Myocardial flow reserve, or MFR, is a quantitative measure of how well the heart’s microvascular plumbing works under stress. It is calculated by dividing myocardial blood flow during pharmacological stress — typically induced with a vasodilator such as adenosine or dipyridamole — by blood flow at rest. A healthy coronary circulation can multiply its flow several-fold when demand rises; an MFR of 2.0 means the heart can only double its perfusion, a level widely regarded as abnormal. Unlike visual perfusion images, which reveal regional defects only when blood flow disparities are severe enough to create contrast between territories, quantitative MFR captures diffuse and microvascular disease that conventional relative imaging can miss entirely.

The ¹³N-ammonia tracer occupies a special place in this field. Short-lived and demanding to produce — it requires an on-site cyclotron because of its roughly ten-minute half-life — nitrogen-13 ammonia nonetheless offers excellent extraction characteristics and a long track record in quantitative myocardial perfusion imaging. The Japanese team, led by Yoshimitsu Fukushima of the Department of Radiology, retrospectively analyzed consecutive adults with suspected or established chronic coronary syndrome who underwent ¹³N-ammonia PET/CT at their center. The cohort spanned two generations of PET scanners, a detail the investigators built directly into their statistical design by stratifying their primary model by scanner generation.

Of the 168 patients studied, 102 — just over 60 percent — had a global MFR below 2.0. These patients showed a distinctive hemodynamic fingerprint: higher resting blood flow and lower stress blood flow than their counterparts with preserved reserve. That pattern is physiologically telling. Elevated resting flow often reflects compensatory mechanisms or altered hemodynamics, while a blunted stress response signals that the coronary microcirculation cannot augment delivery when the myocardium demands it. The gap between those two numbers is precisely what the reserve metric compresses into a single value.

Over a median follow-up of 3.5 years, the study’s primary endpoint — a deliberately hard composite that excluded revascularization procedures — occurred in 28 of the 102 patients with low MFR, a rate of 27.5 percent, versus only 5 of the 66 patients with preserved reserve, or 7.6 percent. The composite counted all-cause death, non-fatal myocardial infarction, heart-failure hospitalization, and malignant ventricular arrhythmia. By excluding revascularization, the endpoint avoids the circularity that can plague imaging-outcome studies, in which a scan finding triggers an intervention that then counts as an event. The Kaplan-Meier separation between the two groups was stark, with a log-rank P value below 0.001.

The pre-specified Cox proportional hazards model adjusted for age, sex, and the summed difference score — a standard semi-quantitative index of relative ischemia derived from the perfusion images themselves. Even with that adjustment, low MFR remained independently associated with the composite endpoint, carrying a hazard ratio of approximately 4.52 with a 95 percent confidence interval of 1.71 to 11.92. The independence from the summed difference score is the study’s most consequential finding: it means the prognostic signal in MFR is not simply a restatement of visible ischemia but reflects something additional, most plausibly the health of the microvasculature and the myocardium itself.

Because the composite endpoint was weighted toward heart-failure hospitalization, the investigators performed a sensitivity analysis excluding patients who already had heart failure at baseline. The association survived: the hazard ratio was 4.17 with a P value of 0.011. This matters because it suggests reduced flow reserve is not merely a marker of established pump dysfunction. It aligns with a growing body of evidence linking coronary microvascular dysfunction to the later development of heart failure, including heart failure with preserved ejection fraction, a condition in which the muscle stiffens and fills poorly despite a seemingly normal pumping fraction. Prior work from groups including Taqueti and colleagues has shown that global coronary flow reserve predicts adverse events independently of angiographic stenosis severity, and meta-analyses have consolidated the prognostic value of PET-derived flow measures across tracers and populations.

The study also waded into a technical controversy that has divided the cardiac PET community: whether raw MFR should be corrected for the rate-pressure product, or RPP, the product of heart rate and systolic blood pressure that serves as a proxy for myocardial oxygen demand. Proponents of RPP correction argue that it adjusts for hemodynamic variability between rest and stress acquisitions; critics counter that it can distort the physiological meaning of the reserve and obscure genuine microvascular impairment. In this cohort, RPP correction reclassified 52 patients — 31 percent of the sample — across the 2.0 threshold, and the movement was predominantly downward, meaning correction pushed patients into the abnormal category. Event rates told a coherent story: patients reclassified downward had a 7.0 percent event rate, while those impaired on both the uncorrected and corrected values had a 29.0 percent rate, with a four-group log-rank P value of 0.003.

