Cardiac catheterization in MRCP

Cardiac catheterization in MRCP

I found questions about cardiac catheterization are always very challenging in MRCP Part 2 exam. When I sat for my Part 2 three years ago, they would usually show you the pressure and saturation from a cardiac catheterization and ask you what the underlying cardiac lesion is, however, I notice that recently they have switched the way of asking this type of question. They prefer to give you a case with important physical signs and ask you to choose the correct cardiac catheterization results.

Anyway, start form basic first, remember the normal and pressure of each cardiac chamber as below,

Left heart
Aorta-------120/80 ( pressure)---------98% (saturation)
LV----------150/5-10------------------98%
LA--------------------------------------98%

Right heart
RA------------0-8 (mean pressure)-----74%
RV-----------15-30/0-8----------------74%
PA-----------15-30/3-12---------------74%
SVC-------------------------------------74%
IVC-------------------------------------70%
PCWP--------1-10 ( mean)

There are two main groups of questions in MRCP, either a saturation or pressure problem, we would talk about saturation problem first today.
I would give you a few examples and explain to you the underlying cardiac lesions,

Case 1:

---------------Pressure mmHg --Saturation%
Right heart
SVC ------------------5-------------- 72
RA -------------------6-------------- 76
RV----------------- 25/0-5 ----------76
PA -----------------25/10----------- 77

Left heart
LV ---------------140/0-12---------- 97
Aorta --------------140/75 -----------97

You notice that the saturation at the superior vena cava is 72% and increases to 76%, if you remember your anatomy, blood from SVC would go to right atrium (RA) and the saturation should be the same ( see above image again), therefore , there must be presence of mixture of blood from more oxygenated blood from left atrium and right atrium. Yes, you are right, the diagnosis is atrial septal defect!

Case 2:

----------------Pressure (mmHg) ----Oxygen saturation (%)
SVC--------------- - ---------------------72
RA ------------------7--------------------72
RV----------------- 50/12----------------86
PCWP-------------- 16 ------------------- -
LV -----------------90/12----------------96
Aorta ---------------100/50---------------97

This question is easy, you notice there is a sudden increase in oxygen saturation from RA to RV, therefore, there must be mixture of blood over RV and LV, the diagnosis is Ventricular septal defect( VSD).

Case 3:

-------------------Pressure (mmHg)------ Oxygen saturation (%)
IVC -------------------------------------------60
RA ---------------------20---------------------66
RV--------------------- 100/20---------------- 67
PA ---------------------100/30---------------- 67
LV ----------------------100/10 ---------------70
Aorta-------------------- 105/80---------------70

This case is more complicated, however, stay calm, apply basic principles. You notice that there is an increase of oxygen saturation form IVC to RA ( sounds like it is an atrial septal defect). However, you notice that RV’s pressure is high and even equals to that of LV’s. Another abnormality you notice is the saturation of LV and aorta is low ( as compared to more than 95% in normal subjects). So…… the diagnosis is Eisenmenger’s syndrome secondary to ASD.

Case 4:

----------------------------Pressure (mmHg) --------Oxygen saturation (%)
Superior vena cava ----------------------------------------77
RA -----------------------------6--------------------------78
RV -------------------------------------------------------- 78
PA ---------------------------50/20----------------------- 86
PCWP--------------------------16-----------------------------
LV--------------------------120/11------------------------96
Aorta------------------------- 130/60----------------------97

This case is simple, you notice there is high pressure present over Pulmonary artery with sudden increase in oxygen saturation, therefore mixture of blood must be present over the pulmonary artery. Yes, you are right, you are dealing with Patent Ductus arteriousus.

Ok, that is enough for today, we have learn about cardiac lesions that give you abnormal oxygen saturation during cardiac catheterization, I would talk more about valvular heart lesions that give your abnormal pressure during cardiac catheterization in future posts.