2 CHAPTER 1 Cardiac investigations Exercise ECG A commonly used test involving a treadmill, blood pressure (BP) meas- urement, and continuous electrocardiograph (ECG) monitoring. Overall sensitivity for coronary heart disease is around 68 % and speci \201 city is 77 % . This increases when considering prog nostically signi \201 cant disease, which has a sensitivity of 86 % . The test improves to have a predictive accuracy of > 90 % in intermediate- to high-risk patients (older men wit h ischaemic symptoms). The test is of least value in populations that are least likely to b e suffering from ischaemic heart disease; e.g. asymptomatic middle-aged women have a positi ve predictive value of <50 % . Indications \200 Diagnosis of ischaemic heart disease (IHD): intermediate- or high-probability IHD, vasospastic angina. Post-myocardial infarction (MI): pre-discharge (submaximal test in days 4 \200\2237 to assess prognosis, decide upon exercise program, and evaluate treatment) , late post-discharge (symptom-limited 3 \200\2236 weeks). Pre- and post-revascularization. \200 Evaluation of arrhythmias: optimizing rate-responsi ve pacemaker function, evaluation of known or suspected exercise-induced arrhythmias, and e valuation of treatment of above. Contraindications \200 Fever/acute viral illness. \200 Myocarditis/pericarditis. \200 Severe aortic stenosis. \200 Aortic dissection. \200 Uncontrolled hypertension. \200 Overt cardiac failure. \200 Unstable angina or acute phase of MI. \200 Signi \201 can t resting arrhythmia (e.g. uncontrolled atrial \201 brillation or complete heart block). Known severe left main stem (LMS) or LMS equivalent disease. \200 Physical disability. \200 ECG abnormality rendering interpretation of ST segment dif \201 cult (e.g. left bund le branch block (LBBB), left ventricular hyphetrophy (LVH) with strain or digoxin ECG chang es). When to stop \200 Target heart rate achieved (tests have better sensitivity and speci \201 city if the target heart rate is reached ( > 85 % of 220 minus age in years for men or 210 minus age in years for women). \200 Worsening angina or excessive breathlessness. \200 Dizziness. \200 Fatigue/patient requests to stop. \200 Atrial arrhythmia other th an ectopic beats. \200 Frequent ventricular ectopic beats or ventricular tachycardia (VT) . EXERCISE ECG 3 Worsening ST segment shift (elevation or depression) at least 2 mm depression but up to 5 mm depression. BP fall or failure to rise. \200 Exaggerated hypertensive response to exercise (systolic blood pressure (SBP) > 220 mmHg). New high-grade atrioventricular (AV) block or bundle branch block. Criteria for a positive test Normal Upsloping ST depression Planar ST depression Downsloping ST depression Planar or downsloping ST depression of at least 1 mm 80 ms after the J point (junction between the QRS and ST segment). ST elevation. * \200 Increase in QRS voltage (ischaemic left ventricular (LV) dilatation) . \200 Failure of BP to rise during exercise (ischaemic LV dysfunction). * \200 Ventric ular arrhythmias. * \200 Typical ischaemic symptoms during exercise. \200 Inability to increase heart rate. * Features that are indications for urgent angiography: Also ST depres sion at low workload (<<6 minutes Bruce) in multiple lead groups, persisting into recovery, > 2 mm, downsloping pattern. Causes of false-positive tests \200 Cardiomyopathies. \200 Hypertension. \200 LVOT (l eft ventricular out \202 ow tract) obstruction. \200 Mitral valve prolapse syndrome. \200 Hyperventilation. \200 Resting ECG abnormality (LBBB, pre-excitation, digoxin). \200 Electrolyte abnormalities (hypokalaemia). \200 Tricyclic antidepressants. \200 Sy ndrome X. \200 Coronary artery spasm. \200 Sympathetic overactivity. 4 CHAPTER 1 Cardiac investigations National Institute for Health and Clinical Excellence (NICE) guidance 2010 \200\224 chest pain of recent onset 1 Historically, exercise ECG testing has been the cornerstone of inves - tigation of patients presenting with stable anginal chest pain. However, sensitivity and speci \201 city are poor compared with other investigations. Recent UK guidelines discoura ged the use of exercise ECG in patients without known coronary artery disease. Instead, NICE recommended cardiac computed tomography (CT) for patients with low likelihood of signi \201 cant coronary artery disease, a func- tional test such as dobutamine or exe rcise echocardiography for those with intermediate likelihood, and invasive coronary angiog raphy for those with high likelihood. 