Subxiphoid is the only window available? No problem!
You are performing physical examination (POCUS) on a mechanically ventilated patient with heart failure. Unfortunately, you are not able to get adequate cardiac views from parasternal and apical windows. Not an uncommon scenario in those with expanded lungs or crowded ribs. Furthermore, the patient is leaning towards their right and it is difficult to reposition. As you know, left lateral is the preferred position for parasternal and apical cardiac views where feasible. Patient’s position also makes right upper quadrant (the VExUS window) difficult to access. In such cases, subxiphoid views can answer most of the focused questions that we encounter during nephrology consults. Let’s see how.
How is the right atrial pressure (RAP)?
Cannot reliably estimate RAP in a mechanically ventilated patient by IVC POCUS but it’s still helpful to take a look. For example, a small, collapsible IVC can provide a clue to bleeding or volume depletion. Conversely, a big, round IVC suggests high RAP (better than ‘8mmHg’ reported on formal echo [that’s what is reported by default in any mechanically ventilated patient]). In this case, IVC appears full, measuring close to 2 cm in diameter. Patient is relatively small.
How is the left ventricular systolic function?
On this subxiphoid 4-chamber view, LV is poorly contracting. So, the ejection fraction is very low.
Is there a pericardial effusion? None seen on above image.
Now let’s get subxiphoid short axis view by rotating the transducer counterclockwise as shown in the illustration below. It’s similar to parasternal short axis but a slightly tilted version because we are imaging from a different window.
It again shows that the LV function is poor and there is no pericardial effusion. Is there a D-sign indicative of RV pressure or volume overload? No, the interventricular septum is bowing to the right and not flattened here. Also, LV seems dilated.
From the above view, fan the transducer superiorly (towards patient’s head) to see more structures of interest as demonstrated below.
What is the stroke volume?
Apical 5-chamber view could not be obtained in this patient. So, what’s the alternative? You could do right ventricular outflow tract (RVOT) velocity time integral (VTI) from the subxiphoid short axis view and use it as a surrogate for LVOT VTI because what goes through right ventricle should come out of the left ventricle assuming there is no intracardiac shunt. RVOT VTI <16 cm is generally considered reduced. Here, it’s extremely low even if you account for minor angle issues (ideally, flow must be parallel to Doppler cursor; here it’s slightly off). In addition, observing RVOT Doppler pattern (? Notching) gives an idea about precapillary component of pulmonary hypertension.
Is there venous congestion?
Hepatic and portal veins can be accessed through subxiphoid window in transverse plane. From the transverse IVC view, if you fan superior, hepatic veins come into view and portal vein is seen if you fan inferiorly. Here, hepatic vein Doppler shows S<<D pattern suggestive of moderate congestion. Similarly, portal vein pulsatility fraction is 50%, suggestive of moderate to severe congestion. Femoral vein Doppler (component of extended VExUS) shows increased pulsatility as well.
Another question that comes up while interpreting hepatic vein Doppler is the presence of tricuspid regurgitation (TR). TR can be qualitatively assessed from subxiphoid short axis view at the aortic valve level. Here, the high velocity regurgitant jet (mixed colors) seems to be occupying more than 50% of the right atrium; qualitatively, we can say TR is moderate to severe. It has implications for the end goal of decongestive therapy.
Interestingly, after 2 Liters of ultrafiltration, portal vein waveform has normalized and hepatic vein slightly improved. IVC diameter and TR remained almost the same. Follow up images obtained using a handheld ultrasound device.
Below are follow up images after achieving 3 liters net negative fluid balance after the previous dataset. TR appears to have improved though qualitatively it’s still moderate. However, Hepatic vein waveform has considerably improved (S slightly less than D) and portal vein remained continuous. This Hepatic trace is difficult to interpret without EKG (i.e., identify which is S vs D). IVC diameter also improved despite being on mechanical ventilation. White dots on IVC M-mode are air bubbles from saline flush.
Summary: Don’t underestimate the value of subxiphoid window!