Those reclassification figures carry practical weight. If nearly a third of patients change risk category depending on whether a correction is applied, laboratories must be transparent about which value they report. The authors conclude that the uncorrected global MFR should be the primary reported metric, with any RPP-corrected value explicitly labeled as such. Their data suggest that uncorrected MFR below 2.0 identifies higher-risk patients independently of relative ischemia, and that correction, while informative, should supplement rather than replace the raw physiological measure. This position echoes recent comparative studies, including work from Houston and elsewhere examining corrected versus uncorrected reserve in patients without obstructive coronary disease, and a 2026 multicenter analysis confirming MFR’s prognostic value for mortality in ¹³N-ammonia imaging.

Limitations are worth keeping in view. The study was retrospective and single-center, and its cohort of 168 patients, while adequate for the pre-specified model, came from a Japanese population imaged across two scanner generations — a heterogeneity the authors addressed statistically but which nonetheless reflects real-world practice rather than a controlled trial. The endpoint composite, though hard, was dominated by heart-failure hospitalizations, so the findings speak most directly to heart-failure-related risk rather than to sudden death or arrhythmia in isolation. Still, the message for clinicians is concrete: when a quantitative ¹³N-ammonia PET study returns a global flow reserve below 2.0, that number deserves attention in its own right, not merely as a footnote to the perfusion images. For patients with chronic coronary syndrome, the microcirculation’s reserve capacity may be one of the most powerful predictors of what comes next.

Subject of Research: Prognostic value of ¹³N-ammonia PET myocardial flow reserve in chronic coronary syndrome

Article Title: Reduced ¹³N-Ammonia PET Myocardial Flow Reserve and Heart-Failure–Related Risk Independent of Relative Ischemia in Chronic Coronary Syndrome

Article References: Fukushima, Y., Kobayashi, R., Yodogawa, K., Shimizu, S., Imai, S., Hayashi, H., & Kumita, S. (2026). Reduced ¹³N-Ammonia PET Myocardial Flow Reserve and Heart-Failure–Related Risk Independent of Relative Ischemia in Chronic Coronary Syndrome. European Journal of Nuclear Medicine and Molecular Imaging. https://doi.org/10.1007/s00259-026-08183-9

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08183-9

Keywords: myocardial flow reserve, ¹³N-ammonia PET, chronic coronary syndrome, heart failure, coronary microvascular dysfunction, rate-pressure product, myocardial perfusion imaging, risk stratification, cardiac PET, prognosis, ischemia, nuclear cardiology

The study, published in the European Journal of Nuclear Medicine and Molecular Imaging, followed 1,007 consecutive patients with suspected ischemic heart disease who underwent dynamic technetium-99m sestamibi myocardial perfusion imaging on a CZT D-SPECT camera between June 2018 and May 2021. The investigators deliberately excluded patients who underwent early revascularization within 90 days of the scan, a design choice that removes the circularity of counting procedures prompted by the test itself. During a median follow-up of 49 months, 191 patients, or 19 percent of the cohort, experienced a major adverse cardiovascular event, defined as a composite of cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, hospitalization for heart failure, or late coronary revascularization.

The technology at the heart of the study represents a quiet revolution in nuclear cardiology. Conventional single-photon emission computed tomography produces static images of relative perfusion, essentially a comparison of one region of heart muscle against another. That approach can miss disease that is diffuse rather than focal, because when blood flow is uniformly reduced across the heart, no single region stands out as abnormal. Cadmium-zinc-telluride detectors changed the equation by dramatically improving sensitivity and count efficiency, making it feasible to track a radioactive tracer bolus as it moves through the bloodstream and into the heart muscle. By fitting kinetic models to that dynamic data, the scanner can calculate absolute myocardial blood flow in milliliters per gram of tissue per minute, a true physiological measurement rather than a visual impression.

