Value of multiplane transesophageal echocardiography in determining aortic valve area in aortic stenosis*

Echocardiography is the main imaging method in evaluating aortic valve morphology and function and remains a method of choice for assessing the aortic root, together with multidetector computer tomography and cardiac magnetic resonance. Although transthoracic echocardiography is very useful in clinical practice, transesophageal echocardiography (TEE) is indicated in the evaluation of cardiac and aortic structure and function in situations in which the findings may alter the management, or the results of transthoracic echocardiography are nondiagnostic. Therefore, the superior image quality offered by TEE due to probe proximity is sometimes necessary for a detailed morphological aortic valve and aortic root examination and the diagnosis of aortic valve dysfunction.

Aortic stenosis (AS) is the most common valvular heart disease. Echocardiography is the fundamental standard method for establishing etiology, severity stratification, and the indication for valvular replacement.

The quantification of AS is performed by measuring transaortic blood flow velocity, followed by the pressure gradient assessment. Calculating the aortic valve area, generally independent of the blood flow, is essential for its comparison against velocity and pressure parameters. A concordance between area, velocity, and pressure usually exists, and a lack of correlation should point to possible forms such as low-flow, low-gradient or paradoxical low-flow, and low-gradient AS.

Identifying new pathophysiological varieties of AS—associated with obstructive septal hypertrophy, with systolic aortic regurgitation, or in the context of a noncompliant left ventricle with a presystolic flow induced by atrial contraction—could become a challenge for echocardiography.

Echocardiography is the key tool for the diagnosis and evaluation of aortic stenosis. Because clinical decision-making is based on the echocardiographic assessment of its severity, it is essential that standards are adopted to maintain accuracy and consistency across echocardiographic laboratories. Detailed recommendations for the echocardiographic assessment of valve stenosis were published by the European Association of Echocardiography and the American Society of Echocardiography in 2009. In the meantime, numerous new studies on aortic stenosis have been published with particular new insights into the difficult subgroup of low gradient aortic stenosis making an update of recommendations necessary. The document focuses in particular on the optimization of left ventricular outflow tract assessment, low flow, low gradient aortic stenosis with preserved ejection fraction, a new classification of aortic stenosis by gradient, flow and ejection fraction, and a grading algorithm for an integrated and stepwise approach of aortic stenosis assessment in clinical practice.

Current guidelines place emphasis on the determination of aortic valve area (AVA) for defining an appropriate treatment strategy. Invasive and non-invasive modalities are used to perform planimetric [transesophageal echocardiography (TEE) and cardiac multidetector computed tomography (MDCT)] and calculated [catheter examination (CE), transthoracic echocardiography (TTE)] AVA measurements.

We investigated 100 patients admitted to evaluate the AVA using cardiac MDCT (CT), TEE/TTE as well as invasive CE.

In all 100 patients we calculated a mean AVA of 0.79 ± 0.29 cm² (female 50/100, 0.70 ± 0.19 cm², male 0.9 ± 0.21 cm²) determined by all investigated examinations (mean ± SEM). AVA measurements determined by CT were significantly greater (0.86 ± 0.25 cm²) than those determined by CE: 0.75 ± 0.18 cm², p = 0.01. Echocardiographically determined AVA was comparable to CE (statistically not significant). Similar results were seen in all patients regardless of gender, presence of atrial fibrillation, and heart rate. We calculated a mean AVA for each patient and evaluated the variance of the AVA determined through investigated specific examinations as the bias. Overall, we found for CT 0.13 ± 0.1 cm², CE 0.13 ± 0.11 cm², TEE 0.16 ± 0.09 cm², and for TTE 0.16 ± 0.08 cm² a specific statistical non-significant variance. On subgroups: sinus rhythm, atrial fibrillation, females, males or combination, we found no further significant relevance for the specific variance.

Our data suggest the feasibility of cardiac MDCT to evaluate the correct AVA regardless of rhythm, heart rate, and sex. The planimetric concept to determine the AVA with CT displaces the “gold-standard” CE with respect to elucidating the potencies for complications, i.e. cerebral stroke. Regardless of CT's accessing of AVA measurement the TTE examination should remain the primary method of screening for aortic valve pathologies.