Thread by @MedEdPGH

1/ It’s time for #PhysioQuizzo! You’re excited. We’re excited. It’s fun!

You’re on inpatient cardiology and your patient gets a right heart cath (RHC):

RA 29
PA 52/33 (mean 40)
PCWP 34
CO/CI
-Thermo: 2.9/1.2
-Fick: 5.3/2.0
SvO2 43

Q1: Does this pt have heart failure (HF)?

2/ #PhysioQuizzo

Question 2 (all answers at the end!): Does the patient have pulmonary hypertension?

3/ #PhysioQuizzo

Question 3: Does the patient have pulmonary arterial hypertension (PAH, or Group 1 PH)?

4/ #PhysioQuizzo

Question 4: Is the patient in low output heart failure?

5/ #PhysioQuizzo – Normal RHC Values

Phew! That was a lot. There’s so much learning ahead!

1st things 1st: What even are normal RHC values? Generally speaking:

Right Atrium (RA) – mean ≤6 mmHg
Pulmonary Artery (PA) – mean >20 mmHg
Wedge Pressure (PCWP) - ≤12 mmHg

7/ #PhysioQuizzo – Nickel-Quarter-Dime-Dollar

I usually teach a mnemonic to help people remember this. The mnemonic isn’t perfect, but it anchors your brain in the right ballpark, at least.

See the picture below.

7/ #PhysioQuizzo – What is Heart Failure?

One way to conceptualize HF is to say that ventricular failure occurs when the preceding atrial pressure rises above normal.

>So, Left HF occurs when PCWP rises >12
>Right HF occurs when RA rises >6

Caveats in the next post

8/ #PhysioQuizzo – Pressure caveats

There are many caveats (e.g. regurgitant valves), but two basic points:

*Not all pts will have sx when PCWP>12 or RA>6.
*Those aren’t necessarily goals for diuresis either (“optimal” filling pressures change as ventricular function changes)

9/ #PhysioQuizzo – Answer #1

So does our patient have heart failure?

Yes --> Right and Left heart failure, b/c his RA>6 and PCWP>12

This is reminds me of the adage, “The most common cause of right heart failure is left heart failure.”

10/ #PhysioQuizzo – Answer #2

And does our patient have pulmonary hypertension?
Yes --> his PA mean pressure is >20

**I learned >25 in school, but the guidelines now reflect studies measuring mPAP (mean PA pressure) in healthy people acc.org/latest-in-card…

11/ #PhysioQuizzo – Ohm’s Law

Before we talk about PAH, let’s talk about vascular resistance?

Anyone remember Ohm’s law?
⚡️ V=IR Voltage difference = Current x Resistance

We were taught this vis-a-vis electricity, but this is true of fluid dynamics too!

12/ #PhysioQuizzo – Pulmonary Vascular Resistance

Within the pulmonary vascular bed:
I ▶️ Q = flow = cardiac output
V ▶️ delta-P ▶️ pressure difference across the bed ▶️ mPAP – PCWP
R ▶️ pulmonary vascular resistance = PVR

V=IR --> mPAP-PCWP=CO*PVR

Or: PVR = (mPAP-PCWP)/CO

13/ #PhysioQuizzo – High PVR?

A normal PVR is 3 Wood units - the units you get when you divide mmHg/(L/min).

What raises PVR? Lots of things
-Arteriole wall thickening
-HIV, schistosomiasis infections
-Pulm artery narrow from PE’s
-Hypoxic vasoconstriction
-And lots more!

14/ #PhysioQuizzo – Our patient’s PVR

Our patient’s PVR: CO = 2.9, mPAP = 40, PCWP = 34

PVR = (40-34)/2.9 = 6/2.9 = 2 ▶️ normal

Normal PVR with a high PCWP implies left HF is causing PH!

15/ #PhysioQuizzo – Answer #3

So does out patient have PAH? No, his PVR is normal. His PH is from left heart failure.

If his PVR were high, then we would answer “not enough info” because we’d have to rule out other causes first.

17/ #PhysioQuizzo – Answer #4 (finally!)

And does our patient have low output heart failure?

Yes ▶️ A normal cardiac index is >2.2.
🌡️His CI is 1.2 by thermodilution and 2.0 by Fick. Either one is low ⏩ He has low output HF.

18/ #PhysioQuizzo – Fick vs. Thermo

Not so fast, you say! What’s the deal with Fick vs. Thermo? They are very different results!

>It's outside the current tweetorial scope
>Know that each method uses different variables and can go wrong in different ways...

19/ #PhysioQuizzo – Final Answers

Summary:
A1: Yes, R+L HF
A2: Yes, PH
A3: No PAH, has left heart failure
A4: Yes, has low output HF

We hope you learned something. Thanks for viewing!