STRATIFICATION OF PATIENTS ACCORDING TO PRIOR CARDIOPULMONARY DISEASEAND PROBABILITY ASSESSMENT BASED ON THE NUMBER OF MISMATCHED SEGMENTAL EQUIVALENT PERFUSION DEFECTS - APPROACHES TO STRENGTHEN THE DIAGNOSTIC-VALUE OF VENTILATION-PERFUSION LUNG SCANS IN ACUTE PULMONARY-EMBOLISM

A categorical diagnosis of ''high probability'' or ''intermediate prob ability'' encompasses a spectrum of diagnostic probabilities of pulmon ary embolism (PE) that is not communicated to the referring physician. The diagnostic value of ventilation/perfusion lung scans, in the pres ent investigation, was strengthened by use of a table to determine the likelihood of PE in individual patients on the basis of the observed number of mismatched segmental equivalent perfusion defects. In additi on, we tested the hypothesis that stratification of patients according to the presence or absence of prior cardiopulmonary disease may enhan ce the ventilation/perfusion scan assessment of the probability of PE among both of these clinical categories of patients. Data were derived from the collaborative study of the Prospective Investigation of Pulm onary Embolism Diagnosis (PIOPED). Ventilation/perfusion lung scans we re evaluated in 378 patients with acute PE and 672 patients in whom su spected PE was excluded. Among patients with no prior cardiopulmonary disease, -1.0 mismatched segmental equivalents was indicative of PE in 102 of 118 (86 percent) vs 113 of 155 (73 percent) among patients wit h prior cardiopulmonary disease (p<0.02). Among patients with prior ca rdiopulmonary disease, greater-than-or-equal-to 2 mismatched segmental equivalents were required to indicate greater-than-or-equal-to 80 per cent probability of PE. Stratification on the basis of the presence or absence of prior cardiopulmonary disease, therefore, enhanced the abi lity of ventilation/perfusion scan readers to assign an accurate posit ive predictive value and specificity to individual patients based on t he observed number of mismatched segmental equivalent defects. Among p atients with no prior cardiopulmonary disease, fewer mismatched segmen tal equivalent defects were required to indicate a high probability of PE than were required by PIOPED criteria. The findings from some of t hese patients, by PIOPED criteria, would have indicated intermediate p robability. Some indeterminate probability readings, therefore, will b e eliminated among patients stratified with no prior cardiopulmonary d isease.