DK2985_C000 1..28 - AlSharqia Echo Club

Intracavitary Contents 521and angles to detect the presence of vegetations. Infectioninvolving mechanical prosthetic valves usually begins inthe perivalvular area at the annular insertion site andlater extends along the struts where it may interfere withthe motion of the occluder. Echocardiographically, thesmooth contour of the ring may appear thickened, afinding sometimes difficult to differentiate from thrombusor pannus formation. When .40% of the sewing ring isinvolved by the infectious process, loosening of thesutures leads to dehiscence and rocking of the prosthesis.In bioprosthetic valves, in addition to similar involvementof the sewing ring, the infection may also deform anddestroy the tissue cusps (11).XI.PATENT FORAMEN OVALEThe prevalence of patent foramen ovale (PFO) is higher inpatients with unexplained cerebrovascular accidents(CVA) than in the general population (up to 75% vs25–30%). Furthermore, patients with PFO and previousCVA have a risk of recurrent events in the range of 1.7–4.7% per year. The presence of an atrial septal aneurysmor a Chiari network is associated with a higher prevalenceof significant PFO. Recent studies have demonstrated thata larger PFO size as measured by 2D echocardiography isassociated with an increased risk of stroke (8,31).Transesophageal echocardiography is the most usefuland reliable tool to detect the presence of a PFO (seeFig. 24.6). The size of the PFO is assessed semiquantitativelyby observing the number of contrast microbubblesinjected through a peripheral vein crossing from RA toLA through the PFO. A large shunt is deemed presentwhen more than 20 microbubbles enter the LA in fewerthan three beats. The ability to detect the PFO and itsdegree of right-to-left shunting is influenced not only bythe size of the orifice, but also by the quality of the contrastagent (mixture of agitated saline and blood, dosage, routeof administration), the position of the patient and the use ofadequate provocative maneuvers (such as the Valsalvamaneuver). Color Doppler flow is initially used to assessthe direction of flow from the IVC towards the fossaovalis and the direction of the shunt, if present, both atrest and with provocative maneuvers. The injection of agitatedsaline contrast through a peripheral vein is also usedboth at rest and with provocative maneuvers to differentiatea resting PFO vs a provocable one. Provocative maneuversare designed to induce a sudden inversion of theRA–LA pressure gradient to open up the membrane ofthe fossa ovalis: enhanced right-to-left shunt is noted(A)(B)LASVCRAIVC CANNULA(C)Figure 23.36 Intraoperative contrast examination. (A, B) Mid-esophageal bicaval view during a contrast study to rule-out the presenceof a patent foramen ovale. Note the inferior vena cava (IVC) cannula inserted prior to cardiopulmonary bypass. (C) A two-syringe systemwas used (LA, left atrium; RA, right atrium; SVC, superior vena cava).