1 National Institute for Health and Clinical Excellence (March 2010). Chest pain of recent onset , Y http://guidance.nice.org.uk/CG95. This page intentionally left blank 6 CHAPTER 1 Cardiac investigations Cardiac computed tomography In the past decade, major advances in CT technology have enable d cardiac CT to emerge as a non-invasive alternative to conventional invasive coro- nary an giography. Coronary artery calcium scoring Calci \201 ed coronary plaque represents approximately 20 % of the total coro- nary artery plaque burden. Therefore, the degree of coronary calci \201 cation can be used as a surrogate for coronary artery atherosclerosis. A calcium score is obtained through a low-radiation unenhanced (i.e. no iodinated contrast) scan. The degr ee of calci \201 cation in each coronary vessel is then expressed as a \201 gure and sum med to give the total coronary artery calcium score, commonly using the Agatston scale. A s core of 0 corre- lates with a low risk of coronary artery disease, whereas a score of > 400 correlates with high risk of signi \201 cant atherosclerotic plaque burden. Clinical studies have shown that the calcium score provides addi- tional information for ca rdiovascular risk strati \201 cation above and beyond traditional factors such as age, sex , hypertension, family history, hyperlip- idaemia, and diabetes. CT coronary angiography CT coronary angiography is performed by injecting iodinated contras t into the peripheral veins. When the level of contrast in the aorta reaches a speci \201 ed level, the scan is launched and images are acquired. The images are then analyzed using computer software, which allows manipulation in two dimensions and three-dimensional (3D) r econstruction of the cor- onary arteries and cardiac chambers, also known as \200\230volum e rendering \200\231. Technical considerations Temporal versus spatial resolution The principal challenge to imag ing the coronary arteries using CT is to achieve high temporal resolution. Temporal resolut ion is de \201 ned as the time taken to acquire an image. As the beating heart moves, it n eeds to be \200\230frozen \200\231 during image acquisition. Motion is greatest during sys tole, whereas the heart is relatively still during diastole. Images acquired during diastol e are therefore most likely to be motion free, allowing accurate interpretation and diagnos is. A CT scanner must therefore be capable of acquiring images rapidly during the short dia stolic phase when the heart is motionless. Imaging small structures such as coronary arteries requires high spatial resolution. Spatia l resolution is de \201 ned as the narrowest distance between two objects that can be dist inguished by the detector. CT spatial resolution is determined by the voxel size (i.e. 3D p ixel). Heart-rate control The duration of systole is relative \201 xed at different heart rates, but the duration of diastole varies greatly. A slow heart rate (i.e. <65 bpm (beats per mi nute)) is preferable, to ensure motion-free imaging of the coronary arteries. CARDIAC COMPUTED TOMOGRAPHY 7 Oral beta-blockade given 1 \200\2232 h before the scan is widely used in the United States. Alternatively, intravenous beta-blockade with serial boluses of metoprolol administered to the patient on the CT gantry has been shown to be a safe, fast, and effective method of ac hieving optimal heart- rate control. Premedication with two days of oral beta-blockers (to be taken the day before and on the day of the scan) is also effective and minimizes the nee d for administration of intravenous metoprolol at the time of the scan. Calcium-channel blo ckers are a practical alternative in patients with a contraindication to beta-blockers Strategies for reducing radiation effective dose A number of strategies have emerged to red uce the effective dose of ionizing radiation per scan: \200 reduction of \201 eld of vi ew ( \200\230carina to base of heart \200\231) \200 tube voltage reduction in non-obese p atients (from 120 kV down to 100 kV) electrocardiographically controlled tube current modulation (current is reduced in systole and increased in diastole) electrocardiographically controlled prospective gating (tube is only switched on at