Focused Echo for Pulmonary Embolism in Patients with Abnormal Vital Signs

PE Abn Vitals

Increased Sensitivity of Focused Cardiac Ultrasound for Pulmonary Embolism in Emergency Department Patients With Abnormal Vital Signs

Acad Emerg Med Nov 2019 - Pubmed Link


Take Home Points

1. A negative focused echocardiography can significantly lower post-test probability for PE in patients with tachycardia and hypotension.

2. This protocol, optimized for sensitivity, is less specific for PE than prior studies have shown.


Background

Pulmonary embolism (PE) and POCUS are best buds. Despite the fact that people have been using a focused echo (aka FOCUS) to rule in signs of right heart strain for a long time, this modality has been less successful at ruling out PE. The authors cite a meta-analysis showing a sensitivity of 53% - gross! Other methods have been assessed for this such as TAPSE and recently ESN. Now these authors are smart- they recognized that the real question we want to know is, “in this sick patient in front of me, is there a big PE that I need to treat?” In patients who are less sick, you have time to do other tests. Their previous work (on the TAPSE article above), had a subgroup analysis of tachycardic and hypotensive patients (n = 17) that showed a 100% sensitivity of FOCUS. So now in this study, they look at a more specific population than in other studies; they look at only patients with abnormal vital signs and suspected PE to see if perhaps in this population, FOCUS could be used to rule-OUT this important diagnosis.


Check out The Evidence Atlas - Echo for a review of prior evidence on point of care echocardiography.


Questions

What are the diagnostic test characteristics of a focused cardiac ultrasound for evidence of pulmonary embolism in patients with a HR ≥ 100 bpm or systolic blood pressure < 90 mm Hg?

Additionally, planned an a priori subgroup of those with HR ≥ 110


Population

Prospective observational multicenter convenience sample

6 urban academic medical centers in the US


Inclusion:

  • Suspected PE undergoing CT angiography who received Focused cardiac ultrasound (FOCUS)

  • Emergency physician or study investigator was available to obtain FOCUS

  • ≥ 18 years old

  • Tachycardia (HR ≥ 100 bpm) OR hypotension (systolic blood pressure < 90 mm Hg). This had to be confirmed again prior to ultrasound (if BP, needed to be measured twice after initially low).


Exclusion:

  • Prisoners, wards of the state

  • Non-English speaking patients

  • Unable to obtain echocardiographic data


Design

Patients were enrolled in ED when one of study investigators was present

Patients were identified if they had a chest CT angiography ordered and also had tachycardia or hypotension

They then had vitals rechecked by study team to confirm


Then they underwent bedside FOCUS (see protocol below)

If any part of FOCUS was abnormal → considered positive


The result of the FOCUS was compared to the CTA as read by radiologist

FOCUS interpreted prior to CTA results whenever possible; if not, the performing team was blinded to CTA results

Inter-rater reliability for RV enlargement, septal flattening, tricuspid regurgitation, McConnell’s sign calculated by sending images to the investigators

There were also 8 patients that received two near simultaneous FOCUS to assess inter-rater reliability.


Primary outcome was the sensitivity of FOCUS for PE in these patients with abnormal vital signs

Secondary outcomes were specificity and likelihood ratios and the diagnostic test characteristics for individual components of the FOCUS

They calculated power to minimize their confidence interval → needed 120 patients assuming a sensitivity > 90%


Who did the ultrasounds?

7 ultrasound fellowship-trained attending emergency physicians

3 emergency medicine residents

3 medical students


All received standardized training - brief video and 1-hour didactic meeting. Small subset (2 residents) received additional didactic training, third resident is primary author

Students did not have significant prior ultrasound experience. Had to complete 20 FOCUS examinations with feedback prior to enrolling.


The Scan

Phased Array transducer

Phased


The typical 4 focused cardiac windows: parasternal long, parasternal short, apical four chamber, subcostal

These signs counted as positive for PE in this study:

  • TAPSE < 2.0 cm

  • RV ≥ LV

  • Septal flattening

  • Tricuspid regurgitation (✳any amount was considered abnormal✳)

  • McConnell’s sign


Learn how to do Ultrasound for PE from 5 Minute Sono!

5minsono


Check out RV Pathology on the POCUS Atlas!

thePOCUSAtlas


Results

143 patients eligible

Exclusions:

  • Four did not speak English

  • 3 because unable to obtain any FOCUS windows


N = 136

  • 37 (27.2%) had a PE

  • 16% of patients with PE were hypotensive

  • 76.6% of normotensive patients had signs of RVD on FOCUS

  • PE and Non-PE groups were similar but PE group had much higher the amount with signs of DVT (37.8% vs 7.1%)


Primary Outcome

HR ≥ 100 or SBP < 90 mm Hg

Sensitivity of FOCUS for PE = 92% (CI 78-98%)

-LR 0.13 (CI 0.04-0.38)


HR ≥ 110 (n = 98)

Sensitivity of FOCUS for PE = 100% (CI 88-100%)

-LR 0


Secondary Outcomes

For HR ≥100

  • TAPSE 2.0 cm was most sensitive component 88% (CI 72-97%) - LR 0.17

  • FOCUS was 64% specific (CI 53-73%), +LR 2.5

  • McConnell’s signs was most specific 99% (CI 94-100%) +LR 33.7 (CI 4.6-249)

  • Septal flattening was next most specific +LR 5.9 (2.7-13.2)


For HR ≥110

  • TAPSE 2.0 cm was most sensitive component 93% (CI 75-99%). -LR 0.11 (CI 0.03-0.40)

  • FOCUS was 63% specific (CI 51-74%), +LR 2.7TA

  • McConnell’s signs was most specific 100% (CI 95-100%).


