Before each injection, a system test was carried out in order to adjust the kilovolt (peak) for 100 percent quality; the intensity of current was automatically adjusted. Images were recorded with 50±3 (SD) kVp and 112±2 (SD) mA. Focal spot size was 0.6 mm; dose, 18 jiR per frame; image intensifier field size, 6 indies; spatial resolution, 64 line pairs/cm; brightness conversion factor, 103 candelas-sq m~KmR. The actual magnification, evaluated from the size of the intracoronary catheter tip in all dogs, was 2.3 ±0.1 (SD) times.
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The Role of Coronary Arteriography in Demonstration of Mural Thrombosis after Angioplasty (3)
The Role of Coronary Arteriography in Demonstration of Mural Thrombosis after Angioplasty (2)
Protocol
A 5F or 7F Sones catheter (USCI Division, CR Bard Inc, Billerica, Mass) was advanced through the left carotid artery into the left anterior descending coronary artery (LAD). A steerable guide wire (USCI) was then advanced under fluoroscopy through the Sones catheter into the proximal LAD. The Sones catheter was then removed, and a Gruentzig catheter (USCI; balloon size, 25.0 mm in length and 3.0 mm in diameter) was advanced over the guide wire into the LAD, as distally as possible. Angioplasty was performed with four balloon insufflations, 30 s each, with a 60-s interval; the first two were at 10 atm, and the last two were at 8 atm. The Sones catheter was then placed again into the proximal LAD and was flushed continuously with 0.9 percent NaCl solution, 0.3 ml/min, with heparin, 10 IU/ml. Arteriograms were obtained at 5, 15, 30, 60, and 120 min after angioplasty. Immediately after the last arteriogram, the dogs were killed with pentobarbital and KC1.
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The Role of Coronary Arteriography in Demonstration of Mural Thrombosis after Angioplasty (1)
Thrombosis has been recognized as an important component of vascular response to coronary angioplasty, since it underlies acute complications and can contribute to late restenosis. Recognition of intracoronary thrombi may have significant consequences in patient management. The accuracy of arteriography for demonstration of intracoronary thrombi after angioplasty is unclear. Early studies indicated a high sensitivity for arteriography in demonstration of occlusive thrombosis in acute myocardial infarction. However, later reports showed little sensitivity for this method in detection of nonocclusive thrombi in unstable angina, as compared with angios-copy. The specificity of arteriography is also not defined. After angioplasty, the discrepancy between the high incidence of thrombosis in experimental models and the observed low clinical incidence of arteriographic thrombosis suggests poor sensitivity of arteriography. Initial angioscopic and intravascular ultrasound studies in man are also consistent with this idea. However, the extent of arteriographic inaccuracy, as well as possible factors influencing thrombus demonstration, are unknown.
In order to gain insight into these questions, we analyzed the relationship between coronary arteriographic abnormalities immediately before death and the histologic extent of mural thrombosis in dogs submitted to balloon dilation of intact coronary arteries.
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (23)
Without clinical studies to establish acceptable levels of agreement between PA oximetry catheters and bench oximeters, no true statistical conclusions can be drawn regarding the clinical performance of these devices; however, the lack of agreement with manufacturers’ published specifications (± 2 percent compared with CO-oximetry) demonstrated herein and the wide 95 percent confidence limits for total variability indicate that these devices are probably most useful as trend indicators. Determination of a patient’s actual Sv02 requires the use of a conventional bench oximeter such as a CO-oximeter.
