[Pre-ejection flow in the left ventricular outflow tract elucidated by pulsed Doppler technique].
Pulsed Doppler technique has elucidated the blood flow towards the cardiac base in the left ventricular (LV) outflow tract prior to onset of ejection flow. This pre-ejection flow (PE flow) is observed immediately after the beginning of atrial contraction and it lasts until immediately after completion of mitral closure. This study was designed to clarify the mechanism and physiological significance of PE flow by investigating the temporal relationship between PE flow and cardiac dynamics and by examining its velocity distribution in the LV outflow tract. Observations were made for 21 healthy subjects (H), 12 patients with atrial fibrillation (Af), three with first degree AV block and two with second degree AV block of the Wenckebach type. A Doppler-Echocardiograph (Hitachi Medico EUB-10B) was used, and PE flow was detected in all subjects. The Doppler frequency, which corresponded to blood flow velocity, increased when the sampling site was near the tip of the anterior mitral valve leaflet as opposed to the upper portion of the LV outflow tract. Results of the temporal analysis of PE flow were as follows: The PE flow pattern was monophasic both in H and patients with Af. Its peak appeared 0.18 +/- 0.05 (mean +/- SD) sec after the beginning of the P wave and 0.02 +/- 0.02 sec after the Q wave in H, but 0.06 +/- 0.01 sec after the Q wave in Af. In first degree AV block, the PE flow consisted of two peaks. The interval between the first PE flow peak and the beginning of the P wave was constant and nearly 0.2 sec apart. It was nearly the same as in H. The second peak occurred 0.05 sec after the Q wave as in Af. In second degree AV block of the Wenckebach type, the first peak occurred at constant interval following the P wave, while the second peak related to left ventricular contraction and disappeared when an atrial contraction failed to initiate a ventricular response. These findings indicate that PE flow consists of two components with different mechanisms. 1) The first component is caused by the atrial blood inflow turning up from the apex towards the cardiac base. This flow component may participate in closure of the anterior mitral leaflet. 2) The second component consists of a rise in LV pressure due to LV contraction, and achieves complete closure of the mitral leaflets. We conclude that PE flow with its atrial and ventricular components contributes to closure of the mitral leaflets.
D000368:Aged; D001281:Atrial Fibrillation / Q000503:physiopathology*; D001783:Blood Flow Velocity; D002302:Cardiac Output; D005260:Female; D006327:Heart Block / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012212:Rheology