Pulmonary embolism

Pulmonary embolism is a common medical problem whose incidence is likely to increase in our aging population. Although it is life-threatening, effective therapy exists. The treatment is not, however, without significant complications. Thus, accurate diagnosis is important. Unfortunately, the clinical manifestations of pulmonary embolism are nonspecific. Furthermore, in many patients the symptoms of an acute embolism are superimposed on underlying chronic heart or lung disease. Thus, a high index of suspicion is needed to identify pulmonary emboli. Laboratory parameters, including arterial oxygen tensions and electrocardiography, are as nonspecific as the clinical signs. They may be more useful in excluding another process than in diagnosing pulmonary embolism. The first radiologic examination is the chest radiograph, but the clinical symptoms are frequently out of proportion to the findings on the chest films. Classic manifestations of pulmonary embolism on the chest radiograph include a wedge-shaped peripheral opacity and a segmental or lobar diminution in vascularity with prominent central arteries. However, these findings are not commonly seen and, even when present, are not specific. Even less specific findings include cardiomegaly, pulmonary infiltrate, elevation of a hemidiaphragm, and pleural effusion. Many patients with pulmonary embolism may have a normal chest radiograph. The chest radiograph is essential, however, for two purposes. First, it may identify another cause of the patient's symptoms, such as a rib fracture, dissecting aortic aneurysm, or pneumothorax. Second, a chest radiograph is essential to interpretation of the radionuclide V/Q scan. The perfusion scan accurately reflects the perfusion of the lung. However, a perfusion defect may result from a variety of etiologies. Any process such as vascular stenosis or compression by tumor may restrict blood flow. In addition, areas of the lung that are not well ventilated will be poorly perfused. Thus, a ventilation scan and a chest radiograph are essential to optimal interpretation of the perfusion scan. Ventilation/perfusion scans are interpreted as degrees of probability of pulmonary embolism. Emboli are not present in patients with a normal V/Q scan. An embolus is unlikely (10%-15%) among patients with a low-probability V/Q scan. However, small emboli that are nonocclusive may be present, and pulmonary arteriography may be used to further evaluate patients with a high clinical suspicion of pulmonary embolus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Acute pulmonary embolus mimicked on V/Q scan by sarcoidosis

Acute pulmonary embolus is a common problem requiring evaluation in the emergency setting. Following the initial chest radiograph, the most common imaging test requested is the ventilation perfusion lung scan. We describe a patient with sarcoidosis and a false positive ventilation perfusion lung scan caused by bilateral hilar adenopathy compressing the proximal pulmonary arteries. This case illustrates that patients with hilar adenopathy and suspected pulmonary embolus may have unreliable ventilation perfusion scans, and should be referred to arteriography or CT for evaluation, rather than for a ventilation perfusion lung scan.     

Pulmonary embolism with unilateral lung scan defects and matching infiltrates.

Ten patients with matching ventilation-perfusion lung scan defects and corresponding pulmonary infiltrates were evaluated with segmental pulmonary angiography. All ten patients presented with sudden onset of pleuritic chest pain and fever. Pulmonary emboli were documented in three of the ten patients (30%). The remaining seven patients had pneumonia or atelectasis. The findings emphasize the non-diagnostic nature of lung scans which show only matching ventilation and perfusion defects in regions of pulmonary infiltrates. Segmental pulmonary angiography is recommended for differentiating pulmonary embolism from atelectasis or pneumonia in these patients.     

Ventilation-perfusion lung scan for the detection of pulmonary involvement in Takayasu's arteritis.

The aim of study was to analyse ventilation and perfusion (V/Q) lung scan findings in a series of Italian patients with Takayasu's arteritis. Eighteen consecutive patients underwent V/Q lung planar scintigraphy and single-photon emission tomography (SPET). Before perfusion scan acquisition was started, a first-pass study with (99m)Tc-macroaggregates of albumin was performed to assess the right ventricular ejection fraction (RVEF). All patients had normal chest X-rays and were symptom free at the time of the investigation. They also underwent echocardiography to evaluate pulmonary artery pressure and in 13 patients respiratory function tests were performed. In four patients, perfusion lung scan was repeated after 1 year. In 10/18 patients (55.5%), 43 unmatched lobar, segmental or subsegmental perfusion defects were found on planar images; ventilation scintigraphy was normal in all cases. On SPET images, 55 defects were found; no defects were found with SPET in the remaining patients who had normal planar images. All patients had normal RVEF and 5/13 patients had mild restrictive-obstructive lung disease. The pulmonary artery pressure was increased in two patients with perfusion defects. In the four patients who had repeat scintigraphy, all defects remained unchanged. The prevalence of lung perfusion abnormalities observed in Italian patients with Takayasu's arteritis is within the range of values reported in other countries, and V/Q planar scintigraphy is sufficient for the screening of patients.     

