Mitral isthmus – Cardiology MCQ – Answer

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Mitral isthmus – Cardiology MCQ – Answer

Mitral isthmus, often targeted during ablation of atrial fibrillation is between the mitral valve and – Correct answer: a) Left inferior pulmonary vein

It is a narrow isthmus of myocardium between the lateral mitral annulus and the left inferior pulmonary vein [1]. It was first described by Luria DM et al 2001 during left accessory pathway ablation [2]. It was considered to be analogous to the cavotricuspid isthmus in the right atrium which is targeted for atrial flutter ablation. Feasibility and safety of ablation of the isthmus for atrial fibrillation was first reported in 2004 by Jaïs P et al [3]. Prior to that, ablations were done in isolated case reports of atypical perimitral flutter.

It is bounded by the lateral mitral annulus and left inferior pulmonary vein ostium. As it is adjacent to left atrial appendage and coronary sinus (epicardial), assessment of bidirectional block after ablation is feasible [1].

As extensive ablation is often needed, including within the coronary sinus to achieve isthmus block and close relation to vital structures like left circumflex artery and esophagus, various complications have been reported [1]. These include cardiac tamponade, damage to left circumflex coronary artery and atrio-esophageal fistula.

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  1. Wong KC, Betts TR. A review of mitral isthmus ablation. Indian Pacing Electrophysiol J. 2012 Jul;12(4):152-70.
  2. Luria DM, Nemec J, Etheridge SP, Compton SJ, Klein RC, Chugh SS, Munger TM, Shen WK, Packer DL, Jahangir A, Rea RF, Hammill SC, Friedman PA. Intra-atrial conduction block along the mitral valve annulus during accessory pathway ablation: evidence for a left atrial “isthmus”. J Cardiovasc Electrophysiol. 2001 Jul;12(7):744-9.
  3. Jaïs P, Hocini M, Hsu LF, Sanders P, Scavee C, Weerasooriya R, Macle L, Raybaud F, Garrigue S, Shah DC, Le Metayer P, Clémenty J, Haïssaguerre M. Circulation. 2004 Nov 9; 110(19):2996-3002.