Cath Basics Notes; Shunting, Mixing, Streaming

Source:

McGoon, Dwight C, On the unmuddling of shunting, mixing, and streaming. J Thorac Cardiovasc Surg, 1990; 100:77-82.

Shunting = blood goes back to same artery/capillary bed it came from last

Mixing = intercirculatory exchange of blood, whereby it goes from one system to the other

Streaming = when blood from both circulations meet in the same chamber but do not completely blend

Shunting

-50% L-->R shunt @ VSD means that 1/2 of the pulm vn return to LA goes thru the VSD to the PAs again

-so Qp is 2x that of Qs (Qp:Qs = 2)

-Here, we are describing a system where the blood from one side (R side) is going to the L and then shunted back to the right side. It is being recirculated to the same side of the circulatory system that it came from (it's going back to the same capillary bed that it came from). Consider calling it a pulmonary or systemic recirculatory shunt.

Mixing

-Better to refer to it as Intercirculatory Mixing

-dTGA pts have in-parallel systemic and pulm circulations instead of serial circulations. This is incompatible with life unless there is some intercirculatory pathway- an ASD or a VSD, to allow for intermixing of the oxygenated blood fr Pulm Vns with the desaturated systemic blood return.

-Blood going through the ASD/VSD in this case should not be referred to as a shunt, because a shunt is defined by the amt of venous blood returning centrally in one circ system that ends up in the arterial outflow of the same system (e.g. for a VSD the amt of Q that returns fr PVns to L side and then goes back to the PA (the artery fr the system it came from...))

-Here, there is mixing, where blood from one circulation is crossing to the other (and staying there... it goes through the other arterial system/capillary bed, not the one that it came from, unlike w shunting)

-Actually w TGA, the shunting is the blood that does not mix (doesn't cross the VSD/ASD) and thus returns to the capillary bed/artery that it just came from. Thus w dTGA if no ASD or VSD, there would actually be 100% shunting (!)

-With mixing, the volume of blood going fr one circ system to the other has to be the same as the vol of blood going fr the other circ system the first one... (must have equal mixing in opposite directions) bc otherwise you would just be draining fr one circ system to the other until there is nothing left in the first system.

Streaming

-Better to call it Common Chamber Streaming

-Streaming is discussed in situations when there is an intracardiac or GA septum that is absent or there is anomalous venous return so that all the systemic and pulmonary Q pass through a common chamber and are thus blended. AKA there is a chamber that is common to both circulations. (e.g. common atrium, single ventricle heart, truncus, DORV)

-Use the word blending instead of the commonly used work mixing, because mixing is different (it should be mainly be used for intercirculatory exchange of blood, like w TGA, as oppose to when the two circulations meet at a common chamber).

-There isn't necessarily complete blending of blood in the common chamber- may have common chamber streaming where blood is incompletely mixed, Q in Ao is not the same as Q in PA

-may have advantageous streaming... or disadvantageous streaming - it regards how much of the Q is recirculated (disadvantageous) vs how much is effective flow (advantageous)

-streaming comes into play with DORV (e.g. favorable streaming w subAo VSD vs unfavorable w SubPA VSD (=Taussig Bing, acts like a TGA), also w other xx like truncus TAPVR etc

Streaming- Is it favorable or not?

-if more than half the flow coming into the common chamber goes to where it should NOT go, then it is unfavorable, if less than half goes to where it should NOT go, then it is favorable, and if the same amt goes to where it should go as to where it should NOT go, then there is complete blending (and thus no streaming). Examples: