Right Heart Catheterization — Hemodynamic Calculations

Normal Hemodynamic Values

Chamber	Systolic / Diastolic	Mean
RA	a: 2–10 v: 2–10	0–8
RV	15–30 / 0–8 (EDP)	—
PA	15–30 / 4–12	9–18
PCWP	a: 3–15 v: 3–15	4–12
Aorta	100–140 / 60–90	70–105

Parameter	Normal Range
Cardiac Output (CO)	4–8 L/min
Cardiac Index (CI)	2.5–4.0 L/min/m²
Stroke Volume (SV)	60–100 mL/beat
Stroke Volume Index (SVI)	33–47 mL/beat/m²
SVR	10–20 WU (800–1600 dyn·s·cm⁻⁵)
PVR	< 2 WU (< 160 dyn·s·cm⁻⁵)

All pressures in mmHg. WU = Wood units. Conversion: WU × 80 = dyn·s·cm⁻⁵

Fick Cardiac Output

CO (L/min) = VO₂ (mL/min) Hb × 13.6 × (SaO₂ − SvO₂)

VO₂Oxygen consumption (mL/min) — measured or estimated (LaFarge) HbCBC hemoglobin (g/dL) — single value, NOT co-oximetry 13.6= 1.36 (mL O₂/g Hb) × 10 (dL → L conversion) SaO₂Arterial oxygen saturation (Ao sat, decimal form) SvO₂Mixed venous oxygen saturation (PA sat, decimal form)

Expanded O₂ Content Form

CaO₂ = Hb × 1.36 × SaO₂ (mL O₂/dL — arterial O₂ content)
CvO₂ = Hb × 1.36 × SvO₂ (mL O₂/dL — venous O₂ content)
CO = VO₂ ÷ [(CaO₂ − CvO₂) × 10]

Always use CBC Hemoglobin. Co-oximetry Hb may vary between AO and PA samples due to measurement artifact — but Hb concentration is physiologically identical throughout the circulation (it is the same blood). Using different Hb values for arterial and venous content introduces artificial error. Always use the single CBC value.

VO₂ Estimation Methods

LaFarge equation (cath lab software): accounts for age, sex, HR — preferred estimate
Flat assumption: 125 mL/min/m² or 3 mL/kg/min — less accurate, common fallback
Gold standard = measured VO₂ via metabolic cart — rarely available in practice

Cardiac Index & Stroke Volume

CI (L/min/m²) = CO ÷ BSA

SV (mL/beat) = (CO × 1000) ÷ HR

SVI (mL/beat/m²) = SV ÷ BSA

CI < 2.2 L/min/m²: hemodynamically significant low cardiac output
SVI < 35 mL/beat/m²: reduced — important threshold in low-flow AS assessment

Vascular Resistance & Pressure Gradients

Pulmonary Gradients

TPG = mPAP − PCWP (transpulmonary gradient, mmHg)

DPG = dPAP − PCWP (diastolic pulmonary gradient, mmHg)

Pulmonary Vascular Resistance (PVR)

PVR (Wood units) = mPAP − PCWP CO dyn·s·cm⁻⁵ = WU × 80

PVR	Interpretation
< 2 WU	Normal
2–3 WU	Borderline / mildly elevated
3–5 WU	Moderately elevated
> 5 WU	Severely elevated

Systemic Vascular Resistance (SVR)

SVR (Wood units) = MAP − mRAP CO dyn·s·cm⁻⁵ = WU × 80

SVR	Interpretation
10–20 WU (800–1600)	Normal
> 20 WU (> 1600)	Elevated (vasoconstriction, cardiogenic shock)
< 10 WU (< 800)	Low (sepsis, vasodilatory shock, cirrhosis)

PAPi — Pulmonary Artery Pulsatility Index

PAPi = sPAP − dPAP mRAP = PA pulse pressure mean RA pressure

Context	PAPi Cutoff	Interpretation
General	> 1.0	Adequate RV function
Acute RV MI	< 0.9	Predicts RV failure / need for MCS
Pre-LVAD	< 1.85	Predicts RV failure post-implant
Cardiogenic shock	< 1.0	RV dysfunction contributing to shock

Pearl: PAPi integrates RV contractility (PA pulse pressure) with RV preload (RAP). A low PAPi means poor RV output relative to its filling pressure. Most useful in acute settings: RV MI, pre-LVAD assessment, and cardiogenic shock.

