Transthoracic echocardiography

The TTE questions are increasing in their number and the expected level of detail.

• Question 16 from the second paper of 2020
• Question 17.1 from the second paper of 2014 (peri-arrest findings)
• Question 17.2 from the second paper of 2014(peri-arrest findings)
• Question 3.2 from the first paper of 2009 (LVOT obstruction)
• Question 29.2 from the second paper of 2008 (severity staging of aortic stenosis)
• Question 8.3 from the second paper of 2010 (severity staging of aortic stenosis)
• Question 13.1 from the first paper of 2008 (severity staging of aortic stenosis)

Somehow, the college has focused their echocardiographic interest on aortic stenosis. Of the six  past paper questions which concern TTE data interpretation, two are about AS. Question 17.1 and Question 17.2 from the second paper of 2014 are perhaps more relevant, as the discussion revolves around the identification of peri-arrest findings on TTE images. Assessment of valve dysfunction (eg. severity staging of aortic stenosis) is covered in greater detail in the Cardiothoracic Intensive Care section, and no further time will be spent here on the TTE assessment of valvular disease.

The use of echocardiography in cardiac arrest

Question 17.1 from the second paper of 2014 asked about the utility of TTE in cardiac arrest, and particularly which the most appropriate view is. The answer to the latter is inevitably the subcostal view; it would be insane to interfere with CPR by trying to shove the probe on the chest. The former is best answered in a "critically evaluate" pattern, even though the college question itself did not demand such depth.

An ideal resource for answering such a question would have to be this 2012 article by Price et al. In addition to this earlier article, Berg (2018) is worth reading for the pros and cons, as the paper comes from the more modern era during which the enthusiasm  for intra-arrest ultrasound has somewhat cooled. 

Rationale for the use of TTE during an arrest

• Cardiac arrest is caused by numerous aetiologies, of which only a few can be diagnosed by virtue of rhythm analysis or history and examination.
• Many of the "non-shockable" causes of cardiac arrest can be identified or confirmed by TTE, including the following:
  • Cardiac tamponade (RV collapse in systole, large effusion)
  • Massive PE (RV diltation, empty LV, D-shaped septum)
  • Hypovolemia (empty chambers, collapsed IVC)
  • Tension pneumothorax (chest US rather than cardiac echo)
• Other basic tools of assessment are already in routine use (eg. SpO₂ monitoring and EtCO₂ monitoring)

Advantages of intra-arrest TTE

• Non-invasive
• More effective in determining cardiac activity than palpation of central pulses
• May be effective in identifying a shockable rhythm when the ECG is impossible or unhelpful
• Allows US guidance of remedial procedures, eg. pericardiocentesis
• Allows real-time monitoring of the effectiveness of fluid resuscitation
• Allows the identification of regional wall motion abnormalities during periods of ROSC, which might result in an earlier decision to proceed with angiography
• May aid in the decision to stop resuscitation
• Non-experts can be easily trained to perform brief focused TTE.
• Pauses in CPR which are expected to last longer in the first place may be used as opportunities to use ultrasound (eg. intubation)

Disadvantages of intra-arrest TTE

• Intrudes upon team attention (it is another screen to mindlessly watch)
• Takes focus off resuscitation
• Requires significant skill to perform
• Images may be of poor quality in many circumstances
• Uninformative images may be misinterpreted and inaccurate management decisions could be made.
• So far, there has been no evidence of improved outcome
• It may result in an unacceptable interruption to CPR. in't Veld et al (2017) and Clattenburg et al (2018) found that the use of ultrasound prolonged off-the-chest pauses from an average of 11 seconds to 17 seconds, with the additional six seconds being wasted on image acquisition. Most interestingly, the ultrasonography pause was longer when the operator was also leading the arrest. 

Evidence and consensus guidelines regarding intra-arrest TTE

• Memtsoudis et al (2006) - 22 of non-cardiac surgical patients who had an unexpected cardiac arrest; the use of TOE in the operating theatre was evaluated. Of the 22, 18 had major changes made to their management on the basis of TOE findings. In-hospital survival was 32%.
• Blyth et al (2012) - meta-analysis of TTE as predictor of survival in cardiac arrest. 11 papers with a total of 558 patients were included. Intra-arrest TTE which demonstrated cardiac inactivity was strongly associated with the inability to restore spontaneous circulation. There was also a small, nonzero chance of ROSC with a motionless heart: 2.4% of patients with a motionless left ventricular wall would go on to achieve ROSC.. Pooled sensitivity was 91% and specificity was 80%. Research such as this is frustrated by unclear methodology: was the TTE performed in the first minute of CPR, or in the fortieth minute? Most people would agree that there is a difference in the way you would interpret the findings.
• Anderson et al (2014) - swine model of cardiac arrest; ultrasound-guided compressions improved coronary perfusion pressure, because the rescuers were able to see how well (or poorly) they were compressing the left ventricle.
• Flato et al (2015) - observational cohort of 49 ICU patients. TTE changed management in 51% and there was a surprising number of "pulseless" patients who actually had cardiac activity on TTE. These patients actually had a much better rate of ROSC (~70%) in comparison to the truly pulseless patients who had no cardiac motility (who had ROSC rates of around 20%). The authors concluded that intra-arrest TTE can identify potentially salvageable patients.

Support for this practice among published  guidelines

• ARC Guideline 11.6 (2010) gives a Class B recommendation to the use of ultrasound in cardiac arrest, but on the basis of weak (Level IV) evidence.
• Intensive Care Society recommends "Focused Intensive Care Echo"(FICE) to be among the basic competencies for intensivists.
• ASEP/ASE consensus statement (2010)  recommends FOCUS ( focused cardiac ultrasound ) in a complimentary diagnostic role.
• ILCOR (2015) demur making any recommendation, saying that it "may be considered" as an adjunct only where "a qualified sonographer is present and use of ultrasound does not interfere" with CPR.

Fatal echocardiographic abnormalities

Question 17.2 from the second paper of 2014 asked for the candidates to identify characteristic abnormalities seen on the TTE during a cardiac arrest. A picture is worth a thousand words:

In answer to Question 16 from the second paper of 2020, the single best view to assess the pericardial tamponade is through a subxiphoid view. At least that's what it sounds like the examiners wanted ("which view", they asked, implying one view). Most echosavvy people will agree that to fully appreciate the effusion and its haemodynamic effects you would need to image it in at least a couple of different planes. Loculated effusions could have disproportionate regional effects, and limited views can give rise to the misidentification of all kinds of sonolucent friendlies (eg. ascites, pericardial cysts). If there is an effusion, it is also very easy to overestimate its size. D'Cruz & Constantine (1993) detail these pitfalls in their paper, for the interested reader with infinite time.  

The subxiphoid view, however, has a couple of benefits:

• It is available while CPR is in progress, 
• It is convenient to perform this in a supine patient, and
• The most dependent portion of the heart is nearest to your probe, and that is where the effusion is most likely to be

Echocardiographic features of cardiac tamponade are listed elsewhere.