Zepbound for HFpEF: the SUMMIT trial and the cardiology routing problem

In the SUMMIT trial, tirzepatide cut the composite of cardiovascular death and worsening heart-failure events by 38 percent in patients with HFpEF and obesity. HFpEF, the stiff-ventricle form of heart failure, is about half of all heart-failure cases and long had few drug options. The FDA never added a heart-failure indication for Zepbound. Its label, revised April 2026, still lists only weight reduction and obstructive sleep apnea, so writing it for HFpEF is off-label and coverage has to be built on obesity or sleep apnea. This is the first time cardiology sits in the GLP-1 prescribing conversation at scale.

What SUMMIT found

SUMMIT randomized 731 adults with HFpEF (LVEF 50 or higher) and BMI 30 or higher to tirzepatide or placebo for 52 weeks, on top of standard care including diuretics, SGLT2 inhibitors and an MRA where indicated. Tirzepatide was titrated to the tolerated maintenance dose of 5, 10 or 15 mg weekly.

The composite gives a hazard ratio of 0.62 (95 percent CI 0.41 to 0.95, p = 0.026), a 38 percent relative-risk reduction. The 6.9-point KCCQ gap clears the 5-point threshold counted as clinically important. The 6-minute walk improved 18 meters more on tirzepatide. GI side effects (nausea, diarrhea) matched earlier tirzepatide trials, with no unexpected cardiovascular signals.

The label and coverage problem

SUMMIT did not produce a heart-failure indication. The April 2026 label carries two: weight reduction in adults with obesity or overweight plus a weight-related condition, and moderate to severe obstructive sleep apnea in adults with obesity. Writing Zepbound for HFpEF is legal and off-label, which shapes how you get it paid for.

• Medicare Part D reaches Zepbound through the sleep-apnea indication, not heart failure. Copays generally run tier 3 specialty, $50 to $200 a month.
• Commercial plans that exclude obesity drugs do not open for a cardiology diagnosis. The plans that pay do it under the obesity benefit, or under sleep apnea when a sleep study supports it.
• Documentation (echocardiogram, NYHA class, ICD-10 I50.30 or I50.32, the heart-failure medication list) does not open a path on its own. It strengthens the medical-necessity case on an obesity prior authorization.

The cardiology routing problem

HFpEF is managed by cardiology, and cardiology offices are broadly not set up to prescribe and titrate GLP-1. So cardiology identifies the SUMMIT-type patient and refers to obesity medicine, endocrinology or primary care, which writes the off-label prescription and does the prior-authorization work while cardiology keeps managing volume status, diuretics and the SGLT2. A primary-care clinician can write Zepbound off-label for a cardiology-confirmed diagnosis, though willingness varies. Telehealth obesity-medicine programs that handle complex comorbidities, Form Health, Knownwell and 9amHealth, are absorbing this referral flow.

What SUMMIT does not show

• HFrEF (LVEF 40 or lower): not established. No GLP-1 has a completed phase 3 trial in HFrEF as of mid-2026, and the pathophysiology differs, so the benefit does not read across.
• HFmrEF (LVEF 48 to 49): a gray zone. Only HFpEF at LVEF 50 or higher has SUMMIT behind it, and both are off-label anyway.
• Non-obese patients: BMI 30 or higher was required. Normal-weight HFpEF is a different phenotype.
• Mortality: the 52-week trial was underpowered for CV death alone, so a mortality reduction is not established.

Semaglutide and the class

STEP-HFpEF (Kosiborod, NEJM 2023) ran semaglutide 2.4 mg against placebo in 529 HFpEF patients with obesity for 52 weeks: KCCQ-CSS improved 16.6 versus 8.7 points (a 7.8-point gap), the 6-minute walk gained 21.5 meters more than placebo, and weight fell 13.3 versus 2.6 percent. Its HF-event composite was numerically lower but not powered for it. SGLT2 inhibitors got there first (EMPEROR-Preserved, DELIVER) and are first-line for HFpEF per the 2022 AHA/ACC/HFSA guideline, so most patients should already be on empagliflozin or dapagliflozin before Zepbound is added. The two work through different mechanisms and are additive, not a replacement.

Monitoring, cost and the AF overlap

HFpEF patients are usually on diuretics, and adding tirzepatide drives more fluid loss through reduced intake and weight loss, so diuretic doses often need downward titration with close renal-function and electrolyte monitoring. Patients on insulin or a sulfonylurea need dose reductions to avoid hypoglycemia, and patients on an MRA need potassium watched. New or worsening dyspnea after starting Zepbound needs cardiology review, since severe nausea and vomiting can mimic decompensation. Roughly 35 to 50 percent of HFpEF patients also have atrial fibrillation, and rate or rhythm control continues during treatment.

When coverage fails, LillyDirect sells Zepbound vials for $299 to $449 a month cash. At SUMMIT effect sizes, the number needed to treat to prevent one composite event is roughly 17 over the trial year, so the cost-effectiveness math favors high-risk, high-symptom patients. More trials are extending the evidence: STEP-HFpEF-DM (semaglutide with T2D, reported 2024), SUMMIT-2, and FLOW-HF.

For the drug profile see Zepbound, and for the sleep-apnea coverage route see obstructive sleep apnea.

See today's cash price and our full score, plus the programs that prescribe off-label for comorbidities, on the Knownwell review page.