475 TEE in aortic dissection TEE can demonstrate the presence of an intimal \202 ap in the ao rta with great accuracy (sensitivity of 99%, speci \201 city of 98%). Key views \200 Presence of intimal \202 ap in the following: \200 \200 \200 Coronary artery involv ement (30 \200\22345 ME AV SAX) Aortic valve for regurgitation, annular dilation, cusp in volvement (120 ME AV LAX) Site of intimal rupture, color Doppler to determine true and fa lse lumen Aortic rupture with collection around aorta Pericardial effusion Thrombus or spon taneous contrast in false lumen Ascending aorta Descending aorta Aortic arch (120 ME AV LAX, 30 ME ascending aortic SAX) (0 desc aortic SAX, 90 descending aorti c LAX) (0 UE aortic arch LAX, 90 UE aortic arch SAX) \200 \200 \200 Blood pressure control (i.e., B-blockers) should be initiated prior to TEE an d adequate sedation should be given to avoid hypertension during esophageal intubation. Pitfalls There are blind spots in the proximal arch. Aortic artifacts (imaging artifacts that mimic dissection) \200 Artifacts have parallel position to the aortic wall and are motion dependent on true struct ures. Blood \202 ow velocities are similar on either side of the artifact. Use superposit ioning of color Doppler over the artifact without mosaic pattern to indicate turbulence and \202 ow that does not follow an anatomical structure. \200 An equivocal TEE examination should prompt the use of another imaging modality such as CT o r MRI. Aortic intramural hematoma (AIH) This appears as an area of wall thickness >7 mm with or wi thout the pres- ence of an echolucent space in the aortic wall. It may be dif \201 cult to dif- ferentiate from an atherosclerotic plaque or penetrating aortic ulcer, and other imag ing modalities such as CT or MRI may be required. Diagnosis of AIH (cid:116) \200 7 mm crescent or circular thickening of aortic wall \200 \200 Extending 1 \200\22320 cm longitudinal No intimal \202 ap or Doppler \202 ow in thicken ed aortic wall CHAPTER 12 Stress testing and cardiac imaging 476 TEE in endocarditis Box 12.5 TEE is more sensitive (sensitivity >90%) than TTE for the detection of vegetations (sensiti vity <60%) in infective endocarditis (IE), especially if the vegetations are <5 mm in size. TEE is the preferred diagnostic test \200 \200 \200 \200 Patients with poor TTE windows Prosthetic valve endocarditis Intermediate or high clinical suspicion for IE with negative TTE IE with complications (i.e., abscess, hemodynamically si gni \201 cant valvular insuf \201 ciency) Some authorities feel that all patients with clinical IE should have TEE for early detectio n of complications such as perivalvular abscess formation, and for Staphyloccocus aureus IE , where the risk of complications is high. This approach is also cost-effective. A negative TTE and TEE has a negative predictive value of 95%. If clinical suspicion remain s high, however, TEE should be repeated in 7 \200\22310 days, as small vegetations (<2 mm) may be missed on the initial study. Echocardiographic criteria for diagnosis of IE according to Duke classi \201 cation \200 Vegetations: irregular mobile echodensities usually seen along lines of valve closures down stream from regurgitant \202 ow. These are typically located on the atrial side of the mi tral valve (anterior lea \202 et more common) and the ventricular side of the aortic valve . Myocardial abscess by ventricular septum, mitral valve, and papillary muscle. TEE has a s ensitivity of 80%, compared to 30% for TTE. Prosthetic valve dehiscence. New valvular regur gitation. most commonly occurs in the aortic root followed \200 Other complications that can be diagnosed by echocardiography include lea \202 et perforat ion, \201 stula, and chordal rupture. Key views \200 \200 \200 \200 Aortic valve, aortic root (30 \200\22345 ME AV SAX, 120 ME LAX) Mitral valve views (see p. 37) Tricuspid valve (0 ME four chamber, 120 TG LAX) Pulmonary valve (90 ME RV in \202 ow \200\223out \202 ow) TEE is useful prior to surgery to exclude involvement of other valves and to look for an ab scess or other complication that may require additional surgical procedures (see Box 12.6). Sensitivity of TEE and of TTE are com- parable for the detection of right-sided vegetation s. TEE IN ENDOCARDITIS 477 Pitfalls Valve strands (Lambl \200\231s excrescences), chordal structures from myxoma- tous degeneration, and nonspeci \201 c valvular thickening may be mistaken as vegetations, lea ding to a false-positive result. Box 12.6 Echocardiographic features requiring surgical referral \200 Acute severe aortic or mitral regurgitation causing LV failure or hemodynamic compromise Pr osthetic valve dehiscence, especially if hemodynamic compromise Myocardial abscess Vegetati ons with recurrent embolization despite antibiotics Mitral valve vegetation >10 mm due to