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Internal and Emergency Medicine

, Volume 13, Issue 4, pp 567–574 | Cite as

Diagnostic accuracy of focused cardiac and venous ultrasound examinations in patients with shock and suspected pulmonary embolism

  • Peiman Nazerian
  • Giovanni Volpicelli
  • Chiara Gigli
  • Alessandro Lamorte
  • Stefano Grifoni
  • Simone Vanni
EM - ORIGINAL

Abstract

Evaluating the diagnostic performance of focused cardiac ultrasound (US) alone and combination with venous US in patients with shock and suspected pulmonary embolism (PE). Consecutive adult patients with shock and suspected PE, presenting to two Italian emergency departments, were included. Patients underwent cardiac and venous US at presentation with the aim of detecting right ventricular (RV) dilatation and proximal deep venous thrombosis (DVT). Final diagnosis of PE was based on a second level diagnostic test or autopsy. Among the 105 patients included in the study, 43 (40.9%) had a final diagnosis of PE. Forty-seven (44.8%) patients showed RV dilatation and 27 (25.7%) DVT. Sensitivity and specificity of cardiac US were 91% (95% CI 80–97%) and 87% (95% CI 80–91%), respectively. Venous US showed a lower sensitivity (56%, 95% CI 45–60%) but higher specificity (95%, 95% CI 88–99%) than cardiac US (both p < 0.05). When cardiac and venous US were both positive (22 out of 105 patients, 21%) the specificity increased to 100% (p < 0.01 vs cardiac US), whereas when at least one was positive (54 out of 105 patients, 51%) the sensitivity increased to 95% (p = 0.06 vs cardiac US). Focused cardiac US showed good but not optimal sensitivity and specificity for the diagnosis of PE in patients presenting with shock. Venous US significantly increased specificity of cardiac US, and the diagnosis of PE can be certain when both tests are positive or reasonably excluded when negative.

Keywords

Pulmonary embolism Shock Right ventricular dysfunction Ultrasound Echocardiography Venous compression ultrasonography Diagnostic accuracy 

Introduction

Patients with pulmonary embolism (PE) presenting with shock represent 3–10% of all patients with acute PE and are at high risk for death in the short-term. To expedite the diagnosis, international guidelines suggest the use of focused trans-thoracic echocardiography looking for signs of right ventricular (RV) dilatation/dysfunction [1, 2, 3]. In recent years ultrasound technology has rapidly improved, giving the possibility of an accurate bedside examination using mobile devices. This technical improvement is associated with a widespread use of point-of-care ultrasound (US) that is nowadays growingly considered a standard-of-care for acute patients [4]. However, performing an echocardiographic examination in critically ill patients may be challenging for difficulties in obtaining views of sufficient quality in the extreme emergency, which may make problematic their interpretation [5]. Furthermore, it is well-known that echocardiographic signs of RV dilatation/dysfunction could be due to pre-existing conditions that cause pulmonary hypertension or by other acute diseases also involving the right ventricle, such as acute coronary syndrome [7], adult respiratory distress syndrome [8] and severe sepsis [9, 10], making sometimes problematic the differential diagnosis with PE.

Although, the diagnostic accuracy of transthoracic echocardiography in all patients suspected of PE and the role of this tool for prognostication of patients with an already diagnosed PE are known, data about the role of transthoracic echocardiography in the subgroup of patients with shock and suspected PE in emergency are lacking. In fact, only a single study with few, highly selected patients specifically evaluate this issue [6].

The aim of the present study is to evaluate the diagnostic performance of focused cardiac US in patients with shock and suspected PE and to investigate if a combination with venous US might improve diagnostic accuracy in the emergency setting.

Methods

Study design and setting

This is a prospective diagnostic accuracy study. Study patients were recruited from June 2012 to April 2015 in the Emergency Departments (EDs) of two Italian university hospitals with an annual census of 50,000 and 100,000 visits, respectively. The local ethics committee approved the study. Written informed consent was obtained for inclusion in the study.

