Citations

The square-wave electromagnetic flowmeter was used to assess the upstream sampling dye-dilution technic for quantitating aortic regurgitation by simultaneous determinations of the regurgitant fraction by flowmeter, as given by the ratio of regurgitant volume to total stroke volume (RV/TSV) and the identical ratio of regurgitant flow to total forward flow (Q R /Q F ), and the regurgitant fraction by dye curve, as given by the ratio of the areas of the immediately appearing portion of the left ventricular curve to the area of the femoral artery dye curve (LV A /FA A ), after injection of indicator approximately 1 cm downstream to the aortic valve. A good correlation (r = 0.91) was found between these two independent methods which can be represented by the regression equation Q R /Q F = 0.82 (LV A /FA A ). This correlation indicates that the concept that the regurgitant fraction of indicator (LV A /FA A ) is proportionate to the regurgitant fraction of blood (RV/TSV) is valid. The observed systematic difference between flow-meter and dye-curve regurgitant fractions may be due to the fact that time-average rather than volume-average concentrations of the indicator are obtained by sampling of blood through eatheters. Two different and independent calibration technics were used to establish a calibration factor for converting recorded flowmeter deflections to volumetric units for measurement of rates and volumes of blood flow in the ascending aorta. The first technic involved simultaneous recording of dye-dilution curves and velocity pulses in the ascending aorta by the flowmeter before the production of aortic regurgitation. The second involved bidirectional perfusion of the isolated aorta at known rates of blood flow with simultaneous flowmeter recordings at the termination of each experiment. The data obtained validated the use of the flowmeter for measurements of total stroke volume and regurgitant stroke volume. The close correspondence between flowmeter recordings of the regurgitant flow and hydraulic estimates of regurgitant flow, based on the size of the defect in the aortic valve measured at necropsy and continuous records of the pressure gradient across the valve, also lent strong support to the validity of these measurements. The relationship Q R = Q S (Q R /Q F )/(1 - Q R /Q F ) can be used to estimate regurgitant flow from values of the regurgitant fraction (Q R /Q F ) and the systemic flow (Q S ). The mathematical relationship of the regurgitant fraction to regurgitant flow, determined by the dilution-curve technic, plus the variability obtained between simultaneous flowmeter and dilution-curve estimates of regurgitation, indicate that the error in the estimation of regurgitant flow by the dye-dilution technic is least for small-to-moderate degrees of regurgitation and increases progressively with the severe degrees of regurgitation associated with regurgitant fractions of greater than 0.6. On the basis of 231 simultaneous determinations by the indicator-dilution and flowmeter technics carried out in nine dogs, and assuming that the flowmeter values were uniformly correct, it was estimated that the standard deviation of the errors in measurement of regurgitant flow by the upstream sampling dye-dilution method in these experiments was 0.15 L per minute for regurgitant fractions below 0.6. and that this variability increased so that the standard deviation was 1.3 L per minute at regurgitant fraction levels of 0.9 to 1.0. The results of determinations carried out over a range of heart rates from 39 to 216 beats per minute indicate that the indicator-dilution method is applicable over a wide range of heart rates. The observed changes in aortic regurgitation with variation in heart rate correlated closely with the changes estimated by hydraulic equations based on the hydrodynamics of steady flow through an orifice. The increase in regurgitant stroke volume with increased duration of diastole at slow heart rates was disproportionately greater than the increase in total stroke volume, so that the effective forward (systemic) flow fell to extremely low levels at slow heart rates, particularly in dogs with large defects in the aortic valve. The applicability of the upstream sampling indicator-dilution technic to the detection and estimation of the severity of aortic regurgitation in human beings merits further study.

