Septal structure and function relationships parallel the left ventricular free wall ascending and descending segments of the helical heart.

OBJECTIVE Determine if ventricular septum structure and function relationships parallel the left ventricular free wall descending and ascending segments of the helical heart. METHODS Forty pigs (30-38 kg) were studied physiologically by sonomicrometer to determine if septal fiber orientation resembled responses in the free wall. Following pilot studies in the non-bypassed heart, a right ventriculotomy was made to place septum crystals with fiber orientations that were either perpendicular to or reflected simultaneous free wall measurements. Postbypass measurements tested responses to positive (dopamine) and negative (esmolol) inotropic agents. RESULTS Similar oblique fiber directions were found for baseline percent systolic shortening (SS%) in the free wall and septum; free wall descending and ascending SS% were 21+/-3% and 10+/-3%, and 13+/-2% and 12+/-2%, respectively, in the septum. Conversely, impaired shortening occurred when transverse fiber direction was tested. Both oblique areas demonstrated comparable time-delay changes between free wall and septal descending and ascending segment at onset (75+/-11 ms) and termination (86+/-21 ms) of contraction. Dopamine increased heart rate and caused a similar increase of free wall descending and ascending segment SS% to 24+/-2% and 14+/-3% (p<0.05), and septal SS% response to 16+/-2% and 15+/-2% (p<0.05), and comparable decrease of time-delay changes of shortening between ascending and descending segments of 54+/-6 ms and 68+/-10 ms, respectively (p<0.05). Conversely, esmolol decreased heart rate and similarly reduced SS% in left ventricular free wall (descending: 18+/-4%; ascending: 7+/-4%; p<0.05) and septum (descending: 10+/-2%; ascending: 10+/-3%; p<0.05). Time-delay of contraction between segments was increased to 91+/-4 ms (p<0.05), but the hiatus at the end of shortening remained unchanged, due to prolonged endocardial contraction. CONCLUSIONS Septal structure and function relationships parallel the left ventricular free wall ascending and descending segments, thereby supporting the helical heart fiber spatial relationships. The oblique fiber orientation may make the septum become the 'lion of right ventricular function'.