VA-ECMO’s Hidden Blind Spot: Coronary Arteries May Starve for Oxygen While Peripheral Readings Look Normal

Patients supported with veno-arterial extracorporeal membrane oxygenation, or VA-ECMO, are usually monitored with an array of devices that sample oxygenation at peripheral sites: blood gases drawn from a radial artery, near-infrared spectroscopy pads placed on the forehead, pulse oximeters clipped to a finger. A new editorial published in the journal Critical Care argues that this entire apparatus may be looking in the wrong place when the threat is to the heart itself. The authors, Ignazio Condello and Youssef El Dsouki, contend that a patient’s coronary arteries can be perfused with poorly oxygenated blood even while every peripheral measurement suggests that oxygenation is satisfactory. They call this phenomenon selective coronary hypoxemia, and they frame it not as a newly discovered syndrome but as a clinically relevant monitoring blind spot that deserves systematic investigation.

The core of the argument is geometric. During peripheral VA-ECMO, deoxygenated blood is drawn from a vein, oxygenated in an external membrane lung, and returned to the arterial system, typically through a femoral artery cannula. When the patient’s own left ventricle still ejects blood and the lungs are severely impaired, the aortic root, the most proximal arterial territory and the origin of the coronary arteries, may be filled with poorly oxygenated native blood, while the oxygenated extracorporeal stream returning from the femoral cannula preferentially supplies more distal territories. The editorial stresses that this possibility is not new: previous computational, experimental and clinical observations have already demonstrated the potential for inadequate myocardial or aortic-root oxygenation during VA-ECMO, and contemporary nomenclature of the dual circulation created by ECMO has emphasized the limitations of peripheral measurements in defining oxygenation across vascular territories. What the authors add is a framework for recognizing and studying the problem.

A crucial conceptual distinction runs through the editorial. Reduced coronary arterial oxygenation, reduced myocardial oxygen delivery and myocardial ischemia are related but separate phenomena. Myocardial oxygen delivery depends not only on the oxygen content of the blood entering the coronary arteries but also on coronary blood flow and hemoglobin concentration. Ischemia, in turn, reflects the balance between oxygen supply and myocardial demand. A drop in the oxygen content of aortic-root blood may therefore set the stage for trouble without by itself producing ischemia, and the authors repeatedly warn against conflating the three.

Why would conventional monitoring miss the problem? The editorial’s answer is that each monitoring modality interrogates a specific anatomical or vascular compartment. Cerebral near-infrared spectroscopy reflects regional cerebral tissue oxygenation. Radial NIRS has been investigated as a non-invasive approach to detecting differential upper-body oxygenation during VA-ECMO. But neither directly measures the oxygenation of blood entering the coronary arteries. Increasing the frequency of sampling improves temporal surveillance, the authors note, yet it cannot correct this spatial limitation: the issue is not how often you look, but where.

The risk, they argue, may actually increase during myocardial recovery. As native cardiac ejection rises, the mixing zone between the patient’s own desaturated blood and the oxygenated extracorporeal stream may migrate distally while severely impaired pulmonary gas exchange persists. Although coronary perfusion occurs predominantly in diastole, the oxygen content of coronary arterial blood depends on which blood occupies the aortic root. As native ejection grows stronger, oxygenated extracorporeal blood may be progressively displaced from the proximal aorta even while lung function remains poor. This anatomical condition may reduce coronary arterial oxygen content, though its effect on actual myocardial oxygenation will still depend on coronary blood flow, hemoglobin concentration and myocardial oxygen demand.

The clinical picture is equally nonspecific. New ST-segment changes, ventricular arrhythmias, ventricular dysfunction or unexpectedly delayed myocardial recovery may raise concern at the bedside, but none of these signs is specific for selective coronary hypoxemia. The exposure itself is configuration-dependent: femoral arterial return produces retrograde aortic flow, whereas axillary or central return changes the direction and location of extracorporeal blood delivery. Yet the effect of any configuration on coronary arterial oxygenation depends on cannula position, jet direction, native cardiac output, extracorporeal flow and pulmonary gas exchange. Moving the arterial return proximally may improve upper-body oxygenation but does not necessarily ensure adequate oxygenation at the coronary ostia, and increasing VA-ECMO flow may likewise fail to restore aortic-root oxygenation.

