Just knowing the pathology of STEMI it's hard to buy that an effect of this size (in the Ireland study) is largely due patient's not seeking care on weekends unless you're somewhere extremely rural as this isn't your average heart attack.
If this was about ACS (acute coronary syndrome) in general I'd be more suspicious that patient delays are a relevant confounder, but we have other literature to support the trend (granted with some conflicting studies).
from [1]: > Many studies have shown an excess of cardiovascular events on Mondays (1,3,10,16,18,19). A relative trough has been seen on Saturdays and Sundays I compared with the expected number of cases. A similar pattern was seen in most subgroups irrespective of age, gender, cardiac medication, and in-fart characteristics (first or recurrent, Q or non-Q, site). The frequency of morning infarction is greater during the working week than on weekends, suggesting a superimposition of work-related stress on endogenous circadian rhythms.
>Circadian variation is found on all days of the week including weekends' when the morning peak is less obvious.
I haven't looked at the methodology of the cited studies but they include 6 references for your perusal.
[0]https://onlinelibrary.wiley.com/doi/abs/10.1002/clc.22 [1]https://onlinelibrary.wiley.com/doi/epdf/10.1002/clc.4960261... [2]https://europepmc.org/article/med/12061302