Cardiac Ischemia Timing

As with anything we do, the answer isn’t black and white and lies somewhere in the middle. Taking a step backwards, in order to transport a patient on a STEMI bypass, we need to consider multiple variables, including the presence of “chest pain or equivalent consistent with cardiac ischemia/myocardial infarction” and time (time of onset of current episode of pain <12 hours).

Just a reminder however, this bypass criteria only applies to those patients having a STEMI – patients can still be having a myocardial infarction and have a “normal” ECG. Remember, the ECG is just a test, and no test can rule in or rule out a disease (i.e. a patient can have a completely normal ECG but still have a PE, dissection, acute coronary syndrome, etc.).

While this bypass criteria is quite clear with respect to duration of time, there’s not a great definition of “chest pain or equivalent.” Nowhere does it speak to duration of symptoms.

Looking at that, we can define it in the context of acute coronary syndrome (ACS). ACS is an umbrella term to encompass NSTEMI, STEMI, or unstable angina, and is a dynamic process. With the absence of troponins, it’s almost impossible to contrast these pathologies prehospitally and one we don’t want to miss.

ACS presents with a spectrum of symptoms, and all of these can overlap with other less benign conditions. Statistically, most patients (90%) with chest pain will not be having ACS, but this is not a diagnosis to miss or undertreat. No one finding in isolation (history, physical assessment, ECG) is going to provide us a reliable rule in or rule out criteria. This is why it’s important to take everything into account and not rule out the diseases of exclusion (GERD, anxiety, etc.). The evidence you gather are all further data points that will allow for a more robust clinical decision making and putting everything together for a risk stratification. When assessing these patients, it’s important to consider the sum of all parts and recognize the limitations of the prehospital assessment. This starts with considering some of the “classic” risk factors such as age (>65), gender (male), family or personal history of coronary artery disease, high cholesterol, diabetes, smoking, and obesity. It’s also important to consider some other conditions that can predispose the body to a more atherosclerotic environment, such as chronic kidney disease, HIV, auto immune disorders, substance use, and chronic alcohol use. These should all be considered as part of your assessment.

Looking at subjective symptoms, we often focus on the “classic” symptoms of ACS, but there are more subtle complaints that we need to be aware of (e.g. GI issues, syncope, presyncope, SOB, nausea, dizzy, weakness, diaphoresis, jaw pain, etc.). We often miss these patients, dismiss their symptoms and label them as atypical.

A statement we’ve all said is “It can’t be cardiac because they don’t have ‘chest pain’”. Unfortunately, however, this cohort of patients are often missed, and have a worse mortality than those that complaining of chest pain. It is especially true for elderly patients, those with diabetes, and women, to have ACS without having chest pain. We in turn often inappropriately lower our concern, and these subsets of patients receive a delay to care, diagnosis, and treatment. Thus, we should be concerned when there are anginal equivalents, especially in the context of cohorts that have been shown to be routinely missed.

The Journal of the American Medical Association (JAMA) published a review (Does This Patient With Chest Pain Have Acute Coronary Syndrome?: The Rational Clinical Examination Systematic Review) asking the question how likelihood a patient was to have ACS based on their symptoms. It found that the accuracy of risk factors and symptoms was generally poor, and that any individual element in isolation was unlikely to be helpful in making an ACS diagnosis, and like we’ve highlighted, that incorporating all elements of the history and physical examination performed better.

Let’s put it all together with some examples: If you reach out for a glass of water and develop a little bit of chest pain that’s entirely reproducible, and have the absence of any risk factors, it’s probably safe to say ACS is unlikely (but not zero). Conversely, if you have an 80-year-old with a previous CABG, complaining of chest pain, diaphoresis, and REPRODUCIBLE chest pain, that’s in no way reassuring as they have so many risk factors. You can see how the reproducible aspect needs to be taken in context with the entire clinical picture. I encourage you to read that article (referenced here) for more of their findings.

So, circling back to your question, it would be reasonable to treat this patient under the cardiac ischemia directive, even though the symptoms were short lasting and self-limiting. There is no time frame for considering cardiac schema While this can be an anginal event, this is very difficult to differentiate prehospitally from ACS, and we should err on the side of caution.

This is especially true given that our mainstay treatment, ASA, has a huge mortality benefit, with an exceptional number needed to treat, a wide therapeutic window, and a low risk profile (unless they have a huge contraindication).

This also begs the question, is there a role for nitro? Nitro is a medication that provides symptom relief through vasodilation, is certainly helpful for patients with who are hypertensive with CHF, it can help for cocaine induced chest painm but there’s no mortality benefit shown. There are also downsides and risks of nitro given its ability to produce hypotension, and we’d want to withhold it for patients who are pre-load dependant (aortic stenosis, RV infarct, inferior MI, etc.). In the patient you presented above, a patient who is pain free, there is no role for nitro.