Ventilation-perfusion lung scan for the detection of pulmonary involvement in Takayasu's arteritis

The aim of study was to analyse ventilation and perfusion (V/Q) lung scan findings in a series of Italian patients with Takayasu's arteritis. Eighteen consecutive patients underwent V/Q lung planar scintigraphy and single-photon emission tomography (SPET). Before perfusion scan acquisition was started, a first-pass study with ^99mTc-macroaggregates of albumin was performed to assess the right ventricular ejection fraction (RVEF). All patients had normal chest X-rays and were symptom free at the time of the investigation. They also underwent echocardiography to evaluate pulmonary artery pressure and in 13 patients respiratory function tests were performed. In four patients, perfusion lung scan was repeated after 1 year. In 10/18 patients (55.5%), 43 unmatched lobar, segmental or subsegmental perfusion defects were found on planar images; ventilation scintigraphy was normal in all cases. On SPET images, 55 defects were found; no defects were found with SPET in the remaining patients who had normal planar images. All patients had normal RVEF and 5/13 patients had mild restrictive-obstructive lung disease. The pulmonary artery pressure was increased in two patients with perfusion defects. In the four patients who had repeat scintigraphy, all defects remained unchanged. The prevalence of lung perfusion abnormalities observed in Italian patients with Takayasu's arteritis is within the range of values reported in other countries, and V/Q planar scintigraphy is sufficient for the screening of patients.     

Diagnosis of pulmonary embolism with spiral CT as a second procedure following scintigraphy

Our objective was to evaluate, in a routine clinical setting, the role of spiral CT as a second procedure in patients with clinically suspected pulmonary embolism (PE) and abnormal perfusion scan. We prospectively studied the role of spiral CT in 279 patients suspected of PE. All patients started their diagnostic algorithm with chest radiographs and perfusion scintigraphy. Depending on the results of perfusion scintigraphy, patients proceeded to subsequent levels in the algorithm: stop if perfusion scintigraphy was normal; CT and pulmonary angiography if subsegmental perfusion defects were seen; ventilation scintigraphy followed by CT when segmental perfusion defects were seen; and pulmonary angiography in this last group when results of ventilation/perfusion scintigraphy and CT were incongruent. Reference diagnosis was based on normal perfusion scintigraphy, high probability perfusion/ventilation scintigraphy in combination with abnormal CT, or pulmonary angiography. If PE was present, the largest involved branch was noted on pulmonary angiography, or on spiral CT scan in case of a high-probability ventilation/perfusion scan and a positive CT scan. A distinction was made between embolism in a segmental branch or larger, or subsegmental embolism. Two hundred seventy-nine patients had abnormal scintigraphy. In 27 patients spiral CT and/or pulmonary angiography were non-diagnostic and these were excluded for image analysis. Using spiral CT we correctly identified 117 of 135 patients with PE, and 106 of 117 patients without PE. Sensitivity and specificity was therefore 87 and 91%, respectively. Prevalence of PE was 53%. Positive and negative predictive values were, respectively, 91 and 86%. In the high-probability group, sensitivity and specificity increased to 97 and 100%, respectively, with a prevalence of 90%. In the non-high probability-group sensitivity and specificity decreased to 61 and 89%, respectively, with a prevalence of 25%. In a routine clinical setting single-detector spiral CT technology has limited value as a second diagnostic test because of low added value in patients with a high-probability lung scan and low sensitivity in patients with non-high-probability lung scan result.     

