Why HFpEF with Obesity Has Resisted Treatment — Until Now

Heart failure with preserved ejection fraction (HFpEF) affects approximately half of all heart failure patients and has historically lacked disease-modifying pharmacological therapies, particularly in the obesity-driven phenotype. Unlike heart failure with reduced ejection fraction (HFrEF), where neurohormonal blockade produces clear survival benefits, HFpEF is mechanistically heterogeneous — and its obesity-related subtype is dominated by an adipose-cardiac axis that standard heart failure medications do not address.

Retrieved literature from the American Heart Association characterises the pathophysiology of obesity-related HFpEF as driven by epicardial and pericardial fat accumulation, which mechanistically constrains cardiac volume, elevates right- and left-heart filling pressures, and promotes diastolic dysfunction. Skeletal muscle dysfunction and systemic inflammation compound these structural abnormalities, creating a multi-target disease that is poorly served by single-mechanism agents.

The left ventricular diastolic dysfunction seen in this phenotype is quantified clinically by the E/e’ ratio — the ratio of transmitral to annular velocity — and by left atrial volume index (LAVI), both of which rise as filling pressures increase. These structural markers have now become pharmacodynamic endpoints in tirzepatide’s clinical programme, providing objective imaging evidence beyond patient-reported symptom scores.

Prior to the SUMMIT trial, the most relevant clinical precedent was the STEP-HFpEF trial, which demonstrated that semaglutide — a mono-GLP-1 receptor agonist — significantly improved Kansas City Cardiomyopathy Questionnaire Clinical Summary Score (KCCQ-CSS) and reduced body weight in patients with HFpEF and obesity. STEP-HFpEF provided the mechanistic and clinical foundation for the SUMMIT design, positioning tirzepatide’s dual agonism as a potential advance over the semaglutide benchmark.

The SUMMIT Trial: Phase III Design, Endpoints, and Primary Outcomes

The SUMMIT trial is a randomised, double-blind, placebo-controlled Phase III clinical trial that evaluated tirzepatide in patients with HFpEF and obesity, publishing primary results in 2024 in the New England Journal of Medicine. Tirzepatide significantly improved symptoms and physical limitations (KCCQ-CSS), exercise capacity (6-minute walk distance), and reduced heart failure events and cardiovascular death versus placebo in this population.

Enrolled patients were required to have an ejection fraction of ≥50%, obesity defined as BMI ≥30 kg/m², and NYHA class II or greater symptoms — a design that deliberately targets the obesity-related HFpEF phenotype where the adipose-cardiac axis is the primary pathological driver. The two co-primary endpoints were:

• Change from baseline in KCCQ-CSS — a validated patient-reported outcome measuring symptoms and physical limitations in heart failure, widely accepted by regulators as a clinically meaningful endpoint.
• Change in 6-minute walk test distance — an objective measure of exercise capacity that captures functional improvement beyond symptom burden.

Secondary endpoints included a composite of worsening heart failure events and cardiovascular death, providing hard clinical outcome data to complement the functional endpoints. The trial’s positive results across both co-primary and secondary endpoints represent a landmark outcome in a disease area where prior large trials of conventional heart failure therapies have largely failed to demonstrate consistent benefit.

“Tirzepatide significantly improved symptoms and physical limitations, exercise capacity, and reduced heart failure events and cardiovascular death in patients with HFpEF and obesity — a population with historically no disease-modifying pharmacological options.”

Dual GIP/GLP-1 Mechanism: How Tirzepatide Targets the Adipose-Cardiac Axis

Tirzepatide’s mechanistic differentiation from earlier GLP-1 receptor agonists rests on its simultaneous activation of both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor, producing complementary effects on the adipose-cardiac axis that are not achievable with mono-GLP-1 agonism alone.

GLP-1 Receptor Activation

GLP-1 receptors are expressed in cardiomyocytes, vascular smooth muscle, and inflammatory cells. GLP-1 agonism suppresses appetite, reduces systemic inflammation, lowers sympathetic tone, and decreases neurohormonal activation — all pathways relevant to diastolic dysfunction in HFpEF. According to a review published in The Lancet, reduced neurohormonal activation is a key GLP-1 receptor-mediated benefit in heart failure. Reduced systemic inflammation and sympathetic nervous system activity are also highlighted as mechanisms relevant to the HFpEF phenotype.

GIP Receptor Activation — The Differentiating Mechanism

GIP receptors are expressed prominently in adipocytes. GIP receptor agonism promotes adipocyte lipid clearance and reduces ectopic fat deposition — including epicardial fat and myocardial steatosis — which are direct mechanical contributors to pericardial constraint in HFpEF. Research published in Cell Metabolism characterises GIP receptor agonism as the pharmacological feature that differentiates tirzepatide from semaglutide, producing synergistic effects on body weight, glycaemia, and cardiometabolic risk factors through complementary adipose tissue remodelling.