speci \201 c phase of the cardiac cycle, usually mid-diastole or 75 % of th e R \200\223R interval). By combining these techniques, the effective dose for CT coronary angi- ography is now appr oaching 1 mSv (milli-Sievert). Sensitivity and speci \201 city Modern 64-slice and above CT scanners have been shown to p rovide excellent sensitivity (95 % ) and speci \201 city (83 % ). As a consequence, CT cor onary angiography has a very high negative predictive value (upwards of 95 % ). The princip al clinical application of CT coronary angiography is to rule out signi \201 cant coronary artery disease in patients with low to inter- mediate cardiovascular risk. 8 CHAPTER 1 Cardiac investigations Clinical applications of cardiac CT Comparison with traditional invasive coronary angiograp hy Traditional cardiac catheterization remains the gold standard for diag- nosing coronary artery disease. It has excellent temporal and spatial resolution and allows for interventio n if signi \201 cant disease is identi \201 ed. However, it is invasive and exposes the p atient to potential vascular com- plications, including MI, stroke, and vascular-access com plications. With new 256- or 320-detector CT, the extended coverage and scan time of less than 0.5 s al lows the entire heart to be imaged in a single heartbeat. Compared with conventional angiog raphy, CT has a lower spatial resolution (0.4 \200\2230.6 mm vs. 0.2 mm) and temporal resol ution (60 \200\223220 ms vs. 8 ms). Comparison with functional tests Historically, non-invasive functional tests (e.g. exercise tolerance testing, stress echocardiography, nuclear imaging, positron emission tomography (PET), perfusion magnetic resonance imaging (MRI)) have been used to select those patients deemed at intermediate risk who are likely to require invasive coronary angiography and int ervention. However, many of these tests are labor intensive and not all are readily availab le in every hospital. In addition, the false-positive rate is substantial, leading to patie nts with normal coronary arteries undergoing unnecessary cardiac catheterizations. Indications for cardiac CT The principal role of cardiac CT in current clinical practice is to rule out or detect coronary artery disease. CT is particularly good at assessing anomal ous coronary arteries and coronary artery bypass graft patency. Additional indications These include: \200 screening for coronary artery disease (i.e. ca lcium scoring). \200 detection of coronary artery disease in patients at low to intermedi ate risk. assessment of coronary artery bypass grafts (CABGs). \200 assessment of anomalous coronar y arteries. \200 pulmonary vein mapping prior to electrophysiological studies/ablations. \200 assessment of congenital heart disease anatomy. \200 evaluation of intracoronary m asses. \200 evaluation of suspected aortic dissection. \200 assessment of coronary sten t patency. \200 assessment of plaque morphology \200\224soft/calci \201 ed/mixed. CLINICAL APPLICATIONS OF CARDIAC CT 9 Advantages and disadvantages of cardiac CT Advantages \200 Fast. \200 Non-invasive (avo ids vascular risks of invasive angiography). \200 Inexpensive. \200 Identi \201 es CAB G graft origin/target/patency. \200 Plaque characterization \200\224i.e. ability to asses s not just the vessel lumen but also the vessel wall (soft/calci \201 ed/mixed morphology). Disadvantages \200 Ionizing radiation. \200 Dif \201 cult to interpret degree of steno sis if there is signi \201 cant coronary calci \201 cation. Dif \201 cult to see into stents and assess patency. \200 Dif \201 cult to interpret de gree of stenosis at CABG graft anastamosis. \200 Requires regular and slow heart rates. Future applications of cardiac CT CT perfusion imaging New CT techniques are now enabling i ntegration of anatomical assess- ment of the coronary arteries with functional information. Intravenous contrast is injected and the myocardium is scanned repeatedly over a period of time. The \201 rst pass of contrast through a region of interest is tracked to produce t issue-speci \201 c time \200\223density curves, which are then interpreted to determine bl ood \202 ow within the tissue. However, using current CT technology, the predominant barr ier to use of CT perfusion in routine clinical practice is high radiation doses. Multimodality hybrid imaging An alternative to CT perfusion imaging is integration of the a natomical information from CT angiography with the functional information from stress echoc ardiography, single photon emission computed tomog- raphy (SPECT), PET, or perfusion MRI. C linical studies have shown that fusing functional and anatomical information increases the sensitivity and speci \201 city when compared with each modality in isolation. 