The Heart-Rate Response Hiding in a Cardiac PET Stress Test

Every regadenoson stress study produces a second number alongside myocardial blood flow: how far the heart rate climbed. Cardiac PET is built around the flow measurements, and that’s where attention goes. But two large outcome studies now suggest the heart rate response deserves a closer look, even with flow numbers sitting right next to it.

What to do with it is the harder question. A marker can sharpen a risk model without telling anyone how to treat the patient differently.

What the regadenoson study found

Joaquim Barreto and colleagues went back through 4,611 patients who had rubidium-82 PET/CT for a 2026 retrospective study. They called the heart rate response blunted when the rate rose less than 20% above its resting value.

Over a median of 3.3 years, the blunted group had 16.2 events per 100 patient-years. The normal group had 5.5. The composite counted death, myocardial infarction, stroke and heart-failure hospitalization.

Adjustment narrows that gap considerably. The adjusted hazard ratio was 1.70 (95% CI, 1.50 to 1.94). That’s a real signal, but it isn’t the threefold difference the raw rates seem to show. And when the researchers added heart rate response to a model that already held clinical variables and myocardial blood flow, the area under the ROC curve rose by 0.017. It adds prognostic information at the margin. Flow assessment still carries the study.

What the heart rate response measures

The 2026 American Society of Nuclear Cardiology stress-testing guideline describes the rise under vasodilator stress as generally brisk, though smaller than what exercise or dobutamine produces. Expressing it as a percentage adjusts for where the patient started.

The guideline ties the response to autonomic function and notes that it carries prognostic weight after adjusting for clinical and imaging findings. It also keeps the heart rate response separate from the drop in blood pressure.

One terminology trap is worth flagging. The percentage rise during regadenoson isn’t the same measurement as heart rate recovery after exercise, and the two shouldn’t be swapped in a report or in a conversation with a patient.

Other PET data point in the same direction

A 2025 Houston Methodist study of 7,808 regadenoson rubidium-82 PET patients found the same pattern from a different angle. Patients whose heart rates responded more had fewer deaths or heart-failure hospitalizations, even after adjusting for clinical and PET variables, including myocardial flow reserve.

The association was stronger in patients with higher ejection fractions, so ventricular function appears to shape what the signal means. That study used a stress-to-rest heart rate ratio and a different outcome definition, though. Its numbers and the 2026 study’s shouldn’t be blended into a single estimate.

Prediction still needs a clinical purpose

For a lab thinking about reporting heart rate response explicitly, the first questions are about consistency. Is it calculated the same way on every patient? Is the resting value clearly identified? Does the report keep the measured number apart from any explanation of it?

The bigger question belongs to the referring physician. Would knowing the result change follow-up or treatment in a way that helps the patient? Observational data can’t answer that. Nor does it hand anyone a heart rate cutoff that proves vasodilation was adequate or inadequate.

So the heart rate response has earned a place as context on a cardiac PET study. How big a place depends on what it helps clinicians do, not on how dramatic an unadjusted comparison looks.