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This study compares the ability of 3 thrombolytic drugs to promote clot lysis using a new in vitro testing procedure. Whole blood samples from 132 patients were tested using 5 different concentrations of tissue-type plasminogen activator (t-PA), streptokinase (SK) and urokinase. A mixture of blood and thrombolytic drug was placed on a dryreagent test card containing reptilase, buffers and paramagnetic particles where clot formation occurred. Analysis of the motion of the clot-embedded paramagnetic particles caused by an oscillating magnetic field was used to define the lysis onset time. The slope of the linear regression plot of lysis onset time versus 1/[drug concentration] defined the kinetic rate constant (k) for each drug in each patient. Higher values of k indicated greater resistance to in vitro clot lysis. In the patients studied, there was a large range of k values for t-PA and SK (coefficient of variation 143 and 137%, respectively) but a smaller range of k for urokinase coefficient of variation 32%). The coefficients of variation for t-PA and SK observed in the study group were five- to 10-fold greater than the coefficients of variation determined for replicate test measurements. Resistance to all SK concentrations tested was found in 9% of the patients. in vitro sensitivity to thrombolysis was compared among the drugs by correlating the derived k values. These comparisons indicated no relation for any of the drugs; many patients had a relatively low k value for 1 drug, while having a relatively high k value for a different drug. Preliminary results in 6 patients with acute myocardial infarction tested prospectively with a clinical version of this system identified 1 patient in whom there likely was a failure of the thrombolytic drug. These data suggest that in vitro testing before the administration of a thrombolytic drug is feasible and may be clinically useful in determining the drug choice for an individual patient. (Am J Cardiol 1994;73:544-549)

Although the biplane area-length method would be optimal for all left ventriculograms, 2 contrast injections are needed in laboratories with single-plane imaging equipment. The purpose of this study was to develop practical guidelines to identify the need for biplane left ventriculography in laboratories with single-plane equipment. From a retrospective analysis of 91 consecutive biplane ventriculograms (group 1), guidelines were identified that predicted when the ejection fraction calculated by the biplane method would differ significantly from the single-plane value. These guidelines were derived from information immediately available to the operator in the laboratory at the time of the procedure. Patients in group 1 were divided into 3 subgroups: biplane exceeding single-plane ejection fraction by [is greater than or equal to] 0.05 (n = 20); single-plane exceeding biplane election fraction by [is greater than or equal to] 0.05 (n = 14); and ejection fractions within [+ or -] 0.04 by the 2 methods (n = 57). By multivariate analysis, the only predictor of a higher ejection fraction calculated by the biplane method was an anterior wall motion abnormality. This finding was tested prospectively in a separate group of 60 patients (group 2). Left ventriculograms in group 2 patients were stratified before analysis by the presence or absence of an anterior wall motion abnormality. in patients with anterior wall motion abnormalities, the biplane ejection fraction was greater than the single-plane value by 0.05 [+ or -] 0.04 (range -0.03 to +0.15). In contrast, this difference in patients without anterior wall motion abnormalities was -0.01 [+ or -] 0.04 (range -0.09 to +0.06; p

Inferior ST-segment elevation during anterior wall acute myocardial infarction (AMI) due to left anterior descending (LAD) coronary artery occlusion is unusual and was not previously investigated. This study tested the hypothesis that inferior ST-segment elevation during anterior AMI predicts a specific angiographic morphology that satisfies 2 necessary conditions: (1) mass of ischemic anterior wall myocardium is relatively small, resulting in a weaker anterior injury current and less reciprocal inferior ST-segment depression; and (2) there is concomitant inferior wall transmural ischemia that further shifts the inferior ST segments upward. The study group consisted of 42 consecutive patients with anterior AMI undergoing angiography at 4.1 days (range 0 to 14). Coronary angiograms were examined for 3 features: (1) site of LAD artery occlusion (a distal obstruction implying a smaller mass of ischemic anterior wall myocardium), (2) LAD artery extension onto inferior wall of left ventricle (termed a 'wrap around' vessel), and (3) collateral flow from LAD artery to inferior wall. The latter 2 features would be expected to contribute to inferior wall transmural ischemia. Acute inferior ST-segment elevation (sum of ST-segment deviation in leads II, III and aVF [is greater than or equal to] 3.0 mm) was seen in 7 patients (16%). A greater number of LAD artery branches proximal to the site of occlusion was significantly correlated with less inferior ST-segment depression (r = 0.59, p

