Echocardiography has revolutionized the management of patients with valvular heart disease (1). Not only is it a robust diagnostic tool, but echocardiography also facilitates noninvasive temporal follow-up of the progression of disease processes. With the introduction of transesophageal echocardiography (TEE), intraoperative decision-making is also enhanced for both diagnosis and follow-up of valve replacement or repair procedures. The power of this imaging device lies in the excellent correlation (both anatomically and physiologically) with findings at cardiac catheterization (2). However, on the basis of the technical quality of the echocardiographic examination, as well as anatomic and physical characteristics of the valve, clinically significant discrepancies can occur between findings at cardiac catheterization and echocardiographic/Doppler (3) assessment that may lead to an inappropriate surgical decision. Although described in the literature, it seems that clinicians may not fully appreciate the potential implications of these discrepancies. The presented case offers an example of such a situation, reviews the causative factors, and offers the cardiac anesthesiologist a potential approach to validating either set of findings.
A 79-yr-old woman presented for mitral valve replacement and possible aortic valve replacement. One month before admission, she reported to her cardiologist the onset of chest pain at rest, paroxysmal nocturnal dyspnea, and exacerbation of shortness of breath while exercising as well as at rest. Her medical history was significant for bronchial asthma and bronchitis with a restrictive lung disease pattern on her pulmonary function tests, type II diabetes mellitus, and hypothyroidism.
Her preoperative cardiac evaluation consisted of cardiac catheterization and transthoracic echocardiography (TTE). Two weeks before surgery, she underwent cardiac catheterization. The pertinent findings relative to the aortic valve include: left ventricular pressure 167/10 mm Hg and pull-back aortic pressure 161/58 mm Hg with a peak-to-peak aortic valve gradient of 11.7 mm Hg, a calculated aortic valve area 1.3 cm2, and a cardiac output (CO) of 4.5 L/min (Fig. 1). The results of the TTE performed 1 wk before surgery are listed in Table 1 (Figs. 2A and 2B). Briefly, the aortic valve was moderately sclerotic with moderate aortic stenosis. Doppler assessment across the aortic valve rendered a maximal velocity of 3.97 m/s with an associated peak aortic valve gradient of 63 mm Hg and a mean aortic gradient of 34 mm Hg. The aortic valve area was 1 cm2 (continuity equation). The mitral valve was moderately sclerotic with moderate stenosis, and an eccentric, moderate mitral regurgitant jet was seen. There was no left ventricular (LV) outflow tract gradient at rest or with Valsalva maneuver. The LV ejection fraction (LVEF) was 60%.
In view of the conflicting data between the TTE and cardiac catheterization, further anatomic and hemodynamic examination were planned during surgery. Preoperative anesthetic evaluation revealed a 59-in. and 68-kg woman, ASA class IV. No other significant history or physical findings were uncovered.
After the induction of anesthesia and orotracheal intubation, a low profile HP Sonos 5500 TEE probe (5 MHz) was passed with ease. The pertinent aortic valve findings include (Table 1): the midesophageal short axis view revealed a mild-to-moderate calcified yet flexible tri-leaflet valve with an aortic valve area obtained by planimetry of 1 cm2 and an annulus diameter of 1.7 cm. Continuous-wave Doppler interrogation of the aortic valve, in both the transgastric 120 degrees as well as in the deep transgastric views, revealed a peak transaortic velocity of 3.74 m/s. Using similar views, pulsed-wave Doppler interrogation of the LV outflow tract rendered a velocity of 1.43 m/s. The calculated aortic valve area by continuity equation was 0.9 cm2. The corresponding peak gradient was 55 mm Hg, and the mean gradient was 31 mm Hg. In addition to the aortic valve findings, moderate mitral regurgitation and mitral stenosis were noted. The LVEF was normal (60%). During the TEE examination, the hemodynamic values of the patient included arterial blood pressure 110/55–140/60 mm Hg, sinus rhythm with a rate of 55–60 bpm, and a CO, obtained by thermodilution method, of 4.5 L/min. Given the disparity between the echocardiographic calculations and the cardiac catheterization findings, the aortic valve gradient was directly measured simultaneously in the left ventricle and ascending aorta, and the results, obtained in duplicate, revealed left ventricle 120/10 mm Hg and ascending aorta 116/64 mm Hg and the repeat left ventricle 130/6 mm Hg and ascending aorta 136/50 mm Hg. On the basis of these data showing minimal transvalvular aortic gradient by direct pressure measurement, and the clinical symptoms and surgical considerations, the surgeon decided to replace only the mitral valve with a porcine bioprosthetic valve. After cardiopulmonary bypass (CPB), a repeat intraoperative TEE was obtained (Table 1). A normal functioning bioprosthetic mitral valve with no pathological regurgitant jet was observed. Interrogation of the aortic valve showed no change from pre-CPB examination. The LVEF was normal. During the TEE examination, the arterial blood pressures varied between 85/45 mm Hg and 110/45 mm Hg, the heart rhythm was paced (DDD mode) with a rate of 86 bpm, and the CO was 5.3 L/min.
The postoperative course was uneventful. On the sixth postoperative day (POD 6), a TTE was performed, and the pertinent results for the aortic valve were the following (Table 1): the aortic valve leaflets appeared to be flexible with no significant restriction in motion and Doppler assessment across the aortic valve revealed an unchanged maximal velocity of 3.80 m/s, corresponding to a peak gradient of 57 mm Hg and a mean gradient of 33 mm Hg. The pattern of the Doppler envelope suggested a fixed obstruction. However, interrogation of the LV outflow tract did not identify a fixed valvular obstruction. The patient was discharged on POD 7. Her presenting symptoms were much improved at the 6 mo follow-up evaluation.