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (22)
Because therapy may be either instituted or withheld on the basis of information obtained from this type of monitor, it is essential to understand the performance characteristics of available systems. The overall performance of Oximetrix 3 and SAT-2 compared with CO-oximetry was nearly identical (Table 4). Differences in performance of oximetry PA catheter systems, therefore, do not appear to be caused by inherent limitations of two-wavelength systems as previously thought. Regression analysis and correlation coefficients for Oximetrix 3 and SAT-2 are similar. Bias and precision are also quite similar in magnitude; however, there is a directional difference in bias between the Oximetrix 3 group (negative bias) and the SAT-2 group (positive bias). While a similar correlation coefficient and bias were obtained in the HEM0PR02 group, precision appears worse. Both ambiguity and RMSE have been proposed as global indicators of performance relative to a criterion standard. The Oximetrix 3 group and SAT-2 group have virtually identical ambiguity (5.05 vs 5.29) and RMSE values (3.64 vs 3.92). The performance achieved by the HEM0PR02 group is apparently worse when compared by these two tests (ambiguity = 7.52, RMSE = 5.71).
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (21)
The square root of the average intrapatient variance, referred to here as ESD, is a measure of reproducibility within a given patient. As shown in Figure 3, the intrapatient reproducibility of in vivo vs in vitro Sv02 is better than would be expected if one looked only at the precision for the entire group (see Table 4). The comparison of ESD of the three systems shows better intrapatient reproducibility than would be expected from group performance. Clinically, therefore, if in vivo Sv02 is to be used only as a trending monitor, each of these in vivo systems might be expected to perform similarly.
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (20)
Thus, a decline in the oximeter system reading from 70 percent to 64 percent likely represents an actual change in the patients condition. It does not predict the actual value of the patients Sv02.
The assessment of agreement between clinical measurements may also be influenced by the passage of time. Previous studies have demonstrated that the performance of in vivo oximetry systems may deteriorate with the passage of time. During our 24-h study period, there was no statistically significant change in the bias observed in either Oximetrix 3 or SAT-2. The HEM0PR02 group did exhibit a significant (p<0.05) change in bias over the course of the study, paradoxically showing improved performance as the study progressed (Fig 2).
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (19)
Large random measurement errors (differences between in vivo and in vitro SvOJ resulting in wide 95 percent confidence intervals cannot be corrected by simple software manipulation. We have presented both 95 percent confidence limits for both total variability and intrasubject variability. The 95 percent confidence interval based on total variability defines the limits of agreement present in circumstances when oximetry PA catheters are used to guide therapeutic interventions when the goal is to identify the patients actual Sv02.
A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (18)
Despite the limitations noted, there are differences in the performance of the three systems. The difference plots of in vivo vs in vitro Sv02 (Fig 1) demonstrate that both Oximetrix 3 and SAT-2 have a systematic error or inaccuracy (bias) that is consistent. The Oximetrix 3 group consistently underestimated in vitro SvOa by approximately two percentage units (bias =—1.98 percent saturation), while the SAT-2 group consistently overestimated in vitro Sv02 (bias= +1.80 percent saturation). The respective underestimation and overestimation within these two groups were constant over the range of values tested. The HEM0PR02 group also demonstrated an overall tendency to underestimate in vitro Sv02 (bias = – 2.28 percent saturation); however, this systematic error was not constant over the range of values tested. The bias demonstrated by the HEM0PR02 group appears proportional to the value tested, ranging from nearly — 5 percent saturation at low target Sv02 values (40 percent to 50 percent) to approximately — 1 percent at the higher target saturation values (80 percent to 90 percent).
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A Comparison of Three Pulmonary Artery Oximetry Catheters in Intensive Care Unit Patients (17)
Thus, it is more appropriate to test a null hypothesis of difference, with an alternative hypothesis of similarity. When this more direct null hypothesis is rejected, we conclude that the measures are similar with high probability. The second approach presented herein uses a null hypothesis that each catheter (in vivo) mean differs from CO-oximetry (in vitro) by more than 2 percent of the in vitro mean. The corresponding alternative hypothesis states that the measures are similar within these limits. These tests for equality require that the level of agreement to be considered as “equality” be established before statistical testing. No data in the literature establish an acceptable level of agreement between PA oximetry catheters and bench oximeters. Consequently, we are unable to test whether the performance of catheters in question differs significantly from bench oximetry clinically. However, the performance of these devices does not match, with high probability, the performance specifications published by their respective manufacturers.
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