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Effect of cardiac cycle on ultrasound assessment of endothelial function
Michael L Chuang1, Pamela S Douglas, Elizabeth A Bisinov
1University of Wisconsin Atherosclerosis Imaging Research Program, University of Wisconsin Medical School, Madison 53792, USA.
Insights
Brachial artery diameter significantly varies with the cardiac cycle. Accurate endothelial function assessment, including flow-mediated dilation (FMD), requires electrocardiogram (ECG)-triggered imaging to avoid errors.
Area of Science:
- Cardiovascular Physiology
- Medical Imaging
- Vascular Biology
Background:
- Endothelial function is crucial for cardiovascular health.
- Ultrasound is commonly used to measure brachial artery diameter for assessing endothelial function.
- Cyclic variations in arterial diameter throughout the cardiac cycle are not always accounted for in imaging protocols.
Purpose of the Study:
- To investigate the impact of non-ECG-triggered imaging on ultrasound measurements of brachial artery diameter.
- To quantify the potential errors in assessing endothelial function (flow-mediated dilation and nitroglycerin-mediated vasodilation) due to ignoring cardiac cycle variations.
- To determine if ECG-triggered imaging is essential for accurate and reproducible measurements.
Main Methods:
- Brachial artery diameters were measured throughout the cardiac cycle in 24 subjects using R-wave-triggered ultrasound imaging (7.5-MHz transducer, 41.7-66.7 ms acquisition).
- Measurements were taken at rest, during reactive hyperemia, and after nitroglycerin administration.
- Cardiac cycle-related variation was calculated as the maximum percent change from end-diastolic diameter.
Main Results:
- Brachial arterial diameters exhibited significant variation throughout the cardiac cycle, comparable in magnitude to changes induced by hyperemia and nitroglycerin.
- Ignoring cardiac cycle timing led to dramatically different (p < 0.05) calculated values for flow-mediated dilation (FMD) and nitroglycerin-mediated vasodilation.
- Apparent FMD values could be nearly three times the true FMD, with non-ECG-triggered imaging artifactually normalizing truly impaired FMD.
Conclusions:
- Brachial arterial diameter varies significantly throughout the cardiac cycle.
- ECG-triggered imaging is mandatory for accurate and reproducible clinical and research measurements of artery diameters and endothelial function (FMD).
- End-diastolic measurement may be a preferred time-point for diameter assessment within the cardiac cycle.
Abstract:
To investigate the effects of non-ECG-triggered imaging during ultrasound studies of endothelial function, brachial artery diameters were measured throughout the cardiac cycle at rest, during reactive hyperemia, and after administration of nitroglycerin. R-wave-triggered imaging using a 7.5-MHz ultrasound transducer with acquisition every 41.7-66.7 ms was performed in 24 subjects. Cardiac cycle-related variation was computed as the maximum per cent change from the end-diastolic diameter. The range of possible errors in flow-mediated dilation (FMD) and nitroglycerin-mediated vasodilation that may result from ignoring cyclic variations in diameter was determined for each condition. True FMD, true nitroglycerin-mediated vasodilation, and the maximum and minimum values that could be erroneously calculated for FMD if timing was ignored all differed dramatically (p < 0.05). The range of apparent FMD values that could be measured was nearly three times the true FMD value. Ignoring temporal position within the cardiac cycle artifactually increased calculated FMD into the normal range, despite truly impaired FMD. Peak arterial dilation occurred before end-systole and greater baseline vessel compliance was associated with greater FMD. Brachial arterial diameters vary significantly throughout the cardiac cycle. The magnitude of this variation is similar to the arterial dilation induced by reactive hyperemia and nitroglycerin, making ECG-triggered imaging mandatory for accurate and reproducible clinical and research measurements of artery diameters and FMD. Measurement of diameters at end-diastole may be preferred to other time-points in the cardiac cycle.