It’s not often that a pair of studies completely challenges our assumptions in cardiology, but new data presented at HRS 2026 suggests myocardial infarction might not be the main cause of sudden cardiac death (SCD).
- The WHO defines SCD as an unexpected death within an hour of symptoms or within 24 hours of last being seen alive and in which a cardiac cause is assumed without autopsy.
- Since the 1970s, the hypothesis has been that ~80% of SCD cases are due to MI.
- This thinking stemmed from early SCD autopsies, but those cases were limited, and referral bias likely played a role.
Despite how far cardiology has come in treating the heart, annual SCD incidence remains high. This prompted researchers to continuously watch presumed SCD cases in San Francisco County for 12 years. What they found completely overturned our current understanding of SCD.
- Among 943 cases studied, only 41% of those with confirmed SCD showed MI as cause of death.
- Of those MI deaths (n=237), 90% showed evidence of CAD, with 95 identified as acute MI and 119 as healed MI.
Researchers then used the autopsy data to conduct a second study and found that…
- Out of the 943 cases examined, 58% had SCD due to arrhythmic causes, meaning that an implanted or external defibrillator might have been able to save them.
So what to do with this data?
- For starters, it helps us understand that sudden cardiac death isn’t so sudden after all, and what we call SCD is the manifestation of undetected arrhythmia or heart disease.
- It could also encourage strengthening screening programs and expanding heart disease prevention beyond just avoiding MI.
The Takeaway
While seemingly small in scope, these two studies represent a watershed moment in our understanding of sudden cardiac death. It’s clear now that it isn’t a random event spurred on by a freak heart attack, but rather the manifestation of undetected heart disease.
