DK2985_C000 1..28 - AlSharqia Echo Club

144 Transesophageal EchocardiographyUntil now, with the actual diagnostic system, cavitationhas not been shown to occur in the human adult. Acousticcavitation can alter mammalian tissues. Lung lesions areproduced when animals are exposed to diagnostic pulsedultrasound (1 MPa at 2 MHz). There have been noreports of lung hemorrhage with TEE use in humans.Direct mechanical action of cavitation yields pinpointregions of destruction, such as petechial hemorrhage.Concerns about the cavitation phenomenon arise especiallywith the foetus. The World Federation of UltrasoundMedicine and Biology 1998, recommendations state thatthe operator should minimize ultrasound exposure ofhuman postnatal lungs.(A)(B)MAZE CATHETERD. Intensity Measurement and QuantificationThe intensity (I) of ultrasound exposure can be expressedin several ways, with its unit in W/cm 2 . The SPTA correspondsto the highest exposure within the beam averagedover the period of exposure. Another common measureis spatial peak pulse average (SPPA), defined as theaverage pulse intensity at the spatial location where thepulse intensity is maximum.The thermal index (TI) and mechanical index (MI)define exposure level with diagnostic ultrasound (seeChapter 1) (2). The TI assesses the potential for ultrasonicheating and is related to the average intensity and its valueis indicated during Doppler examination (Fig. 7.1). The MIcorresponds to cavitation effect which is related to peakpressure. This value is indicated during 2D exam(Fig. 7.1). These indices have incorporated factors suchas tissue exposure to transmission period, the time theultrasound beam dwells at a specific point (both beingconsiderably shorter than the total examination time).LEFT ATRIUMFigure 7.2 Closure of an atrial septal defect in a 48-year-oldman. A Maze procedure is also performed for chronic atrial fibrillation.At that time the TEE probe is pulled back above the leftatrium to avoid esophageal damage.electrical and thermal energy through the left atrial walltoward the esophagus (4).E. Electrical SafetyIII.PERSONNEL AND EQUIPMENTThe risk of electrical harm with current ultrasound systemsis very low. Erosion or perforation of its protective sheathcan cause the loss of the system grounding. Loss of systemelectrical integrity increases the risk of thermal injury.Nowadays, operating room electrical systems are built insuch a way that it takes two faults to induce an electricalshock. Also, when defibrillation is necessary, the echocardiographysystem does not have to be unplugged (,50 J).There have been reports of esophageal burns, perforation(3) and atrioesophageal fistula with intraoperative radiofrequencyablation of atrial fibrillation (4,5). It is, therefore,recommended to avoid using TEE in patientsundergoing radiofrequency ablation. At the MontrealHeart Institute, we pull back the TEE probe above theleft atrium (LA) during the procedure (Fig. 7.2). Inaddition, isolating scrub in the oblique sinus behind theleft atrial wall could be used to prevent passage ofVarious professional associations have published requirementsfor training, performance and maintenance of TEEexamination skills (6). The TEE examination is performedin various settings, in clinics with outpatients, in operatingrooms, and in intensive care units. Quality personnel,training, and monitoring can greatly reduce complications.Vigilance should be prime. Standard equipment shouldinclude all the proper material required for monitoringand patient resuscitation (Table 7.3).IV. PATIENT EVALUATION BEFORETHE PROCEDUREA. IndicationsThe indications for TEE have increased over the years. Inseveral situations, valuable information can be rapidly