Feasibility and accuracy of bedside transthoracic echocardiography in diagnosis of acute proximal aortic dissection

Background

Acute aortic dissection is a life threatening condition that requires prompt diagnosis and definitive management; dissection involving the ascending aorta is undoubtably an indication for emergent surgical intervention. Previous data suggests that the mortality of type A dissection increases by 1-2% for every hour that passes which further highlights the importance of rapid diagnosis [1-2]. Currently, CT is considered the gold standard that enables the visualization of the entire aorta and can distinguish among the different types of acute aortic syndromes; however this is not always available, requires transferring patients to the CT scanner, and can ultimately generate a significant delay in treatment. Ultrasound is an easily available alternative imaging adjunct that may prove useful in rapid diagnosis of acute aortic dissection, specifically, type A dissection that require emergency surgical intervention.

Feasibility and Accuracy of Bedside Transthoracic Echocardiography in Diagnosis of Acute Proximal Aortic Dissection

 

Clinical Question

What is the accuracy of transthoracic echocardiography (TTE) in the diagnosis of acute type A aortic dissection in comparison to CT (with reference to the intra-operative diagnosis)?

Methods & Study Design

  • Design
    • Retrospective chart review
  • Population
    • This was a single center study involving patients  transferred due to suspected acute type A aortic dissection
    • Cardiac surgery for type A dissection was conducted in 172/178 patients (1 patient refused the operation and died, 5 patients underwent cardiac arrest and died prior to transfer to the operating room)
      • Because intra-operative findings were considered the gold standard reference for the presence of aortic dissection, the 6 patients who died without cardiac surgery were excluded from the final analysis
    • Inclusion criteria:
      • Referral for an urgent surgery due to proximal aortic dissection (Stanford classification Type A)
      • Available results of both CT and bedside TTE
    • Excluded
      • Patients who died prior to cardiac surgery
      • 1 patient who refused surgery
      • Patients who underwent surgical repair of acute type A aortic dissection based on TTE without confirmatory CT
  • Intervention
    • TTE was performed in the emergency department by an “experienced echocardiographer" to evaluate for: maximum ascending aorta diameter, presence of a dissection flap in the ascending aorta, left ventricular ejection fraction, pericardial effusion (and cardiac tamponade), aortic valve morphology and severity of aortic regurgitation
      • Echocardiographic findings were compared to CT findings and intra-operative findings were used as a gold standard
  • Outcomes
    • Identification of type A aortic dissection by TTE
    • Correlation of TTE measurements of maximum ascending aortic diameter with CT and intra-operative findings

Results

    • Statistical analysis with chi square test did not show any statistically significant differences between CT and TTE in the detection of proximal aortic dissection.
    • Additionally, echo revealed concomitant abnormalities (i.e. bicuspid aortic valve, AV calcifications, moderate/severe aortic incompetence, cardiac tamponade), which were all confirmed intra-operatively and influenced the treatment strategy (graft vs. valve-sparing surgery).
    • In patients with any aortic valve abnormalities (bicuspid aortic valve, AV calcifications, significant aortic regurgitation) procedure of choice was replacement by a composite graft (77.59% vs. 49.12%), whereas patients with normal aortic valves were significantly more likely to have the valve sparing surgery (50.88% vs. 22.41%)
    • There was a strong positive correlation between maximum diameter of the ascending aorta measured by TTE and CT (correlation coefficient 0.869)

Strengths & Limitations

  • Strengths
    • This was a feasibility study, and they used a population with known acute type A aortic dissection to determine if TTE could be used to provide both a rapid and reliable diagnosis in proximal aortic dissection
    • Gold standard was intra-operative findings
  • Limitations
    • Retrospective analysis, meaning that the diagnosis of aortic dissection has either already been made or was strongly suspected prior to initiating scanning; some may argue this may falsely increase the noted sensitivity/specificity of TTE
    • All patients who underwent cardiac surgery for acute proximal dissection based on TTE without CT verification (~30% patients at their institution) were excluded from the analysis
    • The TTE was performed by personnel trained in advanced echocardiography which may lower the sensitivity/specificity of these findings in the hands of less experienced operators

Author's Conclusions

"Our data confirm that TTE is a reliable method for diagnosis of proximal aortic dissection. TTE provides a reliable value of maximum diameter of the ascending aorta in comparison to both CT and direct intra-operative measurement. Moreover, TTE gives the additional information that influences the operative technique of choice and identifies the high-risk patients (cardiac tamponade, severe aortic dilatation, severe aortic regurgitation). Our retrospective analysis confirms the pivotal role of TTE in the evaluation of the patients with suspected proximal aortic dissection in emergency room setting."