The Taiwanese team quantified flow using Corridor 4DM software with a net retention model, generating two key parameters for each patient. Stress myocardial blood flow measures how much blood the heart receives when the coronary vessels are dilated by a pharmacological stressor, approximating the demands of exercise. Resting myocardial blood flow captures baseline perfusion, and the myocardial flow reserve, the ratio between the two, reflects how much the coronary circulation can ramp up delivery when the heart demands more. A healthy coronary system can multiply its flow severalfold; a diseased or dysfunctional microvasculature cannot. Using maximally selected rank statistics, a method that searches data for the cut point that best separates outcomes, the researchers determined optimal thresholds of 1.96 mL/g/min for stress flow and 1.98 for flow reserve.

The statistical signal was striking. Patients whose flow measurements fell below these thresholds had significantly worse survival free of major adverse events, with abnormal flow status associated with a chi-square value of 87.2 and a p-value below 0.001. But the more important test was whether these measurements added anything beyond what clinicians already know. In multivariable analysis, the investigators adjusted for clinical risk factors, stress left ventricular ejection fraction, and the stress total perfusion deficit, a quantitative measure of the static perfusion image itself. Even after all of that adjustment, myocardial flow reserve and resting myocardial blood flow remained independent predictors of adverse outcomes, indicating that the flow numbers carried prognostic information that no conventional variable could supply.

Perhaps the most clinically consequential finding concerned patients whose conventional scans looked reassuring. When the researchers restricted the analysis to patients with a stress total perfusion deficit below 15 percent, meaning their static perfusion images showed little or no obvious abnormality, quantitative flow assessment still provided incremental risk stratification. In other words, a patient whose pictures appear normal but whose measured flow reserve is low is not actually at low risk. This addresses one of the most persistent anxieties in cardiology: the well-documented phenomenon of false-negative perfusion images in patients with balanced ischemia or predominantly microvascular disease, where the static image underestimates the true extent of ischemic burden.

The result also illuminates the biology of coronary disease in a broader sense. Angiography, the traditional gold standard, visualizes the large epicardial arteries, but cardiovascular events often arise from disease distributed across the vessel wall or from dysfunction in the thousands of tiny arterioles that regulate perfusion. Quantitative flow imaging interrogates the entire delivery system, from the proximal stenosis to the distal microvasculature, in a single integrated measurement. Prior research with positron emission tomography has established that impaired flow reserve predicts outcomes even in patients without obstructive coronary disease, including those with ischemia and no obstructive coronary arteries, a condition once dismissed as a paradox but now understood as a major source of preventable events.

What makes the new study notable is the platform. Quantitative flow has long been considered the province of PET, which uses short-lived tracers such as rubidium-82, nitrogen-13 ammonia, or oxygen-15 water to perform kinetic imaging with high accuracy. PET cameras, however, are expensive, concentrated in large academic centers, and logistically demanding because of cyclotron-produced tracers. CZT-based SPECT cameras are more widely available and already perform millions of conventional perfusion studies worldwide. Validation work over the past decade, including head-to-head comparisons with nitrogen-13 ammonia PET and with invasive fractional flow reserve, has built the case that dynamic CZT-SPECT can approach PET-grade flow quantification using routine technetium tracers. This study extends that case from diagnostic accuracy to hard outcomes: it demonstrates that the numbers generated on these cameras actually mean something for a patient’s future.

There are caveats worth keeping in view. The analysis was retrospective and conducted at a single institution, and the cohort, drawn from patients referred for clinical perfusion imaging, may not generalize perfectly to screening populations. The researchers used a net retention model rather than full compartmental kinetic modeling, and threshold values such as 1.96 mL/g/min and 1.98 are derived from this specific camera, software, and protocol, so they may require recalibration on other platforms. The authors also note that patients who underwent early revascularization within 90 days were excluded precisely to avoid counting procedures triggered by the scan, and dataset access is available from the corresponding author on reasonable request. Still, the size of the cohort, the length of follow-up, and the rigor of the adjustment analysis place this among the strongest demonstrations yet that SPECT-derived flow quantification carries independent prognostic weight.