Study protocol and population

Consecutive adult patients with shock and suspected PE at the time of the medical evaluation were considered for the study. Shock was defined as systolic blood pressure (SBP) <90 mmHg or a drop of SBP more than 40 mmHg for more than 15 min, with signs of end-organ hypoperfusion (cold extremities, urinary output <30 mL/h, altered mental status, profound asthenia with fatigue and malaise, or respiratory distress). The clinical possibility of PE was established by the attending physician immediately after the initial standard evaluation that included medical history, physical examination, electrocardiogram and arterial blood gas, or pending the results of chest X-ray study, or blood samples comprehensive of d-dimer and troponin levels. Patients with a clear alternative diagnosis such as myocardial infarction, hypovolemic and anaphylactic shock were excluded from the study. Primary trauma patients were also excluded.

Focused cardiac and venous ultrasound examination

Focused cardiac and venous US were performed by one of eight sonographers immediately upon the possibility of a PE diagnosis within 3 h from inclusion and before any second-level diagnostic test. Patients with an unfeasible cardiac US because of poor acoustic window were considered for the analysis of feasibility of the US examination but were excluded from the study for computing diagnostic performance of US.

Sonographer was blinded to the results of other diagnostic tests. All sonographers participating in the study had at least 2 years experience in cardiac and venous US on critically ill patients. US exams were performed using the following multi-probe machines: two MyLab30 Gold, one MyLab40, and one Mylab alpha (Esaote SpA) and one HD7 (Koninklijke Philips N.V). Cardiac US was performed with a 2- to 5-MHz phased-array probe. RV dilatation was diagnosed in the presence of at least one of the following criteria: right/left ventricular end-diastolic diameter ratio 0.9 in the subcostal view or in the apical four chamber view, or right ventricular end-diastolic diameter >30 mm in the parasternal view [11, 12, 13]. Leg venous US was performed by a 4- to 8-MHz linear probe and consisted of short-axis visualization and compression of the common and superficial femoral veins and of the popliteal veins. Deep vein thrombosis (DVT) was defined as absence of vein total collapse during compression [13, 14, 15].

Gold standard for pulmonary embolism diagnosis

PE diagnosis was established when confirmed by a second-level diagnostic tests. Multidetector computed tomography pulmonary angiography (MCTPA) (≥64 row-detectors) was the first choice in both enrolling centers. Alternatively, lung scintigraphy and digital subtraction pulmonary angiography were used. MCTPA was also used to confirm the presence or absence of RV dilatation in false negative and false positive patients. In patients who died before diagnostic completion, PE was considered the cause of death only when confirmed by autopsy. Patients who for any reason did not undergo a second-level diagnostic test or autopsy were excluded from the study. Final diagnosis of shock due to PE or other causes was assigned by an expert in PE diagnosis in each center, who independently reviewed all the available clinical and imaging data.

Statistical analysis

Data points are expressed as mean ± SD. The unpaired Student’s t-test was used to compare normally distributed data. The Fisher’s exact test was used for the comparison of non-continuous variables expressed as proportions. p < 0.05 indicates statistical significance. All p values are two-sided. The diagnostic performances of cardiac US and venous US alone or combined were assessed by calculating sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). The extended McNemar and the McNemar test were used to evaluate if there was significant difference in the sensitivities and specificities of cardiac and venous US [16]. Calculations were performed with the use of SPSS statistical package, version 19.0 (IBM).