a ssociated increased risk of embolism Increase in vegetation size after 2 \200\2234 weeks of antibiotics \200 \200 \200 CHAPTER 12 Stress testing and cardiac imaging 478 TTE/TEE in mitral regurgitation (MR) Assessment of mitral valve (MV) morphology is required to determine the mechanism of regurgitation and associated structural abnormalities: \200 \200 \200 \200 \200 \200 \200 \200 \200 \200 Elongation or rupture of chords Papillary muscle rupture Retraction of chords Prolapse or t ethering of lea \202 ets Subvalvular apparatus thickening or calci \201 cation Annular di lation Annular calci \201 cation LV size and function LA size Regional wall motion abnorma lities may suggest ischemic MR. Key TEE views (see Fig. 12.11) \200 Lea \202 et prolapse or restriction (0 ME four chamber, 45 ME mitral commissural, 90 ME two chamber, 120 ME LAX) Annular diameter (120 ME LAX) Lea \202 et prolapse (0 T G basal SAX) Subvalvular apparatus (90 TG two chamber) Anterior and posterior lea \202 e ts are each divided into three segments to describe location of pathology. \200 \200 \200 Assessment of MR severity (by TEE or TTE) \200 \200 \200 \200 Length/area of regurgitant jet Density of spectral Doppler tracing Timing of MR: early syst olic vs. holosystolic by color M-mode Direction of jet: eccentric or central \200 Coanda effect Doppler may underestimate severity of regurgitation Pulmonary venous systolic \202 ow reversal (see Table 12.4) Calculation of regurgitant volume (RV) and effective r egurgitant ori \201 ce area (EROA) using PISA or volumetric method Other features of sever e MR: \200 \200 : size of eccentric wall-hugging regurgitant jet on color \200 Regurgitant jet width at its origin (vena contracta) >0.7 cm Peak E-wave velocity >1.5 m/se c Proximal isovelocity surface area (PISA) \200 Identify isovelocity hemispheric shells on ventricular aspect of valve in apical view using color Doppler with adjusted aliasing velocity. Measure radius of isovelocity shell (r) and aliasing velocity. Measure MR peak velocity and VTI from spectral tracing. \200 \200 \200 (cm2) = 2(cid:83)r2 x aliasing velocity/MR peak velocity EROA RV (mL) = EROA x MR VTI Volumetric method \200 RV (mL) = Total stroke volume (SV) \200\223 Forward stroke volume \200 \200 \200 Reg urgitant fraction (RF%) Total SV = Mitral in \202 ow volume (in absence of signi \201 cant AR) MV in \202 ow vol ume = MV VTI (from PW Doppler) Forward SV = LVOT VTI x MV area ((cid:83)r2) x LVOT area = RV/Total stroke volume x 100 TTE/TEE IN MITRAL REGURGITATION (MR) 479 90 45 120 TG 0 AM P2 P3 P1 AM AM P2 P1 0 P2 P3 Figure 12.11 Assessment of the mitral valve by TEE. Reprinted with permission from Shanewis e JS, Cheung AT, Arouson S, et al. (1999). J Am Soc Echocardiogr 12(10):884 \200\223900. Table 12.4 Assessment of MR severity Parameter Mild Moderate Severe Jet size <20% LA area 20% \200\22340% LA area >40% LA area LA size Normal Normal/mildly dilated Dilated Vena contracta <0.3 cm 0.3 \200\2230.7 cm >0.7 cm Pulm. vein systolic \202 ow Normal Normal/ blunted Reversal <0.2 cm2 0.2 \200\2230.4 cm2 >0.4 cm2 Regurgitant ori \201 ce area Regurgitant volume <30 mL 30 \200\22360 mL >60 mL Regurgitant fraction <30% 30% \200\22350% >50% CHAPTER 12 Stress testing and cardiac imaging 480 Mitral valve prolapse The mitral valve annulus is a nonplanar, saddle-shaped structure. Mit ral valve prolapse (MVP) due to myxomatous change is diagnosed when the mitral valve lea \202 ets move beyond the \200\234high points \200\235 of the mitral annular plane during s ystole in the long axis view. The A4C or transverse plane 0 view images the \200\234low points \200\235 of the annulus (the distance between low and high points averages 1.4 cm). Thus, to avoid overdiagnosis of MVP, the criteria for diagnosis are as follows. Diagnosis Classical MVP \200 Greater than 2 mm displacement of mitral lea \202 et beyond the mitral annular plane in PL AX view Mitral valve thickness >5 mm Nonclassical MVP \200 The prolapsing lea \202 ets are not thickened (<5 mm) and are unaffected by myxomatous deg eneration. Such patients are not at increased risk of complications such as severe MR, infe ctive endocarditis, and sudden death, compared to those with the classical form of MVP. MVP causes eccentric mitral regurgitation \200 \200 Posterior lea \202 et prolapse produces an anteriorly directed jet. Anterior lea \202 et prolapse produces a posteriorly directed jet. Note that when the MR jet hugs the wall of the left atrium (coanda), the reported severity should be upgraded. The left and right pulmonary veins should be sampled with pulse wave Do ppler imaging to check for systolic \202 ow reversal, suggestive of severe regurgitation. Perioperative assessment during MV repair Optimize loading conditions \200 Ensure that the patient is fully off bypass with a systolic blood