Temporal and Spatial Changes in Left Ventricular Pattern of Flow During Continuous Assist Device “HeartMate II”
The Heartmate II Left Ventricular Assist Device is a new axial impeller pump that is smaller than many existing devices and has no need for percutaneous venting. These features have the potential to reduce complications, lengthen durability, and enhance full implantability and good left ventricular unloading. The optimal operating conditions, however, remain to be elucidated. Changes in pump speed can produce temporal and spatial changes in the pattern of blood flow in the left ventricle (LV). These changes could influence the overall pump flow, cardiac rhythm, left ventricular function, structure, and possibly capacity to reverse remodeling. At different pump speeds, flow inside the ventricle was continuous throughout the cardiac cycle apart from a brief period during isovolumic contraction (arrow) (Figure 1A). At the slow pump speed of 9600 RPM, ventricular early diastolic flow velocity was augmented, particularly at mid-cavity level, where it reached a maximum of 0.6 m/s (Figure 2A). At a speed of 12 000 RPM, the flow pattern became disturbed with aliasing in early diastole at mid-cavity and apical levels (Figure 1B). This disturbance was associated with a striking 5-fold increase in velocity (exceeding 2.0 m/s; Figure 2B). This increase in velocity was the result of a reduced cross-sectional area at the mid-cavity level, which gave the ventricle an hourglass shape. At the same time, the proximal septal segment became reversed, possibly to maintain basal ventricular chamber size. These changes were observed consistently in 3 separate examinations at intervals of 5 weeks. The causes and effects of these changes need to be examined further. Adjustment of pump speed is therefore of central importance to the maintenance of adequate circulation and possibly the capacity of the ventricle to recover.1,2⇓
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
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