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Bidirectional shunt in uncomplicated atrial septal defect
Insights
Many patients with atrial septal defects have significant right-to-left shunts, unrelated to heart failure. These shunts increase with age, suggesting chronic right volume overload contributes to their development.
Area of Science:
- Cardiology
- Pediatric Cardiology
- Congenital Heart Disease
Background:
- Atrial septal defects (ASDs) are common congenital heart conditions.
- The direction and significance of shunting in ASDs can vary.
- Right-to-left shunting in uncomplicated ASDs is not fully understood.
Purpose of the Study:
- To determine the prevalence of right-to-left shunts at the atrial level in patients with uncomplicated ASDs.
- To investigate the characteristics and potential causes of right-to-left shunts in this population.
Main Methods:
- Studied 40 patients with uncomplicated atrial septal defects.
- Measured pulmonary vein to systemic artery oxygen stepdown to detect shunts.
- Utilized oximetric techniques for shunt quantification.
Main Results:
- Six patients (15%) exhibited significant right-to-left shunts (oxygen stepdown ≥ 0.7 vol%, shunt 0.67 L/min/m²).
- These patients had lower arterial oxygen saturation (84-90.5%).
- Patients with right-to-left shunts were older and had smaller left-to-right shunts compared to those without.
Conclusions:
- A notable proportion of uncomplicated ASD patients possess significant right-to-left shunts.
- These shunts are independent of pulmonary hypertension or right heart failure.
- The development of right-to-left shunts appears age-related, possibly due to chronic right volume overload.
Abstract:
The presence of right to left shunts at atrial level in 40 patients with an uncomplicated atrial septal defect was determined by measuring the pulmonary vein to systemic artery oxygen stepdown . In six patients (group 1) a sizeable right to left shunt was found: left atrial oxygen stepdown was greater than or equal to 0.7 vol%, mean right to left shunt 0.67 1/min/m2 (range 0.36-1.0), and arterial oxygen saturation between 84% and 90.5%. The patients in group 1 did not show any differences from those with left to right shunts alone (group 2) as regards sex, cardiac rhythm, heart rate, "a" wave and mean right atrial pressure, end diastolic right ventricular pressure, morphology of diastolic right ventricular pressure curves, pulmonary to systemic vascular resistance ratio, size of the defect, and coexistence of anomalous pulmonary venous drainage. Patients with coexisting right to left shunts were, however, significantly older and had smaller left to right shunts. Thus an appreciable number of patients with uncomplicated atrial septal defects have major right to left shunts which are unrelated to pulmonary hypertension or right heart failure. These shunts may be detected by the usual oximetric techniques and apparently develop with age, which suggests that they result from changes associated with chronic right volume overload.