Evaluation of pulmonary perfusion in lung regions showing isolated xenon-133 ventilation washout defects

Xenon-133 washout phase imaging is often used to help determine whether the etiology of a perfusion defect is embolic or due to pulmonary parenchymal pathology, such as chronic obstructive pulmonary disease. This study was designed to evaluate the pulmonary blood flow patterns associated with isolated defects on xenon washout images. Scintigraphic lung studies were reviewed until 100 cases with abnormal ventilation results were obtained. Ventilation abnormalities were compared with the corresponding perfusion scan results at the same anatomic site. Of the 208 individual lung regions with xenon abnormalities, 111 showed isolated washout defects (that is, with normal washin). Ninety-four of these 111 sites showed either normal perfusion or a small, nonsegmental corresponding perfusion defect. Three segmental perfusion defects were noted in association with isolated xenon retention. In each of these cases, however, the patient was felt actually to have pulmonary embolism. Thus, it is recommended that, for interpretation of scintigraphic images in the assessment of pulmonary embolism, lung pathology associated with isolated xenon retention not be considered a potential cause for large or segmental perfusion defects.     

Very low probability interpretation of V/Q lung scans in combination with low probability objective clinical assessment reliably excludes pulmonary embolism: data from PIOPED II.

Use of a very low probability interpretation of ventilation/perfusion (V/Q) lung scans, if verified by prospective evaluation to have a low positive predictive value (PPV), will reduce the number of nondiagnostic interpretations of V/Q scans and may be particularly useful in patients with a relative contraindication to CT. The purpose of this investigation was to test the hypothesis that a very low probability interpretation of the V/Q scan has a PPV of <10%. METHODS: Data are from PIOPED II (Prospective Investigation of Pulmonary Embolism Diagnosis II). Very low probability criteria are (a) nonsegmental perfusion abnormalities, (b) perfusion defect smaller than corresponding radiographic lesion, (c) > or =2 matched V/Q defects with regionally normal chest radiograph, (d) 1-3 small segmental perfusion defects (<25% of a segment), (e) solitary triple matched defect in middle or upper lung zones, (f) stripe sign around the perfusion defect(s), and (g) perfusion defect from pleural effusion equal to one third or more of the pleural cavity with no other perfusion defect. RESULTS: A very low probability consensus interpretation of the V/Q scan was made in 56% of patients. The PPV of a very low probability interpretation of the V/Q scans was 36 of 440 patients (8.2%). Among patients with suspected pulmonary embolism who had a low clinical probability objective clinical assessment and a very low probability V/Q scan, the PPV was 8 of 259 patients (3.1%). Among women < or =40 y, the PPV of the very low probability V/Q with a low objective clinical assessment was 1 of 50 (2%). CONCLUSION: The very low probability V/Q scan together with a low probability clinical assessment reliably excludes pulmonary embolism.     

The anatomy of radioisotope lung scanning.

An appreciation of the appearances of segmental and lobar defects on a lung scan is important for the diagnosis of pulmonary embolism. The appearances of segmental and lobar ventilation defects of known anatomical location have been examined on 81mKr ventilation scans in normal human subjects, utilizing fibreoptic bronchoscopy to place temporary occlusions under direct vision at the orifices of lobar and segmental bronchi. Scans were obtained in the posterior, posterior-oblique and lateral projections. Anterior views were included if the defects could not be adequately visualized on the other views. The completeness of the occlusion and the site and size of each defect could be confirmed by ventilating the segment itself with 81mKr via the balloon catheter while the occlusion was maintained. Segmental defects located anterior to the hilum of the lung tended to be optimally visualized on the lateral view and defects located posterior to the hilum tended to be optimally visualized on the posterior-oblique view. The size of segmental defects could be underestimated on the lung scan, especially those involving the anterior and lateral basal segments of both lower lobes. Defects involving the medial basal segment of the right lower lobe were undetectable on any view. By implication, the same conclusions apply to 99mTc perfusion scans.     

Transient reverse ventilation-perfusion mismatch in acute pulmonary nitrofurantoin reaction

A 67-yr-old woman with a history of myocardial infarct was admitted to emergency for marked dyspnea, nonproductive cough, nausea and fever. The thorax X-ray revealed a bilateral alveolar and interstitial infiltration pattern with basal accentuation. The cardiac examinations were normal. Technegas ventilation and Tc-99m-macroaggregated albumin (MAA) perfusion scans were performed to rule out pulmonary embolism. Bilateral multiple ventilation defects with normal perfusion was observed. The patient had been taking nitrofurantoin for four days for a bladder infection. Hypersensitivity to nitrofurantoin was suspected and the drug was discontinued. An antihistaminic and anxiolytic medication was started. The majority of the clinical symptoms disappeared within 24 hours. The control chest X-rays disclosed a marked improvement. Ventilation and perfusion scans obtained 48 hours after nitrofurantoin withdrawal were normal. The drug-related pulmonary reactions should be taken into account in patients on medication. Reversible ventilation defects can be the only lung-scintigraphic finding encountered in acute pulmonary nitrofurantoin reaction.     

