113 - Right-to-left transductal flow does not equate to pulmonary hypertension; a neonatal cohort study highlighting the dangers of echocardiogram oversimplification

Poster Number: 113
Publication Number: 113.1972

Background: The presence of bidirectional or exclusive right-to-left flow through the patent ductus arteriosus (PDA) is considered pathognomonic of pulmonary hypertension (PH), alone, or accompanied by other qualifying criteria such as right ventricular systolic pressure (RVSp) and interventricular septal configuration, and may prompt initiation of selective pulmonary vasodilators (e.g., inhaled nitric oxide). Physiologically, transductal flow is simply determined by the pressure gradient; therefore, degrees of right-to-left flow may also be generated in a low systemic vascular resistance (SVR) state (e.g., hypovolemia, sepsis).

Objective: To demonstrate the inadequacy (and inaccuracy) of relying on single echocardiogram findings such a transductal flow to diagnose PH in critically ill neonates.

Design/Methods: Neonates born < 32 weeks’ gestation with bidirectional (>40% of systole) or exclusive right-to-left flow through the PDA within the first postnatal week were identified from the Iowa Neonatal Hemodynamics Database. A random sample (n=10/group) of infants were selected based on comprehensive hemodynamic evaluation [clinical phenotype and targeted neonatal echocardiography (TnEcho)] and categorized as PH vs no-PH. Clinical and demographic data were retrospectively collected (Table 1). Indices of pulmonary hemodynamics, heart function and systemic blood flow were estimated. TnEchos were measured and descriptive statistics performed (Table 2).

Results: Baseline demographic parameters were comparable. The no-PH group was characterized by higher oxygenation index, use of cardiovascular medications, and diastolic hypotension. Of the classic echo parameters for PH diagnosis, only RVSp differed between groups. Infants with a no-PH diagnosis had normal median pulmonary vascular resistance index ( < 4.0) and were unlikely to have right ventricular dysfunction. Importantly, infants in the no-PH group had higher left and right ventricular output.

Conclusion(s): The presence of right-left or bidirectional PDA shunt should not be considered pathognomonic of a diagnosis of PH and absolute need for pulmonary vasodilators. Comprehensive TnEcho evaluation may allow more precision in the selection of cardiovascular treatments specific to the underlying echocardiography phenotype.