Cath Extensions Experimental

(a) Glenn / Fontan: transpulmonary gradient and PVRi

TPG  [mmHg]       = mean cavopulmonary (PA) pressure - mean pulmonary venous atrial pressure (or PCWP)
Qpi  [L/min/m2]   = entered, or Fick: VO2i / ((CpvO2 - CpaO2) x 10)
                    CxO2 [mL/dL] = 1.36 x Hb [g/dL] x sat/100   (dissolved O2 ignored)
PVRi [WU x m2]    = TPG / Qpi
Flag: TPG > 6 mmHg

• The TPG flag is the AHA/ATS 2015 Table 1 description of pulmonary vascular disease: “elevated TPG (mPAP−left atrial pressure or PAWP >6 mm Hg) or high PVRI as observed in patients with cavopulmonary anastomoses without high mPAP” (Abman 2015). The guideline gives no numeric PVRi cut-off for cavopulmonary circulations; its PAH definition uses PVRI >3 WU·m², which is shown for orientation only.
• WSPH 2019 Paediatric Task Force: patients with a Fontan circulation “do not usually fulfil the definition of PH with mPAP >20–25 mmHg” yet develop pulmonary vascular disease, now classed with group 5 PH (Rosenzweig 2019).
• Fick across the lungs holds at steady state because all oxygen uptake occurs in the lungs. It fails when flow enters the lungs from more than one source (antegrade flow, shunts, aortopulmonary collaterals): the measured PA saturation no longer represents all blood entering the lungs. This page does not attempt a collateral correction.
• Commonly quoted pre-Fontan selection limits (for example the Choussat “ten commandments”, 1977 book chapter) are [unverified] and are not used here.

(b) Nakata PA index and McGoon ratio

Nakata index [mm2/m2] = (pi x (RPA/2)^2 + pi x (LPA/2)^2) / BSA      diameters in mm
McGoon ratio          = (RPA + LPA diameter) / descending aorta diameter at the diaphragm

• Nakata 1984 (abstract, verified): normal PA index 330 ± 30 mm²/m², consistent from infancy to adolescence (40 controls). Tetralogy: low output more frequent below 150; “all patients with a PA-index over 100 mm²/BSA can undergo correction safely”. Rastelli: all patients below 200 died; mortality 6% above 200. Fontan: 2 patients below 250 died; 12 of 13 above 250 survived; “those with a PA-index over 250 can be considered good candidates for the Fontan procedure”. Small 1984 cohorts; era-specific.
• Measurement site (just proximal to the first lobar branch) and the BSA formula used by Nakata are from secondary descriptions; the 1984 full text was not retrieved [unverified].
• McGoon ratio: introduced by Piehler et al. 1980 (no abstract on PubMed; full text not retrieved). The definition above follows a 2021 open-access description: “sum of the diameters of RPA and LPA (measured at the distal part proximal to the bifurcation into lobar branches) by the diameter of the aorta at the level above the diaphragm”. Commonly quoted cut-offs (normal about 2.0–2.5; about 1.2 for complete repair of pulmonary atresia with VSD; about 1.8 for Fontan) are [unverified] and are not shown as results.

(c) Gorlin and Hakki valve areas

Flow during the flow period [mL/s] = CO [L/min] x 1000 / (HR [bpm] x period [s/beat])
   period = systolic ejection period (aortic) or diastolic filling period (mitral)
Gorlin area [cm2] = flow / (C x 44.3 x sqrt(mean gradient [mmHg]))
   C = 1 (aortic), 0.85 (mitral);  44.3 = sqrt(2 x 980 cm/s2)
Hakki area  [cm2] = CO [L/min] / sqrt(gradient [mmHg])     (simplified, adult-derived)
Hakki / Gorlin    = HR x period x C x 44.3 / 1000           (Hakki assumes this is about 1)

• Gorlin & Gorlin 1951: the hydraulic orifice formula. The 1951 constants (discharge coefficient 1 for aortic, 0.7 for mitral; 44.5) are as described by Dean & Kern 2022; the mitral coefficient was revised to 0.85 by Cohen & Gorlin 1972. Constants for pulmonary and tricuspid valves are not offered because they could not be verified.
• Hakki 1981 (abstract, verified): “cardiac output (l/min) divided by the square root of pressure differences across the valve”, 100 consecutive adults; correlation with Gorlin unchanged when the peak gradient was used instead of the mean. Dean & Kern 2022: accurate “except in patients with significant bradycardia (<60 beats/min) or tachycardia (>100 beats/min)”. Most children are tachycardic by that standard, so this page shows the Hakki / Gorlin ratio for your heart rate.
• Pediatric limitations. The empirical coefficients come from adults (mostly rheumatic mitral stenosis). In pediatric valvar stenosis, decisions rest mainly on the peak-to-peak gradient and anatomy, not on a Gorlin area. Low flow states underestimate area; regurgitation makes forward output understate transvalvular flow. Gorlin areas in infants are not validated against an anatomic standard.