Computed tomography densitometry of the lung: a method to assess perfusion defects in acute pulmonary embolism

OBJECTIVE: To evaluate the potential of spiral computed tomography (CT) densitometry of the lung to assess segmental perfusion defects in patients with acute pulmonary embolism. MATERIALS AND METHODS: Ten patients with known segmental or lobar perfusion defects on ventilation/perfusion scintigraphy and with normal findings in the contralateral lung segment underwent spiral CT of the thorax before and after the administration of contrast material. Regions of interest were defined in 14 segments with normal perfusion and in 14 segments with reduced perfusion. Three consecutive densitometry measurements were performed in each segment. RESULTS: Those segments with reduced perfusion showed a significantly lower mean CT value on the enhanced scans (-813.4 +/- 57.1 Hounsfield units (HU) vs -794.0 +/- 44.8 HU, P = 0.01) and a significantly decreased contrast enhancement (12.3 +/- 18.2 HU vs 29.8 +/- 16.6 HU, P <0.01) when compared to segments with normal perfusion. Measurements from the unenhanced CT scans were not statistically different between segments with reduced and normal perfusion. CONCLUSIONS: Spiral CT densitometry allows the assessment of at least segmental perfusion defects in patients with acute pulmonary embolism.     

The indeterminate lung scan: its characteristics and its association with pulmonary embolism.

In an unselected series of patients whose only perfusion abnormalities on lung scan matched abnormalities on chest radiograph, the prevalence of pulmonary embolism ranged from 8 to 15%. These estimates depended upon whether only angiographic and autopsy-proven diagnoses were allowed or whether clinical diagnoses were also considered correct. Physical findings and laboratory data, in general, did not contribute to an elucidation of the cause of an indeterminate lung scan. Several radiographic findings with associated perfusion abnormalities (atelectasis alone, multiple infiltrates, bilateral effusions) were not seen in patients with pulmonary embolism. The probability of pulmonary embolism in patients with subsegmental defects alone and matching radiographic findings is about 9%; angiography in these patients would require that nearly two-thirds of the initial patient population undergo this procedure. Patients with larger defects (segmental or lobar) had a higher probability for pulmonary embolism (20--30%) and in these patients angiography is recommended.     

The significance of pulmonary nodules detected by CT but not by chest radiography in tumour staging

Computed tomography (CT) is more sensitive than the chest radiograph in the detection of pulmonary metastases, but specificity is lower because CT detects more small benign nodules. This study assessed the significance of pulmonary nodules demonstrated on CT when the chest radiograph was normal. Staging CT scans of 146 patients with extrathoracic primary tumours were reviewed. Thirteen per cent of CT scans showed pulmonary nodules despite a normal chest radiograph. In over 80% of these cases the nodules were benign. This has implications for accurate staging. When such nodules are demonstrated on CT, comparison with a repeat scan at a suitable interval will increase diagnostic confidence.     

Lung perfusion in patients with pulmonary hypertension: comparison between MDCT pulmonary angiography with minIP reconstructions and 99mTc-MAA perfusion scan

