulsed Doppler probe (Crystal Biotech Inc., Holliston, Massachusetts) was placed around the artery and a circular balloon occluder (R.E. Jones, Silver Springs, Maryland) was placed just distal to the Doppler probe. The pericardium and chest were closed, and the instrumentation leads were placed in a subcutaneous pocket until the time of study.At day 11 after instrumentation, each dog was anesthetized by nicomorphine 10 mg/hr i.v. and ethrane. The subcutaneous pocket was opened, and the wires of the Doppler probe were connected to the appropriate recording equipment (545C-4 Directional Pulsed Doppler Flowmeter, Department of Bioengineering, University of Iowa, Iowa City, Iowa). The pacing electrodes were attached to a trigger unit (Department of Bioengineering, University of Nijmegen, The Netherlands) and the occluder tube was connected to a 5-ml syringe. Both femoral arteries were dissected free. An 8F pigtail manometer catheter (Millar microtipped-catheter transducer SPC-780C) was introduced into the left femoral artery and positioned for simultaneous pressure recording in the left ventricle and the ascending aorta. A 5F left Judkins catheter was introduced into the right femoral artery and advanced into the ostium of the left main coronary artery. Electrocardiogram, left ventricular pressure and its first derivative, aortic pressure, and phasic and mean coronary blood flow velocity in the LCx were recorded on an eightchannel recorder (Hewlett-Packard).After intravenous infusion of 5 mg propranolol during 20 minutes to prevent disproportionate increase in heart rate, an initial dose of dipyridamole (0.75 mg/kg) was administered intravenously during 4 minutes to create maximal dilation ...
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