In dogs studied without thoracotomy the detection of immediately appearing indicator in the left ventricle following its injection approximately 1 cm downstream from the aortic valve can be used as a reliable index of the presence or absence of aortic regurgitation. With this type of injection and under the conditions of these experiments, the ratio of the area encompassed by the immediately appearing portion of the dilution curve recorded from the left ventricle to the area encompassed by the primary portion of the curve recorded at the femoral artery bears a close positive correlation (correlation coefficient: 0.9) to the severity of aortic regurgitation as estimated by back perfusion of the valve at necropsy. Within limitations, the position of the tip of the sampling catheter in the left ventricle in dogs with aortic regurgitation is not an important determinant of the amount of immediately appearing indicator detected in this chamber. Furthermore, although the amount of indicator detected in the left ventricle following injections of very short duration is time-dependent, if the duration of the injection is extended to cover the full systolic or diastolic phase of one heartbeat or continues over one or more heartbeats, the exact timing of this injection in relation to the cardiac cycle is not an important determinant of this variable. It is concluded that under these conditions the positive correlation established between the amount of immediately appearing dye detected in the left ventricle (expressed as the regurgitant fraction) and the severity of aortic regurgitation determined by back perfusion at necropsy can be used as a valid means of estimating the severity of aoritic regurgitation in dogs. The applicability of this indicator-dilution method to the study of clinical aortic reguragitation merits further study.

In summarizing the diagnostic value of the indicator-dilution technics in the study and investigation of congenital heart disease, perhaps a simple listing of the advantages and disadvantages of the technics will suffice. The advantages are as follows: 1. The technics have a high degree of safety. In the more than 3000 cardiac patients in whom they have been utilized there have been no deaths and little or no morbidity. 2. The sensitivity of the technics for the detection and localization of right-to-left and left-to-right shunts is much superior to that of the conventional blood-gas methods. 3. Quantitative determinations of systemic and pulmonary blood flow and intrathoracic shunts by indicator-dilution methods can be made simultaneously over periods of less than 1 minute; when indicator dyes are used, these technics do not require manometrie analyses, accessory respiratory exchange studies, or active cooperation of the patient; and they are independent of foreign (anesthetic) gases in the blood. 4. The technics are versatile and can be extremely useful either for the detection and diagnosis of minimal, relatively simple defects or for the elucidation of the extremely complex types of congenital malformations. 5. The information obtained is of both a qualitative and a quantitative nature; that is, the nature and location of defects can be determined and, in addition, the magnitude and direction of flow through the defects in question as well as the levels of systemic and pulmonary blood flows can be estimated. The disadvantages of the technics are as follows: 1. Rather complicated and sensitive recording equipment is essential. 2. Considerable technical skill is required of the persons carrying out the procedure in the placement of the necessary needles and catheters and in the proper selection of the multiple possible injection and sampling sites reached by these instruments in order to obtain the information needed to establish the diagnosis in question. 3. Correct interpretation of the diagnostic significance of the dilution curves obtained requires careful study and considerable experience by the person responsible for this phase of the investigation. In other words, these technics entail relatively little discomfort and little danger for the patient, but require good equipment and, more important, considerable time, effort and skill on the part of the investigator and his assistants in order to obtain highly successful results.

The effects of passive tilting on the circulatory pressures and on the magnitude of shunts across chronic atrial septal defects were studied in 11 dogs with closed chests. These determinations were performed with the dogs in four positions: 45-degree head-up, 45-degree head-down, right lateral decubitus, and left lateral decubitus. Control values were obtained with the animals in the supine horizontal position. The 45-degree head-up tilt position was associated with an increase in the magnitude of the right-to-left shunt detected after injections of indicator into the inferior vena cava, while change from supine to the 45-degree head-down tilt resulted in a decrease or disappearance of a pre-existing right-to-left shunt detected after similar injections. These effects on the right-to-left shunt were not demonstrable after injections of indicator into the superior vena cava, either during the head-up or head-down tilt, in spite of identical alterations in circulatory pressures. A significant interanimal correlation between the magnitude of the changes in systemic or right atrial pressures and the magnitude of the changes in right-to-left shunts could not be demonstrated. Passive changes in posture from supine to 45-degree head-up or head-down positions were not associated with demonstrable systematic effects on the magnitude of the left-to-right shunts. It is postulated that the descent of the heart and diaphragm during the head-up tilt results in a closer anatomical relation between the ostium of the inferior vena cava and the defect in the atrial septum and consequently an increase in the preferential shunting of inferior caval blood through this defect. In these animals, changing the body position from the supine to the right lateral decubitus position was consistently associated with an increase in the magnitude of the left-to-right shunts across the atrial septal defect and an increase in pulmonary blood flow. Since these animals have preferential shunting of blood from the right lung in the left-to-right direction, it is believed that the increase in blood flow through the dependent right lung is responsible for the observed increase in the left-to-right shunt. The left lateral decubitus position was not associated with appreciable effects on pulmonary blood flow or left-to-right shunting of blood across the atrial septal defect.

