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

2 Replies to “Feasibility and accuracy of bedside transthoracic echocardiography in diagnosis of acute proximal aortic dissection”

  1. Cool article! Question: how likely are the CT surgeons to trust a TTE and prepare for emergency surgery without a CT?

    1. Hi Emily! That is a great question. Since aortic dissection is not common, I personally have not had enough cases to definitively answer this question. The utility of this for the emergency department work up would be that if you have a concerning chest pain story, you can perform a quick bedside echo looking at the aorta for dilation or a flap (or pericardial effusion if it dissected into pericardium). If this exam is positive, then you can get CT surgery on board quickly. If patient is unstable then you can have discussion with them about your findings (and show them clips) and potentially go straight to OR. If pseudostable, you now can expedite your patient to the CT scanner (I would push them over to the scanner myself immediately) and start aggressive heart rate and blood pressure control. This is an extremely time sensitive diagnosis so the sooner we can get information the better. Hope this helps!

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