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

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.