Chapter 10

### INTRODUCTION

Nuclear medicine provides several valuable tools for the assessment of the venous vasculature. Most clinicians are familiar with the lung ventilation/perfusion scan (V/Q) for diagnosis of acute pulmonary embolism (PE), but some changes have been made in how this test is used or even interpreted. Small studies using hybrid single-photon emission computed tomography/computed tomography (SPECT/CT) technology with addition of low-dose CT to V/Q SPECT have shown improvement in the diagnostic accuracy of V/Q scintigraphy in the assessment of suspected PE. Other nuclear medicine examinations assessing the venous system itself, such as for acute deep venous thrombosis (DVT), have failed to achieve widespread use.

### PULMONARY EMBOLISM

Acute PE is a common and frequently fatal condition. PE refers to obstruction of the pulmonary artery or one of its branches by thrombus originating elsewhere in the body. Other materials such as tumor, air, or fat are also well-known causes of PE. PE is associated with a mortality rate of approximately 30% without treatment, primarily the result of recurrent embolism. However, accurate diagnosis followed by effective therapy with anticoagulants decreases the mortality rate to between 2% and 8%.

The clinical presentation of PE is variable and nonspecific, which makes its accurate diagnosis difficult. Risk factors include immobilization; surgery within the past 3 months; stroke; history of venous thromboembolism; malignancy; central venous instrumentation within the past 3 months; chronic heart disease; obesity; heavy cigarette smoking (>25 cigarettes per day); deficiency of antithrombin III, protein C, protein S; and factor V Leiden mutation. PE can be classified as acute or chronic. Patients with acute PE typically develop symptoms and signs immediately after obstruction of the pulmonary vessels. In contrast, those with chronic PE tend to develop slowly progressive dyspnea over a period of years because of pulmonary hypertension. In the Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II) study, the most common symptoms associated with PE were dyspnea at rest or with exertion (73%), pleuritic pain (44%), cough (34%), more than two-pillow orthopnea (28%), calf or thigh pain (44%), calf or thigh swelling (41%), and wheezing (21%). The most common signs were tachypnea (54%), tachycardia (24%), rales (18%), decreased breath sounds (17%), an accentuated pulmonic component of the second heart sound (15%), and jugular venous distension (14%). Circulatory collapse was uncommon (8%). Massive PE may be accompanied by acute right ventricular failure. Symptoms or signs of lower extremity DVT were common (47%).1 Routine laboratory tests, including D-dimer assay, which has high sensitivity and negative predictive value but poor specificity and positive predictive value, are nonspecific. The radiologic diagnostic tests commonly used in the evaluation of patients with suspected PE include chest radiography, radionuclide V/Q scan, CT pulmonary arteriography, and pulmonary angiography. Pulmonary angiography is considered the definitive diagnostic modality or "gold standard" in the diagnosis of acute PE, with a sensitivity of 98% and a specificity of 97%. However, it is infrequently done because it is ...

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