Thank you for the question. While one of the foremost causes of arrhythmia is ischemia it should be noted that this is not a sole cause and therefore ASA would not always be a beneficial treatment option in the setting of arrhythmia.
We would advise that Paramedics use caution when looking to treat patients outside of their intended directives. In your example of a patient who presents asymptomatically with a (presumably) new onset AV block, one would want to ensure that a thorough assessment has been conducted to rule out any subtle signs of ischemia (weakness, shortness of breath, change in exercise tolerance) while at the same time taking in the overall clinical presentation and obtaining a sound past medical history.
If at this point you feel that a particular intervention (ASA or otherwise) would be of benefit to your patient, yet remains outside of your intended treatment directive, we would advise that you utilize the BHP patch process to discuss your findings with one of our physicians. We will always encourage and support Paramedics who use critical thinking and actively advocate for their patients best interests.