Results

Study population

Out of 120 patients considered for the study, 105 patients were included in the final analysis (Fig. 1). Included patients had a mean age of 72.4 ± 13.2 years (range 24–96). Forty-three patients (40.9%) had a final diagnosis of PE. Other causes of shock were sepsis in 34 cases (32.4%) of whom 18 with lung involvement, acute heart failure in 14 cases (13.3%) of whom 5 were due to acute coronary syndrome, severe hypovolemia in 5 cases (4.7%), acute aortic syndrome in 3 cases (2.9%), advanced neoplastic cachexia in 3 cases (2.9%), cardiac tamponade in 1 case (1%), cerebral haemorrhage in 1 case (1%) and unknown in 1 case (1%). Characteristics of patients with and without a final diagnosis of PE are shown in Table 1. Age, gender, risk factors for venous thromboembolic disease, clinical presentation, vital signs and probability of PE according to Wells score, were similar between the two groups. Also blood tests, including determination of blood lactate, troponin and D-dimer, did not differ. In-hospital mortality was similar between the two groups of patients.
Fig. 1

Flow diagram of the study and main results PE pulmonary embolism, US ultrasound, RVD right ventricular dilation, DVT deep vein thrombosis. % refers to included patients

Table 1

Clinical characteristics at presentation of included patients

 

Overall, n = 105

Pulmonary embolism, n = 43

Others, n = 62

p value

Clinical characteristics

 Age (mean ± SD)

72.4 ± 13.2

71.6 ± 13.3

73 ± 13.2

0.6

 Female gender

52 (49.5%)

24 (55.8%)

28 (45.2%)

0.324

Risk factors for VTE

 History of VTE

15 (14.3%)

6 (14%)

9 (14.5%)

0.775

 Immobilization

47 (44.8%)

20 (46.5%)

27 (43.5%)

0.843

 Cancera

29 (27.6%)

14 (32.6%)

15 (24.2%)

0.38

Clinical presentation

 Dyspnea

77 (73.1%)

33 (76.2%)

44 (71%)

0.655

 Cardiac arrest

12 (11.4%)

8 (18.6%)

4 (6.5%)

0.067

 Syncope

35 (33.7%)

19 (45.2%)

16 (25.8%)

0.092

 Chest pain

16 (15.2%)

7 (16.7%)

9 (14.5%)

1

 Heart rate >110/min

63 (60%)

23 (53.5%)

40 (64.5%)

0.313

 Arterial oxyhemoglobin saturation <90%

47 (44.8%)

23 (53.5%)

24 (38.7%)

0.164

Clinical scores

 Wells score (mean ± SD)

4.02 ± 2.41

4.72 ± 2.66

3.62 ± 2.18

0.126

 Wells score >4

40 (38.1%)

18 (41.9%)

22 (38.1%)

0.545

Laboratory findings

 Lactate, mmol/L (mean ± SD)

4.46 ± 3.5

4.2 ± 3.5

5.4 ± 3.6

0.509

 D-dimer, ng/mL (mean ± SD)

5771 ± 10744

8106 ± 11962

4282 ± 9705

0.107

 Troponin I, ng/dL (mean ± SD)

0.71 ± 1.6

0.37 ± 0.75

0.92 ± 1.93

0.056

Outcome

 Death from any cause (in-hospital)

42 (40%)

18 (41.9%)

24 (38.7%)

0.84

Data are presented as no. (%) or mean ± standard deviation (SD)

VTE venous thromboembolism, PESI pulmonary embolism severity index

aActive or under treatment in the last year

Focused cardiac and venous ultrasound

Focused cardiac US was not feasible in five (4.5%) patients. Out of 105 included patients, 47 (44.8%) showed RV dilatation (Video 1). Among these, 39 (78.7%) patients had a final diagnosis of PE. In two patients (4.2%) echocardiography showed the presence of a free-floating thrombus in the right chambers together with RV dilatation (Video 2). Diagnostic performance of cardiac US is reported in Table 2. The rates of false positive and false negative cases are 18.6 and 9.3%, respectively. Table 3 shows the characteristics of the eight false positive and four false negative cases.
Table 2

Diagnostic characteristics of focused cardiac and venous ultrasound as single and combined tests

 

Sensitivity % (95% CI)

Specificity % (95% CI)

PPV % (95% CI)

NPV % (95% CI)

+LR (95% CI)

