Coronary Microcirculation in Aortic Stenosis

Aortic stenosis is a heterogeneous disorder. Variations in the pathological and physiological responses to pressure overload are incompletely understood and generate a range of flow and pressure gradient patterns, which ultimately cause varying microvascular effects. The impact of cardiac-coronary coupling depends on these pressure and flow effects. In this article, we explore important concepts concerning cardiac physiology and the coronary microcirculation in aortic stenosis and their impact on myocardial remodeling, aortic valve flow patterns, and clinical progression.

Imaging for planning of transcatheter aortic valve implantation

Transcatheter aortic valve implantation (TAVI) has proven to be the standard of care for patients with prohibitive and high operative risk; today, it is considered a reasonable alternative to surgical aortic valve replacement in intermediate-risk patients. As indications for TAVI move toward patients at lower risk, safety aspects are becoming even more important. Furthermore, adequate patient selection is key for predictable procedural success with minimal complications, translating into an optimal clinical outcome. Decisions on valve type and size as well as on the access route are based on multimodality imaging including echocardiography, multislice computed tomography, and cardiac catheterization with peripheral angiography. This combination of multiple imaging modalities provides the best picture of a patient's anatomical and physiological suitability for the TAVI procedure. Yet, the reliability of preprocedural imaging is influenced by the quality of the images, which should be as high as possible, and both image acquisition and interpretation should be performed in a standardized manner. This article provides a concise overview of standardized multimodality imaging for the preprocedural planning and assessment of patients undergoing TAVI.

[Low-flow low-gradient aortic valve stenosis : Current evidence]

Many patients with severe aortic stenosis have a "low-flow, low-gradient" aortic stenosis. The management of these patients can be quite difficult, as these patients often show impairment of the left ventricle, which can lead to false measurements of the severity of stenosis and also leads to a higher risk during aortic valve replacement. More diagnostic tools than only standard echocardiography are needed to correctly differentiate true severe aortic stenosis from pseudo severe aortic stenosis.

[Imaging in structural heart disease : Impact on interventional therapy]

For the treatment of structural heart disease, current options in the catheterization laboratory include MitraClip® implantation for treating severe mitral regurgitation, transcatheter aortic valve implantation (TAVI), closure of a patent foramen ovale (PFO) and occlusion of the left atrial appendage (LAA). These treatment options are based on a precise diagnosis provided by modern cardiac imaging, which is indispensable for treatment recommendations. Its importance for supporting the invasive procedures in the catheterization laboratory is less well known. Due to enhanced soft tissue characterization, it complements fluoroscopy and invasive angiography and thus enormously improves the safety of the procedures. In addition, it allows individualized follow-up care. The current article gives an overview of the clinically most frequently used procedures.

[Paradoxical low-flow low-gradient aortic stenosis]

In approximately one third of patients presenting with suspected severe aortic stenosis, there is a discrepancy between a severely reduced aortic valve opening area (< 1 cm(2)) and a non-severe increase of the mean transvalvular gradient (< 40 mmHg). In a substantial number of these cases there is evidence of a severe paradoxical low-flow low-gradient aortic stenosis, characterized by a reduced stroke volume index in the setting of a normal left ventricular ejection fraction. This finding should trigger an extensive diagnostic work-up, including echocardiography, stress echocardiography and computed tomography to rule out measurement errors and to identify the cause(s) of the hemodynamic discrepancy. If the diagnosis of a severe paradoxical low-flow low-gradient aortic stenosis is confirmed and, furthermore, the patient is normotensive and reports stenosis-associated symptoms, the feasibility of an aortic valve replacement should be considered.

Paradoxical low-flow aortic stenosis is defined by increased ventricular hydraulic load and reduced longitudinal strain

AIMS

Patients with paradoxical low-flow severe aortic stenosis (PLF-AS) reportedly have higher left ventricular hydraulic load and more systolic strain dysfunction than patients with normal-flow aortic stenosis. This study investigates the relationship of systolic loading and strain to PLF-AS to further define its pathophysiology.

METHODS

One hundred and twenty patients (age 79 ± 12 years, 37% men) with an indexed aortic valve area (AVAi) of 0.6 cm/m or less and an ejection fraction of 50% or higher were divided into two groups based on indexed stroke volume (SVi): PLF-AS, SVi ≤ 35 ml/m, N = 46; normal-flow aortic stenosis, SVi > 35 ml/m, N = 74). Valvular and arterial load were assessed using multiple measurements, and strain was assessed using speckle-tracking echocardiography.

RESULTS

Patients with PLF-AS were found to have more valvular load (lower AVAi, P = 0.028; lower energy loss coefficient, P = 0.001), more arterial load [decreased arterial compliance and increased systemic vascular resistance (SVR), both P < 0.001] and more total hydraulic load [increased valvuloarterial impedance (Zva), P < 0.001]. Transvalvular gradients and arterial pressures were similar. Longitudinal strain was lower in PLF-AS (P < 0.001), but circumferential and rotation strains were similar. On adjusted regression, AVAi, SVR and longitudinal strain were associated with PLF-AS [odds ratio (OR) = 1.34, P = 0.043; OR = 1.31, P = 0.004; OR = 1.34, P = 0.011, respectively]. When SVR and AVAi were replaced with Zva, longitudinal strain and Zva (OR = 1.38, P = 0.015; OR = 1.33, P < 0.001 for both, respectively) were associated with PLF-AS.

CONCLUSION

Increased hydraulic load, from more severe valvular stenosis and increased vascular resistance, and longitudinal strain impairment are associated with PLF-AS and their interplay is likely fundamental to its pathophysiology.