Likelihood Ratios
Likelihood ratios have been calculated in various studies linking features of the history with acute myocardial infarction (AMI)(11-14) (see Table 3). It numerically indicates the probability of a patient having an AMI based on their description of the pain. Conventionally, a likelihood ratio greater than 10 provides very strong evidence to rule in a diagnosis whilst a ratio less than 0.1 provides very strong evidence to rule it out; ratios greater than 5 and less than 0.2 provide good evidence, and ratios greater than 2 and less than 0.5 provide moderate evidence to rule a diagnosis in or out respectively(15).
Table 3: Value of specific components of the chest pain history for the diagnosis of acute myocardial infarction(11-14)
| Historical factor | Likelihood factor | |||
|---|---|---|---|---|
| Increased likelihood of AMI: Radiation to right arm/shoulder Radiation to both arms/shoulders Associated with exertion Radiation to left arm Associated with diaphoresis Associated with nausea/vomiting Worse than previous angina/similar to previous MI Described as a pressure | [Ref 11] 4.7 4.1 2.4 2.3 2.0 1.9 1.8 1.3 | [Ref 12] 2.9 7.1 – 2.3 2.0 1.9 – – | [Ref 13] 2.6 1.4 – 1.5 2.1 1.9 1.3 1.4 | [Ref 14] 1.3 2.6 1.5-1.8 1.3 1.3-1.4 0.9-1.1 2.2 – |
| Decreased likelihood of AMI: Described as pleuritic Described as positional Described as sharp Reproducible with palpation Inframammary location Not associated with exertion Associated Palpitations Associated Syncope | 0.2 0.3 0.3 0.3 0.8 0.8 – – | 0.2 0.3 0.3 0.2-0.4* – – – – | 0.2 0.3 0.3 0.2 – – – – | 0.4-0.6 0.2 0.3 0.3 0.2 0.6-0.8 0.7 0.4-0.8 |
| *In heterogenous studies, likelihood ratios expressed as a range. | ||||
‘Burning pain’ (LR 1-1.4), ‘improvement with GTN’ (LR 0.93-1.3) and ‘abrupt onset of pain’ (LR 1-1.2) have no meaningful effect on the likelihood ratio of AMI.(14)
Therefore, based on these analyses, chest pain history is a helpful, but not diagnostic, first step in the assessment of these patients. Specifically, no single factor in the history carries with it a consistently powerful enough likelihood ratio to allow the emergency physician to safely discharge a patient without further diagnostic testing. Studies have reiterated that clinician gestalt although suggestive, cannot be used to rule in or rule out ACS.(16)
Learning bite
No single factor in the history alone can confidently rule in or rule out AMI