2014ESC急性肺栓塞诊断和管理指南(英文版)(5)

Taken together,these data suggest that a negative MDCT is an ad-equate criterion for excluding PE in patients with a non-high clinical probability of PE.Whether patients with a negative CT and a high clin-ical probability should be further investigated is controversial.MDCT showing PE at the segmental or moreproximal level is adequate proof of PE in patients with a non-low clinical probability;however,the positive predictive value of MDCT is lower in patients with a low clin-ical probability of PE,and further testing may be considered,especial-ly if the clots are limited to segmental or sub-segmental arteries. The clinical signi?cance of isolated sub-segmental PE on CT angiog-raphy is questionable.This?nding was present in4.7%(2.5–7.6%)of patients with PE imaged by single-detector CT angiography and9.4% (5.5–14.2%)of those submitted to MDCT.136The positive predictive value is low and inter-observer agreement is poor at this distal level.137 There may be a role for CUS in this situation,to ensure that the patient does not have DVT that would require treatment.In a patient with iso-lated sub-segmental PE and noproximalDVT,the decisionon whether to treat should be made on an inpidual basis,taking into account the clinical probability and the bleeding risk.

Computed tomographic venography has been advocated as a simple way to diagnose DVT in patients with suspected PE,as it can be combined with chest CT angiography as a single procedure,using onlyone intravenousinjection ofcontrast dye.In PIOPEDII,combining CT venography with CT angiography increased sensitivity for PE from 83%to90%and had a similar speci?city(around95%);134,138however, the corresponding increase in negative predictive value was not clinically signi?cant.CT venography adds a signi?cant amount of irradi-ation,which may be aconcern,especially in younger women.139AsCT venography and CUS yielded similar results in patients with signs or symptoms of DVT in PIOPED II,138ultrasonography should be used instead of CT venography if indicated(see Section3.10).

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The incidental discovery of clinically unsuspected PE on CT is an in-creasingly frequent problem,arising in1–2%of all thoracic CT exam-inations,most often in patients with cancer,but also among those with paroxysmal atrial?brillation or heart failure and history of atrial?bril-lation.140–143There are no robust datato guide the decision onhow to manage unsuspected PE with anticoagulants,but most experts agree that patients with cancer and those with clots at the lobar or more proximal level should be treated with anticoagulants.144

3.5Lung scintigraphy

Ventilation–perfusion scintigraphy(V/Q scan)is an established diag-nostic test for suspected PE.It is safe and few allergic reactions have been described.The test is based on the intravenous injection of technetium(Tc)-99m-labelled macroaggregated albumin particles, which block a small fraction of the pulmonary capillaries and thereby enable scintigraphic assessment of lung perfusion.Perfusion scans are combined with ventilation studies,for which multiple tracers such as xenon-133gas,Tc-99m-labelled aerosols,or Tc-99m-labelled carbon microparticles(Technegas)can be used. The purpose of the ventilation scan is to increase speci?city:in acute PE,ventilation is expected to be normal in hypoperfused seg-ments(mismatch).145,146According to the International Commission on Radiological Protection(ICRP),the radiation exposure from a lung scan with100MBq of Tc-99m macroaggregated albumin parti-cles is1.1mSv for an average sized adult,and thus is signi?cantly lower than that of CT angiography(2–6mSv).147,148

Being a radiation-and contrast medium-sparing procedure,the V/Q scan may preferentially be applied in outpatients with low clinical probability and a normal chest X-ray,in young(particularly female)patients,in pregnancy,in patients with history of contrast medium-induced anaphylaxis and strong allergic history,in severe renal failure,and in patients with myeloma and paraproteinaemia.149 Lung scan results are frequently classi?ed according to the criteria established in the PIOPED study:normal or near-normal,low,inter-mediate(non-diagnostic),and high probability of PE.94These criteria have been the subject of debate,following which they were revised.150,151To facilitate communication with clinicians,a three-tier classi?cation is preferable:normal scan(excluding PE),high-probability scan(considered diagnostic of PE in most patients),and non-diagnostic scan.135,152,153Prospective clinical outcome studies suggested that it is safe to withhold anticoagulant therapy in patients with a normal perfusion scan.This was recently con?rmed by a ran-domized trial comparing the V/Q scan with CT.135An analysis from the recent PIOPED II study con?rmed the effectiveness of the high-probability V/Q scan for diagnosing PE and of the normal perfusion scan for ruling it out.154Performing onlya perfusion scan is acceptable in patients with a normal chest X-ray;any perfusion defect in this situ-ation will be considered to be a mismatch.155The high frequency of non-diagnostic intermediate probability scans has been a cause for criticism,because they indicate the necessity for further diagnostic testing.Various strategies to overcome this problem have been pro-posed,notably the incorporation of clinical probability.91,156,157 Recent studies suggest that data acquisition in the tomographic mode in single photon emission computed tomography(SPECT) imaging,with or without low-dose CT may reduce the frequency of non-diagnostic scans.152,158–161SPECT imaging may even allow the use of automated detection algorithms for PE.162Large-scale pro-spective studies are needed to validate these new approaches.3.6Pulmonary angiography