−LR (95% CI)

Cardiac US

91% (80–97)

87% (80–91)

83% (74–88)

93% (86–98)

7.03 (4.01–10.99)

0.11 (0.04–0.25)

Venous US

56% (46–61)

95% (88–99)

89% (72–97)

76% (70–78)

11.54 (3.79–46.55)

0.46 (0.40–0.62)

Positive cardiac or venous US

95% (85–99)

79% (72–82)

76% (68–79)

96% (88–99)

4.56 (3.06–5.41)

0.06 (0.01–0.20)

Positive cardiac and venous US

51% (43–51)

100% (94–100)

100% (83–100)

75% (70–75)

Inf (7.23–inf)

0.49 (0.49–0.61)

or means that at least one test was positive; and means that both tests were positive

US ultrasonography, PPV positive predictive value, NPV negative predictive value; +LR positive likelihood ratio, −LR negative likelihood ratio, 95% CI 95% confidence interval

Table 3

Clinical characteristics of patients with false negative and false positive RV dilation

Age, gender

Symptoms of presentation

SBP (mmHg)

RV dilation (cardiac US)

Other findings (cardiac US)

Proximal DVT (venous US)

RV dilation (mCTPA)

Possible cause of misdiagnosis

Final diagnosis

False negative

 65 M

Syncope

95

No

No

No

Yes

Non cooperative (psychotic), single view (subcostal)

Main pulmonary arteries embolism

 73 M

Dyspnea

80

No

No

No

Yes

 

Lobar pulmonary arteries embolism

 75 M

Dyspnea, palpitations

70

No

No

Yes

Yes

 

Lobar pulmonary arteries embolism

 77 M

Dyspnea

80

No

No

Yes

Yes

Dehydration

Lobar pulmonary arteries embolism

False positive

 72 M

Dyspnea, chest pain

80

Yes

RV hypertrophya

No

Yes

Chronic pulmonary hypertension

Respiratory failure in COPD exacerbation

 79 F

Syncope

80

Yes

No

No

Yes

 

Right ventricular infarct with sino-atrial block

 89 F

Dyspnea

85

Yes

No

No

Yes

 

Septic shock in pneumonia

 73 M

Dyspnea

60

Yes

No

No

Yes

Chronic pulmonary hypertension

Septic shock in pleural empyema

 83 M

Dyspnea

105

Yes

RV hypertrophya

No

Yes

Chronic pulmonary hypertension

Respiratory failure in pneumonia, COPD and previous pulmonary embolism

 71 F

Dyspnea

85

Yes

No

No

Yes

 

Septic shock

 88 M

Dyspnea, chest pain

70

Yes

Pericardial effusion

No

No

 

Septic shock in pneumonia with pleuro-pericarditis

 75 F

Syncope, dyspnea

65

Yes

Pericardial effusion

No

Yes

Chronic pulmonary hypertension

Respiratory failure in COPD exacerbation

SBP systolic blood pressure, DVT deep vein thrombosis, COPD chronic obstructive pulmonary disease, mCTPA multi-slice computed tomography pulmonary angiography

aRight ventricle free wall thickness >5 mm

Venous US was feasible in all patients. Proximal DVT was confirmed in 27 patients (25.7%) (Fig. 1), of whom 24 (88.9%) had a final diagnosis of PE, whereas three (11.1%) had not. Venous US showed a significantly lower sensitivity and higher specificity than cardiac US (both p < 0.05) (Table 2).

The combination of cardiac and venous US increases the sensitivity and specificity of the diagnostic strategy compared to cardiac US alone. The criteria of at least one test positive (54 out of 105 patients, 51%) increases the sensitivity to 95% (p = 0.06) with a derived false negative rate of 4.6%. When both tests are positive (21% of patients) the specificity increases to 100% (p < 0.01) (Table 2).

Discussion

This study shows for the first time the diagnostic accuracy of focused cardiac and venous US in a consistent population of patients presenting to ED with shock and suspected PE.