Our Conclusions

Our conclusions are very similar to author findings on this paper. From the emergency department standpoint, we need the ability to distinguish sick patients from not sick patients and TTE in suspected acute aortic dissection does just that. Looking at this data, TTE measurements of maximum ascending aorta diameter correlate very well with intra-operative measurements. Furthermore, TTE is very accurate at identifying complications of type A aortic dissection such as decompensated heart failure (due to acute aortic regurgitation) and cardiac tamponade, both of which will alter surgical management.

What this means is that if you suspect aortic dissection, a bedside echo should be performed immediately looking for ascending aorta enlargement, dissection flap, and/or complications of dissection. If found, cardiac surgery can confidently be consulted and the patient can either be pushed to the operating room if unstable or pushed directly to the CT scanner by the emergency medicine provider. What this does not mean is that your work up stops here if no findings of dissection are found. If you are truly concerned about aortic dissection then the next step is to proceed with CT for definitive rule out. For more information on evaluation of acute aortic dissection, please read our recent case here.

The Bottom Line

The use of TTE in suspected proximal aortic dissection facilitates a rapid and reliable diagnosis, and shortens the delay to definitive treatment in a subset of high-risk patients.

Authors

This post was written by Ryan Shine, MS-4 at UCSD. It was edited by Michael Macias, MD.

References

    1. HIRST AE Jr, e. (2017). Dissecting aneurysm of the aorta: a review of 505 cases. - PubMed - NCBI Ncbi.nlm.nih.gov. Retrieved 26 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/13577293

    2. Hagan PG, e. (2017). The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. - PubMed - NCBI Ncbi.nlm.nih.gov. Retrieved 26 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/10685714

    3. Sobczyk, D., & Nycz, K. (2015). Feasibility and accuracy of bedside transthoracic echocardiography in diagnosis of acute proximal aortic dissection. Cardiovascular Ultrasound, 13(1). doi:10.1186/s12947-015-0008-5

Case # 4: To Bolus or Not to Bolus?

 

 

A 67 year old male with a PMHx of DM presents with a chief complaint of cough and generalized weakness.

Vitals: T 102.4 HR 127 BP 77/58  RR 24 O2 88% on RA

You place the patient on O2 via nasal cannula and activate the sepsis protocol. He is empirically treated with broad spectrum antibiotics and IVFs are started. The chest x-ray shows multifocal pneumonia and you call hospital medicine to admit the patient.  “What’s the blood pressure now,” the hospitalist asks. You glance at the monitor and murmur back, “92/63, but he looks pretty good.” The hospitalist asks you to insert a central line, start vasopressors, and contact the ICU. Instead, you wheel the ultrasound machine into his room, and ultrasound his IVC. Does this patient require a central line and vasopressors?

Answer and Learning Point

Answer

No, the patient’s IVC is small and collapsing almost 75% with normal respiratory variation. This predicts a fluid-responsive state. The patient was given another liter of lactated ringers, his blood pressure improved to 108/69, and his lactate cleared. You start maintenance IV fluids, call the hospitalist back, and the patient is admitted upstairs and does well.

Learning Points

    • Fluid responsiveness is a controversial topic that continues to plague emergency medicine physicians and intensivists alike
    • In patients whom a fluid bolus is being considered, ultrasound can be a useful tool to assess for cardiac function, lung fluid status (interstitial edema) and whether a patient will improve their cardiac output in response to this fluid challenge
    • A recent study showed that the cIVC (inferior vena cava collapsibility) can be used as a predictor of who will be a fluid responder [1]
      • cIVC = (IVC expiratory diameter - IVC inspiratory diameter)/IVC expiratory diameter
      • Patients with a cIVC > 25% are likely to be fluid responders (LR + 4.56)
      • Patients with a cIVC < 25% are unlikely to be fluid responders (LR - 0.16)
    • The IVC should be examined in the subxiphoid region with the probe in a sagittal plane, and can be found by first identifying the right atrium and following this caudally
      • A back-up approach involves using the liver as an acoustic window , placing the probe in the mid axillary line in a coronal plane,  and fanning anteriorly and posteriorly until the IVC is visualized
      • The IVC should be measured 3 cm caudal to the junction of the right atrium and IVC [2]
    • M-mode can be used to evaluate the cIVC and has the advantage of measuring the exact same spot along the IVC over an extended period of time
    • As with all adjuncts to clinical decision making, fluid responsiveness should not be determined solely on a single ultrasound measurement such as cIVC but should be taken into context with the rest of the clinical picture

Author

This post was written by Amir Aminlari, MD, Ultrasound Fellowship Director at UCSD.