pressure of >120 mmHg bef ore assessing the results of mitral valve repair. Give volume or vasoconstrictors as needed to optimize hemodynamics. Assess lea \202 et coaptation and residual regurgitation with c olor Doppler. If there are persistent abnormalities of coaptation with signi \201 cant MR, surgical revision may be indicated. Assess left ventricular out \202 ow tract (LVOT) \200 LVOT obstruction may occur following mitral valve repair, especially if a rigid annuloplast y ring is used, but is uncommon (1% \200\2232%). Obstruction is exacerbated by hypovolemia, and the LVOT gradient should be measured after volume resuscitation. If LVOT obstruction p ersists, the annuloplasty ring may have to be removed. MITRAL VALVE PROLAPSE 481 TEE for MV repair \200 Determination of the prolapsing mitral valve segments should be performed to assist in surg ical planning. Two-thirds of cases of MVP involve the middle scallop (P2 segment) of the po sterior lea \202 et, and most of these cases can be successfully repaired. Ruptured chorda e and \202 ail mitral valve lea \202 ets should be noted. The mitral annulus diameter is also measured (upper limit normal is 35 mm) and presence of annular calci \201 cation not ed. \200 Indications for revision surgery after MV repair \200 \200 \200 \200 Grade 2+ (moderate) MR Persistent LVOT obstruction Mitral stenosis (mean gradient Lea \202 et perforation (cid:116)6 mmHg, MVA <1.5 cm2) CHAPTER 12 Stress testing and cardiac imaging 482 TEE in chronic ischemic MR Mitral valve structure is usually normal and the MR is functiona l. Remodeling of the LV causes apical displacement of the papillary mus- cle and tethering of the mitral valve lea \202 ets, leading to incomplete valve closure. The zone of coaptation is displaced toward the apex and systolic tenting of the mitral valve is seen. LV remodeling and dilation appears to be necessary for severe MR to develop. Isolated segme ntal wall motion abnormalities without LV dilata- tion are not generally associated with se vere MR. Annular dilatation will exacerbate incomplete lea \202 et coaptation. In the presence of an inferior or posterior infarct, the posterobasal wall of the LV may be come akinetic or aneurysmal. This can exert asymmetri- cal traction on the chordae, resulti ng in tethering of the posterior lea \202 et and an eccentric anteriorly directed jet of M R. Key views \200 Restriction of lea \202 et, systolic tenting of MV (0 ME four chamber, 45 ME mitral co mmissural, 90 ME two chamber, 120 ME LAX) Annulus size (120 ME LAX) LV assessment esp ecially the posterobasal wall (90 ME two chamber, 0 TG mid SAX) \200 TTE/TEE for mitral stenosis Determine the mitral valve area using the pressure half-time (P HT) method by measuring the deceleration slope of mitral in \202 ow E-wave velocity (see A ssessment of LV Diastolic Function, p. 464, and Fig. 12.8). PHT is the time interval for the maximal pressure gradient (calculated as max, where Vmax i s the peak E-wave velocity) to decrease to half its level. 4V2 PHT can also be calculated as 0.29 x DT. Valve area (cm2) = PHT/220 TEE can also be used in the assessment of suitability for percutaneous mitral balloon valvu loplasty (PMBV). Contraindications to PMBV \200 LA or LAA thrombus \200 Greater than grade 2 MR Mitral valve anatomy 1. Loss of mobility 2. Thickening 3. Calci \201 cation 4. Subvalvular thickening Assign a score of 0 \200\2234 for each \201 nding and take the sum. A score <8 pre- dicts a favorable outcome following PMBV. TEE FOR PROSTHETIC VALVE DYSFUNCTION 483 TEE for prosthetic valve dysfunction TEE is a valuable method for assessing prosthetic valv e function and their complications: \200 \200 \200 \200 \200 Paravalvular leak Intravalvular leak from degeneration of tissue valve Prosthetic valve obs truction from pannus or thrombus Endocarditis, including valve dehiscence and abscess forma tion Patient \200\223prosthesis mismatch CHAPTER 12 Stress testing and cardiac imaging 484 TEE assessment of mitral valve prosthesis TEE is especially sensitive in detecting mitral r egurgitation in association with prosthetic valves, because the left atrium is imaged in th e foreground and is thus devoid of the artifacts generated by mechanical prostheses. Paravalvular regurgitation The sewing ring of the mechanical prosthesis appears as a bright ring attached to the mitral annulus. If a signi \201 cant circumference of the sewing rin g separates from the annulus (e.g., from endocarditis), a rocking motion of the valve occur s and is characteristic of valve dehiscence. Key views The mitral valve sewing ring should be identi \201 ed and interrogated with colo r \202 ow and continuous wave Doppler. \200 \200 \200 0 ME four chamber 90 ME two chamber 120 ME LAX views of the mitral valve The motion of the prosthetic valve mechanism (e.g., tilting