A 28-year-old woman presents to her obstetrician-gynecologist (OB-GYN) for routine management of her first pregnancy. She was diagnosed with a heart murmur at age 2, but no further workup was done at that time. She reports occasional palpitations since childhood, especially when she is lying down or stressed. She has good exercise capacity and has always been able to keep up with her peers. After hearing a murmur on exam, her OB-GYN orders an echocardiogram, which shows an enlarged right atrium and right ventricle, mild tricuspid regurgitation, mildly elevated right ventricular systolic pressure, and a possible atrial septal defect (ASD). Cardiac magnetic resonance imaging is performed and confirms the presence of a secundum ASD. She undergoes right heart catheterization, which reveals the following hemodynamics:

• 
  

  Atrial septal defect (ASD): An ASD is a persistent communication between the right and left atriums caused by abnormal embryologic development of the atrial septum. The 4 types of ASD in decreasing order of prevalence are secundum (70%), primum (15%-20%), sinus venosus (5%-10%), and coronary sinus (<1%). Sinus venosus ASDs are typically associated with partial anomalous venous return, most commonly of the right upper pulmonary vein.

  
  
• 
  

  Ventricular septal defect (VSD): A VSD is a defect in the ventricular septum resulting in a persistent communication between the left ventricle and right heart. VSDs are named according to the portion of the ventricular septum affected and are classified in the following categories, in decreasing order of prevalence: membranous, muscular, infundibular, inlet, and atrioventricular. Although most VSDs occur as the result of abnormal embryologic development, they may also be acquired in the setting of cardiac surgery or myocardial infarction.

  
  
• 
  

  Patent ductus arteriosus (PDA): The ductus arteriosus is a fetal communication between the pulmonary artery and aorta that closes soon after birth. In a very small minority of patients, the ductus remains patent into adulthood.

  
  
• 
  

  Notable extracardiac shunts: Partial anomalous pulmonary venous return (PAPVR) and pulmonary arteriovenous malformations (AVMs) may also cause shunting detectable in the catheterization laboratory.

• 
  

  It is estimated that 1.6 per 1000 adults are living with intracardiac shunts including ASD, VSD, and PDA.¹

• 
  

  Noninvasive: The ease of diagnosis depends on the size of the shunt. Small shunts require a high index of suspicion, which is often triggered by the observation of chamber dilatation on echocardiogram.

  
  
  
  
  • 
    

    Color Doppler on echocardiogram

    
    
  • 
    

    Bubble study

  
  
• 
  

  Invasive

  
  
  
  
  • 
    

    Angiography: passage of contrast medium across the shunt

    
    
  • 
    

    Catheterization: passage of catheter or wire across shunt

    
    
  • 
    

    Step-up or step-down of oxygen saturation in contiguous cardiac chambers (Figure 3-1)