The editorial also addresses combined strategies such as ECPELLA, in which VA-ECMO is paired with the Impella micro-axial pump. In that setting, the Impella may deliver desaturated left-ventricular blood directly into the aortic root when pulmonary gas exchange remains severely impaired. Conversely, ventricular unloading by the Impella may reduce myocardial oxygen demand. The net effect on the myocardial oxygen supply-demand balance is therefore not predictable from the configuration alone and requires individualized physiological assessment. The authors suggest considering selective coronary hypoxemia when pulmonary gas exchange is poor and native ejection increases despite apparently adequate peripheral oxygenation.

For assessment, they propose combining simultaneous right-radial and femoral blood gases, cerebral NIRS, electrocardiography and echocardiographic evaluation of aortic-valve opening, native ejection and ventricular unloading. New ischemic ECG changes or electrical instability should first prompt exclusion of conventional causes: coronary occlusion, ordinary supply-demand imbalance and mechanical complications. Management options may include improving pulmonary oxygenation, adjusting native and extracorporeal flows, changing the site of arterial return or converting to V-AV ECMO, which adds an oxygenated venous return limb. But the authors caution that the effect of these interventions on coronary oxygenation cannot be assumed and demands individualized assessment. Even flow-reduction trials during weaning alter the mixing zone, perfusion pressure, ventricular loading, native ejection and myocardial oxygen demand simultaneously, so deterioration during such an assessment cannot be considered diagnostic. Most pointedly, they state that VA-ECMO support should not be reduced solely to provoke or diagnose this phenomenon.

One candidate additional signal is the oxygen saturation of blood in the coronary sinus, the vessel that drains venous blood from the myocardium. Coronary sinus oxygen saturation reflects residual oxygen after myocardial extraction and therefore integrates determinants of myocardial oxygen supply and consumption. The editorial cites a study by Kumon and colleagues demonstrating the feasibility of continuous coronary sinus saturation monitoring in six postoperative cardiac-surgery patients, but it emphasizes that this study did not evaluate selective coronary hypoxemia and did not establish the diagnostic performance of the measurement during VA-ECMO. A falling coronary sinus saturation despite preserved peripheral oxygenation could represent a physiological signal of worsening myocardial oxygen supply-demand balance, but it cannot by itself establish reduced coronary arterial oxygenation. The measurement is influenced by coronary blood flow and perfusion pressure, hemoglobin concentration, heart rate, loading conditions, contractility and vasoactive therapy, and aggregate coronary sinus sampling may obscure regional myocardial abnormalities. Because coronary sinus catheterization is invasive and insufficiently specific, the authors relegate it to the status of an exploratory research measurement rather than a validated diagnostic marker.

The path forward, they argue, runs from monitoring blind spot to testable hypothesis. The relevant research question is whether changes in proposed surrogate signals, including coronary sinus saturation, actually correspond to changes in coronary arterial oxygenation. Initial mechanistic validation should incorporate reference measurements of aortic-root or coronary arterial oxygenation, together with coronary perfusion and relevant determinants of myocardial workload, in appropriate experimental models or selected procedural settings. Subsequent clinical feasibility studies could examine whether combinations of peripheral blood gases, NIRS, ECG, echocardiography and coronary sinus saturation identify reproducible physiological patterns associated with these mechanisms. Computational modelling may further characterize native and extracorporeal contributions at the coronary ostia across different support configurations. Direct coronary or aortic-root measurements, the authors insist, should not be advocated for routine clinical monitoring. The editorial’s closing message is that the clinical challenge is not only how frequently oxygenation is measured during VA-ECMO, but whether the sampled vascular territory adequately represents the organ at risk, and that satisfactory oxygenation at peripheral sites does not necessarily establish adequate oxygenation of the blood reaching the coronary ostia.

Subject of Research: Selective coronary hypoxemia during veno-arterial ECMO and the limitations of peripheral oxygenation monitoring

Article Title: Selective coronary hypoxemia during VA-ECMO: limitations of peripheral oxygenation monitoring

Article References: Condello, I., & Dsouki, Y. E. (2026). Selective coronary hypoxemia during VA-ECMO: limitations of peripheral oxygenation monitoring. Critical Care, 30(1), Article 546. https://doi.org/10.1186/s13054-026-06419-6

Image Credits: AI Generated

DOI: 10.1186/s13054-026-06419-6

Keywords: VA-ECMO, coronary hypoxemia, differential hypoxemia, oxygenation monitoring, NIRS, coronary sinus saturation, myocardial ischemia, ECPELLA, aortic root, critical care, extracorporeal life support, monitoring blind spot