Aortic Valve
Christopher A. Troianos1
Christopher A. Troianos2
1OUTLINE AUTHOR
2ORIGINAL CHAPTER AUTHOR
▪ KEY POINTS
The close proximity between the aortic valve and the esophagus permits accurate diagnosis of the mechanism of aortic valve dysfunction, valve sizing for valve replacement, and identification of associated lesions.
Complete evaluation of the aortic valve utilizes two-dimensional imaging and pulsed wave, continuous wave, and color Doppler for quantitative evaluation of stenotic and regurgitant lesions.
Velocity measurement of aortic valve flow provides an estimate of valve gradient using the modified Bernoulli equation. The force of ventricular contraction and transaortic blood flow determine transvalvular velocity in addition to the size of the stenotic orifice. The severity of aortic stenosis is underestimated in patients with severe left ventricular (LV) dysfunction. These patients require area determination to assess the severity of aortic stenosis.
There is often a discrepancy between Doppler- and cardiac catheterization-derived gradient measurements due to differences in technique and measurements. Doppler-derived measurements usually exceed catheterization measurements.
Aortic valve area (AVA) is determined by planimetry or by using the continuity equation.
Aortic insufficiency is caused by conditions affecting the aortic cusps or secondarily from diseases affecting the ascending aorta.
Two-dimensional echocardiography is useful for identifying the etiology of aortic insufficiency and associated lesions but not for assessing the severity of regurgitation.
Color, pulsed wave, and continuous wave Doppler are used to quantify the severity of regurgitation, but each technique has limitations.
TOPIC: ASSESSMENT OF AORTIC VALVE
I. INTRODUCTION
Perioperative echocardiography is used to evaluate aortic valve anatomy, function, hemodynamics, and myocardial and other valvular abnormalities associated with aortic valve lesions.
Doppler echocardiography permits quantitative analysis of stenotic and regurgitant lesions and facilitates informed decisions regarding surgical intervention, the type of intervention (repair vs. replacement), correction of inadequate surgical repair, and reoperation for complications.
II. APPROACH: TEE IMAGING PLANES OF THE AORTIC VALVE
Important transesophageal echocardiographic (TEE) multiplane viewing planes of the aortic valve include the midesophageal short-axis and midesophageal long-axis views, which are best for two-dimensional imaging of the three cusps and their associated sinuses of Valsalva. The deep transgastric long-axis and transgastric long-axis views are best for Doppler assessment and quantitative analysis of valve stenosis or insufficiency.
III. PATHOLOGY
A. Aortic stenosis
The most frequent causes of aortic stenosis include calcific degeneration in the elderly, rheumatic valvulitis, and congenital anomalies (bicuspid, unicuspid)
Leaflet doming and reduced separation (less than 15 mm) on two-dimensional echocardiographic examination are consistent with significant aortic stenosis. Short-axis imaging of the aortic valve also permits direct planimetry of the area; however, inadequate image alignment, heavy calcification, and a “pinhole” valve can be limiting factors for this technique.
Doppler peak velocities are best acquired in the deep transgastric or transgastric long-axis views and generally exceed 3 m/s for significant aortic stenosis.
Differences between preoperative and intraoperative values for pressure gradients associated with aortic stenosis may be due to changes in loading conditions, heart rate, and force of contraction. In addition Doppler “peak instantaneous” gradients may exceed cath labacquired peak-to-peak gradients. Doppler profiles associated with aortic stenosis tend to be symmetrically shaped and must be differentiated dynamic left ventricular outflow tract (LVOT) obstruction which tends to have a more asymmetric, dagger-shaped Doppler flow velocity profile.
The continuity equation uses the ratio between the product of LVOT peak velocity and area, divided by the aortic valve peak velocity to calculate the AVA. The “double envelope” technique, in which the LVOT and aortic valve velocities are visible in a single continuous wave Doppler envelope, may be useful to estimate AVA when stroke volume varies from beat-to-beat as in patient with atrial fibrillation.
Important associated echocardiographic findings in patients with aortic stenosis include the presence of LV hypertrophy and diastolic dysfunction, potential for systolic anterior motion of the mitral valve following aortic valve replacement (AVR), concurrent aortic insufficiency, and other valvular lesions such as mitral regurgitation or stenosis.
B. Aortic insufficiency
Aortic insufficiency is usually caused by either intrinsic valvular disease (i.e., rheumatic, calcific, myomatous, endocarditic, congenital) or secondary to ascending aortic dilatation or dissection.
Aortic valve regurgitation orifice area can be measured directly by planimetry from the midesophageal aortic valve short-axis view by using simultaneous color flow Doppler to identify the persistent valve orifice during diastole. Alternatively, the width of the jet at the orifice/LVOT ratio can be measured from the midesophageal aortic valve long-axis view using color M-mode imaging.
Continuous wave Doppler evaluation of aortic insufficiency from the deep transgastric long-axis or transgastric long-axis views reveals a rapid decline in the deceleration phase (greater than 3 m/s2) with severe aortic insufficiency. However this measurement, along with jet penetration into the LV, can be affected systemic vascular resistance and LV compliance.
Holodiastolic flow in the descending thoracic aorta evaluated with pulse wave Doppler may also correlate with significant aortic insufficiency.
Regurgitant volumes and fractions can also be used to evaluate aortic insufficiency severity using net cardiac flow determined from the pulmonary artery or mitral valve, and aortic valve or LVOT systolic flow obtained from the corresponding areas and velocity time integrals.
Important echocardiographic findings associated with aortic insufficiency include LV volume overload, premature mitral valve closure, and anterior leaflet fluttering. In addition, aortic insufficiency may cause an overestimation of mitral valve area by the pressure-half-time (PHT) method.
TOPIC: SURGICAL CONSIDERATIONS IN AORTIC VALVE
I. INTRODUCTION
The surgical treatment of aortic valve continues to evolve. The development of new valve prosthesis, surgical techniques, and intraoperative echocardiographic assessment of the anatomy and function of the aortic valve contribute to a more individualized approach to each patient.
Intraoperative echocardiography, especially transesophageal echocardiography, offers the surgeon a more detailed and dynamic understanding of the aortic root, valve, and LVOT. In addition to its clinical benefits, routine intraoperative TEE has also been shown to have cost-saving implications in patients undergoing valve surgery.
II. SURGICAL CONSIDERATIONS: AORTIC VALVE REPAIR
In adults, stenotic valves are rarely amenable to repair. Repair of an insufficient aortic valve requires an understanding of the mechanisms of valve failure.
The intraoperative echocardiogram provides the detailed information to help formulate repair plans and assess the results of the repair. Identification of the diseased cusp, mechanism of regurgitation, size of the annulus, and presence of calcification of the aortic annulus are of paramount importance when choosing the repair technique.
In the insufficient tricuspid aortic valve the main cause of prolapse is elongation of the leaflet with prolapse or rupture of the free edge of the cusp at an area of fenestration. In those cases a triangular resection of the leaflet is performed. Frequently an annuloplasty needs to be added to the repair to reduce the circumference of the annulus and increase coaptation.
For repair of a bicuspid aortic valve the technique is very similar, with resection or plication of the redundant central portion of the prolapsing leaflet, at the site of the raphe, followed by annuloplasty.
III. SURGICAL CONSIDERATIONS: AORTIC VALVE REPLACEMENT