Finding | Increased Disease Probability (Positive Likelihood Ratio) |
---|---|

End point septal separation (EPSS) >7 mm | 2.07 |

Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer. |

Finding | Decreased Disease Probability (Negative Likelihood Ratio) |
---|---|

End point septal separation (EPSS) >7 mm | 0.0 |

Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer. |

**Narrative:** This was a prospective observational study (n=80) comparing emergency medicine (EM) physician performed mitral valve EPSS to formal TTE LVEF estimation. A convenience sample of unselected hospitalized patients undergoing comprehensive TTE for any indication was used. While EPSS > 7 mm was noted to be 100% sensitive for predicting severe systolic dysfunction (EF < 30%), a second cutoff of 8 mm was used for assessing any systolic dysfunction. The sensitivity and specificity of an EPSS > 8 mm for any systolic dysfunction were 83.3% (95% CI, 62.6-95.2) and 50.0% (95% CI, 29.2-70.9), respectively. The corresponding positive LR was 1.67, and the negative LR was 0.33.

**Caveats:** Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer.

*Published in collaboration with The POCUS Atlas*

**Author:** Matthew Riscinti, MD

**Published/Updated:** September 13, 2018

LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.

Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.

For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.

He immediately gets an ECG (known here as the "test") showing an obvious STEMI.

Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.

And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.

Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).

(*Thank you to Seth Trueger, MD for this explanation!*)