disc) should be assessed to ens ure the disks are moving freely in 120 ME LAX view. Paravalvular regurgitation is abnormal and may be seen early after valve implantation due t o breakdown of the sutures attaching the valve ring to the annulus either from technical fa ilure or infective endocardi- tis. Paravalvular leaks are more likely in the presence of a calci \201 ed mitral annulus. Intravalvular regurgitation Mechanical prosthetic valves typically exhibit a small volume o f regurgita- tion during valve closure. These \200\234closing jets \200\235 or \200\234cl osing volumes \200\235 are a normal feature inherent in the design of mechanical prostheses and may prevent thrombosis by maintaining continuous blood \202 ow across the valve surf ace. In general, they can be easily distinguished from pathological regurgitation. Causes for abnormal intraprosthetic leak include pannus or thrombus preventing the occluder or disks from functioning properly. Features of normal closing jets \200 \200 \200 Short jets <3 cm length Narrow base <5 mm Early systolic leak Bioprosthetic mitral prosthesis The prosthetic valve should be assessed for the following: \200 \200 \200 \200 Prolapse or \202 ail lea \202 ets Thickened cusps (>3 mm \200\224higher risk of dysfunct ion) Regurgitation (intravalvular and paravalvular) Stenosis/obstruction TEE ASSESSMENT OF MITRAL VALVE PROSTHESIS 485 Prosthetic mitral valve obstruction This may be due to thrombus or pannus formation. Echoca rdiographic \201 ndings include the following: \200 \200 Limited movement of the occluder or disk. High peak transvalvular velocity (>2.5 m/sec) or a prolonged pressure half-time (>200 ms) (see Table 12.5). Table 12.5 Upper limit of pressure half time (ms) for commonly used valves Valve type Max t1/2 (ms) Starr \200\223Edwards 170 St Jude 131 CarboMedics 117 Carpentier \200\223Edwards 171 Native valve 60 CHAPTER 12 Stress testing and cardiac imaging 486 Echocardiography in aortic regurgitation Both TTE and TEE are invaluable in determining the etiology of aortic regurgitation: \200 \200 \200 \200 \200 Aortic root dilation Ascending aortic dissection causing cusp prolapse Vegetations causing cusp perforation or \202 ail Congenital abnormalities (i.e., bicuspid valve) Acquired abn ormalities (i.e., rheumatic heart disease) Color Doppler is used to identify the origin and direction of the regur- gitant jet, either central or eccentric. Occasionally, the regurgitant jet may impinge on the anterior mitral lea \202 et, limiting MV opening in diastole. M-mode can be used to evaluate timing of valve opening and closure and, with color Doppler, measure the regurgitant jet width. The severity of aortic regurgitation should be determined in all cases. These \201 ndings suggest severe regurgitation: Jet diameter/LVOT diameter >65% Vena contracta (diameter of the regurgitant jet at its narrowest downstream of the ori \201 ce) width >0.6 cm Pressure half-time <200 ms Systolic \202 ow reversal in the descending aorta LV dilation (especia lly if chronic) Early diastolic mitral valve closure (best seen on M-mode) \200 \200 \200 \200 Key TTE views \200 PLAX, PSAX at aortic valve level, A5C Key TEE views \200 \200 \200 \200 30 \200\22345 ME AV SAX 120 ME AV LAX 0 deep TG LAX 120 TG LA TEE FOR AORTIC VALVE PROSTHESIS 487 TEE for aortic valve prosthesis Given the orientation of the aortic valve, the sewing ring will obstruct the view of the valve ori \201 ce for mechanical and stented tissue prosthes es. Thus assessment of aortic paravalvular leak on 2-D imaging is limited com- pared to mit ral valve assessment. Continuous wave interrogation is not possible because the LVOT is orientated perpendicular to the ultrasound beam, when the aortic valve is assessed from the standard mid-esophageal views. A combined TTE and TEE approach is required, because TTE is ideally suited for Doppler inte rrogation of the aortic valve given the parallel align- ment of the ultrasound beam with ao rtic valve blood \202 ow in the apical 5-chamber view. Deep transgastric view This view allows imaging of the aortic valve in the foreground and p roper alignment of the Doppler signal from the aortic valve (0 deep TG LAX and 120 TG L AX views). This view is useful to assess the following: \200 \200 \200 \200 Movement of the aortic prosthetic valve mechanism Color \202 ow Doppler interrogation for aortic regurgitation Continuous wave assessment of aortic regurgitation Continuous wave me asurement aortic valve gradient The use of the deep transgastric TEE view is especially useful for assess- ment of aortic p rosthetic valve function when a mechanical mitral prosthe- sis is also present (see Box 12. 