Previous studies on the diagnostic performance of clinical evaluation in patients with suspected PE include only a few patients with signs of circulatory collapse (3–10%) [17, 18, 19], and no study specifically investigates the diagnostic performance of clinical models or laboratory tests such as d-dimer in patients with shock [20, 21]. In our cohort, symptoms, physical signs and laboratory tests do not show any significant correlation with PE (Table 1). Application to our shock patients of a well-validated clinical prediction rule for suspected PE, the Wells score [20], did not discriminate the disease. These data suggests that classical clinical and laboratory data are not accurate in patients with shock, and that there is the need to investigate and validate a specific diagnostic process.

PE is the most frequent cause of acute RV pressure overload [17], and although cardiac US, from a theoretical point of view, represents the possibility of a direct view to diagnose or exclude an acute PE inducing hemodynamic consequences, our data seem to challenge this old dogma (Table 3). Several studies have investigated the diagnostic performance of transthoracic cardiac US in critically ill patients showing high accuracy in discriminating cardiac and extra-cardiac causes of shock [22, 23, 24, 25]. In these studies feasibility was quite high (90–99%). However, only a few patients (fewer than 10%) show RV dysfunction. Our prospective data show that in patients with shock and suspected PE, cardiac US focused on RV dilatation is feasible in the large majority of our patients, but not in the whole population. Moreover, one of the false negative cases in our cohort was mainly due to poor patient compliance and to the incomplete ultrasound evaluation, as only the subcostal view was interpretable. This finding highlights the difficulty in the evaluation of right ventricle dimensions in the emergency setting, and the importance of an optimal interpretation that sometimes needs the evaluation of multiple windows with a sufficient visualization of the valve parts and the whole cardiac chambers to compare their size.

A previous study including only 16 patients with suspected PE presenting with high-risk features to a single ED seemed to suggest that the combination of cardiac and venous US could perform better than single tests [11]. In the study by Kucher et al. [6], where 20 patients with shock were evaluated, cardiac US in expert hands shows a positive and negative predictive value of 100%. Our study, performed in two EDs and specifically designed for the evaluation of RV dilatation in a higher number of patients with shock and suspected PE, reveals quite different data. When we look at cardiac US as a single test to confirm PE diagnosis, we find a high false positive rate. There are three main causes of this result. First, other acute diseases sharing with PE the same RV dilatation pattern, such as sepsis or acute coronary syndromes, may cause misdiagnoses [7, 8, 9, 10]. Second, differential diagnosis between acute and chronic pulmonary hypertension may be difficult [26, 27] and to diagnose a new embolic episode exacerbating pre-existing right ventricular strain due to a chronic condition is even more difficult at bedside [28]. Third, the operators of our study, swayed by the diagnostic hypothesis, might have overestimated the presence of RV dilatation (confirmation bias) [29]. We tried to ascertain this last aspect by confirming the presence or absence of RV dilatation at mCTPA in the subgroup of patients with a false positive cardiac US, and find that only in one case, RV dilatation showed by cardiac US was not confirmed. Although the real accuracy of mCTPA for RV dilatation is under debate [30], our findings seem to exclude the presence of a significant confirmation bias. Whatever the cause, the high false-positive rate of cardiac US seems to preclude its use as a stand alone test in guiding aggressive treatment, such as systemic thrombolysis, in shocked patients with suspected PE. An exception could be the few cases (4.6%) with direct visualization of mobile thrombi in the right heart chambers [31].

On the other hand, cardiac US is negative in about one tenth of patients with high-risk PE. In one case, the misdiagnosis could be attributed to the incomplete acquisition of optimal ultrasound images, and in another, to the coexistence of a profound dehydration state. In this last case, in accordance with the subsequent mCTPA, repeating the test after an appropriate fluid challenge revealed the correct diagnosis. In the other two cases, we could not hypothesize a plausible explanation for the incorrect diagnosis. Our findings highlight the fact that cardiac US in the emergency setting shows a high but not optimal accuracy both to rule-in and rule-out high-risk PE.