Hemodynamic Mechanism: Weight Loss and Pericardial Decompression

An editorial accompanying the SUMMIT publication in the New England Journal of Medicine, authored by Solomon and McMurray, identifies weight reduction as potentially the dominant mechanism of tirzepatide’s benefit in HFpEF. Weight loss reduces pericardial constraint, lowers pulmonary capillary wedge pressure, and improves cardiac reserve — effects that may be independent of any direct cardiomyocyte GLP-1 or GIP receptor activation. This hemodynamic pathway converges with the structural findings from the SUMMIT echocardiographic substudy.

Reverse Cardiac Remodeling: Evidence from the SUMMIT Echocardiographic Substudy

The SUMMIT echocardiographic substudy, published in the Journal of the American College of Cardiology (JACC), provides structural imaging evidence of tirzepatide’s cardiac effects beyond patient-reported outcomes and functional walk tests. Tirzepatide significantly reduced the E/e’ ratio and left atrial volume index (LAVI) in HFpEF patients, with favourable effects on LV diastolic function consistent with reverse cardiac remodelling.

The E/e’ ratio is a non-invasive echocardiographic marker of left ventricular filling pressure — elevated values indicate impaired diastolic relaxation and are a hallmark of HFpEF. Its reduction with tirzepatide treatment represents objective evidence of improved diastolic function, not merely symptomatic relief. LAVI reduction similarly signals structural decompression of the left atrium, which dilates chronically under elevated filling pressures in HFpEF.

The substudy also evaluated changes in left ventricular mass index and right ventricular function, reporting favourable effects consistent with biventricular hemodynamic decompression. These structural changes align with the mechanistic hypothesis advanced in the accompanying NEJM editorial — that weight loss-driven reduction in pericardial constraint is the primary mediator of tirzepatide’s cardiac benefit, acting through reduced biventricular filling pressures rather than direct cardiomyocyte receptor activation.

Eli Lilly’s HFpEF Patent Portfolio: A Dense Thicket of Method-of-Use Claims

Eli Lilly’s patent strategy for tirzepatide in HFpEF is characterised by a deliberate and granular approach to method-of-use claim stratification. In the dataset analysed, Lilly is the sole patent assignee, with at least 10 distinct patent applications identified across US (at least 9 filings), EP, and CN jurisdictions, spanning 2023 to 2025. All filings relate to methods of treating HFpEF with tirzepatide — not to the molecule itself — reflecting a strategy focused on protecting clinical use cases rather than compound novelty.

The portfolio is stratified across multiple dimensions of patient phenotype and treatment context:

• BMI thresholds: Separate filings for BMI ≥30 kg/m² (US20230381271A1), BMI between 30 and 45 kg/m² (US20240342201A1), and BMI ≥45 kg/m² (US20240197856A1), creating layered coverage across the obesity spectrum.
• Comorbidity profiles: Distinct filings covering patients with diabetes (US20240342198A1), hypertension, atrial fibrillation, or prior myocardial infarction (US20240342200A1), and history of myocardial infarction (US20250000890A1).
• Sex and LVEF: A specific filing for female patients with LVEF ≥50% and BMI ≥30 kg/m² (US20240342197A1), acknowledging the known sex disproportion in HFpEF prevalence.
• SGLT2 inhibitor co-administration: A filing specifically claiming methods in patients not receiving an SGLT2 inhibitor (US20240342199A1), delineating tirzepatide’s standalone claim scope relative to the established SGLT2 inhibitor standard of care in HFpEF.
• Dosing regimen: Multiple filings specify a 2.5 mg starting dose with escalation to a maintenance dose of 10 mg or 15 mg, embedding the clinical titration protocol within the IP claims.
• International coverage: EP4454646A1 (European Patent Office) and CN118510546A (China) extend the portfolio beyond US jurisdiction, with the EP filing dated October 2024.

This granular stratification signals a deliberate IP strategy to create a dense thicket of differentiated method-of-use claims across clinically distinct HFpEF subpopulations. By filing separate patents for each patient subgroup, Lilly creates overlapping claim coverage that is more resistant to design-around strategies than a single broad method claim would be. The SGLT2 inhibitor exclusion patent is particularly notable from a competitive intelligence standpoint, as it explicitly addresses the clinical scenario where tirzepatide is used without the standard-of-care SGLT2 inhibitor background therapy — potentially anticipating a regulatory label that may or may not mandate combination use.

According to WIPO data on pharmaceutical method-of-use patent strategies, this type of subpopulation stratification is increasingly common in precision medicine and cardiometabolic drug development, where clinical trial data generates distinct evidence bases for differentiated patient groups that can each support independent patent claims. The PatSnap Insights blog has previously covered how GLP-1 class IP strategies have evolved alongside the broadening clinical evidence base for this drug class.

“By filing separate patents for each patient subgroup — including a specific claim for patients not receiving an SGLT2 inhibitor — Lilly creates overlapping method-of-use coverage that is more resistant to design-around strategies than a single broad claim.”

The EP and CN filings indicate that Lilly is pursuing coordinated international protection for the HFpEF indication, consistent with the global commercial opportunity in a disease that affects hundreds of millions of patients worldwide. The European Patent Office filing (EP4454646A1, published October 2024) covers the same core dosing regimen — 2.5 mg starting dose, escalation to 10 mg or 15 mg maintenance — as the US counterparts, suggesting a unified global claim strategy built around the SUMMIT trial protocol.