Thrombolytic therapy of pulmonary embolism: a comprehensive review of current evidence

Thrombolytic therapy of pulmonary embolism: a meta-analysis

OBJECTIVES

We sought to assess the efficacy and safety of thrombolytic therapy in patients with an acute pulmonary embolism (PE).

BACKGROUND

Thrombolytic therapy is approved for the treatment of acute PE; however, the safety and efficacy of this therapy remain debated.

METHODS

A meta-analysis of randomized, controlled trials comparing thrombolytic agents with intravenous heparin in patients with acute PE was performed. Trials were identified through a combined search of the MEDLINE, EMBASE, and Current Contents databases. Three outcome measures were assessed: 1) mortality, 2) recurrence of PE, and 3) major hemorrhage.

RESULTS

Nine trials including 461 patients were identified. Compared with intravenous heparin, thrombolytic therapy had no significant effect on mortality (relative risk [RR] 0.63, 95% confidence interval [CI] 0.32 to 1.23) or the recurrence of PE (RR 0.59, 95% CI 0.30 to 1.18), but was associated with an increased risk of major hemorrhage (RR 1.76, 95% CI 1.04 to 2.98). These results were homogeneous and largely unaffected by the formulation of thrombolytic agent, the clinical severity of PE, the extent of vascular obstruction determined radiologically, or the methodologic quality of the included trials.

CONCLUSIONS

Compared with intravenous heparin, thrombolytic therapy does not appear to have therapeutic benefit in unselected patients with acute PE, but it is associated with an increased risk of major hemorrhage. Given the small number of patients included in the randomized trials thus far, the negative results in terms of the efficacy outcomes should be interpreted with caution. Definitive evidence of the utility of thrombolytic therapy in this setting requires a large, randomized, controlled trial.

Real-time chest ultrasonography: a comprehensive review for the pulmonologist

This review discusses real-time pulmonary ultrasonography (US) for the practicing pulmonologist. US supplements chest radiography and chest CT scanning. Major advantages include bedside availability, absence of radiation, and guided aspiration of fluid-filled areas and solid tumors. Pulmonary vessels and vascular supply of consolidations may be visualized without contrast. US may help to diagnose conditions such as pneumothorax, hemothorax, pleural or pericardial effusion, pneumonia, and pulmonary embolism in the critically ill patient who is in need of bedside diagnostic testing. The technique of US, which is cost-effective compared to CT scanning and MRI, may be learned relatively easily by the pulmonologist.

Successful thrombolytic therapy for acute massive pulmonary thrombosis after total cavo-pulmonary shunt

A 4-year-old boy with massive pulmonary thrombosis after total cavo-pulmonary shunt was successfully treated by aggressive thrombolytic therapy. In the unique circulation involving total cavo-pulmonary shunt with azygous connection, the clinical manifestations of pulmonary thrombosis are somewhat different from those observed with ordinary biventricular circulation. The patient's hemodynamic state, including central venous pressure and systemic blood pressure, was relatively stable, but there was a dramatic decrease in oxygenation, possibly because azygous continuation allowed reversed blood flow from the superior vena cava to return to the atrium through collateral vessels between the azygous vein and the portal vein. Clinicians should be aware of this complication and unique circulation, and the importance of prompt diagnosis cannot be overemphasize. The effectiveness of the aggressive thrombolytic therapy in this case was noteworthy.

Should thrombolysis be contraindicated in patients with cerebral arteriovenous malformations?

OBJECTIVES

To report the successful and uncomplicated use of systemic thrombolysis for massive pulmonary embolism in a patient with a known cerebral arteriovenous malformation and to suggest that the presence of an unruptured arteriovenous malformation or aneurysm should not be considered an absolute contraindication to systemic thrombolysis.

DESIGN

Case report.

SETTING

A 16-bed adult neurologic/medical intensive care unit in a university hospital.

PATIENTS

A patient developed a massive pulmonary embolism the morning after elective cerebral embolization of a large unruptured cerebral arteriovenous malformation.

INTERVENTION

Radial artery catheterization, arterial blood gas measurements, mechanical ventilation, vasopressors, pulmonary perfusion scan, echocardiogram, head computed tomography, heparin therapy, and systemic recombinant tissue plasminogen activator therapy.

