Utility of POCUS or evaluating aortic syndromes

Integration of transthoracic focused cardiac ultrasound in the diagnostic algorithm for suspected acute aortic syndromes

Kristen La MD PGY1

Ultrasound Journal Club, January 20 2021

Article: 

Nazerian P, Mueller C, Vanni S, Soeiro AM, Leidel BA, Cerini G, Lupia E, Palazzo A, Grifoni S, Morello F. Integration of transthoracic focused cardiac ultrasound in the diagnostic algorithm for suspected acute aortic syndromes. Eur Heart J. 2019 Jun 21;40(24):1952-1960. doi: 10.1093/eurheartj/ehz207. PMID: 31226214.

Introduction and Background

  • Acute aortic syndromes (AAS) are defined by this study as an acute aortic dissection, intramural hematoma, penetrating aortic ulcer, or spontaneous aortic rupture
  • Conclusive diagnosis of AAS is made by computed tomography angiography (CTA), however transesophageal echocardiography (TEE) was also appropriate. 
  • Despite increased use of CTA, AAS remains a very difficult diagnosis to pin down, with misdiagnosis of AAS up to 39%
  • This is further complicated by the fact that presenting symptoms of AAS can be nonspecific.
  • This is a study published in the European Heart Journal. The European Society of Cardiology already recommends transthoracic focused cardiac ultrasound (FoCUS) as a bedside tool to assist with rapid assessment of patients suspected of having AAS. 
  • The European Society of Cardiology also recommends the aortic dissection detection risk score (ADD-RS) to help determine pre-test probability for AAS. 

Objectives

  • Can FocUS help further determine the need for CTA or TEE in patients who have a low risk ADD-RS score?
  • Can we create a reliable algorithm for ruling-out AAS by combining a low ADD-RS, negative FoCUS, and negative D-Dimer level?

Methods

  • This was a secondary analysis of the ADvISED prospective multicentre study, which initially was looking at the use of D-dimer with the ADD-RS score. 
  • Study participants included adults who had one or more of the following symptoms within the past 2 weeks: chest, abdominal, or back pain, syncope, or signs of a perfusion deficit. 
  • Patients who presented as a primary trauma or declined participation were excluded. 
  • Those who performed the ultrasound were physicians with at least one year experience in ultrasound or who were cardiologists. 
  • The ultrasound views used to evaluate the aorta included at least one of the following: parasternal long, parasternal short, apical, suprasternal, subcostal, abdominal, or the carotid artery view. 
  • Ultrasound findings of AAS were defined as either direct or indirect:
    • Direct: intimal flap separating two aortic lumens, intramural aortic hematoma (circular/crescentic thickening of wall measuring > 5mm), penetrating aortic ulcer (crater outpouching of wall with jagged edges)
  • Indirect: thoracic aorta dilatation (diameter at least 4 cm or greater), pericardial effusion/tamponade, aortic valve regurgitation under color doppler
  • Patients were then sorted into high vs low clinical pre-test probability based on their ADD-RS score.
    • Low (ADD-RS ≤ 1): Had a score of zero, or only scored within one risk category
    • High (ADD-RS >1): Scored within more than one risk category. 
  • Patients also had D-dimers drawn, with a negative result if < 500 ng/mL fibrinogen equivalent units
  • Conclusive imaging included CTA, TEE, or MRA.
  • Patients were then determined whether or not they had AAS by two independent physicians who reviewed data from the initial emergency department visit and the follow up period:
    • Positive AAS was confirmed by: imaging, surgical intervention, or autopsy
    • Negative AAS was confirmed by: negative imaging, surgery, autopsy. For those who did not undergo imaging or surgery, case determination was performed during a 14 day follow up telephone call or outpatient clinic visit, at which point it was determined if a diagnosis of aortic disease had been made, repeat ED/hospital visit occurred, or death. If alternative diagnoses were reached or if there was an uncomplicated 14 day follow up, then the patient was concluded to have been negative for AAS. 

Results

  • 864 participants underwent ultrasound, and 839 were analyzed further
  • The most common presenting symptom was chest pain
  • 146 (17.4%) of patients had AAS, and 693 (82.6%) did not have AAS. 
  • Of the FoCUS views used, the left parasternal, apical, and subcostal views were most utilized. 
  • 10% of patients (84 total) were found to have a direct sonographic sign of AAS, with 18 false positives and 80 false negatives. 36.6% (307) patients had indirect signs, with 177 false positives and 16 false negatives. 
  • Data was analyzed using receiver operating characteristic curves (ROC), and it was found that, by combining FoCUS findings with the ADD-RS score, the diagnostic accuracy for AAS was significantly increased (indicated by an increase in the area under the curve). 
  • This was further shown by the utilization of Fagan nomograms, which indicated a post-test probability of :
    • 65% in those with an ADD-RS ≤ 1 and direct FoCUS signs
    • 6% in those with an ADD-RS ≤ 1 and no direct FoCUS signs
    • 28% in those with an ADD-RS ≤ 1and any FoCUS sign
    • 2% in those with an ADD-RS ≤ 1 and no FoCUS sign at all.
  • If patients had a low risk ADD-RS score and a negative FoCUS, the sensitivity for ruling out AAS was 93.8% [88.6 – 97.1%].
  • The study then combined a low risk ADD-RS score, negative FoCUS, and a negative D-dimer test, and found that the sensitivity increased to 100% [97.3-100].

Discussion:

  • While direct FoCUS signs can have a strong specificity for diagnosis of AAS, it is not sufficient as a rule-out tool when used alone (not sensitive enough). 
  • Furthermore, sole utilization of indirect FoCUS signs offers too many false positives, and poses a risk of over-testing. 
  • Combining FoCUS with the ADD-RS tool has additive value, and improves diagnostic accuracy for AAS.
  • When FoCUS and the ADD-RS score are then further combined with the D-dimer, a safe and reliable rule-out strategy is possible. 

Limitations:

  • This was a secondary analysis
  • Advanced imaging was only performed for about half of the participants. Of those who did not get imaging, presence/absence of an AAS diagnosis was determined at a 14 day follow up period. This short clinical follow up may have meant some AAS cases were missed. 
  • This study still needs to be externally validated. 

Conclusion

  • When used alone, FoCUS can best help determine the need for additional imaging (eg by CTA) when direct signs are detected.
  • In patients that have a lower pre-test probability of AAS (designated by a low ADD-RS score ≤ 1), using FoCUS and a negative D-dimer offers a useful rule-out tool for AAS, and the following decision-making tree can be utilized (Figure A):

Figure A

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