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Management of a Symptomatic Patient with a High Transvalvular Gradient Across a Stentless Aortic Valve

McKillop, Caroline Cunningham MD*; Finley, Alan C. MD*; Ikonomidis, John S. MD, PhD, FRCS(C), FACS, FAHA, FACC; Yarbrough, William M. MD; Reeves, Scott T. MD, MBA*

doi: 10.1213/ANE.0b013e31822e0816
Cardiovascular Anesthesiology: Echo Rounds
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Published ahead of print November 3, 2011 Supplemental Digital Content is available in the text.

From the Departments of *Anesthesia and Perioperative Medicine, and Surgery, Medical University of South Carolina, Charleston, South Carolina.

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.anesthesia-analgesia.org).

Reprints will not be available from the authors.

Address correspondence to Caroline Cunningham McKillop, MD, Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, 25 Courtenay Dr., Suite 4200, Charleston, SC 29425. Address e-mail to cunningc@musc.edu.

Accepted June 27, 2011

Published ahead of print November 3, 2011

A 56-year-old woman with a bioprosthetic aortic valve (AV) presented with “severe” aortic stenosis (AS) and a mean gradient of 60 mm Hg on transthoracic echocardiogram.

In 2005, she had a 23-mm Medtronic Freestyle® bioprosthetic AV implanted in the subcoronary position for severe aortic insufficiency. A transesophageal echocardiogram was performed, because a redo AV replacement was being considered. We present her case after obtaining informed consent for this publication.

Her baseline variables consisted of a weight of 86 kg, height of 163 centimeters, heart rate of 50 beats per minute, mean arterial blood pressure of 100 mm Hg, estimated left ventricular ejection fraction of 60%, and a cardiac output of 3.5 L/min. The left ventricular outflow tract (LVOT) diameter measured 19 mm with reduced excursion of the bioprosthetic valve leaflets and turbulent flow across the AV (Video 1, see Supplemental Digital Content 1, http://links.lww.com/AA/A316). The AV short axis demonstrated adequate AV area, but also showed turbulent flow (Fig. 1) (Video 2, see Supplemental Digital Content 2, http://links.lww.com/AA/A317). Doppler interrogation of the AV and LVOT (Fig. 2) demonstrated a mean transvalvular gradient of 21 mm Hg, a peak gradient of 36 mm Hg, and a maximum velocity of 2.96 m/s. The LVOT had a maximum velocity of 1.03 m/s, and the ratio of LVOT peak velocity to AV peak velocity, also known as Doppler velocity index (DVI), was 0.35. AV effective orifice area (EOA) and indexed EOA (iEOA) were calculated to be 1.0 cm2 and 0.51 cm2/m2, respectively (Table 1).

Figure 1

Figure 1

Figure 2

Figure 2

Table 1

Table 1

Transvalvular pressure gradients are frequently correlated with valve area but are also related to transvalvular flow.1 In low cardiac output states, lower gradients are generated and will underestimate the severity of AS. Alternatively, high cardiac outputs can yield high gradients and overestimate stenosis in a mildly stenotic valve. Thus, complete assessment of prosthetic valves should include other indices less affected by blood flow such as the EOA and DVI.

Calculation of the EOA is performed using the simplified continuity equation, a mathematical concept that describes the transport of a conserved quantity of blood, i.e., the blood entering the LVOT must equal the blood leaving across the AV. The quantity of blood is calculated by use of the stroke volume (Table 1).

The calculated EOA is essentially the functional area of the valve and must be compared with the reference EOA provided by the manufacturer. Although EOA is not affected by cardiac output, it is limited by the potential error introduced during measurement of an asymmetrical LVOT. The LVOT diameter is squared in the calculation of the cross-sectional areaLVOT,2 and an error in its measurement potentially underestimates cross-sectional areaLVOT and thus overestimates AS severity. EOA calculation is also confounded by its failure to consider the patient's body size. This limitation can be overcome by calculating the iEOA (Table 1).

