DK2985_C000 1..28 - AlSharqia Echo Club

168 Transesophageal EchocardiographyIdentification of a persistent wall motion abnormalitydoes not distinguish a stunned or hibernating regionfrom infarcted myocardium. Stunning, defined asprolonged postischemic contractile dysfunction of themyocardium, has been observed in several clinical situationsincluding stress-induced angina, unstable angina,thrombolysis, percutaneous transluminal angioplasty, andcoronary artery bypass surgery. Complete recovery ofmyocardial function may require from three days toseveral weeks in the presence of stunning. Hibernation isa state of persistently impaired myocardial and left ventricularfunction at rest due to reduced coronary blood flowthat can be partially or completely restored to normalif the myocardial oxygen supply/demand relationshipis favorably altered, either by improving blood flow(surgery, percutaneous coronary angioplasty) and/or byreducing demand. Perioperatively it is extremely difficultto determine whether new segmental wall motion abnormalityrepresents inadequate revascularization, ongoingischemia, or stunned myocardium, but the distinction isof therapeutic significance and a dobutamine stress echocardiogrammay be useful. Dobutamine has a positiveinotropic effect at low doses (5–10 mg/kg per min),with additional inotropic and chronotropic effects at higherdoses. The increase in systolic blood pressure duringthe infusion of dobutamine can be more pronounced inhypertensive than in normotensive patients. A paradoxicalhypotension can be occasionally observed, and is eitherdue to the vasodilating effect of dobutamine or transientoutflow tract obstruction, but is rarely caused by ischemia(26). Demonstration of increased contractility in anhypokinetic or akinetic region suggests that the regionalsystolic function will improve either after revascularizationin the case of hibernating myocardium (27) or spontaneouslyafter recovery from stunning (28). A biphasicresponse to increasing dobutamine doses characterizedby enhanced thickening at low doses (5–10 mg/kg per min)followed by deterioration of thickening at higher doses(.10 mg/kg per min) is the most accurate echocardiographiccriterion to detect viable but hypoperfused myocardium.Arnese et al. (29) found that the specificity oflow-dose dobutamine echocardiography in predictingrecovery of function after surgical revascularization was95% compared with only 48% for 201-thallium singlephoton emission computed tomography (SPECT) (29).The greater is the number of viable myocardial segments,the greater is the probability of improvement in regionaland global left ventricular function after revascularization.The value of low-dose dobutamine stress echocardiographyfor the assessment of myocardial viability hasbeen compared with that of positron emission tomography(PET) and nuclear perfusion imaging (30). Cumulative(A)BEFORE LAD CLAMPING DURING LAD CLAMPING AFTER LAD UNCLAMPINGTMF (B) TMF (C) TMFEAEAEA(D)LADFigure 8.11 Pulsed-wave Doppler of transmitral flow (TMF) velocities in a 66-year-old man during off-pump bypass surgery. Duringthe clamping of the left anterior descending (LAD), the transmitral pattern changed from a predominant A wave (A), to predominant Evelocity (B) with short deceleration time suggesting a restrictive pattern. This reverted back to baseline after completion of revascularization(C). Intraoperative aspect of the LAD anastomosis (D). (Photo D courtesy of Dr. Raymond Cartier.)