Gut Microbiome in Heart Failure
Definition
The gut microbiome in HF refers to how intestinal microbial composition and function are altered by cardiac dysfunction (gut dysbiosis), and how the resulting microbial metabolites — particularly TMAO and uremic toxins — feed back to worsen HF progression and outcomes. This bidirectional gut–heart axis is an emerging precision medicine target in HF.
Key Concepts
Mechanism of Gut Dysbiosis in HF
- Haemodynamic trigger: Reduced cardiac output → decreased intestinal blood flow → intestinal acidosis and hypoxia → sodium and fluid retention, altered gut microbiome composition. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Structural consequence: Decreased intestinal blood flow + intestinal oedema → increased intestinal permeability → bacterial translocation, growth of pathogenic intestinal mucosal bacteria, and reduced microbiome diversity. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Clinical correlate: Patients with HF have significantly increased pathogenic gut flora (Campylobacter, Shigella, Salmonella, Yersinia enterocolitica, Candida) vs. healthy controls; pathogenic flora levels and intestinal permeability correlate directly with right atrial pressure and clinical HF severity. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Systemic inflammation: Bacterial endotoxin (lipopolysaccharide) enters systemic circulation → potent inducer of TNF-α and IL-6 release → sustains the chronic inflammatory state characteristic of HF. Elevated CRP in HF is partly attributable to gut-origin endotoxaemia. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
TMAO (Trimethylamine N-Oxide) as a Biomarker
Production Pathway
- Dietary choline, phosphatidylcholine, and carnitine are metabolised by specific intestinal bacteria → trimethylamine (TMA) → hepatic FMO3 (flavin-containing monooxygenase 3) N-oxidation → TMAO → renal excretion. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Plasma TMAO levels vary with intestinal bacterial composition and are elevated in HF vs. healthy controls. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Prognostic Evidence
- Acute HF: Elevated TMAO independently predicts in-hospital and 1-year mortality after adjustment for traditional risk factors. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Stable HF: Elevated TMAO predicts 5-year all-cause mortality, maintained in fully adjusted models including cardiorenal and traditional risk factors. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Chronic kidney disease in HF: Elevated TMAO independently predicts CKD development in patients without HF and correlates with CKD severity in patients with HF — reflecting the gut–heart–kidney axis. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Other Uremic Toxins from Gut Dysbiosis
Indoxyl Sulfate
- Source: Dietary tryptophan → gut microbial metabolism → indole → hepatic sulfation → indoxyl sulfate; renally cleared.
- HF evidence: In DCM patients, elevated serum indoxyl sulfate (adjusted for clinical factors, BNP, and eGFR) was significantly associated with increased HF hospitalisations, cardiac death, or both over 5-year follow-up. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
p-Cresyl Sulfate
- Source: Dietary phenylalanine → gut microbial metabolism → p-cresol → hepatic sulfation → p-cresyl sulfate; renally cleared.
- Elevated levels in dysbiosis; contributes to accelerated progression of both HF and CKD. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Therapeutic Interventions Targeting the Gut
Dietary Modification
- Mediterranean diet: Adherence reduces the risk of developing HF by 21% over 10 years (RR 0.79, 95% CI 0.68–0.93; P=0.004) in a large population-based cohort without known CVD. Mechanism includes reduced dietary trimethylamine-producing substrates → lower TMAO production. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- A 5-day diet change is sufficient to alter gut microbiome composition. Vegetarian/vegan diets further reduce trimethylamine substrate availability. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Probiotics
- Multiple probiotic strains shown to reduce blood pressure and cardiovascular risk in non-HF populations.
- HFrEF trial: Saccharomyces boulardii for 3 months → decreased creatinine, uric acid, and CRP + improved LA diameter and LVEF vs. controls. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Oral Charcoal Absorbent (AST-120)
- Non-absorbent gut binder for gut microbial metabolites and their precursors.
- Small trial (n=20, HF + moderate CKD): AST-120 reduced both rehospitalisation and length of stay. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Replication in adequately powered RCTs required before clinical recommendation.
Antibiotic Therapy
- Rifaximin and similar gut-selective antibiotics: reduce endotoxin-related inflammation in cirrhosis; suggested to improve endothelial function and decrease intestinal proinflammatory cytokines in HF in small studies. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- No guideline recommendations for antibiotics in HF specifically for gut microbiome modification.
Contradictions / Open Questions
- Current HF guideline-directed therapy and gut dysbiosis: The effect of standard GDMT (beta-blockers, ACEi/ARNi, MRA, SGLT2i, diuretics) on gut microbiome composition and dysbiosis is largely unstudied — diuretic therapy may decrease intestinal oedema and normalise endotoxin levels, but no systematic study exists. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- TMAO — biomarker or causal mediator? TMAO strongly predicts outcomes, but whether lowering TMAO improves HF outcomes is unproven. Reducing dietary choline/carnitine to lower TMAO would conflict with potential benefits of carnitine supplementation in some HF patients. Causal evidence in humans is lacking. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
- Gut intervention trial evidence is minimal: All HF-specific microbiome intervention studies are small, short-term, or non-randomised. Fecal microbiota transplantation (FMT) has not been studied in HF. RCT-level evidence does not yet exist to support any specific microbiome-targeted intervention for HF outcomes. (sources/HF-Precision-Medicine-AHA-2019, rating: high)
Connections
- Related to entities/Heart-Failure
- Related to concepts/Pharmacogenomics-in-HF
- Related to sources/HF-Precision-Medicine-AHA-2019
- Related to concepts/HFpEF