OBJECTIVES: Alterations in lung perfusion are a well-known feature of pulmonary hypertension (PH) seen on nuclear medicine studies. Abnormal radiotracer distribution in patients with PH may be caused by arterial thromboembolic occlusion, like in chronic thromboembolic pulmonary hypertension, by parenchymal destruction as in interstitial lung disease and pulmonary emphysema or by distal arteriopathy, like in idiopathic pulmonary arterial hypertension and other nonembolic forms. The different imaging pattern on radionuclide perfusion studies represents an important element for differential diagnosis. The aim of this study was to evaluate minimum intensity projection (minIP) images as an alternative to perfusion scintigraphy. We compared lung parenchyma attenuation patterns as depicted in minIP reconstructions with scintigraphic findings of lung perfusion in patients affected by pulmonary hypertension from various etiologies. METHODS: One hundred and seven consecutive patients affected by PH of different etiology (37 of those had chronic thromboembolic pulmonary hypertension) who had undergone both multidetector computed tomography pulmonary angiography and 99mTc-MAA perfusion scan were included. Five-millimeter thickness contiguous axial, coronal, and sagittal minIP images were reconstructed from the contrast enhanced computed tomography datasets. Two radiologists evaluated the images and qualitatively graded pulmonary attenuation as homogeneous, inhomogeneous with nonsegmental patchy defects, or inhomogeneous with segmental defects. The presence of parenchymal and pleural alterations was recorded. MinIP perfusion grading results were then compared with those of perfusion scintigraphy. RESULTS: In 87 of 107 patients (81.3%), the attenuation pattern seen on minIP images (39 homogeneous patterns, 13 with nonsegmental patchy defects, and 39 with segmental defects) correlated with the nuclear medicine scans. In the remaining 20 patients (18.7%), the imaging pattern was discordant because of 7 false-positive and 2 false-negative thromboembolic patterns at minIP and 11 false-positive thromboembolic patterns at perfusion scan. Air-trapping and parenchymal disease caused false-positive findings at minIP and perfusion scans, respectively. The sensitivity and specificity of minIP in detection of a chronic thromboembolic perfusion pattern were 94.5% and 90%, whereas perfusion scan had 100% sensitivity and 84% specificity. CONCLUSION: MinIP reconstructions can identify different patterns of pulmonary parenchymal attenuation, which show high concordance with perfusion patterns seen on radionuclide studies in patients with pulmonary hypertension. MinIP is a promising technique to evaluate lung perfusion in PH and may be used as an alternative to scintigraphy in the diagnostic work-up of these patients.     

The indeterminate lung scan: Its characteristics and its association with pulmonary embolism

In an unselected series of patients whose only perfusion abnormalities on lung scan matched abnormalities on chest radiograph, the prevalence of pulmonary embolism ranged from 8 to 15%. These estimates depended upon whether only angiographic and autopsy-proven diagnoses were allowed or whether clinical diagnoses were also considered correct. Physical findings and laboratory data, in general, did not contribute to an elucidation of the cause of an indeterminate lung scan. Several radiographic findings with associated perfusion abnormalities (atelectasis alone, multiple infiltrates, bilateral effusions) were not seen in patients with pulmonary embolism. The probability of pulmonary embolism in patients with subsegmental defects alone and matching radiographic findings is about 9%; angiography in these patients would require that nearly two-thirds of the initial patient population undergo this procedure. Patients with larger defects (segmental or lobar) had a higher probability for pulmonary embolism (20–30%) and in these patients angiography is recommended.Dr. McNeil is recipient of Research Career Development Award KO4 GM00194     

Diagnostic imaging of post-irradiation changes in the chest

Thirty-nine patients were studied with regard to post-irradiation changes in the chest. Twenty of these were reviewed retrospectively and 19 studied prospectively. All patients had chest radiographs and computed tomography (CT) of the chest following radiotherapy. Nineteen also had ventilation and perfusion studies of the lung, including single photon emission computed tomography (SPECT) and these were correlated with the chest radiographs and computed tomography. The majority showed abnormalities on computed tomography, the commonest being areas of lung opacification and evidence of volume loss. Several patients also showed a reduction in the size of pulmonary vessels. In most but not all, the changes were also seen on the chest radiographs. Abnormalities were not confined to the radiation fields, the vascular changes being present in large areas of lung which had not been directly irradiated. The structural and functional abnormalities correlated well as shown by ventilation and perfusion scintigraphy. However, single photon emission computed tomography was more sensitive than planar scintigraphy in showing perfusion defects, and it also showed some defects in areas of lung which appeared normal on computed tomography and the chest film. Computed and photon emission tomography were considerably more sensitive than chest radiography in showing the changes due to irradiation. The chest radiograph is clearly an insensitive indicator of post-irradiation change in the lung. Functional abnormalities are more profound and extensive than the chest film suggests, even when it is positive. There are clear implications for the planning of radiotherapy fields affecting the chest in patients who have good prospects of long-term survival. The maximum damage is related to irradiation of the hilum or mediastinum and this should be avoided wherever possible.     

