Case vignette
84yo M w/ no medical history p/w syncope to a small community ED. He was walking when he suddenly syncopized and collapsed for a few seconds. He feels fine now. This has never happened before.
HR 110, BP 115/60, T 37, RR 22, SpO2 85% on RA --> 95% on 4L NC
Elderly male appears mildly dyspneic. Clear lung sounds bilaterally. Cardiac auscultation with regular rhythm, tachycardia, and no murmurs. No BLE swelling.
What do you see?
CP8 Apical 4: poor contractility at RV mid/apical segments, RV>LV size, preserved/hyperkinesis of RV apex (McConnell's Sign)
CP8 IVC: >2cm IVC with <50% respiratory variation
What do you do next?
Using POCUS, you note a dilated RV, McConnell's Sign, reduced Tricuspid Annular-Plane Systolic Excursion (TAPSE), and dilated IVC with minimal variation. You suspect a massive PE caused this patient's collapse but wonder if it has moved more distally (e.g., it was in transit when he syncopized). A CTA PE is ordered which shows substantial bilateral PE burden. Cardiac biomarker (troponin, BNP) are elevated.
The patient is not hypotensive or in shock, making this a submassive PE. However, he has imaging and biomarker evidence of right heart strain and a high PESI score. He is transferred to a larger center for consideration of thrombectomy/catheter-directed thrombolysis.
Teaching points. POCUS can be used to augment your pre-test probability of PE, particularly for massive PE. Multiple views have utility, however a number of caveats exist. Understanding when/how to obtain these views and incorporate them into your clinical context is important.
Basic views:
- On parasternal long axis (PLA), RV:aortic:LA diameter should be similar. An enlarged RV is concerning for right heart strain.
- On parasternal short axis (PSA), septal flattening, creating the shape of a "D" in the L ventricle ("D-sign"), is concerning for RV strain.
- On apical 4, normal RV:LV size is ~2:3. A ratio >1:1 is concerning. McConnell's Sign (RV free wall hypokinesis with preserved RV apical motion) has low sensitivity but is concerning. In the apical 4 view, you can also obtain Tricuspid Annular Plane Systolic Excursion (TAPSE) to assess RV ejection fraction. The vertical movement of the tricuspid valve is measured using M-mode. Values <16-18mm are concerning.
- On subxiphoid, a dilated IVC with minimal respiratory variation is concerning for pending or actual obstructive shock.
- Paradoxical septal motion (RV bowing into LV) may be seen in multiple views.
Importantly, right heart strain findings may be chronic and not acute, suggesting a cause other than PE (such as COPD or chronic pulmonary hypertension).
Multiple method exist to differentiate acute and chronic processes, but all have exceptions. A thicker RV may be seen in chronic states, whereas a thinner RV suggests an acute process. To assess this, measure the RV thickness at the end of diastole (when it is most full). A measurement of >5mm is abnormal, with higher values suggesting hypertrophy from chronic processes (though thickening can begin within ~2d).
Advanced users can also calculate R ventricular systolic pressure (RSVP) and pulmonary acceleration time (PAT) to help differentiate chronic from acute R heart strain. To read more about these methods, see this excellent post: https://www.emra.org/emresident/article/bedside-echo/.
POCUS can look for other evidence of PE to increase confidence. For example, you can assess for BLE DVTs. In addition, lung ultrasound can assess for alternative causes (evidence of pneumonia, effusions, etc), or advanced users can assess for subpleural infarcts due to PE.
In sum, look for the findings of R heart strain when you are concerned about PE -- but remember to interpret them in the clinical context and pursue additional testing as appropriate.
Sources:
- Ham J, Stolz L. US - Diagnosing PE: Ultrasound of the Month. Taming the Sru. 10/2018. https://www.tamingthesru.com/blog/ultrasound/case-of-the-month/october. Accessed 4/13/21
- Pellet A, Zeidan A, Avila J. Differentiating Acute Versus Chronic Right Heart Failure with Bedside Echocardiography. EMRA: Ultrasound, Cardiology. 08/2019. https://www.emra.org/emresident/article/bedside-echo/. Accessed 4/13/21.
R Heart Strain + McConnell's Sign