DK2985_C000 1..28 - AlSharqia Echo Club

TEE in Mechanical Circulatory Assistance 319(A)(B)TMFTMFEAIABP ONIABP OFFTEE. Right ventricular output may also be evaluated withCO measurement by thermodilution. By subtracting theassisted flow from this measurement, the portion of COcontributed by the recovering LV can be serially measuredand followed.The weaning of a biventricular assist device is moredifficult to assess: indeed, because venous mixing doesnot occur in the RV, CO determination by thermodilutionis less accurate, while the relative contributions of RV andLV to forward flow cannot be precisely determined (2).For those reasons, TEE may provide useful additionaldata in assessing right and left CO (7).In addition to its role in assessing cardiac function, TEEcan also be used to detect complications in the postoperativesetting of centrifugal circulatory assistance (8). Conditionssusceptible to causing hemodynamic instabilitycan be diagnosed such as the presence of intracardiac (orintracatheter) thrombus (Fig. 14.9), vegetations on thecatheter tip, pericardial tamponade (Figs. 14.10 and14.11), and the displacement or collapse of one of thecannulae.EAFigure 14.4 Effect of the intra-aortic balloon pump (IABP) onthe Doppler transmitral flow (TMF) velocities. When the IABP isturned off, the TMF velocities are reduced with associatedreduction in stroke volume.and global left and right ventricular function, but isfrequently technically difficult and limited in postoperativepatients. The assessment of regional and global ventricularfunction as well as the diagnosis of complicationsbenefits from the availability of TEE (6).The degree and timing of myocardial recovery can beperiodically evaluated in the intensive care unit (ICU) byfrequent assessment of left and right ventricular function.Progressive withdrawal of circulatory support can beinitiated when signs of hemodynamic improvement arepresent.Ventricular assist devices should be removed as soon ashemodynamic competence and stability are restored, asmorbidity significantly increases after 24–48 h of support.Weaning of left ventricular centrifugal mechanical assistancecan be monitored by the gradual pulse pressure restorationat full flow as the left ventricular function recovers on2. Pulsatile Blood PumpsPulsatile VADs are considerably more expensive andcomplex than centrifugal pump systems, both in theirinsertion and operation, but they are capable of producingpulsatile flow with minimal or no trauma to blood cellularelements. Furthermore, their integrated sophisticatedcontrols are largely self-regulating, and despite more operatingmodalities, they usually require minimal supervisionbeyond the first few days after device insertion. Differentmodels of pulsatile VADs are available (Thoratec,Heartmate, Novacor, Abiomed) (Fig. 14.12). Each hastheir own set of indications, contraindications, advantages,and disadvantages. Some are pneumatically driven whileothers are electrically driven. These types of mechanicalassistance can offer a complete circulatory support ofright and/or left ventricular function. They are, ingeneral, used in patients who need a high degree of circulatorysupport for a medium to long-term period, and arealso used as a bridge to cardiac transplantation (2–4).These devices have similar cannulation system set-upsand are ideally suited to patients with unlikely ventricularrecovery who receive mechanical circulatory support as abridge to cardiac transplantation. For support of the systemiccirculation (Fig. 14.3), the inflow cannula isusually inserted in the apex of the LV. In general, theleft atrial inflow cannulation is technically easier toperform but is thought to provide incomplete ventriculardecompression. The outflow cannula goes from theLVAD to the ascending Ao. For support of the pulmonarycirculation, the inflow cannula is generally inserted in the