Single-photon emission computed tomography (SPECT) is an imaging technique in which radioactive molecules in the body emit gamma rays, which are recorded by a moving camera. The information about the arrival of the gamma rays may be used to compute a three-dimensional image of the distribution of the radioactive material within the body. In addition to potentially useful information, the technique has also revealed the existence of unsuspected physiological phenomena whose relevance is not certain. The radioactive substance thallium-201 has been used to monitor the flow of blood in the coronary artery both at rest and after exercise stress. For those patients who cannot exercise, dipyridamole can be injected to reveal a similar picture. The perfusion of areas normally at rest may become temporarily inadequate. However, in 5 to 21 percent of patients, this temporary inadequacy of perfusion shows up only after hours have elapsed, a phenomenon that has been termed reverse redistribution. This reverse redistribution has been associated with coronary artery disease by some researchers, while others have failed to identify a connection. To determine the incidence and importance of reverse redistribution, 90 men with angina pectoris, chest pain indicative of reduced blood flow to the heart, consented to be examined using SPECT imaging after vasodilation with dipyridamole. Images were taken immediately after infusion and four hours later. The patients were also analyzed by angiography, and the quantitative results on artery conditions as determined by angiography (X-ray) were compared with the observed patterns of perfusion on SPECT. In addition, 11 apparently normal volunteers agreed to be subjected to SPECT to serve as control subjects. Reverse redistribution occurred in 2 of 33 segments observed in normal individuals. Among the patients, the occurrence of reverse redistribution was independent of the dimensions of the coronary artery and the degree of arterial occlusion (stenosis). The areas of reverse redistribution were found to have larger proximal diameters. The results indicate that the presence of reverse redistribution is unrelated to the presence of severe coronary artery disease. (Consumer Summary produced by Reliance Medical Information, Inc.)

Several techniques exist for the quantification of absolute coronary artery diameters using radiologic methods. An in vivo assessment of a quantitative technique based on direct digitally acquired images was performed by imaging inflated angioplasty balloons (n = 25), balloon catheter shafts (n = 16) and coronary guidewires (n = 20) at the time of coronary angioplasty. After this, the actual size of the objects was determined with a micrometer. Diameters measured by the quantitative digital method had an excellent correlation with the actual diameters (digital diameter = 0.80 [actual diameter] + 0.32; n = 61; r = 0.97; standard error of the estimate = 0.26 mm; p 1 mm were usually underestimate by the digital technique, although the actual magnitude of the error was small. Objects 1 mm were underestimated by 0.23 [+ or -] 0.19 mm. Based on an analysis of the error present, correction algorithms were formulated and tested prospectively using an additional 29 object measurements. This resulted in an improvement in the quantification of the diameters with a smaller magnitude of error. This in vivo assessment suggests that the rapid on-line assessment of absolute coronary artery diameters is possible, but also demonstrates important errors inherent in this method. (Am J Cardiol 1989;64:131-138)

Cardiac output (CO) is a measure of the volume of blood that the heart pumps per minute, evenly split between blood pumped to the lungs for oxygenation and systemic circulation. Accurate measurement of cardiac output is important for assessing the health of the cardiovascular system. The conventional CO measurement is indirectly measured by measuring oxygen consumption and the difference in oxygen concentration between arterial and venous blood. The patient exhales into a 'Douglas' bag and the oxygen concentration in this volume of exhaled air is measured. The method is fraught with difficulties and accurate measurements can only be achieved with careful attention to technical details. A newer and simpler method of measuring oxygen consumption involves the MRM-2, an electrical oxygen consumption meter produced by Waters Instruments. The device has recently been introduced as a replacement for the Douglas bag. The efficiency of the MRM-2 for measuring CO was assessed. Experimentation has shown that the MRM-2 values for oxygen consumption are consistently lower than those determined by the use of a Douglas bag. Thus the device is, despite its widespread use, less accurate.