The DVI eliminates the error introduced by the LVOT diameter measurement and, similar to the EOA, is not dependent on cardiac output.3 The DVI expresses AV area as the ratio of LVOT velocity to AV velocity (Table 1) and can also be calculated by substituting the velocity time integrals in place of the peak velocities. In a normal AV, the LVOT velocity approaches that of the AV velocity and would yield a DVI of 1. Prosthetic valves are inherently obstructive when compared with native valves, and thus the DVI will always be <1, because blood flow will always accelerate through the prosthetic valve. A DVI <0.25 indicates severe AS in both a prosthetic and native valve.3

Combining the DVI of 0.35 and the EOA of 1.0 cm2, our patient had the equivalent of moderate AS, not severe AS. Furthermore, previous transthoracic echocardiogram demonstrated DVIs consistently ranging from 0.31 to 0.33 and stable EOAs (1.0–1.1 cm2) over a 2-year time span. From these data, we concluded that the discrepancy in gradients was a flow-dependent phenomenon and not a deterioration of valve function. Nonetheless, our patient had prosthetic valve stenosis and the etiology of the stenosis must be considered.

Etiologies of prosthetic valve stenosis include prosthetic valve dysfunction and patient-prosthesis mismatch (PPM). In this patient, the calculated EOA (1.0 cm2) was >1 SD smaller than the reference EOA (1.7 ± 0.5 cm2) indicating some degree of prosthesis dysfunction.3 Stentless AVs are placed via a full root or subcoronary technique (Fig. 3) and are known for their superior hemodynamic profile because of the absence of the rigid sewing ring. However, the subcoronary implantation technique is technically challenging and can result in a reduction of the EOA and higher transvalvular gradients compared with the full root technique.4 The etiology of this suboptimal result includes lack of experience with the surgical technique and oversizing of the valve with redundant valve tissue occupying the outflow tract.4,5 Unfortunately, echocardiographic examination immediately after implantation of a stentless valve is limited because paravalvular edema and hematoma are often present.4

Figure 3

Figure 3

By definition, PPM is present when the EOA of the prosthesis is too small for the patient's body size. PPM is diagnosed when the iEOA is <0.85 cm2/m2 and is severe when the iEOA is <0.65 cm2/m2. Our patient's EOA was 1.0 cm2, body surface area was 1.97 cm2/m2, and iEOA was 0.51 cm2/m2. Although prosthetic valve dysfunction is undoubtedly present, an EOA in the range of 1.2 to 1.6 cm2 (normal reference range, 1.7 ± 0.5 cm2) would yield an iEOA <0.85 cm2/m2 and be consistent with PPM. Additionally, although AV leaflet motion is reduced, the leaflets move well enough to indicate that prosthetic valve dysfunction is not solely responsible for the stenosis. Subcoronary implantation of a stentless valve in small aortic roots contributes to the development of PPM, and the incidence of PPM for 23-mm stentless valves implanted in the subcoronary position at 1 year has been reported to be as high as 40%.5 Despite being outside the normal EOA reference range, prosthetic valve dysfunction was not solely responsible for the moderate AS demonstrated in this patient, but rather a combination of both PPM and prosthetic valve dysfunction was present.

This case highlights that prosthetic valve dysfunction and PPM are both potential etiologies for prosthetic valve stenosis. Pressure gradients are affected by both valve area and flow conditions, thus a thorough examination of prosthetic valve function should include calculation of DVI, EOA, iEOA, and comparison with the manufacturer's reference.

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DISCLOSURES

Name: Caroline Cunningham McKillop, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Caroline Cunningham McKillop approved the final manuscript.

Name: Alan C. Finley, MD.

Contribution: This author helped write the manuscript.

Attestation: Alan C. Finley approved the final manuscript.

Name: John S. Ikonomidis, MD, PhD, FRCS(C), FACS, FAHA, FACC.

Contribution: This author helped write the manuscript.

Attestation: John S. Ikonomidis approved the final manuscript.

Name: William M. Yarbrough, MD.

Contribution: This author helped write the manuscript.

Attestation: William M. Yarbrough approved the final manuscript.

Name: Scott T. Reeves, MD, MBA.

Contribution: This author helped write the manuscript.

Attestation: Scott T. Reeves approved the final manuscript.