Some of the factors that influence the contours and time components of indicator-dilution curves have been examined in dogs and man. These include the dynamic-response characteristics of the sampling-detecting-recording system, variations in the sampling site, quantity of blood and rate of blood flow between injection and sampling sites, vascular obstruction, and local and general alterations in peripheral blood flow. Any or all of these factors may be of importance in the interpretation of changes in indicator-dilution curves in patients with congenital or acquired heart disease.

Background —Although 30-day survival is increased in patients with acute myocardial infarction complicated by cardiogenic shock who undergo coronary revascularization, the longer-term outcome in such patients and the duration of benefit from revascularization are unknown. Methods and Results —We analyzed 30-day survivors of acute myocardial infarction in the Global Utilization of Streptokinase and Tissue-Plasminogen Activator for Occluded Coronary Arteries (GUSTO-I) trial and identified 36 333 who had not had cardiogenic shock (systolic blood pressure <90 mm Hg for ≥1 hour, group 1) and 1321 patients who had shock (group 2). Group 2 patients were older and sicker. At 1 year, 97.4% of group 1 patients were alive versus 88.0% of group 2 ( P =0.0001). Among group 2 patients, 578 (44%) had undergone revascularization within 30 days (group 2A) and 728 (56%) had not (group 2B). Revascularization was not required by protocol but was selected by the attending physicians. At 1 year, 91.7% of group 2A patients were alive versus 85.3% of group 2B ( P =0.0003). With the use of multivariable logistic regression analysis to adjust for differences in baseline characteristics of shock patients alive at 30 days, revascularization within 30 days was independently associated with reduced 1-year mortality (odds ratio 0.6, [95% confidence interval 0.4, 0.9], P =0.007). Conclusions —Most patients (88%) with acute myocardial infarction complicated by cardiogenic shock who are alive at 30 days survived at least 1 year. Shock patients who underwent revascularization within 30 days had improved survival at 1 year compared with shock patients who did not receive revascularization, even after adjustment for differences in baseline characteristics between the 2 groups.

Background —In patients receiving intracoronary stents, stent thrombosis is reduced when ticlopidine therapy is combined with aspirin after the procedure. However, ticlopidine causes neutropenia in 1% of patients when administered for >2 weeks, and little is known about the duration that ticlopidine needs be administered to prevent stent thrombosis. Methods and Results —We analyzed 827 patients undergoing successful stent placement in 1061 coronary segments at Mayo Clinic who were treated between May 1, 1996, and October 31, 1997. Chronic warfarin therapy, cardiogenic shock, and enrollment in research protocols requiring 4 weeks of ticlopidine were exclusion criteria; ticlopidine was discontinued after 14 days in all remaining patients. The mean age of the study population was 64±11 years; 49% had suffered a prior infarction, 20% had undergone coronary artery bypass surgery, and 65% had multivessel disease. The indication for stent placement was dissection or abrupt closure in 31% of patients and suboptimal results from balloon angioplasty in 18%. Placement was elective in 51% of patients, and 10.3% of patients were treated within 12 hours of an acute myocardial infarction. Mean nominal stent size was 3.3±0.5 mm. High-pressure inflations (≥12 atm) were performed in all patients (mean, 17±4 atm). Intravascular ultrasound was used to facilitate stent placement in 8.8% of patients. Abciximab was administered to 38% of patients; 11% of patients who were at increased risk of stent thrombosis were treated with enoxaparin for 10 to 14 days. Adverse cardiovascular events in the 14 days after stent placement occurred in 11 patients (1.3%). Two patients died of nonischemic causes (sepsis and renal failure) in the 15th through 30th days after ticlopidine was stopped. However, there were no cardiovascular deaths, myocardial infarctions, coronary artery bypass operations, or repeat angioplasty procedures between the 15th and 30th days; stent thrombosis did not occur in any patient after ticlopidine had been stopped. No patient developed neutropenia, although 1.8% of the first 489 patients who were closely monitored for side effects from ticlopidine developed side effects requiring its discontinuation, and milder side effects occurred in 4.7%. Conclusions —In patients receiving intracoronary stents, the discontinuation of ticlopidine therapy 14 days after stent placement is associated with a very low frequency of stent thrombosis and other adverse events.