The practical implication is that the same scan that already tells a cardiologist whether part of the heart looks under-perfused can now, with dynamic acquisition and appropriate software, also report absolute flow and reserve, refining risk stratification at little added burden to the patient. For the roughly one in five patients in this cohort who went on to experience a cardiovascular death, heart attack, stroke, heart failure admission, or late revascularization, the difference between a normal-looking image and a low flow measurement may determine whether aggressive prevention is initiated in time. As CZT cameras proliferate and quantification software matures, the study suggests that the future of cardiac nuclear imaging will be measured not in shades of gray on a screen, but in milliliters per gram per minute, numbers that translate directly into forecasts of who lives free of cardiovascular catastrophe and who does not.

Subject of Research: Prognostic value of quantitative myocardial blood flow and flow reserve measured by dynamic CZT-SPECT for predicting major adverse cardiovascular events in suspected ischemic heart disease

Article Title: The prognostic value of quantitative myocardial blood flow and flow reserve by dynamic CZT-SPECT for major adverse cardiovascular events

Article References: The prognostic value of quantitative myocardial blood flow and flow reserve by dynamic CZT-SPECT for major adverse cardiovascular events. (n.d.). https://doi.org/10.1007/s00259-026-08195-5

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08195-5

Keywords: CZT-SPECT, myocardial blood flow, myocardial flow reserve, major adverse cardiovascular events, myocardial perfusion imaging, ischemic heart disease, coronary artery disease, nuclear cardiology, prognosis, risk stratification, technetium-99m sestamibi, coronary microvascular dysfunction

Kawasaki disease is the leading cause of acquired heart disease in children in many parts of the world. The condition, whose exact trigger remains uncertain, produces widespread inflammation of blood vessels, and the coronary arteries are its most vulnerable targets. In a subset of patients, the vessel walls weaken so profoundly that giant coronary artery aneurysms form, measuring far beyond normal arterial dimensions. These aneurysms are not merely cosmetic distortions. Blood stagnates inside them, clots form, and over time the inflamed vessel walls can scar and narrow until the artery closes completely. The result is a cruel paradox: segments of artery that are abnormally wide in one place may be critically obstructed in another, starving the heart muscle of oxygen and setting the stage for myocardial infarction even in childhood.

For this patient, the disease had run an aggressive course. Echocardiography and coronary computed tomography angiography documented giant aneurysms involving both the left and right coronary systems, with occlusive lesions that compromised flow to the heart muscle. Medical therapy alone could not restore perfusion, so the surgical team turned to coronary artery bypass grafting, the standard revascularization strategy for severe Kawasaki-related coronary disease. Surgeons used arterial grafts, including the internal mammary arteries, to create new channels from the aorta to the coronary arteries beyond the blockages. Bypass surgery in children with Kawasaki disease is technically demanding: the target vessels are small, the aneurysmal walls are diseased, and the patient will need these grafts to function for decades. The initial operation succeeded, and the boy recovered with his heart muscle once again receiving blood through the reconstructed pathways.

The danger, however, had not passed. Roughly a year after surgery, surveillance revealed stenosis at the anastomosis, the delicate hand-sewn junction where the right internal mammary artery graft had been connected to the right coronary artery. Anastomotic stenosis is a recognized complication of bypass grafting, arising from scar tissue formation, intimal thickening, or technical factors at the connection site. In adults, such narrowing is often addressed with repeat surgery or percutaneous coronary intervention, the catheter-based family of techniques that includes balloon angioplasty and stent placement. In children, the evidence base is thin. Pediatric coronary arteries are small, the graft anatomy is complex, and the long-term behavior of coronary stents in growing bodies remains incompletely understood. Reports on managing post-CABG anastomotic stenosis in children are so limited that each documented case carries outsized educational value.

The Shanghai team elected to attempt percutaneous salvage. Under angiographic guidance, clinicians advanced a catheter to the narrowed segment, confirmed the severity and extent of the stenosis, and deployed a stent to scaffold the vessel open. Intravascular ultrasound, an imaging tool that provides a cross-sectional view from inside the artery, supports such procedures by characterizing the lesion and verifying that the stent is fully expanded and well apposed to the vessel wall. The procedure restored flow through the right internal mammary artery graft, re-establishing perfusion to the territory it was built to protect. For a patient whose native coronary arteries were already devastated, preserving the patency of even one graft can make the difference between a functioning heart and progressive ischemic damage.

