A Specific Gut Bacteria Pattern Doubles the Risk of a Second Heart Attack

Roughly one in five people who survive a heart attack will experience another major cardiovascular event within five years, yet cardiologists still rely on risk tools that largely ignore the gut. A new analysis from the CORDIOPREV clinical trial, published in the European Heart Journal, changes that picture: a specific gut microbiota signature, identified from fecal samples of 679 coronary heart disease patients followed for seven years, was associated with a hazard ratio of 2.01 for recurrent major adverse cardiovascular events (MACE). In other words, patients whose gut bacteria matched this pattern were roughly twice as likely to suffer a repeat cardiac event.

Ten Bacterial Taxa That Flag Future Cardiac Events

The CORDIOPREV team, led by researchers at the Hospital Universitario Reina Sofía in Córdoba, Spain, identified ten bacterial taxa that together carry stronger predictive power for MACE than any single microorganism. Five of those taxa were more abundant in patients who went on to experience a second event; the other five showed the opposite pattern, appearing at lower levels in the same group. Using these ten taxa, the researchers built an intestinal microbiota risk score that achieved an area under the receiver operating characteristic curve (AUC) of 65.2% in the training set and 68.8% in the validation set. These numbers are modest but meaningful for a biomarker operating entirely from a stool sample, and they place gut microbiota alongside established risk factors rather than replacing them.

The growing recognition that gut microbiota-derived metabolites act as both biomarkers and mediators in cardiovascular disease makes findings like these less surprising than they might have seemed a decade ago. Metabolites such as trimethylamine-N-oxide (TMAO), short-chain fatty acids, and bile acids all connect bacterial communities in the colon to the arteries and heart.

Secondary Prevention: Why Existing Risk Scores Fall Short

Coronary heart disease is, by definition, a recurrent condition. Patients enrolled in CORDIOPREV had all experienced a myocardial infarction or undergone revascularization before the study began, placing them squarely in the secondary prevention category. Cardiovascular disease remains the leading cause of death worldwide, and the challenge of preventing repeat events in people who have already survived one is among the most pressing problems in cardiology. Current clinical scores, which draw on cholesterol levels, blood pressure, age, and smoking status, leave a large fraction of recurrent events unexplained. Adding a microbiota layer could help clinicians identify which high-risk patients need more aggressive lipid-lowering therapy or dietary intervention.

The CORDIOPREV data also revealed that gut microbiota patterns linked to MACE recurrence differ between men and women, a finding that aligns with broader evidence that gut microbiome composition varies by sex and may require sex-stratified modeling to be clinically useful.

How 16S Metagenomics and Random Survival Forests Drove the Analysis

The study drew on a subset of the larger CORDIOPREV trial, which enrolled 1,002 CHD patients. From that group, fecal samples were collected from 679 participants; 132 of them experienced a new MACE over the seven-year follow-up. The team performed 16S metagenomics sequencing on an Illumina MiSeq platform, analyzed with Qiime2 software, to characterize bacterial communities at the genus and higher levels. To identify which taxa carried predictive weight, they used random survival forest analysis, a machine-learning approach that handles the censored data typical of long-term clinical trials and can detect non-linear relationships between microbial features and outcomes.

Lipopolysaccharide (LPS), a molecule shed by gram-negative bacteria and a marker of intestinal barrier leakage, was measured using a limulus amoebocyte lysate test. Patients who experienced new MACE showed a greater post-prandial increase in LPS, a phenomenon called postprandial endotoxemia, that was independently associated with recurrent events. That link to metagenomic and metabolomic analysis as a combined approach for parsing microbiome contributions to disease strengthens the biological plausibility of the overall model.

Diet interacted with the microbiota signal in a clinically relevant way: adherence to a Mediterranean diet (MED) appeared to offer more protection than a low-fat diet specifically in patients with moderate post-prandial LPS increases, suggesting that dietary pattern modulates how gut bacteria influence cardiovascular risk.

Limits of a Single-Cohort Score

The microbiota risk score is a promising proof of concept, but it carries real limitations. The 679-patient cohort, while one of the largest of its kind for this specific question, is still a single-center Spanish population, predominantly middle-aged men with established CHD. Bacterial community composition varies substantially across geographies, ethnicities, and dietary traditions, so a score calibrated on this group may not perform equally well elsewhere. The AUC values, while better than chance, indicate that many individual-level predictions will still be uncertain.

The mechanistic story is also incomplete. The study identifies which taxa are associated with worse outcomes but cannot yet explain precisely how those bacteria drive or protect against cardiac events. Whether the association runs through endotoxemia, altered bile acid metabolism, direct immune signaling, or some combination remains an open question.

Precision Nutrition and Microbiota Modification as the Next Steps

The authors frame their score as a foundation for two near-term clinical directions. First, the risk score could be integrated into existing cardiovascular prediction models to flag patients who need intensified lipid-lowering treatment. Second, the identified taxa could become therapeutic targets, whether through diet, prebiotics, probiotics, or fecal microbiota transplantation. The differential response to Mediterranean versus low-fat diets depending on LPS levels hints that truly personalized dietary prescriptions for cardiac patients may become feasible once the underlying mechanisms are better understood.

Validation in diverse populations is the prerequisite for either path. As the editorial commentary on the paper noted, demonstrating that the score holds up across different ethnicities, sexes, and healthcare systems is the essential first step before clinical adoption. Achieving that will likely require the kind of large-scale, standardized trials with hard cardiovascular endpoints and integrated multi-omics profiling that the field has long called for but rarely completed. The CORDIOPREV team has given those future trials a concrete hypothesis to test.