Echocardiographic evaluation of pressure gradient across the stent in patients treated for coarctation of the aorta

Objective. Stent placement has become a widely used method of treatment for coarctation of the aorta (COA). Our goal was to find echocardiographic indices that would correlate best with directly measured gradients across the coarctation stent. Material and Methods. Pediatric patients with COA who underwent intra-aortic stent placement were evaluated. Patients with more than mild aortic insufficiency were excluded. Aortic pressures above and below the coarctation site were directly measured in the catheterization laboratory. Echocardiography was performed the next morning. Continuous and Pulse Doppler systolic velocity profiles proximal and distal to the stent were recorded. Statistical analysis included Pearson's correlation coefficients and linear regression between the directly measured pressure gradient and strongest correlated factor. Result. Thirty-four patients (F:M = 15:19) were included in the study. The directly measured gradients (DPG) had only weak positive correlations with Doppler peak velocities (r = 0.38, P = .027) or pressure gradients (r = 0.37, P = .03) across the stent. However, there was a strong positive correlation of the directly measured gradients with the continuous wave peak systolic velocity half-time indexed to heart rate (T) (r = 0.62, P = .03), and with the squared early diastolic velocity (V_d²) (r = 0.073, P < .0001). When these two parameters were combined, a linear regression equation DPG =0.06T + 1.58 V_d² - 8.05 showed very strong relations (r = 0.81, P < .0001). A simplified equation DPG = 1.98V_d² + 0.77 also accurately described the relations between the directly measured gradients and squared Doppler-measured early diastolic velocity (r = 0.71, P = .0002). Conclusions. A simple echocardiographic index DPG =1.98V_d ² + 0.77, where DPG is the pressure gradient across the stent, and V_d is the early Doppler diastolic velocity, accurately describes relations between the gradient across the stent and echocardiographic data and should be used for evaluation of patients with stent-corrected COA.