MEASUREMENT AND MAIN RESULTS

The patient required emergent mechanical ventilation and vasopressor support for respiratory and hemodynamic failure. Echocardiogram showed acute right heart failure, and pulmonary perfusion scan demonstrated massive pulmonary embolism. Despite intravenous heparin therapy, the patient had worsening hypotension and acidosis and we therefore treated with recombinant tissue plasminogen activator. Within the next day the patient was weaned from vasopressor support and extubated. Neurologic examination remained normal, and follow-up head computed tomography revealed no evidence of intracranial hemorrhage.

CONCLUSION

Known arteriovenous malformations or aneurysms are considered a contraindication to thrombolysis, although the true risk of thrombolysis-precipitated intracranial hemorrhage is unknown. We believe that this risk is low in the setting of a previously unruptured arteriovenous malformation or aneurysm. The decision to use systemic thrombolysis in a patient with a known vascular malformation should be individualized.

Treatment of venous thromboembolism

Venous thromboembolism (VTE), comprised of pulmonary embolism (PE) and deep vein thrombosis (DVT), is a disease entity with a significant morbidity and mortality. Anticoagulation, initially with intravenous heparin and followed with long term warfarin treatment is the traditional therapy for VTE. Low molecular weight heparin, (LMWH) has a greater bioavailability than unfractionated heparin and can be administered subcutaneously. LMWH has resulted in shorter hospitalizations, reduced inicidents of major bleeding complications, and has moved the treatment of VTE for selected patients to the out-patient setting. Thrombolytic therapy has been recommended in patients with life threatening PE such as those with right ventricular dysfunction or hypotension. There are advances in the technology for clot removal with catheter embolectomy and clot fragmentation. Inferior vena cava filters can be place percutaneously in patients who are at high risk for VTE or those in whom anticoagulation is contraindicated. Since VTE is often asymptomatic, prevention is the most effective means to reduce morbidity and mortality.

Deep Venous Thrombosis and Pulmonary Embolism

Venous thromboembolic disease, including deep venous thrombosis (DVT) and pulmonary embolism (PE), is an under-diagnosed and under-appreciated medical problem that results in significant patient morbidity and mortality. Inadequate venous thromboprophylaxis in surgical as well as medically ill patients results in DVT and PE that negatively impact patient outcomes and increase health-care costs. A high index of clinical suspicion combined with an evidence-based use of diagnostic tests helps identify patients with acute thrombosis. Failure to accurately and promptly diagnose and treat DVT and PE can result in excess morbidity and mortality due to postthrombotic syndrome, pulmonary hypertension, and recurrent thrombosis. Conversely, unnecessary anticoagulation provides risk in the absence of any tangible benefit. The immediate commencement of parenteral anticoagulant therapy with intravenous unfractionated heparin or a subcutaneous low molecular weight heparin (LMWH) upon presentation with DVT or PE (often even before objective diagnosis confirmation) is necessary to minimize propagation, embolization, and recurrence rates. We favor weight-based LMWH therapy in most of our patients with DVT because of the ability to treat exclusively or primarily in the outpatient setting. We still admit patients with PE for a minimum duration of 2 days for close observation. Subsequent conversion to oral anticoagulation with warfarin (target INR of 2.0 to 3.0 in most patients) should include an overlap with parenteral therapy of at least 4 to 5 days and until a stable target INR has been achieved. A minimum of 3 to 6 months of anticoagulation is recommended following a first episode of idiopathic DVT and any PE. A shorter course of therapy may be sufficient following a situational (eg, after surgery and postpartum) or calf DVT. Long-term, and at times lifelong, therapy should be considered in patients with thrombosis in the setting of a persistent acquired or inherited hypercoagulable state. Thrombolytic therapy probably should be reserved for young patients with iliofemoral DVT, any patient with a threatened limb due to impending venous limb gangrene, and those with PE who have objective evidence of cardiopulmonary compromise. Unfavorable risk-to-benefit and cost-to-benefit ratios make more extensive use of thrombolytics undesirable. The prevention of the postthrombotic syndrome with fitted, graduated compression garments and age- and gender-appropriate cancer screening are indicated in all patients with DVT in an attempt to minimize morbidity and mortality. Hypercoagulable state testing is indicated when the results of individual tests will significantly impact the choice of anticoagulant, intensity of therapy, therapeutic monitoring, family screening, family planning, prognosis determination, and most of all, duration of therapy.