Other Findings

Interrater reliability kappa 1.0

  • Lower for individual components (lowest for TAPSE, others were similar)


60 patients (44%) had data missing for tricuspid regurgitation


3 false negatives - all of these had incomplete FOCUS due to difficult windows (although only missing TAPSE in one and TR in other two). All patients had a high pre-test probability (hx of PE, active cancer treatment) and were relatively young (ages 28, 46, and 62) with good cardiovascular health.


Supplemental data show that 2 of the sites enrolled 104 of the 136 patients (76.5%).

Medical students performed 27.9% of exams, residents performed 29.4%.


Limitations

Convenience sample - selection bias. Partial unblinding in two patients (noted to be on heparin infusions). Skilled investigators may have also improved these results over what could be accomplished by a less trained operator.

Excluded patients with difficulty echocardiographic windows. This is always challenging for a diagnostic test because now we don’t know the true accuracy in all comers. We only know the best accuracy if you remove all of the troublemakers. Interestingly, unlike other PE studies, they did not exclude patients with chronic hypertension. This is likely again because they wanted to be as sensitive as possible and that would only hurt their specificity.

I think that the incorporation of TR into the protocol is more problematic than seen in this study. Since they included ANY amount of TR, I think this will cause a large amount of people to have a false positive study. So did they see that in this study? Well the specificity is not good BUT it is likely overestimated because 44% of their patients didn’t even get TR measured! My guess is that if everyone in the study got TR measured like they were supposed to, the specificity would have been worse. This makes the protocol less helpful overall. Worst-case scenario: this turns into the echocardiographic version of the d-dimer if not applied properly.


Discussion

Will you really use your focused echo to rule out PE? These authors are careful to posit that the benefit is likely limited to patients for whom, for some reason or another, get a CT at the moment. I think that this is a reasonable approach. Let’s say there is a theoretical hypotensive, tachycardic patient with dyspnea. They have some risk factors for PE, but I decide they are too unstable to get a CT. I do a focused echo and it's normal. Based on this data, I know that if there is no evidence of right heart strain (including no TR and a TAPSE >2 cm), then PE is very unlikely. I can then pursue alternate diagnoses. I think that this is worth considering, but I would like to see more data confirming this before recommending widespread adoption. In almost all cases, I would likely still obtain the CT if their initial contraindication resolves.

By optimizing sensitivity in this study, specificity is sacrificed. FOCUS was only 64% specific which is much worse than other studies have shown. In fact, this is problematic because it is probably more commonly going to be used (at least in most settings) to rule in the diagnosis. Fortunately, by breaking down the components we can see that the overall specificity was likely hurt by the TR and the higher TAPSE threshold. This might mean we can still trust the specificity of signs such as septal bowing and McConnell’s.

We recently discussed Early Systolic Notching (ESN) as a sign for submassive and massive PE. Although both studies were looking for a high sensitivity, we can’t compare them head to head because of different populations and study designs. The ESN was retrospectively looking at patients who had been diagnosed with a submassive or massive PE. They found that the ESN was 92% sensitive for a submassive or massive PE. In the study at hand, they looked only at only patients with abnormal vital signs (without knowing if they had a PE yet) and they counted any PE, not just submassive or massive ones. So basically these are tools with two different purposes. The ESN is supposed to identify those with large PEs. The current protocol in abnormal vital signs is meant to rule out PE if negative.


Take Home Points

1. A negative focused echocardiography can significantly lower post-test probability for PE in patients with tachycardia and hypotension.

2. This protocol, optimized for sensitivity, is less specific for PE than prior studies have shown.


More Great FOAMed on this Topic

The SGEM - FOCUS on PE in Patients with Abnormal Vital Signs


Our score

3 Probes


Expert Reviewer for this Post

Branditz

Lauren D. Branditz, M.D. @lbranditz

Assistant Director of Point-of-Care Ultrasound and Clinical Assistant Professor in the Department of Emergency Medicine at The Ohio State University


Cite this post as

Michael Prats. Focused Echo for Pulmonary Embolism in Patients with Abnormal Vital Signs. Ultrasound G.E.L. Podcast Blog. Published on February 17, 2020. Accessed on April 03, 2020. Available at https://www.ultrasoundgel.org/86.
Published on 02/17/20 05:00 AM
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