Venous US shows a high feasibility (100%), but low sensitivity (56%) for PE, in accordance with data existing in literature [11, 13]. It is interesting to note that even when venous US is positive, causes of shock other than PE still remain a concrete possibility (PPV 89%).

This study strengthens the importance of including venous US together with focused cardiac US in the diagnostic algorithm for suspected PE in patients with shock [1, 32]. Our study may have important clinical implications. Cardiac and venous US were both positive only in patients with confirmed PE (specificity of 100%). Both of them were positive in about half of the population with a final diagnosis of high-risk PE making those shock patients suitable for immediate systemic thrombolysis or other reperfusion therapies without further testing. Another important speculation based on our data is that when one of the two tests is found positive in the absence of contraindication, anticoagulant treatment should be considered due to the high probability of PE. However, a second-level diagnostic test such as mCTPA or transesophageal echocardiography may be warranted before starting more aggressive treatment. If second-level diagnostic tests are not immediately available or feasible, we recommend consideration of thrombolytic treatment case by case, by balancing the confidence in US findings, the absence of alternative diagnoses, the clinical course, the biomarkers of cardiac damage and the risk of haemorrhage. Finally, the presence of both negative cardiac and venous US excludes the diagnosis of PE with very high probability (NPV 96%), thus allowing a focus on the diagnostic effort towards alternative diagnoses.

Limitations of the study

This study was performed at two tertiary care centers, which may limit its generalizability. US was performed by sonographers with at least 2 years of experience. It remains unknown whether these results can also be extrapolated to other institutions and physicians with less experience.

The aim of our study was to evaluate a basic and easy-to-perform ultrasound technique for a bedside fast examination. For this reason, we chose to focus cardiac US only on RV dilatation, thus avoiding a more comprehensive and advanced cardiac evaluation. The use of color-Doppler or tissue Doppler, the measurement of areas or volumes of cardiac chambers, the measurement of the diameters of the cardiac walls and the evaluation of tricuspid annular plane excursion (TAPSE) and qualitative signs of RV dysfunction, such as D-shape sign or McConnell’s sign, are other technical possibilities to enhance the quality of the US assessment that were not considered in our study. Regarding venous US, we only examined the femoral-popliteal veins without using color-Doppler and without extending the study to inferior vena cava, iliac veins, subpopliteal veins and veins of other districts. Of course, including a more detailed cardiac and venous examination might further improve the accuracy of US, but would significantly increase the time to be spent for each examination and the need for a more advanced skill of the operator. We strongly believe that the sustainability and widespread use of point-of-care US may only happen by experimenting methods of easy acquisition and application.

Conclusions

In patients with shock and suspected PE, focused cardiac US, as a stand alone test, shows a sub-optimal diagnostic performance to rule in and rule out PE. Combination of cardiac and venous US dramatically improve the specificity, allowing to identification of a consistent group of high-risk PE patients without further testing. Combination of negative cardiac and venous US allow reliable exclusion of the disease.

Notes

Acknowledgements

No sponsor funded the study.

Compliance with ethical standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Human and animal rights

This is a prospective diagnostic accuracy study. Study patients were recruited from June 2012 to April 2015 in the Emergency Departments (EDs) of two Italian university hospitals with an annual census of 50,000 and 100,000 visits, respectively. The local ethics committee approved the study.

Informed consent

Written informed consent was obtained for inclusion in the study.

Supplementary material

Supplementary material 1 (M4V 2875 kb)

Supplementary material 2 (M4V 3048 kb)

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Copyright information

© SIMI 2017

Authors and Affiliations

  1. 1.Department of Emergency MedicineCareggi University HospitalFlorenceItaly
  2. 2.Department of Emergency MedicineSan Luigi Gonzaga University HospitalTurinItaly

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