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[The utility of various Doppler parameters at rest and during exercise for the diagnosis of residual stenosis after operation for aortic coarctation. A doppler-nuclear magnetic resonance comparison].

BACKGROUND
The postoperative follow-up of aortic coarctation (AoCo) is often characterized by persistent arterial hypertension, sometimes due to a residual narrowing at the site of surgical repair. A residual stenosis > or = 30% is considered to be significant. Anatomy of the aortic arch is best assessed by angiography, transesophageal echocardiography and magnetic resonance imaging (MRI). The use of these invasive and expensive procedures for routine examination in all patients who develop late systemic hypertension cannot be justified. Consequently, it would appear to be useful to find some noninvasive methods, such as Doppler gradients, that are capable of identifying any residual anatomic narrowing.


OBJECTIVES
We compared different Doppler parameters obtained at rest and during exercise with the degree of narrowing at the site of surgical repair measured by MRI, in order to identify the indices predictive of residual stenosis.


METHODS
Thirty-nine patients (26 M, 13 F) were studied after AoCo repair. Mean age was 21.7 +/- 9.7 years (9-49). Their age at the time of repair was 10 +/- 9.7 years (0.1-27) and the postoperative follow-up was 11.5 +/- 6 years (2-25). Systolic blood pressure measurement and Doppler echo for calculation of the transisthmic gradient at rest and during exercise on a bicycle ergometer were performed in all patients. The peak systolic gradient (PGs) over the isthmus was calculated using the simplified Bernoulli equation: PGs = 4 x (V2(2)-V1(2)), where V1 and V2 are the peak velocities in the ascending and descending aorta. In addition, at the end of exercise the peak diastolic gradient (PGd) was measured at the end of the T wave on the ECG, and the systolic velocity half-time (SVHT), as the time interval from the peak to the half peak systolic velocity. MRI of the aorta was performed to measure the diameter of the isthmus (AI) and of the descending aorta at the diaphragm (DA). Residual narrowing at the isthmus was expressed as stenosis % = [(1-(AI/DA)]%.


RESULTS
At rest: systolic blood pressure 128.3 +/- 22.5 mmHg, PGs 15.9 +/- 8.1 mmHg (1-32). None of the patients had PGd. At peak exercise: systolic blood pressure 207 +/- 37 (160-265) mmHg, PGs 32.3 +/- 14.7 mmHg (8-70), SVHT 96 +/- 23 msec (60-139) and PGd 7.2 +/- 4.8 mmHg (1-17). Stenosis % measured by MRI was 23.1 +/- 14.5% (0-53) and in particular, it was < 30% in 25 patients and > or = 30% in 14 patients. Both the PGs at rest and the other Doppler parameters at peak exercise (PGs, SVHT, PGd) correlated with stenosis %. SVHT together with PGd on exercise Doppler represented the combination of two variables that was best for predicting a residual stenosis. When all three variables obtained by exercise Doppler were combined, every patient with residual stenosis was correctly identified. In particular, the combination (PGs > or = 28 mmHg + SVHT > or = 108 msec + PGd > or = 8 mmHg) identifies all patients with stenosis > or = 30%, while the combination (PGs < or = 38 mmHg + SVHT < 108 msec + PGd < 10 mmHg) excluded those with significant stenosis.


CONCLUSION
Parameters obtained from the transisthmic gradient (PGs, SVHT, PGd) measured at peak exercise by CW-Doppler can diagnose a residual stenosis % in operated AoCo. We propose using this noninvasive method of identifying patients who need to be referred for MRI.