References

Corl KA, e. (2017). Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 19 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/28525778

Nagdev AD, e. (2017). Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 19 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/19556029

Diagnosing Acute Heart Failure in the Emergency Department: A Systematic Review and Meta-analysis

Background

The chief complaint of “dyspnea” represents a very large cohort of patient who present to the emergency department. While acute heart failure (AHF) is a very common diagnosis in the setting of dyspnea, the diagnosis remains challenging when the emergency physician is presented with the undifferentiated dyspneic patient. Interestingly, emergency physicians have varied approaches to the work up and diagnosis of these patients and it is not clear as to which diagnostic element is most crucial in confirming the diagnosis of AHF. Spoiler: Ultrasound proves to be quite useful.

Diagnosing Acute Heart Failure in the Emergency Department: A Systematic Review and Meta-analysis‌

 

Clinical Question

What are the operating characteristics of the diagnostic elements available to the emergency physician for diagnosing acute heart failure?

Methods & Study Design

  • Design
    • This is a systematic review evaluating index test operating characteristics in diagnosing AHF. A medical literature search was performed using PubMed and EMBASE, evaluating peer-reviewed published papers from 1965 through 2015
    • Individual systematic reviews for each index test were conducted by two separate physicians and thereafter reconciled to obtain a comprehensive set of studies on the topic. These were then screened against the inclusion/exclusion criteria for final inclusion into the meta-analysis
    • The reference standard used was a final diagnosis of AHF based on review of clinical data by independent reviewers who were blinded to the study’s primary index test
  • Population
    • All studies included involved patients presenting to the emergency department (ED) with the chief complaint of “dyspnea.”
  • Outcomes
    • Pooled sensitivities, specificities and likelihood ratios (LRs) of index tests for diagnosing acute heart failure in patients presenting to the ED with dyspnea
    • They specifically looked at the following index tests in evaluation of AHF: history and physical exam, ECG, chest x-ray, BNP and NT-ProBNP, lung ultrasound (US), and bedside echocardiography
  • Excluded
    • Patients presenting to urgent care with dyspnea
    • Patients with chronic, compensated heart failure
    • Studies focusing on prognosis or therapeutics and not the diagnosis of AHF
    • Studies with ultrasound images that were not obtained and interpreted by emergency physicians

Results

    • History and Physical: S3 most specific finding for AHF (+LR 4)
    • ECG: Found to be insensitive and unspecific for diagnosing or ruling out AHF
    • CXR: Pulmonary edema was the most specific finding (LR + 4.8). All other imaging findings were insensitive for ruling out heart failure
    • BNP and NT-Pro-BNP: Quite sensitive for ruling out AHF at a threshold of 100/300pg/dL
    • Lung Ultrasound:
      • Presence of >3 B-lines in >2 lung fields is very specific for the presence of AHF
      • Lack of this also sensitive for ruling out acute heart failure
      • High inter-rater reliability
    • Bedside Echo
      • ED provider evaluation of systolic function had high inter-rater reliability with the ultimate ejection fraction assessed by cardiologists on formal echo
      • Restricted Mitral Inflow very specific for ruling in diastolic AHF in patients with preserved systolic function

Strengths & Limitations

  • Strengths
    • Very thorough analysis of the operating characteristics of a plethora of diagnostic elements and sub-elements available to the emergency physician in diagnosing AHF
    • Authors didn’t exclude comorbidities, etiology of AHF or if there was an underlying arrhythmia which increased the generalizability of their results
    • All data was screened and evaluated by two separate physicians
  • Limitations
    • The reference standard was a final diagnosis of AHF made by physicians in retrospective fashion which weakens this as a “gold standard.”
    • The authors did not specifically evaluate or reconcile whether the heart failure was left or right sided
    • Each of the tests or test characteristics were assessed in isolation to determine the likelihood of heart failure. The likelihood of AHF when considering multiple index tests was not assessed
    • As in all large meta-analyses, some spectrum bias may exist as inclusion/exclusion criteria varied among included studies. However, ome of this heterogeneity is likely countered by the pooled analysis and is unlikely to drastically change the calculated LRs

Author's Conclusions

"Bedside lung US and echocardiography appear to the most useful tests for affirming the presence of AHF while natriuretic peptides are valuable in excluding the diagnosis."

