Gorlin Formula Calculator - AVA and MVA From Cath Data

The Gorlin formula is the cath-lab reference for estimating the area of a stenotic cardiac valve, expressed in cm^2, from cardiac output, heart rate, the time the valve is open, and the mean pressure gradient across it. The aortic branch returns the aortic valve area and the mitral branch returns the mitral valve area from the same haemodynamic inputs.

• • Aortic valve area planning: estimate aortic valve area in cm^2 from cardiac output, heart rate, systolic ejection period, and aortic mean gradient, then read the 2020 ACC/AHA severity band on the same screen.
• • Mitral valve area planning: estimate mitral valve area in cm^2 from the same cardiac output and heart rate by switching to the diastolic filling period and mitral mean gradient.
• • Cross-checking the continuity equation: compare a cath-lab value with an echo continuity-equation value when both have been collected on the same patient, and flag the cases where the two methods disagree.

A normal adult aortic valve area is 3 to 4 cm^2 and a normal mitral valve area is 4 to 6 cm^2. The formula returns cm^2 directly, so the result is read against those reference ranges.

The result is a planning estimate. The decision about whether a value warrants valve replacement sits with the cardiology or cardiothoracic surgery team, and the cath report itself is the source of truth.

For a non-invasive echo-based estimate of the same aortic valve area, the Aortic Valve Area Calculator uses the continuity equation from LVOT diameter and VTI measurements.

The calculator converts cardiac output to mL/min, takes the square root of the mean pressure gradient for each branch, multiplies the empirical constant by heart rate by the open-valve time by the square root of the gradient, then divides cardiac output by that product.

• cardiacOutput: cardiac output in L/min, converted to mL/min
• heartRate: heart rate in bpm at the time of the measurement
• systolicEjectionPeriod: time in seconds per beat that the aortic valve is open
• diastolicFillingPeriod: time in seconds per beat that the mitral valve is open
• aorticMeanGradient: mean transaortic pressure gradient in mmHg
• mitralMeanGradient: mean transmitral pressure gradient in mmHg
• mitralConstant: discharge coefficient, 37.7 modern or 31 original 1951

The same cardiac output and heart rate flow into both branches. Switching from aortic to mitral changes the empirical constant from 44.3 to 37.7, the open-valve time from systolic ejection period to diastolic filling period, and the pressure gradient from aortic to mitral.

According to Gorlin and Gorlin, American Heart Journal 1951, the cath-lab hydraulic formula expresses the valve area in cm^2 as cardiac output in mL/min divided by an empirical discharge coefficient times heart rate times systolic ejection period times the square root of the mean transaortic pressure gradient, with the aortic coefficient set to 44.3.

Confirm the heart rate input from the cath report against an ECG strip, and the ECG Heart Rate Calculator returns the rate from R-R intervals in seconds.

Four concepts drive the result. Naming them keeps a cath-lab valve area value from being read as a single lab number, which it is not.

The aortic branch and the mitral branch share the cardiac output and heart rate, so a single cath report supports both valve area calculations without rerunning the formula.

The mean pressure gradient in the Gorlin formula is read from the cath trace, while a current blood pressure reading from the Blood Pressure Calculator gives a useful outpatient context for the same patient.

The form works from a small set of cath measurements. Each input should match what was actually recorded, not an idealised version.

1. 1 Enter cardiac output and heart rate: type the cardiac output in L/min from the cath report and the heart rate in bpm from the same record; these feed both branches.
2. 2 Enter the systolic ejection period: type the time in seconds per beat that the aortic valve is open, from the aortic pressure trace.
3. 3 Enter the diastolic filling period: type the time in seconds per beat that the mitral valve is open, from the cath trace.
4. 4 Enter the aortic and mitral mean gradients: type the mean transaortic and mean transmitral gradients in mmHg; values below 5 mmHg should be confirmed against the pullback.
5. 5 Pick the mitral discharge coefficient: leave the default on 37.7 for the modern clinical convention, or switch to 31 for the original 1951 estimate.
6. 6 Read the result panel: read the aortic valve area, mitral valve area, aortic severity band, mitral severity band, and the low-flow flag together.

With the same inputs as the worked example, the form also returns MVA 1.25 cm^2 with moderate MS, and no low-flow flag because cardiac output stays above 2.5 L/min.

Calculating the aortic and mitral valve areas from a small set of cath measurements has practical benefits over running the math by hand.

• • Two valves, one form: a single form returns both the aortic valve area and the mitral valve area from the same cardiac output and heart rate, so the cath record is read once.
• • Modern and historical coefficients: the mitral constant toggle compares the 37.7 modern default with the 31 original 1951 estimate, useful when reading older cath reports.
• • Built-in severity bands: the aortic and mitral severity bands follow the 2020 ACC/AHA and planimetric thresholds, so the cm^2 result is labelled in plain language.
• • Low-flow safety flag: the result panel flags a low-flow state below 2.5 L/min so the reader knows when the formula is most likely to underestimate AVA.
• • Transparent calculation: the formula box shows the full algebraic form, including the conversion from L/min to mL/min, so the result can be re-derived by hand.

The form is for clinicians, trainees, and patients reviewing a cath report with a clinician. Every input is a cath-lab measurement, so a self-tracked value is not meaningful on its own; the practical use is to re-derive a reported valve area and confirm the cath result.

After a valve area has been read from the cath record, the next cardiovascular risk question is usually LDL, and the LDL Calculator converts total cholesterol, HDL, and triglycerides into an LDL estimate.

Several factors shape the cath-lab valve area result. The most important sit inside the form, with a few caveats that belong outside it.

• • The result is a planning estimate, not a diagnosis. The clinical decision about whether a value warrants surgical or transcatheter valve replacement sits with the cardiology or cardiothoracic surgery team and should consider symptoms, valve morphology, and additional imaging.
• • The mitral constant is empirically derived and depends on the cath method, so the 37.7 default and the 31 alternative are best understood as two calibration points rather than as fixed physical constants.

The 2020 ACC/AHA guideline pairs the aortic valve area with the mean gradient and the peak velocity in the severe range, so a value above the severe band is reassuring only when the gradient and velocity agree.

According to 2020 ACC/AHA Valvular Heart Disease Guideline, Circulation 2021, severe aortic stenosis is an aortic valve area at or below 1.0 cm^2 or a mean transaortic gradient at or above 40 mmHg, and severe mitral stenosis is a mitral valve area below 1.5 cm^2 with symptoms or below 1.0 cm^2 even without symptoms.

According to Gorlin and Gorlin, Journal of the American College of Cardiology 1990, the generalized cath-lab formulation revises the mitral discharge coefficient from the original 1951 estimate of 31 to 37.7, better matching the modern hemodynamic data used in clinical practice.

Aortic stenosis shares risk factors with vascular stiffening, and the Arterial Age Calculator reports a vascular age that pairs with the Gorlin formula severity band.