Pulmonary angiography has for decades remained the‘gold standard’for the diagnosis or exclusion of PE,but is rarely performed now as less-invasive CT angiography offers similar diagnostic accuracy.163Pul-monary angiography is more often used to guide percutaneous catheter-directed treatment of acute PE.Digital subtraction angiog-raphy(DSA)requires less contrast medium than conventional cinean-giography and has excellent imaging quality for peripheral pulmonary vessels in patients who can hold their breath;it is less useful for imaging of the main pulmonaryarteries,due to cardiac motion artefacts. The diagnosis of acute PE is based on direct evidence of a thrombus in two projections,either as a?lling defect or as amputation of a pul-monary arterial branch.94Thrombi as small as1–2mm within the sub-segmental arteries can be visualized by DSA,but there is substan-tial inter-observer variability at this level.164,165Indirect signs of PE, such as slow?ow of contrast,regional hypoperfusion,and delayed or diminished pulmonary venous?ow,are not validated and hence are not diagnostic.The Miller score may be used in quantifying the extent of luminal obstruction.166

Pulmonary angiography is not free of risk.In a study of1111 patients,procedure-related mortality was0.5%,major non-fatal complications occurred in1%,and minor complications in5%.167 The majority of deaths occurred in patients with haemodynamic compromise or respiratory failure.The risk of access-related bleed-ing complications is increased if thrombolysis is attempted in patients with PE diagnosed by pulmonary angiography.168 Haemodynamic measurements should always be recorded during pulmonary angiography for estimation of the severity of PE and because they may suggest alternative cardiopulmonary disorders. In patients with haemodynamic compromise,the amount of contrast agent should be reduced and non-selective injections avoided.169

3.7Magnetic resonance angiography Magnetic resonance angiography(MRA)has been evaluated for several years in suspected PE but large-scale studies were published only recently.170,171Their results show that this technique,although promising,is not yet ready for clinical practice due to its low sensitiv-ity,high proportion of inconclusive MRA scans,and low availability in most emergency settings.The hypothesis—that a negative MRA combined with the absence of proximal DVT on CUS may safely rule out clinically signi?cant PE—is being tested in a multicentre outcome study(e43f5da204a1b0717ed5dd2a NCT02059551).

3.8Echocardiography

Acute PE may lead to RV pressure overload and dysfunction,which can be detected by echocardiography.Given the peculiar geometry of the RV,there is no inpidual echocardiographic parameter that provides fast and reliable information on RV sizeorfunction.This is whyechocar-diographic criteria for the diagnosis of PE have differed between studies. Because of the reported negative predictive value of40–50%,a nega-tive result cannot exclude PE.157,172,173On the other hand,signs of RV overload or dysfunction may also be found in the absence of acute PE and be due to concomitant cardiac or respiratory disease.174 RV dilation is found in at least25%of patients with PE,and its detec-tion,either by echocardiography or CT,is useful for risk strati?cation of the disease.Echocardiographic?ndings—based either on a disturbed RV ejection pattern(so-called‘60–60sign’)or on depressed

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contractility of the RV free wall compared with the RV apex(‘McCon-nell sign’)—were reported to retain a high positive predictive value for PE,even in the presence of pre-existing cardiorespiratory disease.175 Additional echocardiographic signs of pressure overload may be required to avoid a false diagnosis of acute PE in patients with RV free wall hypokinesia or akinesia due to RV infarction,which may mimic the McConnell sign.176Measurement of the tricuspid annulus plane sys-tolic excursion(TAPSE)may also be useful.177New echocardiographic parameters of RV function,derived from Doppler tissue imaging and wall strain assessment,were reported to be affected by the presence of acute PE,but they are non-speci?c and may be normal in haemo-dynamically stable patients,despite the presence of PE.178–181 Echocardiographic examination is not recommended as part of the diagnostic work-up in haemodynamically stable,normotensive patients with suspected(not high-risk)PE.157This is in contrast to sus-pected high-risk PE,in which the absence of echocardiographic signs of RV overload or dysfunction practically excludes PE as the cause of haemodynamic instability.In the latter case,echocardiography may be of further help in the differential diagnosis of the cause of shock, by detecting pericardial tamponade,acute valvular dysfunction, severe global or regional LV dysfunction,aortic dissection,or hypovol-aemia.Conversely,in a haemodynamically compromised patient with suspected PE,unequivocal signs of RV pressure overload and dysfunc-tion justify emergency reperfusion treatment for PE if immediate CT angiography is not feasible.182

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