Acute Coronary Syndrome

Diagnostics and Likelihood Ratios, Explained

Positive Findings (Patient Has This)

Cardiac Risk Increased Disease Probability (Positive Likelihood Ratio)
Abnormal prior stress test 3.1x (2.0-4.7)
Peripheral arterial disease 2.7x (1.5-4.8)
Prior history of CAD 2.0x (1.4-2.6)
Prior MI 1.6x (1.4-1.7)
Diabetes 1.4x (1.3-1.6)
CVA 1.4x (1.1-1.8)
Male gender 1.3x (1.2-1.3)
Hyperlipidemia 1.3x (1.1-1.5)
Hypertension 1.2x (1.1-1.3)
Any tobacco use 1.1x (0.9-1.3)
Family history of CAD 1.0x (0.9-1.2)
Obesity 1.0x (0.9-1.2)
History of CABG 0.97x (0.5-2.1)
Chest pain characteristics Increased Disease Probability (Positive Likelihood Ratio)
Radiation to both arms 2.6x (1.8-3.7)
Pain similar to prior ischemia 2.2x (2.0-2.6)
Change in pattern over prior 24 hours 2.0x (1.6-2.5)
"Typical" chest pain 1.9x (0.94-2.9)
Pain worse with exertion 1.5x-1.8x
Radiation to neck or jaw 1.5x (1.3-1.8)
Recent episode of similar pain 1.3x (1.1-1.4)
Radiation to left arm 1.3x (1.2-1.4)
Radiation to right arm 1.3x (0.78-2.1)
Pain with diaphoresis 1.3x-1.4x
Pain with dyspnea 1.2x (1.1-1.3)
Abrupt onset 1.1x (1.0-1.2)
Any improvement with nitroglycerin 1.1x (0.93-1.3)
"Typical" radiation 1.0x-5.7x
Burning pain 1.0x-1.4x
Associated nausea/vomiting 0.92x-1.1x
Associated palpitations 0.71x (0.37-1.3)
Associated syncope 0.55x (0.39-0.76)
Pleuritic pain 0.35x-0.61x
Physical finding Increased Disease Probability (Positive Likelihood Ratio)
Hypotension (SBP<100) 3.9x (0.98-15)
Lung rales 2.0x (1.0-4.0)
Tachypnea 1.9x (0.99-3.5)
Tachycardia (heart rate>120) 1.3x (0.42-3.94)
Pain reproduced on palpation 0.28x (0.14-0.54)
ECG findings Increased Disease Probability (Positive Likelihood Ratio)
ST depression 5.3x (2.1-8.6)
Ischemic ECG 3.6x (1.6-5.7)
T wave inversion 1.8x (1.3-2.7)
Clinical Decision Tools Summary Likelihood Ratio
HEART score 7-10 13x (7.0-24)
TIMI score 5-7 6.8x (5.2-8.9)
HEART score 5-6 2.4x (1.6-3.6)
TIMI score 3-4 2.4x (2.1-2.7)
HFA/CSANZ rule (high risk) 2.8x (2.6-3.0)
HEART score 4 0.79x (0.53-1.2)
TIMI score 2 0.94x (0.85-1.0)
HEART score 0-3 0.20x (0.13-0.30)
TIMI score 0-1 0.31x (0.23-0.43)
HFA/CSANZ rule (low to intermediate) 0.24x (0.19-0.31)

Abbreviations: HEART, History, Electrocardiogram, Age, Risk Factors, Troponin; HFA/CSANZ, The Heart Foundation of Australia and Cardiac Society of Australia and New Zealand; TIMI, Thrombolysis in Myocardial Infarction.

Negative Findings (Patient Doesn't Have This)

Cardiac Risk Decreased Disease Probability (Negative Likelihood Ratio)
Male gender 0.70x (0.64-0.77)
Prior history of CAD 0.75x (0.56-0.93)
Hypertension 0.78x (0.72-0.85)
Hyperlipidemia 0.85x (0.77-0.93)
Prior MI 0.88x (0.81-0.93)
Diabetes 0.90x (0.86-0.94)
Abnormal prior stress test 0.92x (0.88-0.96)
Any tobacco use 0.96x (0.85-1.1)
Peripheral arterial disease 0.96x (0.94-0.98)
CVA 0.97x (0.94-0.99
Obesity 0.99x (0.88-1.1)
Family history of CAD 0.99x (0.91-1.1)
History of CABG 1.00x (0.92-1.1)
Chest pain characteristics Decreased Disease Probability (Negative Likelihood Ratio)
"Typical" chest pain 0.52x (0.35-0.69)
Pain worse with exertion 0.66x-0.83x
Pain similar to prior ischemia 0.67x (0.60-0.74)
Abrupt onset 0.75x (0.61-0.91)
"Typical" radiation 0.78x-0.9x
Recent episode of similar pain 0.80x (0.71-0.90)
Change in pattern over prior 24 hours 0.84x (0.79-0.90)
Radiation to left arm 0.88x (0.81-0.96)
Pain with dyspnea 0.89x (0.82-0.96)
Any improvement with nitroglycerin 0.90x (0.85-0.96)
Radiation to neck or jaw 0.91x (0.87-0.95)
Pain with diaphoresis 0.91x-0.93x
Radiation to both arms 0.93x (0.89-0.9)
Burning pain 0.97x-1.0x
Associated nausea/vomiting 0.98x-1.0x
Radiation to right arm 0.99x (0.96-1.0)
Associated palpitations 1.0x (0.98-1.1)
Associated syncope 1.1x (1.1-1.1)
Pleuritic pain 1.1x-1.2x
Physical finding Decreased Disease Probability (Negative Likelihood Ratio)
Tachypnea 0.95x (0.89-1.0)
Lung rales 0.95x (0.90-1.0)
Hypotension (SBP <100) 0.98x (0.95-1.0)
Tachycardia (HR >120) 0.99x (0.96-1.0)
Pain reproduced on palpation 1.2x (1.0-1.2)
ECG findings Decreased Disease Probability (Negative Likelihood Ratio)
Ischemic ECG 0.74x (0.68-0.81)
ST depression 0.79x (0.71-0.87)
T wave inversion 0.89x (0.86-0.93)


This rational clinical examination confirms the findings of previous studies indicating that traditional coronary artery risk factors (e.g. diabetes, hypertension, etc.) are not useful predictors of acute coronary syndrome. This systematic review also shows that isolated signs and symptoms are not helpful in identifying the underlying ischemic etiology for chest pain. The review states that the most rational approach would be to use TIMI or HEART tools in combination with the institution's background prevalence of ACS to calculate the initial pre- stress test probability of ACS. Unfortunately, the risk scores alone may not be adequate to lower the probability sufficiently to achieve a desired miss rate lower than 1%.

The authors of this systematic review employed the following definition of ACS as their reference standard: either final hospital discharge diagnosis of ACS [either as determined by the treating physician or by systematic central adjudication by reviewers using a pre specified definition of ACS] or clinical cardiac events [encompassing at least cardiovascular death, myocardial infarction, and revascularization] through 14 days to 6 weeks after presentation). A review of the included trials revealed that some of the studies considered events such as “revascularization” and even “conservative management of coronary artery disease” as indicator of ACS diagnosis at discharge. We acknowledge that this method of determining ACS outcome is far from ideal. Therefore we expect that the results of future high quality trials with a proper gold standard for ACS (death or MI) change the likelihood ratios dramatically.



Shahriar Zehtabchi, MD


February 1, 2017

What are Likelihood Ratios?

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!)