ASA for SVT

The messaging around providing ASA to patients experiencing Supraventricular Tachycardia (SVT) is a common question and it all comes down to Cardiac Ischemia. Therefore, for clarification, not all patients experiencing SVT require ASA, just those that the paramedic suspect are experiencing Cardiac Ischemia.

Firstly, speaking about Cardiac Ischemia and Acute Coronary Syndrome (ACS). 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 with 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 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 is often missed, and has worse mortality than those that complain 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 likely 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, incorporating all elements of the history and physical examination performed better.

Unless the patient has a contraindication to ASA, it should be administered to all patients we suspect of having an ischemic event. ASA has a huge mortality benefit, with an exceptional number needed to treat, a wide therapeutic window, and a low risk profile.

Secondly, speaking to the benefits of ASA for Cardiac Ischemia. ASA has been found to have vascular indications in various situations such as ACS (ST-elevation myocardial infarction (STEMI), non-ST-elevation acute coronary syndromes – non-ST-elevation myocardial infarction (NSTEMI) or unstable angina), secondary prevention after acute coronary syndromes, and management of stable ischemic heart disease. More specifically, ASA can reduce the risk of vascular mortality in patients with a suspected acute MI, it can reduce the combined risk of death and nonfatal MI in patients with a previous MI or unstable angina and can reduce the combined risk of MI and sudden death in patients with stable ischemic heart disease.

ASA is known to have antipyretic, analgesic, and anti-inflammatory properties. It works by irreversibly inhibits cyclooxygenase-1 and 2 (COX-1 and 2) enzymes, via acetylation, which results in decreased formation of prostaglandin precursors. It also irreversibly inhibits formation of prostaglandin derivative, thromboxane A2, via acetylation of platelet cyclooxygenase, thus inhibiting platelet aggregation.

Theoretically, SVT in a vulnerable patient with reduced heart function could lead to something called a type 2 MI. Type 2 MIs are also known as “demand ischemia”. Per the AHA, a type 2 MI is an MI caused by a mismatch between oxygen supply and demand by a pathophysiological mechanism other than coronary atherothrombosis (type 1 MI). The therapy for type 2 MIs is not as clearly defined as it is for type 1 MIs. SVT + ACS would be a very rare presentation, and while not impossible, you can definitely give ASA if you suspect the patient has features of ACS and would therefore benefit from ASA.

Lastly, speaking to SVT. Tachyarrhythmias, defined as abnormal heart rhythms with a ventricular rate of 100 or more beats per minute (bpm), can result from a variety of pathologies. Signs and symptoms related to tachyarrhythmias most commonly include palpitations or chest discomfort, but may also include shock, hypotension, heart failure (HF), shortness of breath, and/or decreased level of consciousness. Symptoms can sometimes be more subtle and may include fatigue, lightheadedness, or exercise intolerance. Some patients may also be truly asymptomatic; this may be more common in non-paroxysmal tachycardias. Determining whether a patient's symptoms are related to the tachycardia depends upon several factors, including age and the presence of underlying cardiac disease. As an example, PSVT with a heart rate of 200 bpm may be tolerated by an otherwise healthy young adult with no or few symptoms (eg, palpitations). On the other hand, SVT at a rate of 180 bpm may precipitate angina in an older adult patient with significant coronary heart disease. In most cases, SVT is considered a stable and mostly benign tachyarrhythmia, often remedied by the (modified) Valsalva Maneuver and/or Adenosine administration. Both of which treatments are also well tolerated by patients. This then often means that ASA administration is not always necessary for patients experiencing SVT.

In conclusion, ASA for SVT is recommended for the patients that we suspect are experiencing Cardiac Ischemia, not just simply given to all patients with SVT.