7). This is because acoustic shadowing from the mitral valve obscures the LVOT in all mid-e sophageal TEE views of the aortic valve. However, this view is not obtainable in all patien ts. Regurgitation is most commonly intravalvular in bioprosthetic valves. The following may be visible on TEE: \200 \200 \200 \200 Cusp thickening (>3 mm predicts risk of valve failure) Cusp tear Cusp prolapse or \202 ai l Valve dehiscence Mechanical aortic valves may normally exhibit a mild degree of early diastolic regurgitatio n, similar to that described above for mechanical mitral valves. Paravalvular regurgitation is usually abnormal and suggests valve dehiscence or technical failure. Key views The aortic valve prosthesis is assessed in the following: \200 \200 \200 \200 30 \200\22345 ME AV SAX 120 ME AV LAX 0 deep TG LAX 120 TG LAX CHAPTER 12 Stress testing and cardiac imaging 488 Box 12.7 Echocardiographic assessment of prosthetic aortic valves Normal mean transvalvular gradient \200 \200 \200 \200 \200 St Jude Medical Medtronic Hall Bioprosthetic valve 14 7 mmHg 14 3 mmHg 13 6 mmHg Signi \201 cant stenosis or obstruction likely \200 \200 \200 \200 Peak velocity of >4 m/sec or mean velocity of 3 m/sec Valve area by continuity equation <1 cm Mean gradient >26 mmHg Dimensionless index <0.25 2 Stentless aortic valves \200 Freestyle or Toronto valve or aortic homografts do not have the disadvantage of a sewing ri ng casting an acoustic shadow on the aortic valve ori \201 ce and TEE gives excellent view s of valve cusps. These valves may be indistinguishable from native valves on echocardiogra m. INTRAOPERATIVE TEE 489 Intraoperative TEE Indications AHA Class I indications \200 \200 Valve repair, congenital heart surgery, HOCM surgery Hemodynamic compromise where LV functi on is unknown or has not responded to therapy Complex endocarditis surgery where perivalvul ar extension is suspected Complex valve replacement, such as homograft valve replacement wi th coronary reimplantation Ascending aortic dissection with aortic valve involvement Perica rdial window surgery in posterior or loculated effusions Intracardiac device placement (i.e ., LVAD) \200 \200 AHA Class II indications \200 ischemia, Surgical procedures in patients at increased risk of myocardial myocardial infarction, or h emodynamic disturbances Valve replacement Cardiac tumor resection, cardiac aneurysm repair, pericardial surgery During and after off-pump coronary bypass surgery for the evaluation o f regional wall motion (see Box 12.8) Evaluation Ascending aortic dissection without aortic valve involvement Cardiac trauma Intracardiac thrombectomy or pulmonary embolectomy Evalua ting anastomotic sites following heart and/or lung transplantation Detect air emboli during cardiotomy \200 \200 \200 \200 \200 \200 \200 of myocardial perfusion, coronary anatomy, or graft patency Key views to assess LV function (see Fig. 12.12) \200 \200 \200 \200 0 ME four chamber 90 ME two chamber 120 ME LAX 0 TG mid SAX Box 12.8 TEE in intraoperative and perioperative period (in ICU) to assess hemodynamic inst ability \200 Coronary artery bypass graft failure: distributions to assess for regional wall motion abno rmalities. The transgastric view shows all three coronary distributions in one view. Hypovo lemia: obliteration Pericardial effusion/hemopericardium Severe LV or RV failure Unsuspecte d severe mitral regurgitation Unsuspected aortic dissection examine LV in all three coronary reduced LV cavity size and end systolic cavity \200 \200 \200 CHAPTER 12 Stress testing and cardiac imaging 490 90 Two chamber 0 Four chamber 120 Long axis 0 Transgastric RCA LAD CX Figure 12.12 Assessment of LV function by TEE. Reprinted with permission from Shanewise JS, Cheung AT, Arouson S, et al. (1999). J Am Soc Echocardiogr 12(10):884 \200\223900. ECHOCARDIOGRAPHIC ASSESSMENT OF CARDIAC MASSES 491 Echocardiographic assessment of cardiac masses Normal anatomy that should not be mistaken f or pathology: \200 \200 \200 \200 \200 \200 Chiari network Eustachian valve near the inferior vena cava in the right atrium Trabeculati ons/pectinate muscles in the left atrial appendage Ridge separating left pulmonary vein and left atrial appendage Highly trabeculated left ventricle as seen in noncompaction False co rds in left ventricle (anomalous mitral cordal apparatus not connected to valve lea \202 e ts) within the right atrium Myxomas are the most common primary cardiac tumor and speci \201 c fea- tures can be delin eated on echocardiogram: \200 They are attached by a stalk to the interatrial septum near the fossa ovalis in 90% cases. 