Anesth Analg 2002;94:857-858
© 2002 International Anesthesia Research Society
CARDIOVASCULAR ANESTHESIA
Prosthetic Valve Malfunction Masked by Intraoperative Pressure Measurements
Kent H. Rehfeldt, MD*, and
Roger L. Click, MD
Departments of *Anesthesiology and Cardiology, Mayo Clinic, Rochester, Minnesota
Address correspondence and reprint requests to Kent H. Rehfeldt, MD, Department of Anesthesiology, Mayo Clinic, 200 First St. S.W., Rochester, MN 55905. Address e-mail to rehfeldt.kent@ mayo.edu.
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Abstract
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IMPLICATIONS: We describe a case in which intraoperative echocardiography recorded an abnormally high pressure gradient across a newly implanted mechanical heart valve. However, inserting pressure-transducing needles on each side of this prosthesis did not confirm the echocardiographic findings. The prosthesis was later confirmed to be malfunctioning and was replaced.
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Introduction
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The benefits of intraoperative transesophageal echocardiography (TEE) during aortic valve replacement are well established (1). Other intraoperative modalities, such as intracardiac pressure measurement with needle catheterization, can also be used to evaluate the results of aortic valve replacement. However, discrepancies between TEE and needle catheterization measurements may occur because of such factors as pressure recovery, the difference between peak-to-peak and instantaneous pressure gradients, and the potential for needle catheterization gradients to be falsely low for a number of technical reasons. We present a case in which intraoperative TEE showed a high mean pressure gradient across a newly implanted prosthetic aortic valve. This gradient was not confirmed by needle catheterization, and the patient left the operating room (OR) only to return 7 days later for replacement of a malfunctioning prosthesis.
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Case Report
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A 65-yr-old man presented to our institution for elective aortic valve replacement. Intraoperative TEE before cardiopulmonary bypass revealed a calcified, stenotic, bicuspid aortic valve. TEE was performed again immediately after separation from cardiopulmonary bypass. Because of acoustic shadowing from the sewing ring and annular calcification, the newly implanted 23-mm St. Jude mechanical prosthesis was difficult to image from an esophageal probe position. However, deep transgastric imaging revealed only mild prosthetic regurgitation. Continuous-wave Doppler interrogation, also performed from the deep transgastric position (Fig. 1), yielded mean pressure gradients of 50–64 mm Hg, much greater than the 16 ± 6 mm Hg mean gradient expected for a 23-mm St. Jude prosthesis (2). On the basis of the TEE findings, the surgeon elected to directly measure the prosthetic gradient. By use of two needles connected via fluid-filled tubing to appropriately zeroed transducers, the surgeon simultaneously recorded the pressure in the left ventricle and ascending aorta. A difference in peak left ventricular and aortic pressures of only 25–30 mm Hg was recorded, with a difference in mean pressures of only 15 mm Hg. On the basis of these measurements, the chest was closed, and the patient was transported to the intensive care unit.
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Figure 1. Continuous-wave Doppler analysis of the newly implanted St. Jude aortic prosthesis from the deep transgastric position. Proper alignment of the Doppler cursor is suggested by the presence of prosthetic valve clicks (arrows) in the spectral recording. A mean pressure gradient of 56.7 mm Hg was recorded.
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Postoperatively the patient remained hemodynamically stable. A transthoracic echocardiogram, routinely performed at our institution after valve surgery, was obtained before hospital discharge, and a mean prosthetic gradient of 40 mm Hg was recorded. Fluoroscopic examination of the prosthesis was performed and showed severe limitation to the opening of both mechanical leaflets (Fig. 2). The patient was taken to the OR, where visual inspection showed that prosthetic leaflet motion was markedly restricted by annular calcification. After prosthesis explantation and annular debridement, the prosthesis was reimplanted, and intraoperative TEE showed a mean gradient across the prosthesis of only 13.6 mm Hg (Fig. 3). The patient left the OR and was subsequently discharged from the hospital.
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Figure 2. Fluoroscopic image of the St. Jude aortic prosthesis recorded at maximal systolic opening. Leaflet excursion is far less than the 85° (dashed lines) expected for this type of prosthesis.
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Figure 3. Continuous-wave Doppler recording across the St. Jude aortic prosthesis from the deep transgastric position after reimplantation. Proper alignment of the Doppler cursor is suggested by the presence of prosthetic valve clicks (arrows) in the spectral recording. A mean pressure gradient of 13.6 mm Hg was recorded.
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Discussion
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This case highlights several important points regarding the intraoperative assessment of aortic valvular prostheses. First, because of acoustic shadowing from the prosthesis and annular calcification, TEE visualization of aortic prosthetic leaflet motion and regurgitant jets may be suboptimal. Second, the maximal instantaneous gradient obtained by echocardiography will be higher than the peak-to-peak value measured by catheterization. Third, the phenomenon of pressure recovery can partially explain the higher gradients recorded by echocardiography, particularly if the TEE Doppler cursor is positioned through the central orifice of a bileaflet mechanical prosthesis (3).
Another important point illustrated by this case is the potential for error when single end-hole needles are used to measure pressure gradients across an aortic prosthesis. Artificially low left ventricular pressure readings can result when a single end-hole needle becomes partially or completely occluded by the ventricular wall (4). Additionally, air bubbles present in the transducer tubing can decrease the measured pressure (5). Artificially high aortic pressures can result when an end-hole needle is positioned so that its orifice faces the oncoming stream of blood being ejected from the heart and some of the kinetic energy of the blood is retrieved as pressure energy (5–7). In the normal aorta, impact energy may add 9 mm Hg to the measured pressure, although this contribution may be increased in the setting of an aortic prosthesis (5). Impact energy can be minimized by using side-hole transducing catheters (6).
Although pressure recovery and the difference between maximal instantaneous and peak-to-peak pressures could have accounted for some of the discrepancy between the TEE and needle catheterization gradients in our case, we believe that these are insufficient explanations for differences in mean gradients as large as 49 mm Hg. Instead, we believe that the needle catheterization gradient was falsely low. Echocardiography, valve fluoroscopy, and the findings at reoperation all suggested prosthetic malfunction. Occlusion of the needle orifice by the ventricular wall, air in the left ventricular transducer tubing, or the addition of impact energy in the aorta could all have contributed to the measurement of a falsely low gradient. In retrospect, additional diagnostic techniques, such as fluoroscopy or epicardial echocardiography, could have been used intraoperatively in an attempt to resolve the discrepancy.
In conclusion, the anesthesiologist should be aware of the limitations of all intraoperative diagnostic modalities and should be ready to consider additional methods of assessment if suspicious or conflicting results arise between any two. Further, as new methods of measurement arrive and are validated, techniques that were previously suggested as "gold standards" should be reconsidered.
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References
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Accepted for publication December 4, 2001.
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November 1, 2005;
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1288 - 1291.
[Abstract]
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Abstract
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