New application of saline contrast-enhanced electrical impedance tomography method for right ventriculography besides lung perfusion: detection of right-to-left intracardiac shunt.

Abstract

Saline contrast-enhanced electrical impedance tomography (EIT) has been used to identify the respiratory failure etiologies through assessment of regional lung perfusion at the bedside. In this study, we introduce a novel approach to detect right-to-left intracardiac shunt based on the center of heart (CoH) parameter determined from the early phase of impedance-time curve after saline bolus injection. The timepoints when the saline bolus enter the heart (T0) and the lung regions (T1) are identified at first. A moving time window from T0 to T1 is then generated with steps of 0.5 s and the slope of the impedance-time curve in each pixel within the window calculated. CoH is calculated as the geometric center of pixel slope values in the right-to-left image direction. To illustrate how this method works in practice, we calculated the CoH values at T0 to T1 in 10 control hypoxic patients with no right-to-left shunt. In addition, we examined two critically ill patients with right-to-left intracardiac shunt. One was postcardiac surgery patient who had a residual atrial septal defect by color doppler of transesophageal echocardiograph. The other patient had a congenital heart disease of ventricular septal defect by color doppler of trans-thoracic echocardiography. A large difference in CoH between T0 to T1 was observed in the two patients with intracardiac shunt than in the control patients (11.06 ± 3.17% vs. 1.99 ± 1.43%, P = 0.030). Saline bolus EIT for lung perfusion might be used as ventriculography to identify the right-to-left intracardiac shunt at the bedside.