Pulmonary Hypertension — Hemodynamic Classification (2022 ESC/ERS)

Type	mPAP	PCWP	PVR
Pre-capillary PH	> 20	≤ 15	> 2 WU
Isolated post-capillary (IpcPH)	> 20	> 15	≤ 2 WU
Combined pre & post (CpcPH)	> 20	> 15	> 2 WU

2022 update: PH threshold lowered from > 25 to > 20 mmHg. PVR threshold lowered from > 3 to > 2 WU. A DPG > 7 mmHg also suggests a pre-capillary component.

Fick vs Thermodilution — Which CO Method to Use?

	Thermodilution (TD)	Fick (Assumed or Measured VO₂)
Pros	Easy, reproducible, less operator-dependent	Physiologically grounded; preferred in low CO, valvular disease, intracardiac shunts
Cons	Inaccurate in: severe TR, low output states, intracardiac shunts	VO₂ often estimated (not measured) → propagation error in CO and all derived values
Best for	Routine hemodynamic screening	Gorlin valve areas, PVR/SVR calculations, structural heart assessment

Practical Rule: If TD and Fick CO differ meaningfully, use Fick for Gorlin and derived hemodynamics — especially in AS, MS, or low output.

Always document in your report:
• Which CO method was used
• Whether VO₂ was measured or estimated

Worked Example — Complete Hemodynamic Calculation

Input Data

VO₂ by LaFarge

VO₂ index = 138.1 − (11.49 × ln 65) + (0.378 × 88) = 123.4 mL/min/m²
VO₂ = 123.4 × 1.51 = 186.3 mL/min

Step-by-Step Calculations

a-vO₂ = 14.3 × 1.36 × (0.928 − 0.536) = 7.62 mL O₂/dL (wide → low output)
Fick CO = 186.3 ÷ [14.3 × 13.6 × (0.928 − 0.536)] = 186.3 ÷ 76.2 = 2.44 L/min
CI = 2.44 ÷ 1.51 = 1.62 L/min/m²
SV = (2.44 × 1000) ÷ 88 = 27.7 mL/beat SVI = 27.7 ÷ 1.51 = 18.3 mL/beat/m²
TPG = 32 − 15 = 17 mmHg DPG = 22 − 15 = 7 mmHg
PVR = 17 ÷ 2.44 = 6.97 WU (557 dyn·s·cm⁻⁵)
SVR = (96 − 16) ÷ 2.44 = 32.8 WU (2623 dyn·s·cm⁻⁵)
PAPi = (47 − 22) ÷ 16 = 1.56

Pearls & Common Pitfalls

Low CO → wide a-vO₂ difference — normal a-vO₂ is 3.5–5.0 mL O₂/dL; values > 5.5 suggest inadequate cardiac output
Estimated VO₂ error — ±25% is common; even small VO₂ errors produce large CO errors. Use LaFarge over flat 125 mL/min/m²
PCWP ≠ LVEDP — PCWP may overestimate (large V-wave, overdamped waveform) or underestimate (mitral stenosis) the true LVEDP
Prominent V-waves in PCWP — always use mean PCWP for calculations, not the peak; a large V-wave suggests significant MR

Atrial fibrillation — hemodynamics vary beat-to-beat; average ≥ 5–10 consecutive cycles for reliable values
TD in severe TR — thermodilution underestimates CO because the cold saline indicator recirculates; use Fick in this setting
PAPi caveats — unreliable when RAP is very low (< 3 mmHg); small denominator creates artificially high PAPi
Safe documentation language: "Hemodynamics calculated using Fick CO with LaFarge estimated VO₂. Findings interpreted in the context of flow conditions."