Imaging findings of pulmonary vascular disorders in portal hypertension

PURPOSE: The purpose of this study was to demonstrate and compare the imaging findings of hepatopulmonary syndrome and portopulmonary hypertension. MATERIALS AND METHODS: We retrospectively reviewed the imaging findings of five patients with hepatopulmonary syndrome and four patients with portopulmonary hypertension. We evaluated chest radiographs, chest and abdominal computed tomography (CT) scans, 99mTc-macroaggregated albumin (MAA) lung perfusion scans, and pulmonary angiograms. RESULTS: In patients with hepatopulmonary syndrome, the presence of peripheral pulmonary vascular dilatation was detected by chest radiograph, chest CT scan, and pulmonary angiogram, especially the basilar segment. 99mTc-MAA lung perfusion scan showed extrapulmonary tracer distribution (brain, thyroid, and kidney), which revealed pulmonary R-L shunting. In patients with portopulmonary hypertension, chest radiographs and chest CT scans showed the classic findings of primary pulmonary hypertension. In patients with both disorders, extrahepatic features of portal hypertension including ascites, splenomegaly, and portosystemic collateral vessels were seen on abdominal CT. CONCLUSION: In conclusion, chest radiographs and CT in hepatopulmonary syndrome usually showed peripheral pulmonary vascular dilatation, whereas those in portopulmonary hypertension showed central pulmonary artery dilatation. The extrahepatic features of portal hypertension might be helpful for the diagnosis of both disorders.     

Ventilation-perfusion lung imaging in nitrofurantoin-related pulmonary reaction.

A woman with a history of multiple drug allergies was admitted for cough and dyspnea. She had been taking nitrofurantoin for 10 days, was febrile, and had a rash on the trunk and extremities. A chest radiograph revealed right-sided pleural effusion and basal markings. Because of suspected nitrofurantoin-related pulmonary reaction, the medication was discontinued and the patient was started on an H2-blocker and intravenous corticosteroids. She improved clinically, and within 24 hours a radiograph revealed that her chest had largely cleared. Restricted distribution of radioxenon, seen initially on a ventilation lung scan, also reverted to near normal by the follow-up. The first perfusion lung scan showed multiple but nonspecific changes; this also came back to near normal. The nitrofurantoin-related pulmonary reaction should be considered in patients who present with pulmonary signs/symptoms while on the medication.     

Radiographic parenchymal opacity, matching perfusion defect, and normal ventilation: a sign of pulmonary embolism? Work in progress

By conventional criteria, perfusion defects that correspond to radiographic parenchymal opacities of similar size have less diagnostic significance for pulmonary embolism (PE) than perfusion defects in areas that are radiographically clear, regardless of the findings on ventilation scan. It was proposed that the demonstration of normal ventilation in areas with matched radiographic opacity and perfusion defects does support the diagnosis of PE. To test this hypothesis, a retrospective review was done of selected cases from a consecutive series of 85 pulmonary angiography studies. Cases were reviewed if the following criteria were met: chest radiography, ventilation-perfusion scintigraphy, and angiography of the relevant regions had all been performed within 24 hours of one another, and there was a radiographic opacity corresponding to the perfusion defect. Sixteen cases fulfilled these criteria. Six patients had normal ventilation in the regions of the radiographic infiltrate and perfusion defect, and all had PE. No patient had an area of opacity and perfusion defect and normal ventilation without PE.     

Bilateral basal Xe-133 retention and ventilation/perfusion patterns in mild and subclinical congestive heart failure

The Xe-133 ventilation pattern in congestive heart failure (CHF) was assessed using 24 inpatient ventilation/perfusion studies performed to rule out pulmonary embolism. Patients with histories of CHF, myocardial infarction (MI), and cardiomyopathy were included in the study. Frank pulmonary edema, pulmonary embolism, and other known lung diseases such as chronic obstructive lung disease, tumor, and pneumonia were excluded. Fifteen of the 24 patients had abnormal ventilation scans. Twelve of the 15 showed bilateral basal Xe-133 retention on washout; the remaining 3 showed diffuse, posterior regional retention. On perfusion scans, 14 of the 15 abnormal ventilation patients showed evidence of CHF such as inverted perfusion gradient, enlarged cardiac silhouette, or patchy perfusion, and all of them had a history of CHF or cardiac disease. Nine of the 24 patients had normal ventilation scans, including normal washout patterns. Seven of the nine had normal perfusion (p less than 0.01). Four of the nine normal ventilation patients had a history of cardiac disease or CHF but no recent acute MI. Bilateral basal regional Xe-133 retention, coupled with perfusion scan evidence of CHF such as inverted perfusion gradient, enlarged cardiac silhouette, and patchy perfusion pattern, appears to be a sensitive and characteristic ventilation/perfusion finding in mild or subclinical CHF.