Low stroke volume index (SVI) in intermediate-risk pulmonary embolism (PE) was associated with increased in-hospital morbidity and mortality, but this technique requires advanced echo skills.
Why does this matter?
We know high-risk PE patients are at greater risk for adverse events (1-3), but it’s more difficult to predict outcomes in intermediate risk PE patients. As PE severity worsens, the RV bows out, intrudes into the LV, and stroke volume drops (see figure). Might SVI be an early marker of disease severity even before a patient becomes hemodynamically unstable?
Intermediate-risk PE… not always intermediate outcome
This was a multicenter retrospective cohort of patients over 18 years old with intermediate-risk PE (sPESI >0). Measurement of SVI was performed using pulse-wave doppler of the LV outflow tract. The primary outcome included cardiopulmonary decompensation (<90 mmHg SBP for >15 min, catecholamine administration for hypotension, intubation or CPR).
In all, 665 intermediate-risk PE patients were included, with 24 (3.9%) suffering the primary outcome. Sensitivity for a cut-point SVI of 20mL/m2 was 83%; specificity 87%; positive likelihood ratio (LR+) 6.5; negative likelihood ratio (LR-) 0.2. We know from PEITHO (4) that the pretest probability of early decompensation for intermediate risk patients (receiving placebo, not tPA) was 5.6%. With that knowledge, let’s work through a clinical scenario. If the current study is correct, a SVI <20mL/m2 would mean a 27.8% post-test probability that the patient would decompensate. If the SVI was >20mL/m2, post-test probability for decompensation would drop to 1.2%. If you knew your patient had more than a 1 in 4 chance of decompensation, you would admit them to the ICU. On the other hand, if you knew the risk of decompensation was 1.2%, you’d likely admit to a regular hospital bed. This could help with resource allocation when ICU beds are scarce.
There are a few limitations worth mentioning. A small number of patients met the primary outcome. Also, this was a retrospective study. Finally, this is an advanced echo technique, beyond the scope of most of us in the ED. As a basic bedside user of POCUS, I (Max) will be sticking to more commonly taught and practiced measures of cardiac function in PE but will keep this in the back of my mind if we get a formal echocardiogram. I (Clay) will look at Max’s screen as he does the bedside echo and wish I could do POCUS that well.
Echocardiography-Derived Stroke Volume Index Is Associated With Adverse In-Hospital Outcomes in Intermediate-Risk Acute Pulmonary Embolism: A Retrospective Cohort Study. Chest. 2020 Sep;158(3):1132-1142. doi: 10.1016/j.chest.2020.02.066. Epub 2020 Mar 31.
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Meyer G, Vicaut E, Danays T, et al; PEITHO Investigators. Fibrinolysis for patients with intermediate-risk pulmonary embolism. N Engl J Med. 2014 Apr 10;370(15):1402-11. doi: 10.1056/NEJMoa1302097.