This manuscript was handled by: Martin J. London, MD.

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APPENDIX: VIDEO LEGENDS

Video 1. Midesophageal aortic valve long-axis view with and without color flow Doppler. The stentless bioprosthetic aortic valve demonstrates reduced leaflet excursion, and flow across the bioprosthetic valve is turbulent.

Video 2. Midesophageal aortic valve short-axis view with and without color flow Doppler. The stentless bioprosthetic aortic valve has adequate opening but turbulent flow conditions.

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REFERENCES

1. 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;41:1–29
2. Baumgartner H, Hung J, Bermejo J, Chamber JB, Evangelista B, Griffin BP, Iung B, Otto CM, Pellikka PA, Quinones M. Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice. J Am Soc Echocardiogr 2009;22:1–23
3. Zoghbi WA, Chamber JB, Dumesnil JG, Foster E, Gottdiener JS, Grayburn PA, Khandheria BK, Levine RA, Marx GR, Miller FA, Nakatani S, Quinones MA, Rakowski H, Rodriguez LL, Swaminathan M, Waggoner AD, Weissman NJ, Zabalgoitia M. Recommendations for evaluation of prosthetic valves with echocardiography and doppler ultrasound: a report from the American Society of Echocardiography's Guidelines and Standards Committee and the Task Force on Prosthetic Valves, developed in conjunction with the American College of Cardiology Cardiovascular Imaging Committee, Cardiac Imaging Committee of the American Heart Association, the European Association of Echocardiography, a registered branch of the European Society of Cardiology, the Japanese Society of Echocardiography and the Canadian Society of Echocardiography, endorsed by the American College of Cardiology Foundation, American Heart Association, European Association of Echocardiography, a registered branch of the European Society of Cardiology, the Japanese Society of Echocardiography, and Canadian Society of Echocardiography. J Am Soc Echocardiogr 2009;22:975–1014
4. Ennker JA, Albert AA, Rosendahl UP, Ennker IC, Dalladaku F, Florath I. Ten-year experience with stentless aortic valves: full-root versus subcoronary implantation. Ann Thorac Surg 2008;85:445–52
5. Lopez S, Mathieu P, Pibarot P, Mohammadi S, Dagenais F, Voisine P, Dumesnil J, Doyle D. Does the use of stentless aortic valves in a subcoronary position prevent patient-prosthesis mismatch for small aortic annulus? J Card Surg 2008;23:331–5
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Clinician's Key Teaching Points By Roman M. Sniecinski M.D., Kent H. Rehfeldt M.D., Martin J. London M.D.
  • Echocardiographic assessment of a transvalvular gradient is commonly used for intraoperative assessment of prosthetic valve function. However, this gradient is flow dependent and can be falsely elevated during high cardiac output states, or falsely decreased in the presence of ventricular dysfunction. The Doppler velocity index (DVI) through an aortic valve prosthesis is the ratio of peak left ventricular outflow tract velocity to peak aortic velocity and is less dependent on cardiac output. Likewise, the effective orifice area (EOA), calculated via the continuity equation, is another parameter that is less flow dependent.
  • Prosthetic valve dysfunction leading to a high residual gradient may be caused by leaflet calcification, thrombosis, endocarditis, or pannus formation (i.e. fibrous tissue occluding the valve). These problems usually result in a calculated EOA significantly less than that provided by the manufacturer and a DVI <0.3 in the aortic position.
  • In this case, the high mean gradient of the prosthetic valve suggested severe prosthetic valve obstruction. However, transesophageal echocardiogram (TEE) examination showed adequate leaflet movement, although the DVI and EOA were moderately reduced. Thus the high gradient was explained by the combination of too small a prosthesis for the patient's body size (commonly termed patient prosthesis mismatch) and suboptimal surgical results from the initial placement of the valve.
  • A thorough TEE interrogation of a prosthetic heart valve includes 2-dimensional examination to determine proper leaflet excursion, annular stability, the presence of any masses, and evaluation of ventricular function. This information provides a contextual framework for the interpretation of Doppler-derived data such as the mean gradient, the EOA, and the DVI.

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© 2011 International Anesthesia Research Society