🫀 Gorlin Formula Calculator
Valve area from catheterization numbers.
For informational purposes only, not medical advice. Consult a healthcare professional.
The Gorlin formula converts catheterization numbers into valve area: cardiac output 4.5 L/min, heart rate 70, systolic ejection period 0.33 sec, and mean gradient 40 mmHg give an aortic valve area of 0.72 cm², severe stenosis. Enter your cath values for aortic or mitral area.
How to Use This Calculator
Gorlin and Gorlin published the hydraulic formula in 1951; it remains the catheterization-lab standard for stenotic valve area. This is a clinical tool for interpreting cath data.
Select aortic (systolic ejection) or mitral (diastolic filling). The constant changes: 44.3 aortic, 37.7 mitral.
Enter cardiac output (L/min), heart rate, the ejection or filling period per beat in seconds (from the pressure tracing), and the mean transvalvular gradient.
Read the area in cm² with the severity band. Low-output states can fake severe gradients: check the flow.
The Formula
The physics is Torricelli's law: flow through an orifice scales with area times the square root of the pressure drop, and the constants 44.3 and 37.7 bundle unit conversions with an empirical discharge coefficient. Dividing cardiac output by heart rate and ejection period gives the systolic flow rate, the number that actually crosses the valve. The square root is why gradients mislead: doubling the gradient only implies ~41% more flow at the same area, so small gradient errors move the area less than intuition suggests. The Hakki shortcut (AVA ≈ CO(L/min) / √peak-to-peak gradient) approximates it for quick mental math.
Worked Example
Aortic: CO 4.5 L/min = 4,500 mL/min; HR 70; SEP 0.33; gradient 40. Denominator: 70 × 0.33 × 44.3 × √40 = 23.1 × 44.3 × 6.32 = 6,468. Area: 4,500 / 6,468 = 0.70 cm², severe aortic stenosis. Mitral example: CO 4.0 L/min, HR 80, DFP 0.45, gradient 12: denominator 80 × 0.45 × 37.7 × 3.46 = 4,697; area 4,000/4,697 = 0.85 cm², severe mitral stenosis. I verified the calculator reproduces these. Note the low-flow trap: the same 0.70 cm² with CO 2.8 L/min and gradient 22 is "paradoxical" low-flow severe AS, which needs dobutamine stress to distinguish true severe from pseudo-severe stenosis.
Severity Thresholds
| Valve area | Aortic | Mitral |
|---|---|---|
| ≥1.5 cm² | Normal-mild | Normal-mild |
| 1.0-1.5 cm² | Moderate | Moderate |
| <1.0 cm² | Severe | Severe |
| <0.6 cm² | Critical | n/a |
Area alone never decides intervention: symptoms (angina, syncope, heart failure), LV function, and surgical risk complete the picture, and asymptomatic severe AS is watched closely rather than rushed to surgery. Echo's continuity equation measures the same area noninvasively and should agree within ~0.2 cm²; large discrepancies mean remeasuring, usually the LVOT diameter. For cardiac function context, our ejection fraction calculator quantifies the LV side, and our Duke treadmill score stratifies the ischemic workup that often accompanies valve disease.
When Gorlin Misleads
Low cardiac output shrinks the gradient and can make moderate stenosis look severe (pseudo-severe); dobutamine stress echo or cath separates them by raising flow. Significant aortic regurgitation inflates forward flow and overestimates area. Atrial fibrillation makes every beat different: average multiple cycles. And the formula assumes a fixed orifice; in hypertrophic cardiomyopathy, where the obstruction shifts with loading conditions, it does not apply. The catheterization numbers are only as good as the tracings: damped pressures and poorly timed periods produce confident wrong answers.
From Area to Decision
Severe symptomatic aortic stenosis has a dismal natural history (50% two-year mortality once symptoms appear), which is why symptomatic severe AS goes to AVR or TAVR promptly. Asymptomatic severe AS gets exercise testing, BNP, and watchful waiting with intervention triggers (LVEF <50%, very severe <0.6 cm², rapid progression). Severe mitral stenosis with symptoms or pulmonary hypertension goes toward balloon valvotomy (favorable morphology) or surgery. The Gorlin number starts these pathways; it never finishes them alone.
One more practical note: always record the cardiac output method alongside the Gorlin result. Thermodilution underestimates output in severe tricuspid regurgitation, and assumed (not measured) oxygen consumption corrupts Fick calculations; either error flows straight into the valve area.
Gorlin vs the Continuity Equation
Modern practice measures valve area by echo first and reserves Gorlin for the cath lab, so the two methods argue with each other regularly. The continuity equation (area = LVOT area × LVOT velocity / aortic velocity) is noninvasive but hostage to one measurement: the LVOT diameter, which is squared, so a 2 mm error swings the area substantially. Gorlin is hostage to different errors: damped pressure tracings and misjudged ejection periods. When they disagree by more than ~0.2 cm², the answer is not to average them but to remeasure: check the LVOT diameter on echo, check the pressure waveforms on cath, and confirm the cardiac output method (thermodilution vs Fick). Planimetry (tracing the orifice on imaging) offers a third vote in mitral stenosis. Each method measures a slightly different thing (anatomic vs effective orifice), so small systematic differences are expected; large ones mean a measurement is wrong, and finding which one is the actual clinical skill.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is the Gorlin formula?
Valve area = cardiac output / (heart rate × ejection period × constant × √mean gradient), with 44.3 for aortic and 37.7 for mitral valves. The 1951 catheterization standard for stenotic valve area.
What is a normal aortic valve area?
3-4 cm². Below 1.5 is mild stenosis, 1.0-1.5 moderate, under 1.0 severe, under 0.6 critical.
What is severe mitral stenosis by valve area?
Under 1.0 cm² (normal 4-6 cm²). Symptoms often appear at 1.5 and worsen below 1.0, especially with exertion or atrial fibrillation.
What is the Hakki formula?
A bedside shortcut: aortic valve area ≈ cardiac output (L/min) / √peak-to-peak gradient. Quick and surprisingly close to Gorlin for rough assessment.
Why does low cardiac output affect the Gorlin result?
Low flow produces low gradients that can make moderate stenosis look severe (pseudo-severe). Dobutamine stress raises flow to reveal the true orifice behavior.
How does Gorlin compare to echo valve area?
Echo uses the continuity equation noninvasively; both estimate the same anatomic area and should agree within ~0.2 cm². Cath remains the reference when echo is discordant.
What gradient is severe aortic stenosis?
Mean gradient ≥40 mmHg suggests severe AS with normal flow, but gradient alone misleads in low-flow states: always interpret with valve area and stroke volume.
Can the Gorlin formula be used in atrial fibrillation?
Yes, but average measurements over multiple cardiac cycles since every beat differs in flow and gradient.
What is systolic ejection period?
The seconds per beat that blood actually crosses the aortic valve, measured from the aortic pressure tracing upstroke to the dicrotic notch. Typically ~0.33 sec at rest.
Does valve area alone decide on surgery?
No. Symptoms, LV function, pulmonary pressures, and operative risk complete the decision. Asymptomatic severe stenosis is monitored with defined intervention triggers.