From the Guidelines
Yes, FMD can be called on vascular ultrasound, but it is not the gold standard imaging method for diagnosing fibromuscular dysplasia (FMD). Vascular ultrasound may identify FMD by showing areas of stenosis and dilation in affected arteries, creating a "string of beads" appearance characteristic of multifocal FMD 1. However, ultrasound has limitations in visualizing certain arterial segments, particularly in deeper vessels or those obscured by overlying structures. The sensitivity of ultrasound for FMD detection varies by arterial location, with better visualization in superficial vessels like the carotid arteries. For definitive diagnosis, catheter-based angiography remains the gold standard, while CT angiography (CTA) and MR angiography (MRA) are preferred non-invasive options with better sensitivity than ultrasound 1. Vascular ultrasound may be useful as an initial screening tool or for follow-up monitoring of known FMD, but negative ultrasound findings don't exclude FMD when clinical suspicion is high, and further imaging would be warranted 1. Some key considerations for assessing FMD on vascular ultrasound include:
- Using a multifrequency linear-array transducer (usually 7 to 12 MHz) for high image resolution 1
- Gating images to a simultaneously obtained ECG recording, because brachial diameter varies significantly during the cardiac cycle 1
- Measuring flow-mediated dilation (FMD) as the nitric oxide–mediated vasodilation produced by increased flow after a period of ischemia 1
- Assessing non–endothelium-dependent (NED) dilation measures the arterial changes induced by administration of a sublingual dose of nitroglycerin, which reflects predominantly the smooth muscle response 1.
From the Research
Vascular Ultrasound and FMD
- Flow-mediated dilation (FMD) can be called on vascular ultrasound, as it is a non-invasive method used to assess endothelial function by measuring changes in the diameter of the brachial artery in response to increased blood flow 2, 3, 4.
- The FMD test is widely utilized in the assessment of endothelial function in humans and has been associated with future cardiovascular events 3, 5.
- Vascular ultrasound is used to measure FMD, which involves the assessment of changes in the diameter of the brachial artery as a result of increased blood flow 2, 4.
Methodology and Applications
- The FMD test incorporates a forearm occlusion and subsequent reactive hyperemia that promotes nitric oxide production and vasodilation of the brachial artery 3.
- The test is performed by qualified and experienced medical staff, and its results can be used to evaluate endothelial function and predict long-term cardiovascular events in subjects without heart disease 2, 5.
- FMD reference values have been established for the evaluation of endothelial function and cardiovascular health, taking into account factors such as age, body mass index, and brachial artery diameter 6.
Technical Considerations
- The FMD test requires a standardized protocol to minimize physiological and technical issues and improve the precision and reproducibility of the assessment 3.
- High-resolution ultrasound and strain gauge plethysmography are used to measure brachial artery diameters and blood flow 4.
- The intraobserver variability in measuring brachial diameters and the variability of the hyperemic response are important considerations in the FMD test 4.