What Does a Qp/Qs of 3.7 in ASD Mean?
A Qp/Qs ratio of 3.7 in atrial septal defect indicates a very large left-to-right shunt with 3.7 times more blood flowing through the pulmonary circulation than the systemic circulation, which strongly warrants closure via transcatheter or surgical repair. 1
Clinical Significance of This Ratio
This ratio far exceeds the 1.5:1 threshold that defines a hemodynamically significant shunt requiring intervention. 1, 2
A Qp/Qs of 3.7 indicates severe volume overload of the right heart chambers, as the right ventricle is pumping nearly 4 times the normal volume with each beat. 1
This magnitude of shunting will cause right atrial and right ventricular enlargement, and the patient is at high risk for developing pulmonary vascular disease if left untreated. 1
Management Algorithm
Step 1: Assess for Pulmonary Hypertension and Pulmonary Vascular Resistance
Before proceeding with closure, you must exclude severe pulmonary hypertension and elevated pulmonary vascular resistance (PVR). 1
Measure pulmonary artery systolic pressure (PASP) and calculate PVR, ideally via cardiac catheterization. 1
If PVR is less than one-third of systemic vascular resistance (SVR) AND PASP is less than 50% of systemic arterial systolic pressure, proceed with closure (Class I recommendation). 1
If PASP is 50% or more of systemic pressure OR PVR is greater than one-third of SVR, closure may still be considered but requires expert evaluation at an adult congenital heart disease center (Class IIb recommendation). 1
Do NOT close the ASD if PASP exceeds two-thirds of systemic pressure OR PVR exceeds two-thirds of SVR, as this indicates severe pulmonary vascular disease or Eisenmenger physiology (Class III: Harm). 1
Step 2: Evaluate Right Heart Size and Function
Confirm right atrial and right ventricular enlargement via echocardiography or cardiac MRI. 1
With a Qp/Qs of 3.7, right heart enlargement is virtually certain and supports the indication for closure. 1, 3
Step 3: Assess for Cyanosis
Check pulse oximetry at rest and during exercise to ensure there is no right-to-left shunting causing desaturation. 1
The presence of cyanosis or exercise desaturation would indicate elevated PVR and contraindicate closure. 1
Step 4: Determine Closure Method
For secundum ASD with favorable anatomy, transcatheter device closure is the preferred approach (Class I). 1
For primum ASD, sinus venosus defect, or coronary sinus defect, surgical repair is required (Class I). 1
Expected Outcomes After Closure
Functional capacity improves significantly after ASD closure, even in patients who consider themselves asymptomatic. 3
In a study of adults with mean Qp/Qs of 2.1, maximal oxygen uptake increased by 14-22% at 6 months post-closure, with improvement seen across all age groups and shunt sizes. 3
Right ventricular dimensions decrease significantly after closure. 3
With your patient's Qp/Qs of 3.7 (substantially higher than the study mean of 2.1), even greater hemodynamic benefit and symptom improvement can be expected. 3
Critical Pitfalls to Avoid
Do not rely on a single non-invasive method to calculate Qp/Qs, as Doppler echocardiography, radionuclide studies, and oximetry show poor inter-method agreement. 4
Cardiac MRI with phase-contrast imaging is now the non-invasive reference standard for measuring Qp/Qs and should be used when available. 2, 5
Never close an ASD based solely on Qp/Qs without assessing pulmonary vascular resistance, as patients with Eisenmenger physiology can have catastrophic outcomes if the "pop-off" valve is eliminated. 1
Patients may underestimate their symptoms; objective exercise testing often reveals functional impairment not apparent from history alone. 3