Our Conclusions

This is one of the most thorough studies available to assess the likelihood that a patient presenting to the emergency department has acute heart failure based on an index test. There are many old standby diagnostic modalities available to emergency physicians including the history, physical exam, and chest x-ray. Unfortunately, these diagnostic elements are relatively non-specific in establishing that a patient’s acute symptoms are likely or unlikely due to heart failure. BNP and NT Pro BNP are quite useful in ruling out heart failure however these tests take time to result. Ultrasound is rapidly becoming a fundamental tool in every emergency physicians tool belt and should be utilized alongside the primary patient assessment in determining the likelihood that a patient has heart failure. The presence or absence of B lines (>3 in at least 2 fields) is quite specific for ruling in heart failure and the absence is nearly as sensitive as a normal BNP or NT Pro BNP, too. And in the event of systolic heart failure, echo is a great modality to rapidly assess a patient’s pump function; our interpretation is consistent with the formal result obtained by cardiologists [2].

Caution must nevertheless be maintained when evaluating these results. The LRs found in these studies were calculated independently of other findings and in reality, the emergency physician takes multiple factors from the history, physical exam, and other diagnostic modalities, to ultimately come to a definitive diagnosis. Essentially, the short answer is that no single test should be taken as definitive in diagnosis of AHF (or any diagnosis for that matter) and the emergency physician should follow a bayesian approach using pre- and post- test probabilities from their fund of knowledge to rule in and rule out cannot miss diagnoses. Lastly, with regards to this study, physicians should be wary about interpreting these results in the context of renal failure primarily but also superimposed pneumonia or underlying concern for pulmonary embolism as these patients were excluded in a number of papers included in this meta-analysis.

The Bottom Line

Bedside ultrasound to evaluate for the presence or absence of pulmonary edema should be an integral part of the emergency physicians approach to evaluating patients to the emergency department with undifferentiated dyspnea.

Authors

This post was written by Matt Correia, MD PGY-2 at UCSD. It was edited by Michael Macias, MD.

References

    1. Martindale JL, e. (2017). Diagnosing Acute Heart Failure in the Emergency Department: A Systematic Review and Meta-analysis. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 14 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/26910112
    2. Moore CL, e. (2017). Determination of left ventricular function by emergency physician echocardiography of hypotensive patients. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 14 August 2017, from https://www.ncbi.nlm.nih.gov/pubmed/11874773

Case # 3: Under Your Skin

A 52 year old male with presents with 4 days of painful swelling and redness to his middle right thigh. Physical exam shows a 3 cm area of erythema that is tender to touch. He denies fever and trauma to the area. A bedside ultrasound is performed as seen below. What is the next step in management?

Vitals: HR 82 BP 110/72 RR 14 O2 98

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Answer and Learning Point

Answer

Incision and drainage. The image above demonstrates a well circumscribed fluid collection within the soft tissue,  without evidence of surrounding cellulitis. The above abscess was incised with immediate release of a large volume of purulent material. The patient did well.

Learning Point

    • Ultrasound is an excellent adjunct to the physical exam in the evaluation of soft tissue infections. It improves accuracy in the diagnosis of superficial abscesses and has been shown to change management in up to 50% of emergency department cases of clinical cellulitis [1,2].
    • The ultrasound image above is atypical for an abscess given the iso-echoic texture appreciated in the fluid and is easily missed if the operator is not aware of this unusual finding. Most abscesses will appear as a hypoechoic fluid collection, however occasionally they may have increased internal echoes which can lead to false negative ultrasound results.
    • This can be avoided by applying gentle pressure to the area of the suspected cellulitis/abscess to evaluate for the "swirl sign" which is indicative of fluid movement within the abscess cavity [Figures 1&2].
    • This can be distinguished from the common pattern appreciated in cellulitis known as "cobblestoning" which indicates increased subcutaneous fluid.
Figure 1: Soft tissue ultrasound demonstrating swirling of iso-echoic fluid collection consistent with abscess. Image courtesy of UOTW.
Figure 2: Additional soft tissue ultrasound demonstrating the "swirl sign." Image courtesy of UOTW.

References

 Tayal VS, e. (2017). The effect of soft-tissue ultrasound on the management of cellulitis in the emergency department.

Squire BT, e. (2017). ABSCESS: applied bedside sonography for convenient evaluation of superficial soft tissue infections.

UOTW: Case 66