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Elevated augmentation index derived from peripheral arterial tonometry is associated with abnormal
Kevin S Heffernan1, Eshan A Patvardhan1, Michael Hession1
1The Vascular Function Study Group, Division of Cardiology, Tufts Medical Center, Molecular Cardiology Research Institute, Boston, MA, USA.
Insights
The augmentation index (AIx) measured by peripheral arterial tonometry (PAT) reflects ventricular-vascular coupling. Abnormal coupling, whether from arterial or ventricular changes, is linked to higher PAT-AIx values.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Vascular Diagnostics
Background:
- Augmentation index (AIx) is typically derived from arterial pressure waveforms.
- Peripheral arterial tonometry (PAT) allows AIx derivation from digital pulse volume waveforms.
- Physiologic correlates of PAT-derived AIx and ventricular-vascular coupling are not well understood.
Purpose of the Study:
- To investigate the relationship between AIx derived from PAT and measures of ventricular-vascular coupling.
- To explore the clinical utility of PAT-AIx in assessing cardiovascular load.
Main Methods:
- AIx was derived from pulse volume waves measured by PAT.
- Effective arterial elastance index (EaI) and left ventricular (LV) end-systolic elastance index (E(LV)I) were calculated using echocardiography.
- The ventricular-vascular coupling ratio was defined as EaI/E(LV)I.
Main Results:
- Patients were stratified into low, optimal, and high ventricular-vascular coupling groups.
- After adjusting for confounders, optimal coupling was associated with lower PAT-AIx (1 ± 4%).
- Conversely, low (13 ± 4%) and high (19 ± 5%) coupling groups exhibited significantly higher PAT-AIx.
Conclusions:
- Abnormal ventricular-vascular coupling, due to increased arterial or ventricular elastance, correlates with elevated PAT-AIx.
- PAT-AIx may serve as a non-invasive indicator of ventricular-vascular coupling.
- Further research is warranted to explore other vascular correlates of PAT-AIx.
Background:
Although typically derived from the contour of arterial pressure waveform, augmentation index (AIx) may also be derived from the digital pulse volume waveform using finger plethysmography (peripheral arterial tonometry, PAT). Little is known regarding the physiologic correlates of AIx derived from PAT. In this study, we investigated the relation of PAT-AIx with measures of ventricular-vascular coupling.
Methods:
Pulse volume waves were measured via PAT and used to derive AIx. Using 2-dimensional echocardiography, effective arterial elastance index (EaI) was estimated as end-systolic pressure/stroke volume index. Left ventricular (LV) end-systolic elastance index (E(LV)I) was calculated as end-systolic pressure/end-systolic volume index. Ventricular-vascular coupling ratio was defined as EaI/E(LV)I.
Results:
Given the bi-directional nature of ventricular-vascular uncoupling as measured by echocardiography, patients were separated into three groups: low EaI/E(LV)I (<0.6, n = 21), optimal EaI/E(LV)I (mean 0.6-1.2, n = 16) and high EaI/E(LV)I (>1.2, n = 10). Adjusting for potential confounders (age, mean arterial pressure, height and heart rate), patients with optimal EaI/E(LV)I had lower AIx (1 +/- 4%, P<0.05) compared to those with low EaI/E(LV)I (13 +/- 4%) and high EaI/E(LV)I (19 +/- 5%).
Conclusions:
Abnormal ventricular-vascular coupling, arising from either increased effective arterial elastance or increased ventricular elastance, is associated with increased AIx as measured by PAT. Additional research is needed to examine other vascular correlates of PAT-AIx.
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