Continuous wave Doppler echocardiography after surgical repair of coarctation of the aorta

Abstract

Objective-To find how closely pressure gradients across the aortic arch derived from Doppler echocardiography reflect gradients measured by catheter after surgical repair of coarctation of the aorta.Design-Pressure drop across the aortic arch was measured simultaneously by continuous wave Doppler and double lumen catheter in 20 patients with repaired coarctation of the aorta.Results-The peak pressure drop estimated by Doppler was almost invariably higher than the peak to peak gradient measured by catheter, as might be expected. Wide variation was seen between the Doppler measured pressure drop and instantaneous peak gradient measured by catheter, ranging from + 22 to -17 mm Hg. The reasons for these differences are unclear but are probably related to a combination of complex flow dynamics in the aortic arch, difficulty in closely aligning the Doppler beam with flow, and inability to measure flow velocity immediately proximal to the site of the surgical repair with continuous wave Doppler.Conclusions-Continuous wave Doppler echocardiography may significantly overestimate or underestimate the pressure drop after repair of coarctation and it should be interpreted with caution in individual patients. Catheterisation with angiography remains the reference standard for assessment of surgical repair of the aortic arch. (Br Heart 1992;68:192-4) Bernoulli equation in patients who had undergone surgical repair of coarctation. Patients and methodsWe studied prospectively 20 patients aged between 4-7 and 33 (mean (SD) 15-5 (5 3)) years with repaired coarctation of the aorta. Catheterisation was carried out either as part of routine late postoperative review of patch aortoplasty or clinical suspicion of residual or recurrent coarctation. At catheterisation, the ascending and descending aortic pressures were measured simultaneously with a fluid filled, thin walled, French 8 double lumen catheter. Before placing the catheter across the aortic arch simultaneous pressures from the two lumens in the descending aorta were recorded to ensure that identical waveforms were obtained. The pressure waveforms from either side of the aortic arch were recorded at 100 mm/s paper speed and were digitised on a graphics pad to compute the peak and peak to peak pressure gradient. A total of five pressure waveforms were digitised and the maximum values taken for comparison with the Doppler derived gradient.During the recording of the pressures peak flow velocity in the descending aorta was measured with a dedicated continuous wave Doppler transducer positioned in the suprasternal notch. The highest peak flow velocity was recorded and the modified Bernoulli equation (four times the square of the peak velocity) was used to calculate the peak pressure drop for comparison with the catheter measurements. The agreement between the catheter and Doppler derived gradients was compared by the method of Bland and Altman.8 Br Heart J 1992;68:192-4

Outcome after extended arch repair for aortic coarctation

“…Echocardiography undoubtedly improves sensitivity in the diagnosis of residual or recurrent arch obstruction but for an accurate estimation of the degree of obstruction across the repair site an assessment of flow velocities just proximal to the stenosis is essential. 22 In practice, given the geometry of the transverse arch, this measurement is usually very difficult to obtain. 22 Nearly all reported series rely on gradients derived from Doppler interrogation across the site of repair alone, which inevitably leads to an overestimation of the true gradient.…”

“…22 In practice, given the geometry of the transverse arch, this measurement is usually very difficult to obtain. 22 Nearly all reported series rely on gradients derived from Doppler interrogation across the site of repair alone, which inevitably leads to an overestimation of the true gradient. 22 In addition work by De Mey et al, 21 who used simulated models of the aortic arch after coarctation repair, showed that Doppler velocities increased as a manifestation of the change in compliance of the repaired vessel wall in the absence of stenosis.…”

“…22 Nearly all reported series rely on gradients derived from Doppler interrogation across the site of repair alone, which inevitably leads to an overestimation of the true gradient. 22 In addition work by De Mey et al, 21 who used simulated models of the aortic arch after coarctation repair, showed that Doppler velocities increased as a manifestation of the change in compliance of the repaired vessel wall in the absence of stenosis. 23 24 Therefore, the large area of scarring related to extensive dissection in extended arch repairs may result in higher systolic descending aortic velocities in the absence of stenosis than in other forms of arch repair potentially due to changes in compliance over a long segment.…”

Late complications in patients after repair of aortic coarctation: implications for management

“…Aortic arch geometry (i.e. hypoplastic arch), complex flow dynamics in the aortic arch, difficulty in closely aligning the Doppler beam with flow, and inability to measure flow velocity immediately proximal to the site of the surgical repair with continuous wave Doppler probably relate to this finding [28][29][30]. At echocardiography, the presence and the degree of antegrade diastolic flow (diastolic runoff, i.e.…”

Echocardiography in adult congenital heart disease

“…With less severe obstruction the signal may be of relatively high velocity but be entirely systolic (fig24). The maximum Doppler and measured catheter gradients correlate poorly with both instantaneous and peak to peak values, whether performed in a primary coarctation51 52 or after surgery 53…”