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Published on: June 21, 2016
Limitations of Doppler echocardiography for the post-operative evaluation of aortic coarctation
S De Mey1, P Segers, I Coomans
1Hydraulics Laboratory, Institute of Biomedical Technology, Ghent University, St-Pietersnieuwstraat 41, 9000, Ghent, Belgium. stefaan.demey@navier.rug.ac.be
Insights
Post-coarctation repair, elevated Doppler velocities and pressure differences persist despite normal arm-leg pressures. This is due to dynamic narrowing and aortic geometry, not significant obstruction.
Area of Science:
- Cardiovascular Surgery
- Medical Imaging
- Hemodynamics
Background:
- Aortic coarctation is a congenital narrowing distal to the left subclavian artery.
- Doppler-derived pressure gradients are used to diagnose aortic coarctation.
- Post-surgical repair, elevated Doppler velocities and pressure differences can persist despite normal arm-leg blood pressure.
Purpose of the Study:
- Investigate the discrepancy between Doppler-derived pressure differences and arm-leg pressure differences after aortic coarctation repair.
- Evaluate the role of anatomical and dynamic factors in post-coarctectomy hemodynamics.
- Validate an alternative method for calculating pressure differences.
Main Methods:
- Reviewed clinical and echocardiographic data from 31 post-coarctectomy patients and 18 healthy controls.
- Utilized a hydraulic latex model of the aorta with added rigid rings to simulate post-surgical scarring and dynamic obstruction.
- Measured Doppler peak velocities and pressure differences in vivo and in vitro.
Main Results:
- Patients showed elevated Doppler peak velocities (2.2 vs. 1.2 m/s) and significant Doppler pressure differences (20 mmHg) but no significant arm-leg pressure difference.
- A mild anatomical stenosis and increased local stiffness were observed in patients.
- The hydraulic model demonstrated that dynamic narrowing increased Doppler velocities and pressure differences without a significant pressure drop.
Conclusions:
- Elevated postoperative Doppler velocities and pressure differences are attributed to mild anatomical narrowing and dynamic obstruction, not significant residual stenosis.
- The specific geometry of the repaired aorta allows for pressure recovery, explaining the discrepancy with arm-leg pressure measurements.
- An alternative pressure difference calculation incorporating velocity and geometry was validated.
Abstract:
Doppler blood flow measurements and derived pressure differences, through the Bernoulli equation, are used in the diagnosis of aortic coarctation, a congenital stenosis distal to the left subclavian artery. Doppler velocities remain elevated at the coarctation site after successful repair of coarctation, leading to high Doppler derived pressure differences without significant arm-leg pressure differences. We studied this apparent contradiction of two diagnostic methods, in vivo using patient and control data, and in vitro using a hydraulic model. Clinical and echocardiographic data from 31 patients, aged 13.0 +/- 4.0, 10.5 +/- 4.7 yr after coarctectomy by end-to-end anastomosis, and 18 age-matched healthy subjects were reviewed. Doppler peak velocities at the aortic isthmus were elevated in patients (2.2 +/- 0.4 vs. 1.2 +/- 0.2m/s, P < 0.001), corresponding to significant Doppler differences (20 +/- 7 mmHg), however, without significant arm-leg pressure differences. In all patients, a mild anatomic stenosis could still be observed. Local stiffness was increased. The hypothesis that the less distensible surgical scar in post-coarctectomy patients leads to a significant dynamic obstruction in systole was validated in a latex model of the aorta. Rigid rings (0.5-1.5 cm), matching the unloaded aortic diameter, were mounted around the aorta. Under loading conditions, Doppler peak velocities increased by 40 +/-7%, yielding Doppler differences of 21 +/- 3 mmHg, without a significant pressure drop. An alternative expression to calculate pressure differences, using both velocity and geometric information, was validated in the model. In conclusion, post-operatively, Doppler velocities remain elevated due to a mild anatomical and significant dynamic narrowing, but the specific geometry, resembling a tubular hypoplasia rather than an abrupt stenosis, permits an almost complete pressure recovery explaining the occurrence of Doppler differences in disagreement with the negligible arm-leg pressure difference.
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