The following are key points to remember from a state-of-the-art review on imaging methods for evaluation of chronic aortic regurgitation (AR) in adults:

1. Purpose: Chronic severe AR involves combined preload and afterload excesses that eventually lead to marked left ventricular (LV) dilation and irreversible LV systolic dysfunction. This paper provides an overview of noninvasive imaging for the evaluation of chronic, native valve AR and the parameters used to determine the timing of intervention.
2. Assessment of AR severity:
   • The physical examination can provide important signs suggesting severe AR, including wide pulse pressure, a prominent diastolic murmur, and bounding pulses.
   • Transthoracic echocardiography (TTE) is the initial imaging test for the evaluation of AR, allowing assessment of AR mechanism and severity, and its hemodynamic impact on the cardiac chambers. An integrative approach that combines quantitative and semi-quantitative methods should be used for the echo/Doppler assessment of AR severity.
   • Transesophageal echocardiography (TEE) can help further define leaflet morphology and AR severity.
   • Cardiac magnetic resonance (CMR) imaging for AR regurgitant volume (RV) and regurgitant fraction is useful when echocardiography is inconclusive or if further evaluation of AR severity is warranted.
   • Although cardiac computed tomography (CT) cannot directly measure flow and is not a first-line imaging tool for the assessment of AR severity, regurgitant orifice area measurement on CT can help quantify AR severity.
3. Assessment of LV response and remodeling: LV dilation correlates with both AR severity and clinical outcomes, and both the European Society of Cardiology (ESC)/European Association for Cardio-Thoracic Surgery (EACTS) and the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines incorporate LV dilation and LV systolic dysfunction in indications for intervention.
   • TTE LV end-systolic diameter (LVESD) >50 mm or LV end-systolic diameter index (LVESDi) >25 mm/m² are Class I (ESC/EACTS) or Class IIa (ACC/AHA) indications for intervention in asymptomatic patients with severe AR. More recent data suggest that LVESDi in the range of 20-25 mm/m² might be a better threshold for surgical referral.
   • LV systolic dysfunction measured by LV ejection fraction (LVEF) is an indication for intervention, with Class I thresholds for intervention of LVEF ≤50% (ESC/EACTS) or LVEF ≤55% (ACC/AHA).
   • Two-dimensional (2D) TTE LV end-systolic volume index (LVESVi) ≥45 mL/m² has been associated with increased mortality risk. Although 3D TTE can overcome reproducibility limitations associated with 2D TTE LV volumes, there is a paucity of prognostic data associating 3D TTE volumes with outcomes.
   • Although a discrete threshold for surgical referral has not been defined, depressed TTE global longitudinal strain (GLS) in the range of -15% to -19% might be useful among patients with severe AR and LV dilation.
   • CMR imaging has utility in assessing LV volumes, LV systolic function (using LVEF and strain imaging), and myocardial fibrosis (by late gadolinium enhancement and extracellular volume [ECV]). Emerging data suggest that CMR LV end-diastolic volume (LVEDV) >246 mL or 129 mL/m², LVESVi ≥43-45 mL/m², GLS worse than -16%, and indexed ECV ≥24% are associated with adverse outcomes.
   • LV volumes and systolic function also can be assessed using functional cardiac CT angiography, albeit with limitations related to radiation exposure, requirement for intravenous contrast, and the necessity of a slow and regular heart rate during acquisition.
4. Integrative imaging: Decisions regarding intervention in patients with AR are dependent on AR severity, symptoms, and LV remodeling.
   • Exercise treadmill stress testing can aid in the assessment of symptoms and exercise tolerance.
   • AR severity requires the correlation of physical findings and data from TTE. Further imaging with CMR or CT can be useful in resolving discrepancies between the physical exam and TTE or in resolving internal discrepancies within the TTE.
   • LV remodeling should be assessed serially, monitoring for changes over time in LV size and systolic function. Monitoring can be with TTE, but CMR or CT should be used if there is poor endocardial definition or borderline findings on TTE.
5. Timing intervention: The authors propose the following model for timing intervention in patients with severe AR:
   • If there are symptoms or limited exercise tolerance, then operate.
   • If current guideline thresholds are reached (LVESDi >25 mm/m² or LVEF <55%), then operate.
   • If the LV is below the lower limits associated with an adverse outcome (LVESVi <20 mm and LVEF >60%), then observe.
   • If the LV is in an intermediate range (LVESDi 20-25 mm/m², LVEF 55-60%), then incorporate other factors including LV volumes (threshold >45 mL/m²), LV GLS, AR RV and regurgitant fraction, plasma biomarkers, and the extent and degree of myocardial fibrosis.

Clinical Topics: Noninvasive Imaging, Valvular Heart Disease

Keywords: Aortic Valve Insufficiency, Cardiac Imaging Techniques, Heart Valve Diseases

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