DK2985_C000 1..28 - AlSharqia Echo Club

340 Transesophageal Echocardiography(A)(B)MVLALVAoRVAortic dilatation: 6.8 cm(C)BEFORE SURGERY(D)AFTER AORTIC ROOTREPLACEMENTASCENDING AORTAAORTIC GRAFTFigure 15.16 Aortic dilatation of 6.8 cm in a patient with mild bicuspid aortic stenosis. (A, B) Mid-esophageal long-axis view. (C, D)Intraoperative findings before and after aortic valve replacement and resection of the aortic aneurysm (Ao, aorta; LA, left atrium; LV, leftventricle; MV, mitral valve; RV, right ventricle). (Photos C and D courtesy of Dr. Michel Pellerin.)centimeters as the catheter is withdrawn beyond the AoVand the pressure recovers in the ascending Ao. As mostof the pressure recovery occurs in the first few centimeters,catheter gradient is unlikely to be affected by pressurerecovery if the downstream measurement is made atleast 5 cm away from the stenotic valve in the ascendingAo. In a patient with at least moderate AS, a smallcaliber ascending Ao (,3 cm) distal to the sinotubularjunction may be the most important factor for the occurrenceof clinically significant pressure recovery (8–11).In patients with an eccentric jet across a stenotic AoV,VanAuker et al. (12) has demonstrated, using a computationalmodel, that for a constant anatomic area, the effectivevalve area decreased, the maximal pressure gradientincreased and, the distance to complete pressure recoveryincreased with the degree of jet eccentricity.MITRAL REGURGITATION. Improper alignment of theDoppler signal may result in the inadvertent measurementof the MR pressure gradient instead of the AoV pressuregradient. This is more likely to occur when the jet ofMR is directed anteriorly towards the wall of the LAbeneath the Ao. It is, therefore, important to differentiatethe characteristics of these two Doppler signals. Themitral regurgitant jet starts earlier with MV closure atthe onset of the isovolumic contraction period comparedwith the AS signal which begins after the isovolumic contractionphase. The mitral regurgitant jet also ends later atthe start of the isovolumic relaxation phase. Mitral regurgitantand AS signal may also be differentiated by the diastoliccompany they keep: the mitral regurgitant signal willbe accompanied by a mitral inflow signal (with E- and A-waves) while the aortic signal may be associated with atypical aortic regurgitant signal (Fig. 15.21).PRESSURE GRADIENT VARIES WITH FLOW. Themeasurement of aortic pressure gradient will overestimatethe severity of AS in high output states while in low outputstates and cardiac decompensation, the ventricle may beunable to generate a significant gradient even if the ASis critical. Blood flow is proportional to the square of thepressure gradient so a small increase in blood flow willtranslate into a more significant change in the measuredpressure gradient.PITFALL OF THE SIMPLIFIED BERNOULLIEQUATION.Software from echocardiography systemsuses the simplified Bernoulli equation to measure pressure