Doctor, There's a Hole in my Heart!?

An interesting article published by one of our staff and residents on morning report can be found here.

A prior blog on the causes of platypnea and orthodeoxia can be found here.

Review of PFO formation:

• The endocardial cushions fuse, separating the heart into R and L sides.

• Early in utero the septum primum grows and fuses with the endocardial cushion, closing the formaen primum, however perorations have developed in the septum primum to fuse, forming the foramen secundum (still allowing right to left shunting)

• A second membrane, the septum secundum, grows on the right atrial side of the septum primum. The septum secundum overlaps the foramen secundum, forming an incomplete septal partition that becomes the foramen ovale. The remaining septum primum forms a flap-like valve over the foramen ovale.
• After birth, normal circulation is established (left sided pressures>right sided) and the flap fuses in 75% of people by age 2. The remainder have a PFO.
• The PFO is completed covered, but not sealed and shunting can occur if there is a reversal in intracardiac pressures (i.e. right to left shunt).
  
• If an open communication exits (no flap) this is an ASD.
  

In studies, PFO prevalance is as high as 25%

A debate on PFO closure (with respect to cryptogenic stroke) can be found in these two Circulation articles: Close v. Don't Close (or at least do an RCT).

Platypnea

PLATYPNEA and ORTHODEOXIA

After discussing an approach to dyspnea on exertion, the symptom of platypnea was discussed.

Platypnea is an increase in dyspnea in the upright position that improves on lying down.

Orthodeoxia is a decrease in oxygen saturation that occurs upon rising from supine.

These often occur together. They happen when there is right to left shunting that only occurs or is more pronounced, in the upright position. Shunts can be intracardiac (ASD, PFO) or intrapulmnary (AVM, hepatopulmonary syndrome).

This often occurs in HHT, when larger pulmonary AVMs are in bases of the bases of the lungs and therefore recevie a greater proportion of blood when the patient is upright. It can also occur for anatomic reasons in patients with intracardiac shunts.

Shunting can be seen with contrast ECHO where agitated saline bubbles are injected into peripheral veins. They appera in the right heart, and if a right to left shunt exists then they will appear in the left side of the heart. If they appear in 1-2 beats, the shunt is intracaridac, in 3-8 beats then it is likely intrapulmonmary.

Shunt fraction can be calculated by testing SaO2 and PaO2 before and after breating 100% oxygen fro 15 minutes. Normal is less than 5%.

International guidelines for the diagnosis and management of HHT (published by Toronto clinicians) can be found here.
A NEJM review of HHT can be found here.
A NEJM review of hepatopulmonary syndrome can be found here.