Echocardiographic evaluation of valvular pathology plays a singular role in the surgical decision-making for valve replacement. Valvular mechanics and the hemodynamic consequences can be rapidly and accurately analyzed by the use of two-dimensional and Doppler ultrasound. Management strategies are predicated on the comparable findings between cardiac catheterization and echocardiography. For Doppler examination, it is usually assumed that the maximal velocity through the aortic valve can only be underestimated due to the ultrasound beam not being parallel to the aortic blood flow (4). In contrast, on the basis of the pressure recovery phenomenon, Doppler-derived pressure gradient measurements may overestimate the degree of severity (5).
The case presented is notable because of the substantial difference in the aortic valve pressure gradient between cardiac catheterization and the echocardiography data obtained pre-, intra-, and postoperatively. These discrepancies may be explained in various ways, including technical quality of the examination, the effects of anesthesia on hemodynamic and Doppler data, interrogation of the mitral regurgitation jet instead of the aortic stenosis jet, not accounting for the possibility of high LV outflow tract and mid-ventricular velocities, and the impact of the pressure recovery phenomenon on catheter-measured gradients.
The accuracy of the echocardiographic data depends on the technical quality of the examination. Given that three experienced echocardiographers independently obtained similar findings, it is unlikely that the discrepant Doppler echocardiographic data were caused by an inadequate examination technique.
Changes in CO (flow) that occur in the anesthetized patient can significantly influence valve function. Measurements obtained during cardiac catheterization and echocardiography examination may be at variance with those performed in the operating room (OR). In our case, not only were the multiple echocardiographic examination findings in the nonanesthetized and anesthetized state consistent with each other, but the hemodynamic findings in the catheterization lab and the OR were also consistent. Thus, it is doubtful that the anesthetized state itself was responsible for the findings.
The most frequent cause of misinterpreting echocardiography aortic stenosis findings is the presence of a mitral regurgitation jet (3). In the transgastric view, while attempting to interrogate the aortic valve, the ultrasound beam may actually be directed towards the mitral valve. The orientation of the mitral regurgitation jet is similar to the aortic stenosis jet, with similar relatively high velocities. In this case, the patient's primary valvular pathology was mitral regurgitation. After mitral valve replacement and the absence of any mitral regurgitation jet, Doppler interrogation of the aortic valve remained unchanged after CPB and after surgery, thus eliminating mitral regurgitation as the cause of discrepancy.
The simplified Bernoulli calculation of the aortic valve gradient from Doppler data includes the assumption that the velocity (V1) in the LV outflow tract is 1 m/s or less in a patient with a normal LVEF. If this assumption is incorrect (e.g., the presence of idiopathic septal hypertrophy, subaortic membrane, hyperdynamic states at the level of the mid-ventricle, increased CO, etc.), an error is introduced in the calculated gradient (6). Our patient's LV outflow tract was small (1.7 cm), and therefore, she may have had a type of functional stenosis with implicitly higher V1. If the increased value of V1 is introduced in the modified Bernoulli equation, the adjusted peak gradients reflect some degree of change (44 mm Hg calculated from 55 mm Hg measured or 49 mm Hg calculated from 58 mm Hg measured).
The pressure recovery phenomenon is another source of discrepancy between catheter and Doppler valvular pressure gradients (7). These differences range from 1–53 mm Hg (mean, 20 mm Hg) (8). Bernoulli's theorem requires that the sum of the pressure head, potential energy, and kinetic energy must be the same in all parts of the system (9). Thus, for an aortic stenotic lesion, the pressure is lowest where the velocity is the highest (vena contracta) and also corresponds to the minimal cross-sectional valve area. Distal to the stenosis as velocity decreases, pressure will increase. The total amount of pressure increase (pressure recovery) is related to the viscous and turbulent energy losses across the stenotic valve. Therefore, Doppler gradients that are measured at the vena contracta will be significantly higher than the catheter measurements taken downstream after pressure has been completely recovered in the ascending aorta. In addition, for a relatively mild stenosis, where the three cusps of the aortic valve form a funnel (rather than a diaphragm), the pressure recovery is greater than in a severely stenotic valve (9). Finally, three gradients can be reported from catheterization data: peak-to-peak, peak, and mean. Studies have shown that the best correlation is found between the mean Doppler gradient and the mean cardiac catheterization gradient measured simultaneously. Usually, the catheterization lab reports a peak-to-peak gradient, which may serve to further accentuate the difference between catheter-derived gradients and Doppler reports (10).
When feasible, planimetry of the aortic valve should be performed. This serves as a cross check for the Doppler calculations (11). In this case, the aortic valve area obtained by planimetry was 1 cm2. This value was inconsistent with the calculated peak gradient of approximately 60 mm Hg. A much smaller value of the aortic valve area would be in agreement with the high velocity, peak, and mean gradients.
Parenthetically, recent studies have shown a close association between the maximal aortic jet velocity as well as its progression over time with clinical outcome (12). In the presented case, although the maximal velocity was high (3.8 m/s), it remained constant over the preceding year.
In conclusion, we present a case in which the echocardiographic and cardiac catheterization data were significantly divergent, and each had their own specific implication for surgical treatment. In such instances, we recommend that the Doppler results be compared with the aortic valve area obtained by planimetry. If the results seem discordant, before making the final surgical decision, the gradients should be checked in the OR by direct pressure measurement in the left ventricle and ascending aorta simultaneously. We have presented several possible explanations for the discordance between Doppler and catheterization data and have proposed some solutions that attempt to reconcile these differences.
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