75% are in the LA. They may have speckled, cystic appearance with frond-like projections. T hey may be multiple. If they occur elsewhere they may be mistaken for thrombus (can be homo geneous in appearance) or other tumors. They may cause valve obstruction. \200 \200 Fibroelastomas are benign tumors attached to cardiac valves. They have a frond-like appeara nce and may mimic vegetations or myxomas. Primary malignant cardiac tumors and cardiac metastases can in \201 ltrate the epicardium, myocardium, and endocardium, or they present as an int- racavity mass. Pericardial involve ment in malignant disease is often associ- ated with a pericardial effusion. Administration of ultrasound contrast can aid in the identi \201 cation of intracardiac ma sses. Vascular masses, such as certain tumors, will take up contrast, whereas nonvascular s tructures such as thrombus or vegetation are less likely to enhance with contrast. CHAPTER 12 Stress testing and cardiac imaging 492 SPECT perfusion imaging Single photon emission computed tomography (SPECT) is an important and well-validated tool used to diagnose obstructive epicardial coronary disease and provid e important prognostic data in patients with known coronary disease. It is the standard tes t to evaluate myocardial perfusion in current practice. SPECT involves the administration of radiolabeled perfusion tracers at rest and during exer cise or pharmacological stress. The radionuclides decay and emit gamma photons, which are d etected by a gamma camera. Myocardial tracer uptake is proportional to regional blood blow, hence allowing one to assess for heterogeneity in perfusion as occurs in patients with phy siologically signi \201 cant coronary stenoses. In order for SPECT imaging to accurately d iagnose coronary disease, the stressor, either exer- cise or pharmacologic, must induce a \202 ow disparity between regions sup- plied by normal and stenotic arteries. The sensitivity and speci \201 city are 88% and 77%, respectively, for the diagnosis of coronary disease in intermediate-risk patients. The two most commonly used radioisotopes in nuclear cardiology are thallium-201 and technet ium-99m (sestamibi and tetrofosmin) (see Table 12.6). Technetium-99m labeled compounds are preferred because the higher energy gamma photons improve image resolution (less scattering and soft tissue attenuation) and there is little to no redistribution, which makes acquisi tion more practical and allows for reimaging, if necessary. The major disadvantage with technetium-99m is hepatic and gastro- intestinal uptake. The primary components of a gamma camera are the following: Lead collimator, which allows o nly photons traveling at 90 to pass Sodium iodide crystal, converting energy of incoming photons into light Photomultiplier tubes, which amplify and convert the light signal into e lectrical current \200 \200 Table 12.6 Radioisotopes used in nuclear cardiology Thallium-201 Technetium-99m Production Cyclotron Mo-99m generator Half-life 73 hr 6 hr Extraction Fraction 85% 65% Uptake mechanism Na-K ATPase Mitochondrial Gamma-ray photopeak 70 \200\22380 keV 140 keV Redistribution Yes Minimal SPECT PERFUSION IMAGING 493 The emission data are reconstructed into tomographic slices by a com- puter for analysis. S tandard image orientation includes short axis, vertical, and horizontal long axis views. Th e standard 16- or 17-segment nomencla- ture as described earlier for echocardiography is us ed for interpretation of perfusion defects. Several computer software programs are commercially available for quanti \201 cation of pe rfusion defects by normalizing perfusion throughout the myocardium and comparing it to a \200\234normal \200\235 reference database. Gated SPECT The acquisition of emission data during SPECT is synced to the cardiac cycle vi a continuous ECG monitoring. The R-R interval is divided into a number of frames where the acquired counts at each position are stored. This provides an accurate assessment of LV vol ume, global and regional cardiac function. Very irregular rhythms, such as atrial \201 brillation, preclude accurate ECG-gating. End ocardial borders are de \201 ned and end-diastolic (EDV) and end-systolic (ESV) volumes ar e determined. Ejection fraction (EF) = (EDV \210\222 ESV/EDV) x 100. Interpretation of myocardial perfusion Thorough and accurate interpretation requires review of the planar and rotating images, tomographic slices, and ECG-gated data as well as the c linical history and indication for the test. Defect severity and extent should be determine d as mild, moderate, or severe and small, medium, or large, respectively. The use of softwa re for defect quanti \201 cation can be helpful in this regard, but should not be solely r elied upon. It is also important to remember that SPECT measures relative perfusion and not absolute blood \202 ow. During stress, blood \202 ow in myocardial regions distal to a physiologically signi \201 cant stenosis (i.e., >50% \200\22370%) is reduced, leading to decreased radi- otracer activity and count density. This is what is measured with SPECT. Interpretation Fixed defect \200 \200 \200 Similar decrease in count density at rest and during stress Represents infarct or scar Shou ld see