Few things are scarier for a physician than a patient struggling to breathe, especially when the cause is unclear. Diagnosing pulmonary embolism remains a challenge in patients who cannot have a CT scan for whatever reason, and bedside echo can be helpful in identifying signs of right heart strain. Right ventricular enlargement, McConnell's sign, and the 60/60 sign have been proposed as diagnostic options, but so far none has proven to be a magic bullet. Could early systolic notching (ESN) be the answer?
Pulse wave Doppler in the parasternal short axis view is used to create a tracing of the blood flow as it leaves the RV. (See image 1.) ESN describes a tracing taken just proximal to the pulmonic valve. Normally, the pulmonary artery pressure and resistance are low, and blood flows easily from the RV through the pulmonary vascular bed, giving a smooth tracing. (Image 2.) The blood ejected from the RV is bounced back by the clot, giving the pattern two peaks or notches. (Image 2.) The earlier in systole the notching occurs, the closer the clot is to the pulmonic valve.
A recent study looked at all patients with suspected PE who had CT imaging and a TTE within 48 hours. (J Am Soc Echocardiogr. 2019;32:799.) All had evaluation of the pulmonic valve and assessment for other signs of RV strain. Only 182 of the initial 5152 patients assessed were enrolled. Exclusion criteria included chronic pulmonary hypertension and lack of central PE. The authors found that ESN was highly sensitive and specific for massive or submassive PE (92% and 99%) compared with McConnell's sign (52% and 97%) and the 60/60 sign (51% and 96%).
What to make of this? It's a great idea. Who wouldn't love a test that would rule in and out massive or submassive PE at the bedside? Unfortunately, I'm not ready to jump on the bandwagon just yet. As anyone who has tried to echo a patient in extremis knows, it's not easy to get a great view of anything, especially the pulmonic valve. I sometimes struggle with this on cooperative patients! The Doppler tracings are not always clear and easy to interpret, especially for someone without a lot of Doppler experience. And perhaps most importantly, this study did not include patients with chronic pulmonary hypertension. This group often has impressive right heart strain, and knowing how to distinguish acute from chronic is crucial.
What do we do instead? Consider using more straightforward findings such as McConnell's sign or RV enlargement combined with clinical history. Throwing in bedside ultrasound of the lower-extremity veins can also help increase your confidence in PE as the diagnosis.
Dr. Buttsis the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans. Follow her on Twitter@EMNSpeedofSound, and read her past columns athttp://bit.ly/EMN-SpeedofSound.