• Review Describes Standardized Approach for MAC Severity Grading and Treatment

    A standardized approach for grading the severity of mitral annular calcification (MAC) and the evaluation of patients for surgical or transcatheter intervention has been set out in a new state-of-the-art review.

    Such framework is important given that the chronic disease process is more frequently encountered in the aging population, a fact that poses “unique challenges” for the heart team, said the authors, led by London’s St Thomas’ Hospital’s Omar Chehab, MBBS, and Ross Roberts-Thomson, MBBS, PhD, also from the Royal Adelaide Hospital, Australia.

    The review was published Monday online, ahead of the Aug. 16 issue of the Journal of the American College of Cardiology.

    MAC in context

    MAC occurs in 10% of people over 60 years of age – a figure that rises to 33% in those over 90 years – resulting in deposition of calcium in and around the fibrous base of the mitral valve, the authors noted. 

    It is associated with atherosclerotic risk factors, including older age, female gender, diabetes, smoking, hypertension, ethnicity, obesity, interlukin-6 (IL-6) and renal failure.

    “The main pathophysiological consequences of MAC are mitral valve dysfunction (stenosis and/or regurgitation), atrial fibrillation (AF), stroke, infective endocarditis, and death,” the authors added.

    In the Framingham study, MAC was associated with an increased risk of both cardiovascular mortality (hazard ratio [HR]: 1.6; 95% confidence interval [CI]: 1.1-2.3) and all-cause mortality (HR: 1.3; 95% CI: 1.1-2.3). After adjustment for other cardiovascular risk factors, “that rose by approximately 10% for each 1 mm increase in depth of calcification,” the authors said. 

    Yet, despite clinicians being increasingly confronted with the challenges of MAC in light of the world’s aging population, the authors highlighted disparate systems for grading severity, as well as an array of technical approaches contributing to “variable outcomes” of surgical mitral valve repair and replacement.

    Transcatheter approaches, meanwhile, are associated with high 30-day and 1-year mortality rates, said the authors, “the reasons for which are not clear.”

    Severity grading

    The authors provide a standardized approach to grading the severity of MAC – of high/prohibitive surgical risk or not – in the management of significant mitral valve disease with MAC.

    “Preprocedural imaging can predict anatomical and clinical outcomes for patients with MAC and should be central to management decisions,” the authors said.

    They noted that MAC is usually first detected using two-dimensional echocardiography, which also enables assessment of mitral valve function.

    However, electrocardiographic gated multidetector computed tomographic imaging (MDCT) provides “superior detail concerning the anatomical extent and severity of annular involvement, enables more reproducible quantification of the thickness and circumferential distribution, and is of particular value when intervention is contemplated,” they stressed.

    Agatston score, calcium volume, or mass can all be used to quantify the severity of MAC and enable the monitoring of temporal progression, the authors added.

    “Recognized limitations include calcium blooming artefact and extension of calcification into adjacent cardiac structures (left ventricular outflow tract [LVOT], myocardium, and coronary arteries).”

    On grading, the authors said that, after referral to a high-volume specialist mitral valve center “where feasible,” the mitral valve heart team should consider:

    1. Surgical risk
    2. Anatomical feasibility of conventional surgery
    3. The role of medical and functional preoptimization
    4. And the patient’s suitability for transcatheter mitral valve replacement (TMVR) if there is a prohibitive surgical risk.

    Together, these considerations should determine whether or not the patient is of high or prohibitive surgical risk, the authors noted.

    Procedural planning

    Preprocedural imaging is also vital in deciding which of the two main strategies for dealing with mitral valve dysfunction accompanying MAC – surgery and transcatheter intervention – the authors said, adding that both approaches carry “potential complexity.”

    Considerations should include;

    • Valve sizing: with a recommendation to localize the mitral valve annulus in the two-chamber and four-chamber views and to use a maximal intensity projection with 3 to 5 mm slice thickness to measure annular dimensions.
    • The risk of transcatheter heart valve (THV) embolism: with a warning that the risk of valve embolism after transcatheter valve in MAC implantation is higher than in mitral valve-in-valve or valve-in-ring procedures, “reflecting difficulties related to valve sizing and insufficient or eccentrically calcified landing zones.” The authors added that “a more comprehensive and standardized approach to planning seems likely to reduce the risk of THV embolism by enabling more systematic evaluation.”
    • New left ventricular outflow tract (NEO-LVOT) assessment: “Factors contributing to neo-LVOT area include device protrusion and flaring, aortomitral angulation, and septal bulge,” the authors said, but noted that simulated implantation of the intended THV can now be undertaken using dedicated computed tomography software packages. “An understanding of specific THV device designs and modes of deployment is essential to reduce complication rates,” they stressed.

    In a flow chart detailing the proposed treatment algorithm for patients with MAC requiring valve intervention, the authors note that clinicians should consider whether patients at high/prohibitive operative risk have a favorable anatomy for TMVR with an acceptable risk of complication.

    For patients who are at high or prohibitive risk, TMVR is suggested, whereas for those who are not, medical management or mitral valve replacement (MVR) is suggested.

    In the patients not at high/prohibitive surgical risk who are suitable for repair, mitral valve repair is suggested.

    For those not at high/prohibitive surgical risk but not suitable for repair, clinicians should ask whether the patient’s anatomy is suitable for replacement. If the answer is yes, MVR is suggested.

    If not, the patients are further subdivided by whether they have favorable anatomy for surgical THV. For those who are, surgical valve in mitral annular calcification (ViMAC) is the treatment route, whereas for those who are not, either TMVR or medical management is the solution (again dependent on whether their anatomy for TMVR is favorable with acceptable complication risk).

    “Despite a limited evidence base, surgical valve repair remains the gold standard of treatment, and there are no robust data regarding the outcomes of surgical valve replacement,” the authors concluded.

    “Surgical and transcatheter ViMAC procedures are still associated with high 30-day mortality.

    “Furthermore, high mortality at 1 year despite initial procedural success reflects the age and comorbidities of this high-risk cohort and emphasizes the critical importance of a holistic heart team–guided approach to patient selection and management.”

    Source:

    Chehab O, Roberts-Thomson R, Bivona A, et al. Management of Patients With Severe Mitral Annular Calcification: JACC State-of-the-Art Review. J Am Coll Cardiol 2022;80:722-738.

    Image Credit: SciePro – stock.adobe.com

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