Diagnosis and treatment of venous thromboembolism

The diagnosis of deep vein thrombosis (DVT) and pulmonary embolism (PE) has been improved and simplified over the past decade thanks to advances in noninvasive and readily accessible technology. With high degrees of sensitivity and specificity, venous ultrasonography is favored as the initial investigation for DVT. To diagnose PE, most clinicians rely on diagnostic algorithms that combine clinical assessment, noninvasive lung studies, and, if necessary, venous ultrasonography of the legs and D-dimer testing. Substantial progress has also occurred in the treatment of acute venous thromboembolism with the introduction of low-molecular-weight heparins. This class of antithrombotic agents has changed initial therapy from an inpatient, intravenous regimen that required laborious monitoring to an outpatient practice using weight-adjusted doses of once-daily subcutaneous injections. In addition, several new anticoagulants with theoretical advantages over existing agents have entered phase III studies. Aspects of thrombosis treatment that remain controversial include vena caval interruption and the indications for thrombolysis and surgical thromboembolectomy.

Pulmonary embolism

Pulmonary embolism (PE) is a common problem for which prompt diagnosis and treatment is essential to minimize mortality. The clinical presentation is more variable than sudden dyspnea and chest pain, especially in the critical care patient. Recognition of venous thromboembolic (VTE) risk factors can help develop a good clinical suspicion for PE. A wide range of diagnostic tests are available to the clinician. The ventilation/perfusion scan, pulmonary arteriogram, and lower extremity investigations are still important for diagnosis. Other noninvasive tests such as spiral CT with venography, echocardiography, and D-dimers are becoming more accepted. Heparin is the mainstay of PE therapy, but thrombolytic treatment may be lifesaving in the unstable patient. VTE prophylaxis should be considered in all post-operative or critical care patients.

Early intervention in massive pulmonary embolism. A guide to diagnosis and triage for the critical first hour

The diagnosis of massive pulmonary embolism should be considered expeditiously in all patients with unexplained hypotension, syncope, cardiac arrest, or hypoxemic respiratory failure. The presence of right ventricular overload on physical examination or electrocardiogram is an especially important clue. Depending on local expertise and the patient's stability, V/Q scanning, CT angiography, echocardiography, and right heart catheterization can be useful in establishing a diagnosis of pulmonary embolism. Supportive treatment includes oxygen, vasoactive medicines, and sometimes fluids. Although heparin is important in nearly all patients, 70% to 80% of patients also require an IVC filter, thrombolysis, or embolectomy.

Major pulmonary embolism: review of a pathophysiologic approach to the golden hour of hemodynamically significant pulmonary embolism

Major pulmonary embolism (PE) results whenever the combination of embolism size and underlying cardiopulmonary status interact to produce hemodynamic instability. Physical findings and standard data crudely estimate the severity of the embolic event in patients without prior cardiopulmonary disease (CPD) but are unreliable indicators in patients with prior CPD. In either case, the presence of shock defines a threefold to sevenfold increase in mortality, with a majority of deaths occurring within 1 h of presentation. A rapid integration of historical information and physical findings with readily available laboratory data and a structured physiologic approach to diagnosis and resuscitation are necessary for optimal therapeutics in this "golden hour." Echocardiography is ideal because it is transportable, and is capable of differentiating shock states and recognizing the characteristic features of PE. Spiral CT scanning is evolving to replace angiography as a confirmatory study in this population. Thrombolytic therapy is acknowledged as the treatment of choice, with embolectomy reserved for those in whom thrombolysis is contraindicated.

Use of thrombolytic therapy to treat heparin-refractory pulmonary embolism in a menstruating patient

A 26-year-old woman developed an acute pulmonary embolism at the beginning of her menstrual cycle and was admitted to the hospital. When she failed initial standard treatment with heparin, the only other therapeutic option was a thrombolytic agent such as recombinant tissue plasma activator (rt-PA). Use of these agents, however, carries a large risk of major bleeding complications and brings concern of increased menstrual blood flow and duration. A literature search of the use of thrombolytic agents in menstruating patients found only limited reports. Our patient responded well to rt-PA therapy Her hemoglobin levels remained stable, and she experienced no bleeding complications. Careful monitoring and caution are recommended when administering thrombolytic agents to menstruating patients.

