Abstract
Hemodynamic and mechanical effects of a left ventricular assist device (LVAD) implanted between the left ventricular apex and the descending thoracic aorta (apical bypass) were studied in the in vivo acute experiments on mongrel dogs with normal hearts. Bulk and regional mechanics of the left ventricle were investigated by using implantable miniature sonomicrometers. LVAD was driven in five pumping modes: electrocardiogram synchronous modes with the duty factors of 1:1, 2:1 and 4:1, and asynchronous modes with the pulse rates of 60 and 80 beats/min (bpm). In all the pumping modes but 4:1 mode, almost total bypass was obtained. Moreover, neither the whole left ventricle nor the regional cardiac muscles virtually worked under LVAD pumping in the above pumping modes, and almost 100% of the ventricular work was unloaded. The above results reveal the possibility that the apical bypass method is more effective in circulatory assist and in ventricular unloading compared with the atrial bypass method in which LVAD is implanted between the left atrium and descending thoracic aorta.
