DK2985_C000 1..28 - AlSharqia Echo Club

302 Transesophageal Echocardiography3. Phosphodiesterase InhibitorsPhosphodiesterases inhibitors prevent the breakdown ofcyclic adenosine monophosphate (AMP), prolonging itseffectiveness and augmenting its physiologic response.In addition to positive inotropic properties, phosphodiesterasesinhibitors cause vasodilatation. The bypiridinesinamrinone (formerly amrinone) and milrinone are twodrugs of this class commonly used during cardiacsurgery. In cardiac surgical patients, a milrinone loadingdose of 50 mg/kg followed by a continuous infusion of0.5 mg kg per min resulted in a plasma concentration inexcess of 100 ng/mL, producing a substantial hemodynamiceffect (the plasma concentration associated witha 50% increase in cardiac index was 167 ng/mL) (37).Using both standard hemodynamic measurements andechocardiography, Kikura et al. (38) studied the effectsof milrinone in cardiac surgical patients immediatelyafter separation from CPB: left ventricular function andhemodynamic parameters were improved in patientsalready treated with catecholamines and/or vasodilatorsunder constant loading conditions ensured by constantreinfusion from CPB reservoir. A loading dose of50 mg/kg and a loading dose plus three different continuousinfusions (50–75 mg/kg þ 0.5–0.75 mg kg per min)produced an increase in cardiac index and SVI with adecrease in peripheral vascular resistance. No significantchanges in HR, main arterial pressure (MAP), PCWP,and CVP as well as the EDA measured by TEE werenoted. However, velocity of circumferential shorteningcorrected for HR, an index of cardiac performance notaffected by preload, significantly increased and was positivelycorrelated with the milrinone serum concentration(r ¼ 0.43). Amrinone and milrinone were found to havesimilar hemodynamic effects in patients undergoingelective cardiac surgery (39).Milrinone also improves diastolic parameters inpatients with heart failure, reducing diastolic pressure atany given volume while elevating the maximum rate ofrise of left ventricular pressure (18%) and decreasing themean aortic pressure. The peak left ventricular fillingrate increased by 42% and the PCWP decreased (40).Using TEE in cardiac surgery, Lobato et al. (41) observedthat CPB was associated with a 20% decrease in leftventricular compliance as measured by change in leftventricular end diastolic area (LVEDA) in relation to theleft atrial pressure (41). Administration of milrinoneafter CPB was associated with a partial return of leftventricular compliance to pre-CPB values.Phosphodiesterase inhibitors can also improve rightventricular function and reduce right ventricular afterloadafter cardiac surgery. Using right ventricular pressure–area relationship obtained by TEE, Ochiai et al. (42)found that the administration of amrinone in thepostoperative period results in improved right ventricularcontractility, as reflected by an increase in end-systolicelastance.Despite the favorable effects on left and right ventricularfunction, administration of phosphodiesterase inhibitorsmay cause a decrease in preload and afterload whichcould require substantial volume loading (which can beguided by TEE) and administration of vasoactive agentslike phenylephrine, norepinephrine and dopamine.PhenylephrinePhenylephrine, an a 1 -adrenergic agonist, is frequentlyadministered to increase arterial pressure during anesthesia.In patients with coronary artery disease, an intravenousbolus may cause a transient increase in the leftventricular wall stress with an impairment of left ventricularglobal function, as suggested by the observed decreasein FAC (Fig. 13.20) and mVcf c . As these indices of leftventricular global function are afterload-dependent, theimpairment of left ventricular function with phenylephrinemost likely reflects the increase in left ventricular wallstress rather than altered intrinsic myocardial contractility.Phenylephrine given to patients with valvular aorticstenosis (AS) did not exhibit any negative effect on theirventricular performance: ventricular afterload in thisgroup of patients is mainly dependent on the pressuregradient across the aortic valve (AoV) rather than on theSVR (43).D. Internal Mammary DissectionDuring this period, TEE may be used to monitor the globaland segmental ventricular function (Chapters 8 and 9), andto detect the occurrence of pneumothorax and hemothorax.E. Arterial CannulationThe role of TEE and EAS imaging to position the aorticand femoral cannula has been discussed above. Whilethe frequency of intraoperative aortic dissection duringcardiac surgery is infrequent at 0.16%, its mortalityamounts to 20% if discovered intraoperatively vs 50%for dissections diagnosed postoperatively. After CPB,TEE can detect aortic dissection involving the proximalaortic arch at the aortic cannulation site, which canextend distally (Fig. 13.21). Although the site of theinitial intimal tear is most often located at the site of arterialcannulation, dissection can also originate distally fromthe trauma induced by the jet of blood from the aorticcannula to a fragile atherosclerotic Ao (44). The incidenceof retrograde ilioaortic dissection may be as high as 3%with common femoral artery cannulation for standardCPB. However, falsely positive TEE diagnosis of