Aortic valve area
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Aortic Stenosis Microchapters |
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Diagnosis |
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Treatment |
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Percutaneous Aortic Balloon Valvotomy (PABV) or Aortic Valvuloplasty |
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Transcatheter Aortic Valve Replacement (TAVR) |
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Case Studies |
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Aortic valve area On the Web |
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American Roentgen Ray Society Images of Aortic valve area |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Lakshmi Gopalakrishnan, M.B.B.S. [2]
Overview
Normal aortic valve offers little or no resistance to the blood flow across the valve despite the high flow velocities. With progressive aortic stenosis, the aortic valve orifice offers progressively greater resistance to the blood flow through the valve with subsequent reduction in the pressure gradient between the left ventricle and the aorta. Therefore, using both the pressure gradient across the valve and the surface area of the valve the severity of aortic stenosis can be estimated. The latter can be calculated using echocardiographic flow velocities while the trans-valvular pressure gradient can be calculated using the following equation:
Pressure Gradient = 4 x (velocity of blood through the valve)2 mmHg
However, the absence of a large gradient across the aortic valve does not exclude the presence of critical aortic stenosis as evidenced by the presence of low gradient, low ejection and subsequent low flow aortic stenosis that is associated with poor clinical outcomes. Therefore, it is for this reason that the best measure of the severity of aortic stenosis is the aortic valve area and not the aortic valve gradient.
Cardiac Catheterization
- Simultaneous measurement of left ventricular output (measures the flow through the aortic valve) and the pressure gradient across the aortic valve provides the essential variables that is required to calculate the aortic valve area and resistance.[1][2]
- According to the current recommendations, following dobutamine infusion, if the aortic valve area increases to >1.2 cm2, and the mean pressure gradient rises above 30 mmHg, such patients may benefit from aortic valve replacement. Failure to achieve these improvements has shown to be associated with higher early surgical mortality in comparison to patients who can augment their contractility and gradient: 32-33% versus 5-7%, respectively. Additionally, 5-year survival was lower in patients who could not augment their contractility in comparison to those who could: 10–25% versus 88%, respectively.
Aortic Valve Area:
Aortic valve area can be calculated by the following two equations:
Gorlin Equation:
Aortic Valve Area (cms2) = (Stroke volume (mL/beat) ÷ Systolic ejection period (secs/beat)) ÷ ( 44.3 x square root of mean systolic pressure gradient between the left ventricle and aorta (mmHg))
Hakki Equation:
Aortic Valve Area (cms2) = (Cardiac output (liters/minute)) ÷ (Square root of mean systolic pressure gradient between the left ventricle and aorta (mmHg))
Aortic Valve Resistance:
- Cannon JD Jr et al, described the benefit of calculating aortic valve resistance in conjunction with the Gorlin formula to differentiate patients with true severe aortic stenosis from those with mild aortic stenosis.[3] The clinical implication of this differentiation is that patients with mild aortic stenosis may not benefit from aortic valve replacement.
- Patients with high cardiac output with minimal or no increase in pressure gradient also fall into the category of mild aortic stenosis and may not benefit from aortic valve replacement.
- Furthermore, aortic valve resistance is less flow-dependent than aortic valve area which is of particular benefit in patients with low output aortic stenosis.[3]
Aortic Valve Resistance (dyne seconds per cms5) = { (Mean Pressure Gradient between the left ventricle and aorta (mmHg) x Heart Rate (beats/min) x Systolic ejection period (secs/beat) ) ÷ Cardiac output } x 1.33
- Unsteady fluid-dynamics support the use of aortic valve area calculation over other measures of aortic stenosis including aortic valve resistance.[6][7][8]
References
- ↑ Hirshfeld JW, Kolansky DM. Valve function: Stenosis and regurgitation. In: Diagnostic and Therapeutic Cardiac Catheterization, 2nd ed, Pepine CJ, Hill JA, Lambert CR (Eds), Williams & Wilkins, Baltimore 1994. p.443
- ↑ Carabello BA, Grossman W. Calculation of stenotic valve orifice area. In: Cardiac Catheterization and Angiography, 3rd ed, Grossman W (Ed), Lea and Febiger, Philadelphia 1986. p.143.
- ↑ 3.0 3.1 Cannon JD, Zile MR, Crawford FA, Carabello BA (1992). "Aortic valve resistance as an adjunct to the Gorlin formula in assessing the severity of aortic stenosis in symptomatic patients". Journal of the American College of Cardiology. 20 (7): 1517–23. PMID 1452925. Retrieved 2012-04-12. Unknown parameter
|month=ignored (help) - ↑ Badano L, Cassottano P, Bertoli D, Carratino L, Lucatti A, Spirito P (1996). "Changes in effective aortic valve area during ejection in adults with aortic stenosis". The American Journal of Cardiology. 78 (9): 1023–8. PMID 8916482. Retrieved 2012-04-12. Unknown parameter
|month=ignored (help) - ↑ Ford LE, Feldman T, Chiu YC, Carroll JD (1990). "Hemodynamic resistance as a measure of functional impairment in aortic valvular stenosis". Circulation Research. 66 (1): 1–7. PMID 2295132. Retrieved 2012-04-12. Unknown parameter
|month=ignored (help) - ↑ Bermejo J, Antoranz JC, Burwash IG, Alvarez JL, Moreno M, García-Fernández MA, Otto CM (2002). "In-vivo analysis of the instantaneous transvalvular pressure difference-flow relationship in aortic valve stenosis: implications of unsteady fluid-dynamics for the clinical assessment of disease severity". The Journal of Heart Valve Disease. 11 (4): 557–66. PMID 12150306. Unknown parameter
|month=ignored (help);|access-date=requires|url=(help) - ↑ Kadem L, Rieu R, Dumesnil JG, Durand LG, Pibarot P (2006). "Flow-dependent changes in Doppler-derived aortic valve effective orifice area are real and not due to artifact". Journal of the American College of Cardiology. 47 (1): 131–7. doi:10.1016/j.jacc.2005.05.100. PMID 16386676. Retrieved 2012-04-12. Unknown parameter
|month=ignored (help) - ↑ Otto CM (2006). "Valvular aortic stenosis: disease severity and timing of intervention". Journal of the American College of Cardiology. 47 (11): 2141–51. doi:10.1016/j.jacc.2006.03.002. PMID 16750677. Retrieved 2012-04-12. Unknown parameter
|month=ignored (help)