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Multimodality imaging anatomy of interatrial septum and mitral annulus
  1. Francesco Fulvio Faletra1,
  2. Laura Anna Leo1,
  3. Vera Paiocchi1,
  4. Susanne Schlossbauer1,
  5. Jagat Narula2,
  6. Siew Yen Ho3
  1. 1 Cardiac Imaging Department, Cardiocentro Ticino, Lugano, Switzerland
  2. 2 Icahn School of Medicine at Mount Sinai, New York, New York, USA
  3. 3 National Heart and Lung Institute, London, UK
  1. Correspondence to Professor Francesco Fulvio Faletra, Cardiocentro, CH-6900 Lugano, Switzerland; francesco.faletra{at}


The detailed anatomy of the interatrial septum (IAS) and mitral annulus (MA) as observed on cardiac magnetic resonance, computed tomography and two-dimensional/three-dimensional transthoracic and transesophageal echocardiography is reviewed. The IAS comprises of two components: the septum primum that is membrane-like forming the floor of the fossa ovalis (FO) and the septum secundum that is a muscular rim that surrounds the FO. The latter is an enfolding of atrial wall forming an interatrial groove. Named Waterston’s groove, it is filled with adipose tissue on the epicardial side. Thus, the safest area for transseptal puncture (TSP) is within the limits of the FO floor, which provides direct interatrial access. While crossing an intact septum is a well-established procedure, TSP is a more complex and time-consuming procedure in the presence of patent foramen ovalis, aneurysmal FO or atrial septal defect closure devices. MA comprises two distinctive segments: an anterior-straight and a posterior-curved segment. The posterior MA is a thin, discontinuous fibrous ‘string’, interspersed with adipose tissue, where four components converge: the atrial and ventricular musculature, epicardial adipose tissue and the leaflet’s hinge line. In parts of where this fibrous string is deficient or absent, the posterior leaflet is inserted directly on ventricular and atrial myocardium rendering the MA less robust and producing an ‘asymmetric’ dilation. The marked vulnerability of posterior MA to calcifications might be due to its insertion on the crest of ventricular myocardium being subject to friction injury due to the contraction and relaxation of LV.

  • advanced cardiac imaging
  • cardiac computer tomographic (CT) imaging
  • cardiac magnetic resonance (CMR) imaging
  • echocardiography
  • interventional cardiology and endovascular procedures

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  • Contributors We declare that this paper is not under consideration elsewhere; none of the paper’s content has been published; all the authors have read and approved the manuscript.

  • Funding FFF reports several talks supported by Philips.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.