Abnormal chest radiographs preceding VQ scans: Does the type of abnormality matter?

Introduction: Abnormal chest radiographs (CXR) have been considered to affect the interpretation of Ventilation/Perfusion scans (V/Q) for the investigation of suspected Pulmonary Embolism (PE). Recommendations suggest a V/Q scan only if a contemporaneous CXR is normal. Impact of individual CXR abnormalities on the outcome of V/Q scan has not been fully explored. Aim: To study the impact of individual CXR abnormalities suggestive of a range of cardiopulmonary diseases on V/Q scan results for the investigation of suspected PE. Method: All V/Q scan and preceding CXR reports from February '08-January '09 at our 960 bed teaching hospital were included in the study. Results: Data for a total of 1041 subjects who had a CXR prior to V/Q was collected. Total number of V/Q done on those with abnormal CXR findings was 345. The CXR abnormalities were classified as per the underlying cardiopulmonary pathology suggested by the report. Table 1 Low probability V/Q Intermediate probability V/Q High probability V/Q Total Normal CXR-Number (%) 590 (85%) 41 (6%) 65 (9%) 696 COPD-Number (%) 55 (81%) 2 (3%) 11 (16%) 68 Atelectasis-Number (%) 34 (71%) 5 (10%) 9 (19%) 48 Effusion-Number (%) 57 (79%) 9 (13%) 6 (8%) 72 Pulmonary Oedema-Number (%) 35 (95%) 2 (5%) 0 (0%) 37 Infection-Number (%) 57 (80%) 7 (10%) 7 (10%) 71 Discussion: Regardless of whether the CXR report preceding the VQ scan was suggestive of infection, effusion, congestion or “COPD”, the proportion of low probability VQ scans was high (71-95%). This proportion was particularly high at 95% (and with no high probability scans) in those with CXRs suggestive of pulmonary oedema/congestion. When used in the correct clinical context a V/Q scan can be used with a high degree of accuracy despite certain CXR abnormalities.