associated regional wall motion abnormality on gated movies Reversible defect \200 \200 \200 Decreased count density during stress with normalization at rest Represents ischemia (see F ig. 12.13) May or may not see regional wall motion abnormalities CHAPTER 12 Stress testing and cardiac imaging 494 Figure 12.13 SPECT myocardial perfusion images during stress (top row) and at rest (bottom row) in the standard short axis (top), vertical long axis (middle), and horizontal long axi s (bottom) views. In this example, there is inferior and inferolateral wall ischemia. Partially reversible defect \200 Decreased count density during stress with incomplete normalization at rest Implies peri-in farct ischemia Artifacts \200 \200 Usually \201 xed, mild defects with normal regional function Due to photon attenuation/sc attering, patient motion, instrumentation problems Breast attenuation Diaphragmatic attenua tion \200 \200 Motion artifact eliminated with motion correction software Attenuation c orrection algorithms can improve identi \201 cation of artifacts and improve speci \201 c ity of SPECT interpretation \200 \200\224anterior, anterolateral defects \200\224inferior wall defects This can be reduced with prone imaging Left lateral supine/decibutus imaging can aid in ide nti \201 cation causes the \200\234hurricane sign \200\235 and can be reduced or SPECT PERFUSION IMAGING 495 Summed stress score (SSS) This is a semiquantitative method of interpreting defect severity and extent. Each segment is assigned a score of 0 to 5, ranging from normal to absent upta ke. The individual scores are added. The higher the SSS, the greater the annual cardiac eve nt rate (see Table 12.7). SPECT clinical applications Coronary artery disease Although exercise ECG is still the pref erred initial test in evaluating inter- mediate-risk patients with chest pain, exercise per fusion imaging is indi- cated (ACC/AHA Guidelines) in the following situations: \200 \200 \200 Pre-excitation/Wolf \200\223Parkinson \200\223White (WPW) Resting ST depression >1 mm (i.e. , LVH, digoxin effect) Prior revascularization Vasodilator stress perfusion imaging with adenosine or dipyridamole is recommended in patie nts with LBBB or ventricular pacemakers, as exer- cise SPECT often leads to false-positive septal defects. Patients who are unable to exercise should also undergo pharmacological (ei ther adenos- ine/dipyridamole or dobutamine) stress perfusion imaging (Table 12.8). Although exercise or vasodilator stress perfusion imaging is an AHA/ ACC Class IIB indicati on as the initial test in patients with a normal resting Table 12.7 Summed stress score Score Interpretation 0 \200\2233 Normal 4 \200\2238 Mild 9 \200\22313 Moderate >13 Severe Table 12.8 Indications for pharmacological stress agents Indication Preferred agent Inability to exercise Adenosine/dipyridamole Asthma/COPD Dobutamine High-grade AV block Dobutamine Caffeine/theophylline use Dobutamine LBBB Adenosine/dipyridamole Post-MI Adenosine/dipyridamole Speci \201 c A 2a receptor agonists are now available with fewer side effects. CHAPTER 12 Stress testing and cardiac imaging 496 ECG, this is an appropriate use according to the 2005 ACCF/ASNC Appropriateness Criteria. Other useful applications of SPECT perfusion imaging in patients with coronary disease include the following: \200 \200 \200 \200 Determine lesion severity prior to planned revascularization Assess the response to medical therapy Risk strati \201 cation post-MI Risk strati \201 cation prior to noncardiac surg ery Results of SPECT perfusion imaging provide important prognostic infor- mation in patients w ith coronary disease, in addition to other clinical vari- ables. The risk of future cardiac events is related to the extent and severity of perfusion defects. Viability testing \200 Thallium rest: 24-hour redistribution imaging. Normalization of perfusion on delayed imagin g following reinjection implies viability. Technetium-99m. Tracer uptake >50% of normal imp lies viability. Normal regional function on gated SPECT imaging also suggests viable myocar dium. \200 Acute chest pain \200 Normal rest myocardial perfusion during active chest pain excludes ischemia/infarction with a negative predictive value of 99%. Stress myocardial SPECT perfusion imaging is a valuabl e diagnostic modality in the evaluation of low- to intermediate-risk patients with chest pa in, a nondiagnostic ECG, and normal biomarkers in emergency department chest pain centers ( ACC/AHA Class I indication). High-risk \201 ndings on SPECT Findings with 3% \200\2235% risk of cardiac death or MI pe r year include the following: \200 Transient ischemic dilatation due to global subendocardial ischemia during stress. There is increased risk even if there are no perfusion defects. Large reversible anterior wall defe ct LV systolic dysfunction