This study found that ME/CFS patients who experience dizziness or fainting when standing up (orthostatic intolerance) have smaller hearts and pump less blood with each beat compared to ME/CFS patients without these symptoms and healthy people. The researchers used ultrasound imaging to measure heart size and function in different groups and discovered that about half of ME/CFS patients with orthostatic intolerance had unusually small left heart chambers.
Why It Matters
This study identifies a potential cardiac mechanism for orthostatic intolerance, a debilitating symptom affecting many ME/CFS patients. Understanding that a subset of ME/CFS patients have measurably smaller hearts and reduced cardiac output could lead to targeted diagnostic approaches and interventions tailored to this physiological abnormality.
Observed Findings
Patients with ME/CFS and orthostatic intolerance had significantly smaller left ventricular dimensions and lower cardiac output compared to ME/CFS patients without orthostatic intolerance and healthy controls.
54% of ME/CFS patients with orthostatic intolerance had left ventricular end-diastolic dimensions below 40 mm, compared to only 5% of ME/CFS patients without orthostatic intolerance.
65% of ME/CFS patients with orthostatic intolerance had reduced cardiac index (<2 L/min/m²), versus 5% of those without orthostatic intolerance, 27% with isolated orthostatic intolerance, and 11% of controls.
Cardiothoracic ratio, blood pressure, and left ventricular mass were all significantly reduced in ME/CFS patients with orthostatic intolerance.
Inferred Conclusions
A small left ventricle with low cardiac output appears to be a characteristic feature of ME/CFS patients with orthostatic intolerance.
Me/CFS patients with orthostatic intolerance constitute a distinct, well-defined subgroup of ME/CFS characterized by measurable cardiac abnormalities.
Small heart size may contribute to orthostatic intolerance through reduced cerebral and systemic blood flow.
Remaining Questions
What causes the heart to become or remain small in this ME/CFS subgroup—is it deconditioning, autonomic dysfunction, viral damage, or something else?
Does treating or addressing the small heart size and low cardiac output improve orthostatic intolerance and ME/CFS symptoms?
What This Study Does Not Prove
This study demonstrates association but does not prove causality—it is unclear whether small heart size causes ME/CFS and orthostatic intolerance, or whether they result from a common underlying process. The cross-sectional design cannot establish whether cardiac changes precede symptom onset. Additionally, the study does not determine why some ME/CFS patients develop small hearts while others do not.
Tags
Symptom:Orthostatic IntoleranceFatigue
Biomarker:Blood Biomarker
Method Flag:Weak Case DefinitionSmall SampleExploratory Only
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →