Tissue Plasminogen Activator for the Treatment of Acute Pulmonary Embolism: VentUation/Berfusion Scans

21 Apr

VentUation/Berfusion Scans

Ventilation scans and perfusion scans (V/Q scans), as well as plain chest roentgenograms were obtained before the pulmonary arteri­ogram, perfusion scans were performed again after double-blind treatment at intervals of 24 hours, 48 hours, and 7 days. All V/Q scans were obtained with wide field-of-view gamma cameras (di­ameter 38.1 cm) fitted with low-energy all-purpose collimators. Perfusion scans were obtained following the injection of 4 mCi of •Тс macroaggregated albumin. Eight images were made with the patient in the anterior, posterior, anterior oblique, posterior oblique, and lateral positions. Seven hundred and fifty thousand counts were obtained for each image except for the laterals which were made with 500,000 counts for the initial lateral, with the other lateral image obtained over the same amount of time.

Perfusion scans were graded by two readers who evaluated the perfusion defects without knowledge of therapy. Baseline mis­matched perfusion defects (defects not associated with radiographic or ventilation abnormalities) were assessed as follows: Each segment of the lung was assumed to constitute 11 percent of the involved lung. The number of mismatched segments in each lung, therefore, was multiplied by 11 percent to determine the percentage of the involved lung that showed a mismatched perfusion defect. In this series, no patient had a new significant consolidation of the lung during the course of the 7 days of follow-up V/Q studies.

Hemodynamic Measurrrtwnts

Pressures in the right atrium, right ventricle, and pulmonary artery were measured in triplicate with fluid-filled catheters prior to the injection of contrast material. Cardiac output was measured in triplicate by the indicator dilution technique. Total pulmonary resistance (dynes’s’cm) was calculated as the fraction of pulmonary arterial mean pressure (mm Hg) divided by cardiac output (L/min) times 80. Hemodynamic measurements were repeated 90 minutes after the onset of therapy (which was 30 minutes before the repeat pulmonary arteriogram). The heart rate, respirator) rate, and blood pressure were recorded during these intervals as well as after 24 hours, 48 hours, and 7 days.
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Coagulation Studies

Fragment-D dimers were measured prior to thrombolytic therapy and after therapy at intervals of 90 minutes, 3 hours, 24 hours, and 7 days. Fragment-D dimer was measured by an agglutination assay using a monoclonal antibody covalently coupled to latex beads. Fibrinogen was measured using the method of Clauss. Aprotinin was added to the collection tubes to counteract proteolysis generated by plasm in in vitro.

Statistical Methods

Study data were analyzed with methods for continuous variables, presented as means and standard deviations. Comparisons were made between two treatment groups using unpaired Student’s f- tests with the exception of total pulmonary resistance which was compared using repeated measures analysis of variance. The analysis of variance was based upon measurement variation esti­mated from triplicate measurements. Because of an expected greater variability in response to therapy among patients treated with rt- PA than among patients treated with heparin alone, the study was designed from its inception to assign twice as many patients to treatment with rt-PA than to treatment with heparin alone. As a consequence of an early termination of the study due to slow recruitment, the number of patients in each treatment group would allow detection of differences in means of 1.68 standard deviations with 80 percent power when testing at the 5 percent (two-tailed) level.