post-stress Defects in multiple coronary territories Ischemic EC G changes during vasodilator stress Increased lung tracer uptake (>0.5 for thallium-201) du e to increased pulmonary capillary wedge pressure \200 \200 \200 \200 Balanced ischemia Because SPECT imaging measures relative perfusion, a patient with multi- vessel coronary disease where perfusion is globaly reduced with stress may have a relativel y normal, though false-positive study. Ancillary data from the stress protocol (especially abnormal exercise ECG or hemodynamics) and gated SPECT images (i.e., global or regional LV dysfunction) should be carefully review ed for \201 ndings consistent with signi \201 cant coronary disease. PET SCANNING 497 PET scanning Positron emission tomography (PET) is a nuclear imaging technique that uses sh ort half-life radionuclides incorporated into radiopharmaceuticals allowing quantitative as sessment of various aspects of cardiac function in different regions of the heart: \200 \200 \200 Global and regional left ventricular function Myocardial blood \202 ow Myocardial metabol ism: glucose and fatty acid metabolism; myocardial oxygen consumption Pharmacology: innerva tion; myocardial ACE and angiotensin II receptors B-adrenergic and muscarinic receptors; sympathetic Clinical applications In current clinical practice, cardiac PET is used primarily for the a ssessment of myocardial viability and measuring myocardial perfusion in patients with equiv ocal SPECT imaging (i.e., obese patients) (see Fig. 12.14). Myocardial perfusion The radionuclides most commonly used in practice are Rb-82 and N-13 am monia. The advantage of these PET tracers over SPECT tracers is the higher energy of the re sulting photons (511 keV), which dramatically improves image resolution and test speci \201 city by decreasing soft tissue attenuation and scatter. The short half-life of these tracers, however, requires on-sight produc- tion and limits th e application with exercise stress. Interpretation of tomo- graphic PET imaging is similar to that described earlier for SPECT imaging. Identi \201 cation of myocardial viability A valuable clinical application of PET scanning is the determination of myo- cardial viability in patients with ischemic cardiomyopathy wh o may bene \201 t from surgical or percutaneous coronary revascularization. Studies have d emonstrated that PET imaging has high sensitivity for predicting recov- ery of contractile function after revascularization and have also provided major insights into the mechanisms underlying left ventricular dysfunction in patients with coronary artery disease. Perfusion is measured using either Rb-82 or N-13 as described above. Metabolism is assessed using 18- \202 uorine-labeled glucose (FDG), which is taken up by viable myocardial tissu e. A perfusion \200\223metabolism mismatch implies viable hibernating myocardium and predic ts functional recovery following revascularization. Research applications The large variety of compounds available for study using PET permits interro- gation of many facets of cardiac function, providing important in vivo mecha- nist ic information (see Box 12.9). These measurements also allow analysis of the mechanisms und erlying the bene \201 t of established and novel therapies. Examples include the following: Myocardial blood \202 ow and microvascular function: isch emic heart disease, hypertrophic cardiomyopathy, dilated cardiomyopathy, aortic stenosis, s yndrome X. CHAPTER 12 Stress testing and cardiac imaging 498 Myocardial metabolism and cardiac energetics: ischemic cardiomyopathy, dilated cardiomyopat hy. Cardiac autonomic function: hypertrophic cardiomyopathy, dilated cardiomyopathy, arryht hmogenic right ventricular dysplasia, autonomic neuropathy, long QT syndrome. Figure 12.14 Example of an uninterpretable SPECT perfusion study in an obese patient due to signi \201 cant attenuation, scattering, and poor spatial resolution (top). A Rb-82 PET s tudy on the same patient clearly demonstrates normal myocardial perfusion (bottom). PET SCANNING 499 Figure 12.14 (Cont \200\231d.). CHAPTER 12 Stress testing and cardiac imaging 500 Box 12.9 Comparison of PET with conventional SPECT imaging Advantages \200 Short half-life of radionuclides allows ef \201 cient same-day rest/stress protocols \200 \200 \200 Better spatial resolution Accurate attenuation correction, allowing absolut e quanti \201 cation of radiopharmaceutical concentration Can assess perfusion and metabol ism 1/2 is 75 seconds 1/2 is 10 minutes Rb-82 T N-13 T O-15 water T 1/2 is 2 minutes \200 Disadvantages \200 Expensive \200 Limited availability \200 Most tracers require cycl otron for production. Rb-82 is generator produced Dif \201 cult to perform with exercise s tress because of short half-life of tracers EQUILIBRIUM RADIONUCLIDE ANGIOGRAPHY (ERNA) 501