Tirzepatide cut blood volume, blood pressure and inflammation in SUMMIT heart failure analysis

A secondary analysis of the SUMMIT trial found that tirzepatide reduced estimated blood volume, systolic blood pressure and systemic inflammation in people with obesity-related heart failure with preserved ejection fraction (HFpEF), while markers of kidney and heart muscle injury improved ^[1]. The analysis, published in Nature Medicine, looked at how the drug produced its heart failure benefit rather than testing whether it worked ^[1].

Tirzepatide is a dual GIP and GLP-1 receptor agonist ^[1]. SUMMIT enrolled 731 patients with obesity-related HFpEF at 129 centers in 9 countries, randomly assigning 364 to tirzepatide and 367 to placebo between April 20, 2021, and June 30, 2023, with data collection through July 2, 2024 ^[1]. At the start, average body mass index was above 38, mean estimated glomerular filtration rate (eGFR) was 55.3 ml/min/1.73 m², more than half had stage 3 or worse chronic kidney disease, and 66% had elevated C-reactive protein (CRP) ^[1]. The trial's main result — that tirzepatide reduced cardiovascular death or worsening heart failure, eased symptoms and improved exercise tolerance — was reported separately ^[1].

At 52 weeks, compared with placebo, tirzepatide lowered systolic blood pressure by an estimated treatment difference of 5 mmHg (95% confidence interval −7 to −3; P < 0.001), reduced estimated blood volume by 0.58 liters (95% CI −0.63 to −0.52; P < 0.001), reduced CRP by 37.2% (95% CI −45.7 to −27.3; P < 0.001), raised eGFR by 2.90 ml/min/1.73 m² per year (95% CI 0.94 to 4.86; P = 0.004) and reduced troponin T by 10.4% (95% CI −16.7 to −3.6; P = 0.003) ^[1].

Two other markers moved in the same direction but did not reach statistical significance at 52 weeks. NT-proBNP fell 10.5% (95% CI −20.7 to 1.0%; P = 0.07) and the urine albumin-to-creatinine ratio fell 15% (95% CI −28 to 0.1; P = 0.051). The urine albumin reduction was larger and statistically significant at 24 weeks, a 25% decrease (95% CI −36 to −13%; P < 0.001) ^[1].

The blood pressure effect was visible at 4 weeks, grew through 24 weeks and held at 52 weeks. Changes in diastolic blood pressure were minimal and not statistically significant at either 24 or 52 weeks, while pulse pressure was significantly reduced at each time point ^[1].

In post hoc exploratory analyses, the drop in estimated blood volume was correlated with lower blood pressure, reduced microalbuminuria, better scores on the Kansas City Cardiomyopathy Questionnaire Clinical Summary Score and a longer 6-minute walk distance. The CRP decrease correlated with lower troponin T and a longer 6-minute walk distance ^[1]. These analyses were exploratory, so they show that the measures moved together, not that one caused another. Blood volume itself was estimated rather than directly measured ^[1].

Why it matters for patients

Roughly two-thirds of people with HFpEF have obesity, and obesity-related HFpEF is described as the most advanced form of cardiovascular–kidney–metabolic disease ^[1]. The analysis suggests the heart failure benefit seen in SUMMIT came alongside less circulatory volume and pressure overload and less systemic inflammation, with improvement in kidney filtration and reductions in two markers of organ injury ^[1].

The group studied had substantial disease at baseline: mean 6-minute walk distance was 303 meters, mean symptom score was 54, nearly half had been hospitalized or made an urgent care visit for worsening heart failure in the prior 12 months, and 41% had elevated high-sensitivity troponin T ^[1].

This was a secondary look at a completed trial, and it does not report new information about how well the drug works overall or about its risks ^[1]. The numbers are group averages from one trial population, and the correlation analyses were exploratory ^[1].

What happens next

The main SUMMIT results were reported separately, and this mechanistic analysis does not describe any further trial or regulatory step ^[1]. The trial is registered as NCT04847557 ^[1].