Glycaemic disturbances early after MI, including hyperglycaemia below the diagnostic threshold for diabetes, are associated with a progressively higher risk of adverse outcomes, with a near-linear association between fasting glucose and outcomes observed across all patients.
Key Findings
Results
A stepwise increase in MACE risk was observed across glycaemic categories compared with normoglycaemia following myocardial infarction.
HRs compared with normoglycaemia: pre-diabetes/possible diabetes HR 1.07 (95% CI 1.00 to 1.14), possible diabetes HR 1.22 (95% CI 1.11 to 1.34), new-onset diabetes HR 1.22 (95% CI 1.08 to 1.37), and known diabetes HR 1.73 (95% CI 1.64 to 1.82)
MACE was a composite of all-cause mortality, MI, and ischaemic stroke until end of follow-up (30 June 2018)
During a median follow-up of 4.7 years, 9,321 patients experienced MACE
The study included 47,558 patients over age 18 attending cardiac rehabilitation post-MI with available glycaemic information
Results
Pre-diabetes and possible diabetes were common among post-MI patients, as was known diabetes.
Pre-diabetes and possible diabetes were present in 20.6% of the cohort
New-onset diabetes was identified in 3.2% of patients
Known diabetes was present in 21.1% of patients
Together, over 44% of the post-MI cohort had some form of glycaemic disturbance beyond normoglycaemia
Results
Fasting glucose showed a near-linear association with adverse outcomes across all patients regardless of diabetes status.
The near-linear association between fasting glucose and outcomes was observed across all patients in the cohort
This relationship was present irrespective of diabetes status
This finding suggests fasting glucose is a continuous risk marker rather than a threshold-dependent one in the post-MI setting
Results
Glycated haemoglobin (HbA1c) appeared predictive of outcomes mainly in patients with established diabetes.
HbA1c was assessed alongside fasting glucose as a measure of glycaemic control
Unlike fasting glucose, HbA1c's predictive value for adverse outcomes was concentrated in those with known diabetes
This distinction suggests differential utility of the two glycaemic markers in risk stratification after MI
Methods
The study was a retrospective registry-based cohort study using data from SWEDEHEART between 2006 and 2017.
Patients were registered in the cardiac rehabilitation registry within the Swedish Web-system for Enhancement and Development of Evidence-based care in Heart disease Evaluated According to Recommended Therapies (SWEDEHEART)
All patients were over the age of 18 attending cardiac rehabilitation post-MI
Inclusion required available information on glycaemic levels
Secondary outcomes included all components of MACE individually, CV mortality, and hospitalisation for heart failure
Results
Even hyperglycaemia below the diagnostic threshold for diabetes was associated with increased risk of adverse cardiovascular outcomes after MI.
The pre-diabetes category showed a statistically significant elevated MACE risk (HR 1.07, 95% CI 1.00 to 1.14) compared with normoglycaemia
The findings support close follow-up of at-risk patients irrespective of diabetes status
The authors note these findings support action 'beyond routine screening' for patients with sub-diabetic hyperglycaemia
What This Means
This research examined how blood sugar levels measured shortly after a heart attack relate to future cardiovascular risks. Using data from nearly 48,000 Swedish heart attack patients enrolled in cardiac rehabilitation between 2006 and 2017, the researchers found that even mildly elevated blood sugar — levels below what is needed to diagnose diabetes — was associated with a meaningfully higher risk of experiencing another heart attack, stroke, or dying over an average follow-up period of about 4.7 years. The more elevated the blood sugar, the higher the risk, with people who had known diabetes facing the greatest increase in risk (73% higher than those with normal blood sugar).
The study also found that fasting glucose (a single blood sugar measurement taken after not eating) showed a nearly continuous, straight-line relationship with bad outcomes across all patients, meaning risk increased steadily with each increment of blood sugar — there was no clear 'safe' threshold below which risk stopped rising. In contrast, HbA1c, a measure of average blood sugar over several months, was mainly useful for predicting outcomes in people who already had a diabetes diagnosis.
This research suggests that doctors monitoring patients after a heart attack should pay close attention to blood sugar levels across the full range, not just in those formally diagnosed with diabetes. People with borderline or newly detected elevated blood sugar after a heart attack may benefit from closer follow-up and potentially earlier intervention, even if they do not yet meet the criteria for a diabetes diagnosis.
Haider A, Hagström E, Ishak D, Hadziosmanovic N, Norhammar A, Velders M, et al.. (2026). Diabetes status, fasting glucose and HbA1c, and outcomes after myocardial infarction: a retrospective registry-based Swedish cohort study.. BMJ open. https://doi.org/10.1136/bmjopen-2026-121970