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Eur J Cardiothorac Surg 2006;29:S75-S97
© 2006 Elsevier Science NL

Structure/function interface with sequential shortening of basal and apical components of the myocardial band

^a Option of Bioengineering, California Institute of Technology, Pasadena, CA, USA
^b Department of Medicine, David Geffen School of Medicine at UCLA, USA
^c Department of Surgery, Division of Cardiothoracic Surgery, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, 62-258 CHS, Los Angeles, CA 90095-1701, USA

Received 17 February 2006; accepted 27 February 2006.

^_* Corresponding author. Address: Department of Surgery, Division of Cardiothoracic Surgery, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, 62-258 CHS, Los Angeles, CA 90095-1701, USA. Tel.: +1 310 206 1027; fax: +1 310 825 5895. (Email: gbuckberg{at}mednet.ucla.edu).

Objective: To study the sequential shortening of Torrent-Guasp's ‘rope-heart model’ of the muscular band, and analyze the structure–function relationship of basal loop wrapping the outer right and left ventricles, around the inner helical apical loop containing reciprocal descending and ascending spiral segments. Methods: In 24 pigs (27–82 kg), temporal shortening by sonomicrometer crystals was recorded. The ECG evaluated rhythm, and Millar pressure transducers measured intraventricular pressure and dP/dt. Results: The predominant shortening sequence proceeded from right to left in basal loop, then down the descending and up the ascending apical loop segments. In muscle surrounded by the basal loop, epicardial muscle predominantly shortened before endocardial muscle. Crystal location defined underlying contractile trajectory; transverse in basal versus oblique in apical loop, subendocardial in descending and subepicardial in ascending segments. Mean shortening fraction average 18 ± 3%, with endocardial exceeding epicardial shortening by 5 ± 1%. Ascending segment crystal displacement followed descending shortening by 82 ± 23 ms, and finished 92 ± 33 ms after descending shortening stops, causing active systolic shortening to suction venous return; isovolumetric relaxation was absent. Conclusions: Shortening sequence followed the rope-like myocardial band model to contradict traditional thinking. Epicardial muscle shortened before endocardial papillary muscle despite early endocardial activation, and suction filling follows active systolic unopposed ascending segment shortening during the ‘isovolumetric relaxation’ phase.

Key Words: Helical ventricular myocardial band • Isovolumetric contraction and relaxation • Sonomicrometer crystals • Systolic ventricular filling

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