(d) Acute vasoreactivity testing (AHA/ATS 2015)

Recommendation (Class I, LOE B): positive response = "a ≥20% decrease in PAP and pulmonary vascular
   resistance (PVR)/systemic vascular resistance (SVR) without a decrease in cardiac output"
   This page reads it strictly: mPAP falls ≥20% AND PVR/SVR falls ≥20% AND cardiac index does not fall.
Section 3.2.5, IPAH / isolated PHVD, two definitions:
   (1) mPAP decrease of at least 10 mmHg to <40 mmHg with a normal or increased CO
   (2) mPAP decrease ≥20%, increase or no change in cardiac index, decrease or no change in PVR/SVR
Shunt lesions (recommendations):
   "Repair should be considered if PVRI is <6 WU·m2 or PVR/SVR <0.3 at baseline" (Class I, LOE B)
   With R-to-L shunting and PVRI ≥6 or PVR/SVR ≥0.3: "repair can be beneficial if AVT reveals
   reversibility of PAH (absolute PVRI <6 WU·m2 and PVR/SVR <0.3)" (Class IIa, LOE C)
   PVRI ≥6 or PVR/SVR ≥0.3 with minimal AVT response: "Repair is not indicated" (Class III, LOE A)

• Quoted from the guideline full text (ahajournals.org, retrieved October 2026). “Without a decrease in cardiac output” is applied as test cardiac index ≥ baseline; measurement noise makes a tiny fall ambiguous, so look at the numbers.
• Ambiguity: the Class I sentence can also be read as requiring only a 20% fall in mPAP plus some fall in PVR/SVR. Definition (2) above is that looser reading, so both are shown.
• Definition (1) “normal or increased” CO: “normal” is not defined in the text, so this page requires an unchanged or higher cardiac index. Adult (Sitbon) criteria are usually quoted as reaching “≤40 mmHg” [unverified]; this page follows the guideline text, “<40”.
• WSPH 2019 Paediatric Task Force: “it is advised to use the Sitbon criteria for AVT in children”, with inhaled NO 10–80 ppm as the preferred agent (Rosenzweig 2019). It also notes that specific criteria for a positive response predicting operability in shunt lesions “remain lacking”.
• Guideline caution: “Testing with 100% oxygen in children with CHD has been criticized because oxygen consumption cannot be measured simultaneously and the arteriovenous O₂ difference becomes very small”.

References

• Abman SH, Hansmann G, Archer SL, et al. Pediatric Pulmonary Hypertension: Guidelines From the American Heart Association and American Thoracic Society. Circulation 2015;132(21):2037-2099. doi:10.1161/CIR.0000000000000329
• Rosenzweig EB, Abman SH, Adatia I, et al. Paediatric pulmonary arterial hypertension: updates on definition, classification, diagnostics and management. Eur Respir J 2019;53(1):1801916. doi:10.1183/13993003.01916-2018
• Nakata S, Imai Y, Takanashi Y, et al. A new method for the quantitative standardization of cross-sectional areas of the pulmonary arteries in congenital heart diseases with decreased pulmonary blood flow. J Thorac Cardiovasc Surg 1984;88(4):610-619. PMID 6482493
• Piehler JM, Danielson GK, McGoon DC, et al. Management of pulmonary atresia with ventricular septal defect and hypoplastic pulmonary arteries by right ventricular outflow construction. J Thorac Cardiovasc Surg 1980;80(4):552-567. PMID 6158634 (full text not retrieved)
• McGoon ratio definition as described in: Correlating computed tomographic angiography of pulmonary circulation with clinical course and disease burden in patients with tetralogy of Fallot and pulmonary atresia. Eur J Radiol Open 2021;8:100363. doi:10.1016/j.ejro.2021.100363
• Gorlin R, Gorlin SG. Hydraulic formula for calculation of the area of the stenotic mitral valve, other cardiac valves, and central circulatory shunts. I. Am Heart J 1951;41(1):1-29. doi:10.1016/0002-8703(51)90002-6 (full text not retrieved)
• Cohen MV, Gorlin R. Modified orifice equation for the calculation of mitral valve area. Am Heart J 1972;84(6):839-840. doi:10.1016/0002-8703(72)90080-4 (full text not retrieved)
• Hakki AH, Iskandrian AS, Bemis CE, et al. A simplified valve formula for the calculation of stenotic cardiac valve areas. Circulation 1981;63(5):1050-1055. doi:10.1161/01.cir.63.5.1050
• Dean LS, Kern MJ. Measuring Valve Gradients and Areas. J Soc Cardiovasc Angiogr Interv 2022;1(5):100433. doi:10.1016/j.jscai.2022.100433