I wrote previously about my first study testing a novel method to estimate right atrial pressures at the bedside. In that study, 55 patients underwent right IJ ultrasound and right atrial depth measurement, and a cutoff at the supraclavicular point was used to try to rule in or out high pressure. This was then compared to the results from right heart caths performed by multiple interventional cardiologists blinded to the ultrasound results.
The problem with this study strategy, as I learned, was two-fold:
Different cardiologists have slightly different zeroing techniques which can result in relatively large differences in right atrial pressures
Using cutoff points artificially reduces the perceived accuracy. For example, if a patient's right atrial depth is 8 mm and there is no JVD present at the supraclavicular point, then this method would predict that the right atrial pressure was less than or equal to 8 mm. But if the actual pressure was 8.5 mmHg, then this would be counted as incorrect even though it was almost exactly correct.
With these limitations in mind, we completed another study (in pre-print, submitted for publication) with only one interventionalist using one zero point (mid-anterior-posterior diameter). We wanted to see how close we could get to the actual right atrial pressure, as well as how often it was within 3 mmHg.
Clinically, a simple method that could get accurate right-sided pressures within 3 mmHg would have a profound impact on diuretic management and the need for a right heart cath.
The subjects were any adult patients needing a right heart cath for any reason. The only patients excluded were those with a right IJ catheter present, intubated or on positive pressure ventilation, or if the left ventricular outflow tract was not visible in the parasternal long-axis view.
The ultrasound exam was performed 2 hours or less prior to the RHC, and the results were recorded into the database prior to the RHC. The interventional cardiologist was also blinded to the ultrasound results. The ultrasound technique was as follows:
Each ultrasound exam took just a couple of minutes. The jugular vein was easily visualized in every patient. Only one patient was enrolled in which the left ventricular outflow tract (LVOT) could not be visualized in the parasternal long-axis view.
For some real cases using this method, see my internal medicine grand rounds here (JVP exam starts at minute 28, cases start at minute 39):
Results
We included 39 patients in our final analysis. Overall, this method was very accurate. It was within 3 mmHg 75% of the time (as compared to about 30% accuracy of IVC), and it was within 5 mmHg for the remaining cases. The only exception was a patient with a right atrial pressure of 19. The 'Wine bottle sign' could not be visualized because the JVD went above the mandible. It was technically correct, since it was entered as "greater than 11," but recorded as equal to 11 for the correlation calculation.
Our correlation coefficient was 0.75, and R^2 was 0.56.
Now compare the above graphs to those from a prospective blinded study of IVC compared to right atrial pressure obtained from right heart cath:
Both IVC diameter and collapsibility index were extremely poor predictors actual right atrial pressure. The researchers of this study concluded that "echocardiographic RAP estimation based on the IVC is highly inaccurate irrespective of the scheme used and should be avoided whenever possible."
Compared to VExUS
VExUS, or venous excess ultrasound, is a brilliant technique that has gained a lot of steam lately. It uses the IVC diameter in addition to doppler waveforms of the hepatic vein, portal vein, and/or renal vein to determine a VExUS score that correlates to the level of venous congestion. Dr. Abhilash Koratala (@NephroP) who we featured in The POCUS Manifesto, is one of the biggest VExUS proponents and posts daily on Twitter about it. In general, as right atrial pressure rises, congestion increases, and the doppler waveforms become more and more abnormal.
Yet, if you can get accurate right atrial pressure measurements with this method, do other methods like VExUS add clinically important information?
The benefit to VExUS is you can evaluate organ-specific blood flow/congestion which may be helpful in certain situations. The downsides to VExUS include:
It requires relatively advanced sonographic skills like pulsed wave doppler.
It is very difficult to perform on a handheld Butterfly IQ probe and therefore limits its clinical utility in different settings (outpatient clinics, hospital floors without ultrasound machines, etc)
It can be difficult to acquire the images in certain obese patients or tachypneic patients
There can be false positives, as ultimately it is inferring the right atrial pressure and not measuring it directly.
Overall, VExUS is a great method for qualitatively measuring volume status and venous congestion. There are many excellent YouTube videos explaining VExUS in detail here, here, or here. At the very least, it seems clear that this IJ POCUS method could replace IVC in the VExUS congestion evaluation, and possibly provide an alternative to VExUS alltogether.
Comments