Journal Article

Active myocyte shortening during the ‘isovolumetric relaxation’ phase of diastole is responsible for ventricular suction; ‘systolic ventricular filling’

Gerald D. Buckberg, Manuel CastellÁ, Morteza Gharib and Saleh Saleh

in European Journal of Cardio-Thoracic Surgery

Published on behalf of European Association for Cardio-Thoracic Surgery

Volume 29, issue Supplement_1, pages S98-S106
Published in print April 2006 | ISSN: 1010-7940
Published online April 2006 | e-ISSN: 1873-734X | DOI: https://dx.doi.org/10.1016/j.ejcts.2006.02.043
Active myocyte shortening during the ‘isovolumetric relaxation’ phase of diastole is responsible for ventricular suction; ‘systolic ventricular filling’

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  • Anatomy
  • Clinical Pharmacology and Therapeutics
  • Cardiovascular Medicine

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Objective: To study the ‘isovolumetric relaxation’ phase of rapid ventricular filling by analysis of the shortening of cardiac muscle in the endocardial and epicardial segments of the left ventricle in the dual helical model of the ventricular band, described by Torrent-Guasp. Methods: In 10 pigs (27–82 kg), temporal shortening by sonomicrometer crystals was recorded while recording ECG, and measuring intraventricular pressure and dP/dt with Millar pressure transducers. Results: The following sequence was observed; shortening began in descending or endocardial segment, and 82 ± 23 ms later it was initiated in the epicardial or ascending segment of the band. The descending segment stops shortening during the rapid filling phase of fast descent of ventricular pressure, but the ascending segment shortening continues for 92 ± 33 ms, so that active shortening continues during the period of isovolumetric relaxation. During the rapid filling phase, dopamine decreased the interval between completion of endocardial and termination of epicardial contraction from 92 ± 20 to 33 ± 8 ms. Conversely propranolol delayed the start of epicardial shortening from 82 ± 23 to 121 ± 20 ms, and prolonged the duration of endocardial contraction, causing a closer (21 ± 5 ms vs 92 ± 20 ms) interval between termination of contraction of endocardial and epicardial fibers. The resultant slope of the rapid descent of the left ventricular pressure curve became prolonged. Conclusions: These time sequences show that ongoing unopposed ascending segment shortening occurs during the phase of rapid fall of ventricular pressure. These active shortening phases respond to positive and negative inotropic stimulation, and indicate the classic concept of ‘isovolumetric relaxation’, IVR, must be reconsidered, and the new term ‘isovolumetric contraction’, IVC, or systolic ventricular filing may be used.

Keywords: Isovolumetric relaxation; Isovolumetric contraction; Helical heart; Ventricular myocardial band; Systolic ventricular filling

Journal Article.  6212 words.  Illustrated.

Subjects: Anatomy ; Clinical Pharmacology and Therapeutics ; Cardiovascular Medicine

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