High dose and short-term streptokinase infusion in patients with pulmonary embolism: prospective with seven-year follow-up trial

BACKGROUND

High dose and short-term streptokinase infusion has proved to improve survival among few patients with pulmonary embolism and cardiogenic shock, without increasing hemorrhagic complications. However its efficacy and safety in terms of long follow-up and in major number of patients requires to be established.

METHODS

Patients with pulmonary embolism proved through high probability V/Q lung scan, suggestive echocardiogram, or deep venous thrombosis were enrolled. All were assigned to receive 1,500,000 IU in one-hour streptokinase infusion. The primary end point was efficacy and safety of streptokinase regimen in terms of pulmonary arterial hypertension, right ventricular dysfunction, perfusion abnormalities, recurrence, mortality and hemorrhagic complications. In long-term follow-up, we assessed functional class, recurrence, chronic pulmonary arterial hypertension, postthrombotic-syndrome and mortality.

RESULTS

A total of 40 consecutive patients (47.3+/-15.3 years of age) with large or massive pulmonary embolism were enrolled. In 35 patients high dose and short-term streptokinase regimen reversed acute pulmonary arterial hypertension, clinical and echocardiographic evidence of right ventricular dysfunction and improved pulmonary perfusion without increasing hemorrhagic complications. In acute phase 5 patients died, necropsy study performed in 4 patients showed massive pulmonary embolism and right ventricular myocardial infarction, without significant coronary arterial obstruction. Risk factors for mortality and recurrence were: right ventricular global hypokinesis (p<0.0001), 6 hours or over between onset symptoms and streptokinase regimen (p=0.02), severe systolic pulmonary arterial hypertension (p=0.001) right ventricular hypokinesis (p=0.001), hypoxemia (p=0.02) and right ventricular acute myocardial infarction (p<0.0001). Right ventricular hypokinesis (p=0.02) was the only independent risk factor for recurrence. In a seven-year follow-up of the original 35 patients who survived in acute phase, 2 patients were lost and 33 are alive, in functional class I, without recurrence or chronic pulmonary arterial hypertension.

CONCLUSIONS

Our report indicates that among properly selected high-risk PE patients, short-term streptokinase infusion is effective and safe.

Emergency department management of pulmonary embolism

There are several points that bear repetition. First, consider the diagnosis of PE in all patients presenting with chest pain, dyspnea, syncope, oxygen desaturation, or unexplained hypotension. Evaluate these patients in a rational manner. At any individual hospital, develop algorithms with consultants so that when one is faced with a patient with a PE, the flow of both diagnostics and therapeutics flows smoothly and rapidly. Consider the concept of risk stratification, and remember that not all patients with PE are created equal. In particular, be on the same page with all consultants regarding the use of right heart echocardiography, both for its potential diagnostic capabilities and for its ability to identify patients who could be at greater risk for bad outcomes.

Thrombolysis during cardiopulmonary resuscitation in fulminant pulmonary embolism: a review

OBJECTIVE

To review current knowledge on thrombolysis in patients with fulminant pulmonary embolism (FPE) who need cardiopulmonary resuscitation (CPR).

DATA SOURCES

The bibliography for the study was compiled through a search of different databases between 1966 and 2000. References cited in the articles selected were also reviewed.

STUDY SELECTION

The selection criteria included all reports published on thrombolysis, pulmonary embolism, and CPR, from case reports and case series to controlled studies.

DATA SYNTHESIS

Very few studies evaluated thrombolysis in cases of FPE that required CPR and most of these were clinical case reports and case series with a low level of scientific evidence. There has been no clinical trial to address this issue.

CONCLUSIONS

FPE can frequently produce cardiac arrest, which has an extremely high mortality despite application of the usual CPR measures. The administration of thrombolytic therapy during CPR could help to reduce the mortality, although it has classically been contraindicated. There are no published clinical trials or other high-grade studies that evaluated the efficacy and safety of this approach. From the few existing studies, it can be inferred that thrombolysis may be efficacious and safe for patients with FPE who need CPR. However, a clinical trial is required to provide evidence of value for sound clinical decision-making.

Thrombolysis with recombinant tissue plasminogen activator during cardiopulmonary resuscitation in fulminant pulmonary embolism. A case series

OBJECTIVE

To describe our outcomes using thrombolysis during the cardiopulmonary resuscitation (CPR) of patients in cardiorespiratory arrest (CA) caused by fulminant pulmonary embolism (FPE).

DESIGN

A case series.

SETTING

Intensive care units of a district hospital and a referral centre.

