Silent Myocardial Infarction and Subsequent Ischemic Stroke in the Cardiovascular Health Study

Presented at the International Stroke Conference 2020 by Alexander Merkler, MD (New York City, NY, USA)

Introduction and methods

One in four strokes have no known etiology. These are known as embolic strokes of undetermined source (ESUS). For a long time, it has been known that clinically apparent MI is a well established risk factor for cardiac embolism and stroke. However, it is unknown whether silent MI increases the risk of stroke. Silent MI is defined as ECG or cardiac imaging evidence of MI without clinical recognition of an event. Silent MI is as common or even more common as clinically apparent MI. This analysis of the Cardiovascular Health Study investigated the association between silent MI and incident ischemic stroke.

The Cardiovascular Health Study enrolled 5201 participants ≥65 years of age in the US between 1989-1990 and followed them for CV events. A total of 4224 participants were included in this analysis. These participants had no prevalent stroke at baseline, no baseline ECG evidence of MI and complete information about covariates. All participants underwent annual ECGs from baseline (1989-1990) through 1998-1999. The exposures of interest were incident silent MI or incident overt MI. Overt MI exposure was divided into short term (within 30 days following MI) and long-term exposure (>30 days following MI). The primary outcome was incident ischemic stroke. Secondary outcome was incident ischemic stroke subtype (non-lacunar, lacunar or other determined/unknown stroke subtype). Median follow-up was 9.8 years.

Main results

• During follow-up 362 participants (9.8%) had incident silent MI, 421 (10%) had incident overt MI and 377 (8.9%) had incident ischemic stroke.
• After adjustment for age, sex, race and CV risk factors, silent MI (as compared to no MI) was significantly associated with risk of ischemic stroke (HR 1.47, 95%CI 1.01-2.16). There was also a significant association between long-term risk after overt MI and ischemic stroke (HR 1.60, 95%CI 1.04-2.44). Of note, there is a dramatic association between short term risk after overt MI and ischemic stroke (HR 80, 95%CI 53-119).
• Secondary analysis showed that silent MI was significantly associated with non-lacunar ischemic stroke (HR 2.18, 95%CI 1.24-3.83), but not with lacunar stoke (HR 0.49, 95%CI 0.12-2.07) nor other determined/unknown stroke subtypes (HR 1.30, 95%CI 0.73-2.32). The association between silent MI and non-lacunar stroke subtypes was similar to the association between overt MI and long-term risk of non-lacunar stroke (HR 2.18, 95%CI 1.15-4.17).

Conclusion

This analysis of the Cardiovascular Health Study showed that silent MI was significantly associated with incident ischemic stroke. This association seems to be driven by non-lacunar ischemic stroke. More data or a dedicated RCT are necessary to determine the optimal antithrombotic treatment for patients with stroke and evidence of silent MI.

-Our reporting is based on the information provided during the International Stroke Conference 2021-