The Path of Least Resistance

A 27-year-old woman with history of methamphetamine abuse and hepatitis C developed acute hypoxemia 2 days after a cesarean section (performed for intrauterine growth retardation). Physical exam revealed a loud P2, pan-systolic murmur at the left lower sternal border and a right parasternal heave. Vitals were notable for SpO2 of 78-85% on a non-rebreather. A chest computed tomography scan showed no pulmonary embolism or parenchymal lung disease. Transthoracic echocardiogram revealed an under-filled left ventricle (LV), a severely dilated and dysfunctional right ventricle (RV), severe tricuspid regurgitation (TR), an estimated RV systolic pressure of 100-105 mmHg, and a small (1 cm) secundum atrial septal defect (ASD) with predominantly right-to-left shunt (Figure 1).

Figure 1: Transthoracic Echocardiogram

Figure 1
(A: parasternal long-axis view) Grossly dilated RV. (B: parasternal short-axis view) Severely enlarged RV with septal flattening and a small, compressed LV. (C: apical four-chamber view) Severely enlarged right atrium and RV, again with septal flattening and a small, compressed LV. (D: Color Doppler across tricuspid valve) Regurgitant tricuspid valve jet of 4.3 m/s, with an estimated RV systolic pressure of approximately 90 mmHg, which is severely elevated and indicates pulmonary hypertension.

A right heart catheterization showed the following:

  • Pulmonary artery (PA) saturation: 48%
  • Superior vena cava saturation: 51%
  • Inferior vena cava saturation: 53%
  • Pulmonary veins (PV) (right middle and left upper) saturation: 99%
  • PA pressure (systolic/diastolic/mean): 105/40/63 mmHg
  • Pulmonary capillary wedge pressure): 9 mmHg
  • Left atrium: 9 mmHg
  • LV: 140/9 mmHg
  • Cuff (right arm) blood pressure (systolic/diastolic/mean): 119/83/95 mmHg
  • Using mixed venous saturation of = 52%, PA = 48%, pulmonary veins = 99%, aortic = 83%, and hemoglobin 10 g/dL
  • Qp = 3.4 L/min; Qs = 5.6 L/min; Qp:Qs = 0.6:1
  • Pulmonary vascular resistance (PVR) = 15.9 Wood units; systemic vascular resistance = 15 Wood units

Intracardiac echocardiography confirmed a small secundum ASD with right-to-left shunting (Figure 2).

Figure 2: Intracardiac Echocardiography

Figure 2
Secundum ASD with right-to-left shunting.

Which of the following is the best initial step in management of this patient?

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