BASIC CARDIAC ECHO
- Terminology
- The questions to ask
- How to scan
- Cardiac anatomy on US
TERMINOLOGY
ACRONYMS
A4C: apical 4 chamber
A5C: apical 5 chamber
ACEM: Australasian College for Emergency Medicine
ASUM: Australasian Society for Ultrasound in Medicine
IVC: inferior vena cava
LA: left atrium
LV: left ventricle
LVEF: LV ejection fraction
LVIDd: LV internal diameter in diastole
PE: pulmonary embolus
PLAX: parasternal long axis
PSAX: parasternal short axis
PTX: pneumothorax
RA: right atrium
RV: right ventricle
RVOT: RV outflow tract
LEVELS OF CARDIAC ECHO
[Just what is ‘basic cardiac echo’ anyway?]
There are a lot of different names & types of cardiac echo out there, which can be confusing. Basically, imagine three levels of cardiac echo, each one more complex. The differences between each are outlined below.
CREDENTIALING
This course satisfies the ‘echocardiography in life support’ module for ACEM (and for ASUM when that module is finalised).
PRINCIPLES OF BASIC CARDIAC ECHO
- Opportunistic: you often can’t achieve all views in the critically ill but you can usually obtain at least one useful view of the heart
- Qualitative: ‘gross visual’ assessment (no measurements)
- Simple: limited to 2D ‘B’ mode scanning
- Caricatural: as Lichtenstein pointed out, life threatening abnormalities are usually bloody obvious on US. For example:
- If a PTX is causing life threatening respiratory distress, it won’t be a small one.
- If a PE is causing shock, it will be large enough to distend the IVC and stretch the RV.
THE FOCUSED QUESTIONS
In the shocked, dyspnoeic, or arrested patient we ask the following questions:
IS THE HEART BEATING?
- In the arrested patient, cardiac standstill carries a significantly worse prognosis and many clinicians would cease resuscitation at this point.
IS THERE A TAMPONADE?
- This is a clinical question: IE the single most important features is that the patient is critically shocked.
- One needs to ID a pericardial effusion (NB this can occasionally be subtle / localised, but will usually surround the heart & be present throughout the cardiac cycle)
- The easiest, most reliable US feature of tamponade [versus simple effusion] is the presence of distended veins (IVC and elsewhere). Other features such as RV diastolic collapse can be subtle.
IS THE IVC / LV/ RV LARGE/SMALL/GROSSLY NORMAL?
-
See the relevant sections of this manual.
IS LV/RV CONTRACTION GROSSLY NORMAL?
- See the relevant sections of this manual.
BEFORE YOU START
ANATOMY
The right side of the heart lies in front of the left. That means it’s closer to the probe on all views except the apical.
The heart is a complex structure: like a hand (RV) wrapped around a fist (LV).
Patient position: obviously this depends on how sick is your patient!
If you can move them at all, then it’s worth knowing that:
- Supine is best for the subcostal windows
- For the parasternal and apical windows, left lateral is best (pillow wedged under right shoulder) to get the heart out from under the sternum, and left hand behind head to open up the rib spaces
PROBE AND SCANNER SETTINGS:
- As mentioned above, you can get away with the curvilinear ‘FAST’ probe on abdo/ FAST settings.
- However, the cardiac (sector array) probe and cardiac preset will provide better images of fast moving structures (eg the valves) and its smaller ‘footprint’ of the probe allows scanning between the ribs.
WHERE TO SCAN – THE CARDIAC WINDOWS
- Subcostal/subxyphoid long axis
- Parasternal long (PLAX) and short (PSAX)
- Apical 4 chamber (A4C) and 2 chamber (A2C)
SUBCOSTAL LONG AXIS VIEW
- The subcostal/subxyphoid window is familiar to those who perform EFAST scans and is often the most reliable view because it uses the liver as a window.
- Sometimes it’s the only possible window (e.g. during CPR)
- Patient position:
- Supine is best
- A deep breath improves the image (pushes liver under the probe and bowel gas away)
- Knees bent also helps (relaxes the abdominal wall muscles)
- Probe just under the xiphisternum, angled up under the ribs (= towards the heart)
- Probe marker:
- On abdominal preset: to patient’s right = 9 o’clock
- On cardiac preset: to patient’s left = 3 o’clock
Anatomy: the RV is above the LV and the liver is at the top of the screen. The cardiac apex should point to the right of the screen.
PARASTERNAL LONG AXIS VIEW (PLAX)
- The right ventricle (RV) ‘hides’ behind the sternum in this view, so don’t base RV assessment on this window!
- Probe to the left of the sternum, angled straight down (= towards the heart)
- Probe marker:
- On abdominal preset: to patient’s left elbow = 5 o’clock
- On cardiac preset: to patient’s right shoulder = 11 o’clock
- Angled along the long axis of the heart, not the patient
- Rotate the probe until the heart comes into view
- Sometimes you need to move up / down to the next intercostal space, and/or slide the probe laterally.
- Try and angle the probe so that you scan see the following simultaneously:
- The aortic and mitral valves (AV & MV)
- The left atrium, left ventricle (NOT including the apex), the aortic root (Ao) and the RV outflow tract (RVOT).
PARASTERNAL SHORT AXIS VIEW (PSAX)
- Probe in same position as for PLAX
- Probe is now rotated clockwise so that:
- On abdominal preset: to patient’s right elbow = 8 o’clock
- On cardiac preset: to patient’s left shoulder = 2 o’clock
- Angled along the short axis of the heart
- In this view, the heart appears in transverse section
- Then tilt the probe from apex to base of the heart. This allows a number of different ‘slices’ to be obtained:
- PSAX- AV [level of aortic valve]
- PSAX-MV [level of mitral valve = base of LV]
- PSAX-PAP [level of papillary muscles]
- PSAX-APICAL [level of apex]
- In basic cardiac echo, we can’t usually see the RV very well because it’s lurking in the near field, under the sternum. So all we are really looking at is the LV:
- Its size
- Its global function (leave the regional wall motion abnormalities to the fancier scans)
- Most importantly, its shape: is it an ‘O’ or a ‘D’?
- ‘O sign’ = normal state of affairs = LV is higher pressure than RV
- ‘D’ sign = cor pulmonale = RV is higher pressure than the RV
- It’s best to look at the level of the papillary muscles if at all possible.
APICAL FOUR CHAMBER VIEW (A4C)
APICAL FOUR CHAMBER VIEW (A4C)
- Either slide the probe down the heart to the apex, or place the probe at the point of apex beat (usually 5th intercostal space, near anterior axillary line)
- Probe angled up along the axis of the heart, more or less towards the patient’s head
- Probe marker:
- On abdominal preset: to patient’s right elbow = 8-9 o’clock
- On cardiac preset: 2-3 o’clock
- Angled along the heart’s long axis
- In this view, the heart appears in transverse section
- In basic cardiac echo, this view helps identify right sided pathology (e.g. dilated RV) and also pericardial effusions
APICAL TWO CHAMBER VIEW (A2C)
Top tips:
- Probe in same position as for A4C but rotated anticlockwise so that marker is at 11 0’clock on cardiac preset.
- In basic cardiac echo, this window is rarely helpful! That’s because it’s really just looking at the anterior and inferior walls of the LV, for regional wall motion abnormalities.