PATIENTS

Six patients that suffered CA secondary to an FPE.

INTERVENTIONS

Administration of recombinant tissue plasminogen activator during usual CPR manoeuvres when there was a strong suspicion of FPE. Permission for the thrombolytic therapy was sought from family members in all cases.

RESULTS

Four out of the six patients survived and remain symptom-free. The thrombolysis was not associated with any fatal complications.

CONCLUSIONS

Early thrombolysis during CPR manoeuvres for CA apparently caused by an FPE may reduce the mortality rate among these patients.

Radionuclide imaging of acute pulmonary embolism

From the prospective and outcome-based studies that have been carried out in the past few years, the following conclusions regarding the diagnostic evaluation of patients with suspected PE can be made: 1. A normal V/Q scan interpretation excludes the diagnosis of clinically significant PE. 2. Patients with a very-low- or low-probability V/Q scan interpretation and a low clinical likelihood of PE do not require angiography or anticoagulation. 3. Patients with a very-low- or low-probability V/Q scan interpretation, an intermediate or high clinical likelihood of PE, and negative serial noninvasive venous studies of the lower extremities do not require anticoagulation or angiography. If serial noninvasive venous studies of the lower extremities are positive, patients should be treated. 4. Clinically stable patients with an intermediate-probability V/Q scan interpretation require noninvasive venous studies of the legs and, if negative, require CT angiography or pulmonary angiography for a definite diagnosis. 5. Clinically stable patients with a high-probability V/Q scan interpretation and a high clinical likelihood of PE require treatment and need no further diagnostic tests to confirm the diagnosis. 6. Clinically stable patients with a high-probability V/Q scan interpretation and a low or intermediate clinical likelihood of PE require noninvasive venous studies of the legs and, if negative, often require CT angiography or pulmonary CT for a definitive diagnosis.

Treatment of venous thromboembolism in cancer patients

The management of deep vein thrombosis (DVT) and pulmonary embolism (PE) in patients with cancer can be a clinical dilemma. Comorbid conditions, warfarin failure, difficult venous access, and a high bleeding risk are some of the factors that often complicate anticoagulant therapy in these patients. In addition, the use of central venous access devices is increasing but the optimal treatment of catheter-related thrombosis remains controversial. Unfractionated heparin (UFH) is the traditional standard for the initial treatment of venous thromboembolism (VTE) but low molecular weight heparins (LMWHs) have been shown to be equally safe and effective in hemodynamically stable patients. For long-term treatment or secondary prophylaxis, vitamin K antagonists remain the mainstay treatment. However, the inconvenience and narrow therapeutic window of oral anticoagulants make extended therapy unattractive and problematic. As a result, LMWHs are being evaluated as an alternative for long-term therapy. New antithrombotic agents are being tested in clinical trials and may have the potential to replace conventional treatment. The role of inferior vena cava filters in cancer patients remains ill defined but these devices remain the treatment of choice in patients with contraindications for anticoagulant therapy.

Acute and Chronic Pulmonary Emboli

Under most circumstances, the goal of treatment of pulmonary embolism is the prevention of recurrent embolic events, achieved through conventional anticoagulant therapy with unfractionated heparin or a low molecular weight heparin, followed by warfarin therapy for a minimum of 6 months. When acute pulmonary embolism is associated with significant right ventricular dysfunction or systemic hypotension, more aggressive intervention may be warranted. Under these circumstances, potential interventions include thrombolytic therapy (either systemic or catheter-directed), placement of an inferior vena caval filter, catheter-based embolectomy, or surgical embolectomy. Chronic thromboembolic pulmonary hypertension may develop in a small minority of patients who survive an acute, massive embolic event or who have suffered recurrent thromboembolic events. Due to the fixed nature of the pulmonary vascular obstruction, vasodilator therapy has proven far less effective in chronic thromboembolic disease than it has in primary pulmonary hypertension and other secondary forms of pulmonary hypertension. Correction of hypoxemia and volume overload and the prevention of recurrent embolic events are essential. Definitive therapy, however, requires surgical intervention to remove the chronic thromboembolic obstruction and to restore patency of the pulmonary vascular bed.