The technical logic of the intervention rewards close attention. A bypass graft is only as good as its weakest point, and the anastomosis is inherently the most vulnerable: it is a junction between two vessels of different calibers and compliance, joined by suture in tissue that is actively remodeling. When scar narrows that junction, the entire graft is throttled regardless of how healthy its length may be. A stent acts as an internal splint, mechanically resisting the inward recoil of scarred tissue. In this case, the stent was positioned to hold open the outflow of the arterial graft into the right coronary artery, converting a failing surgical connection into a widely patent conduit. Follow-up imaging confirmed the result, and myocardial perfusion imaging performed six months after the procedure showed only mild reversible ischemia at the apex and apical inferior wall, with tracer uptake replenishing at rest, an encouraging functional signature of restored blood supply.

Beyond the procedural success, the case underscores a principle that pediatric cardiologists emphasize repeatedly: Kawasaki disease is not an acute illness that ends when the fever resolves. Children with giant coronary aneurysms require lifelong surveillance, because complications can emerge years or decades after the initial inflammation. Aneurysms can thrombose, calcify, and stenose silently. Bypass grafts, which behave in children much as they do in adults but must endure far longer, can fail gradually or suddenly. The stenosis in this patient appeared a full year after CABG, a delay that illustrates why serial echocardiography, coronary imaging, and functional assessment such as stress myocardial perfusion imaging are indispensable in this population. A single reassuring scan is never a discharge from care.

The report also highlights the multidisciplinary nature of modern management for these patients. Caring for a child with Kawasaki-related giant aneurysms draws on pediatric rheumatology for control of inflammation, noninvasive cardiology for imaging and functional assessment, cardiac surgery for revascularization, and interventional cardiology for catheter-based rescue. Each decision, from the choice of antithrombotic therapy to the selection of graft targets to the timing of intervention on a stenotic anastomosis, must be individualized to anatomy that is often unlike anything seen in adult practice. The authors frame their experience as a guide to such individualized management, noting that percutaneous coronary intervention can be an effective therapeutic option in selected pediatric cases, even in the challenging setting of a post-surgical graft complication.

For the broader clinical community, the message is twofold. First, stent implantation deserves consideration as a salvage strategy when a bypass graft fails in a child, provided the anatomy is suitable and an experienced interventional team is available; repeat sternotomy in a patient with diseased, aneurysmal coronaries carries substantial risk, and a catheter-based solution may offer a safer path to restored perfusion. Second, the case is a reminder that the frontier of pediatric cardiology increasingly involves adults-in-the-making: children who survived acute Kawasaki disease in the era of modern diagnosis now live for decades with coronary anatomy that demands the full toolkit of cardiovascular medicine. As the surviving cohort grows, so too will the need for evidence on how best to monitor, maintain, and when necessary rescue the surgical and catheter-based repairs that keep their hearts supplied with blood. This single patient’s successful stent rescue adds a concrete data point to a sparse literature, and it offers reassurance that when a child’s bypass graft begins to fail, the interventional catheter lab may hold the answer.

Subject of Research: Stent implantation to treat anastomotic stenosis of a coronary bypass graft after CABG in a child with Kawasaki disease

Article Title: Salvage stent implantation for anastomotic stenosis after coronary artery bypass grafting in Kawasaki disease: a case report

Article References: Zheng, Y., Zhao, L., Dai, G., Chu, C., Zhao, Q., Wang, F., Lin, Y., He, L., & Liu, F. (2026). Salvage stent implantation for anastomotic stenosis after coronary artery bypass grafting in Kawasaki disease: a case report. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07668-8

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07668-8

Keywords: Kawasaki disease, coronary artery aneurysms, coronary artery bypass grafting, percutaneous coronary intervention, stent implantation, anastomotic stenosis, pediatric cardiology, internal mammary artery graft, myocardial perfusion imaging, revascularization, restenosis, children's heart disease