Pulmonary embolism in the elderly

The elderly are at increased risk for pulmonary embolism because of both the conditions common to this age group, and the immobility that often accompanies them. Whether aging alone represents a hypercoagulable state is unclear. The incidence of pulmonary embolism rises with age, however, as does pulmonary embolism mortality. The diagnosis of pulmonary embolism is difficult and frequently missed because elderly patients and their physicians may attribute nonspecific symptoms to underlying cardiopulmonary disease or to age itself. Routine laboratory examinations are also nonspecific. Lower extremity studies to diagnose DVT should always be pursued because a positive study results in identical treatment, without the need for further testing. D-dimer concentrations are useful when low, but are commonly elevated in the elderly because of other comorbid conditions. Lung scanning remains the most common initial study to diagnose pulmonary embolism, although spiral CT is as sensitive and specific. Pulmonary angiography should always be considered when the initial studies are nondiagnostic and clinical suspicion is high, and this test is well tolerated in the elderly. The role of newer diagnostic techniques, such as MR imaging, cannot be determined until well-designed outcomes trials are completed. Prophylaxis with appropriate pharmacologic agents or mechanical measures should be administered not only to patients undergoing hip or knee reconstruction surgery, but to all bed-ridden elderly medical and general surgery patients. Treatment for pulmonary embolism with anticoagulation reduces the mortality rate and should be administered in all elderly patients without contraindications. In addition, thrombolysis should be considered for all hemodynamically unstable patients with pulmonary embolism, regardless of age. Vena caval filters are warranted when anticoagulation is contraindicated, although evidence of the long-term benefit of these devices is lacking. At present, pulmonary embolism is underdiagnosed and undertreated in the elderly. By heightening awareness of this diagnosis and its appropriate management in this age group, considerable morbidity and mortality may be avoided.

Emergency bedside echocardiography as a tool for early detection and clinical decision making in cases of suspected pulmonary embolism--a case report

Massive pulmonary embolism (PE) constitutes the most unexpected cause of death in necropsy. Consequently, prompt diagnosis and treatment is considered imperative. This article reports the case of a 37-year-old man who presented with cardiogenic shock due to PE as detected with bedside echocardiography in the emergency department. The authors wish to emphasize the usefulness of emergency bedside echo-Doppler for a prompt diagnosis and treatment of this life threatening condition.

Anticoagulation for venous thromboembolism. What are the current options?

Venous thromboembolism remains an important cause of considerable morbidity and mortality. Low-molecular-weight heparin appears to be a safe and effective alternative to unfractionated heparin for inpatient treatment. In addition, we recommend considering its use in outpatient treatment in selected patients. When warfarin therapy is initiated, the starting dose should approximate the suspected maintenance dose. The optimal length of anticoagulation after an initial episode of venous thromboembolism is 6 months unless a persistent risk factor is identified. Thrombolytic therapy for hemodynamically stable patients remains controversial, primarily because of the potential for devastating complications.

Management of deep venous thrombosis and pulmonary embolism

The management of deep venous thrombosis (DVT) and pulmonary embolism (PE) is changing dramatically. The US Food and Drug Administration has approved outpatient treatment of DVT with the low-molecular-weight heparin enoxaparin as a bridge to warfarin. Warfarin use is improved by avoiding loading doses and by recognizing previously unappreciated interactions and potentiation with commonly used medications such as acetaminophen. The importance of isolated calf and upper-extremity venous thromboses has been validated, so that patients with these conditions routinely undergo anticoagulation. Risk stratification for PE is becoming more sophisticated because practitioners now assess right ventricular function (usually by echocardiography) instead of relying solely on systemic arterial blood pressure and heart rate to determine prognosis. Among patients with massive DVT or hemodynamically unstable PE, thrombolysis, thrombectomy, and embolectomy (often performed in an interventional angiography laboratory) are being used with increasing skill and improved outcomes.

Advantages of diagnostic nuclear medicine part 2: cardiac and other nonmusculoskeletal disorders

Advances in nuclear medicine have improved the detection and localization of very small abnormalities. Radionuclide imaging of myocardial perfusion is very useful for detecting coronary artery disease in patients who have an ambiguous presentation, such as those with chest pain syndrome and a nondiagnostic exercise test. Scintigraphy is also useful for diagnosing pulmonary thromboembolism, hyperthyroidism, testicular torsion, and fevers of unknown origin. In addition, improvements in positron-emission tomography and imaging with isotope-labeled monoclonal antibodies now permit detection and staging of prostate and brain malignancies and diagnosis of infections such as osteomyelitis.