10 CHAPTER 1 Cardiac investigations Transthoracic echocardiography Introduction Despite dramatic advances in new cardiac imagin g technologies, echocar- diography remains the most important diagnostic imaging tool in cl inical practice. Since its development by Edler and Herz almost \201 ve decades ago, and routine clinical implementation a decade later, echocardiography has developed into an intu itive, comprehensible, and practical method to rapidly and repeatedly evaluate cardiac morp hology and function. Competent interpretation of the echocardiographic examination \201 r st requires an understanding of the physical principles underlying the various technique mo dalities. Ultrasound physics All forms of ultrasonic imaging are based on generation of high-frequenc y ( > 1 MHz) acoustic pressure waves from a transducer comprising one or more piezoelectric crystals. Current is passed across the latter, leading to material deformation and wave tr ansmission. The piezoelectric element also serves as a receiver, and waves returning from i nsoni \201 ed objects (e.g. walls, valves) deform the crystal(s), which, in turn, generate a current that can be sampled over time. Because the velocity of sound is constant, object location (spatial resolution) can be determined based on the timing of the returning signa l. The amplitude of the returning signal is based on the angle of incidence (surfaces perpe ndicular to the ultrasound beam are stronger re \202 ectors) and the interface of acoustic impedances (greater differences such as occur in the left ventricle at the tissue \200\223 blood interface lead to greater re \202 ectivity). Returning ultrasound information is pro cessed for maximum image integrity and then mapped to pixels for display and storage. Whil e many institutions continue to store images on videotape, image degradation necessarily in curred by this medium, as well as ease-of-use issues, have led to increased implementation of digital storage, primarily on dedicated \201 le servers. M-mode This was the \201 rst available form of echocardiography and, while still availabl e on modern machines, has largely disappeared from routine use in modern laboratories. M- o r \200\230motion \200\231-mode images depict a single line of ultrasound over time (Fig. 1 .1 ). The information is graphic in nature and requires considerable experience for accurat e interpretation. Its advantage lies in its high sampling rate ( > 1 kHz) and resultant abi lity to depict rapidly moving structures that may be of interest from a didactic or physiol ogical perspective. TRANSTHORACIC ECHOCARDIOGRAPHY 11 Chest wall RV AO AV LV LA MV Chest wall RV outflow RV VS AO AV LV MV LA PW e ANT f POST 2. Mitral stenosis 1. Normal mitral valve OPEN Reduced e \200\223f slope CLOSED CLOSED 3. Aortic regurgitation 4. (a) Systolic anterior leaflet movement (SAM) in HOCM Fluttering of anterior leaflet (b) Mitral valve prolapse (late systole) Fig. 1.1 Normal M-mode echocardiogram (AV = aortic valve; HOCM = hypertrophic obstructive c ardiomyopathy; VS = interventricular septum; LA = left atrium; LV = left ventricle; MV = mi tral valve; PW = posterior wall of LV; RV = right ventricle). After R Hall. Med Int 17 : 77 4. Reprinted with permission from Longmore M, Wilkinson I, Davidson E, Foulkes A, and Ma \201 A (2010). Oxford Handbook of Clinical Medicine . 8th ed. Oxford: Oxford University Pre ss. 12 CHAPTER 1 Cardiac investigations Two-dimensional (2D) or sector scanning (Fig. 1.2) When an ultrasound beam is swept across a chosen cardiac window, rapid sequential sampling can be performed, leading to display of multiple \200\230scan lines \200\231 of information and a sector image created nearly inst antan- eously. Since a \201 nite number of scan lines is possible, interpolation of data between lines is performed and an image slice or sector (hence the term \200\230sector sca nning \200\231) is stored in digital form. Through reiterative acquisition over a cardiac c ycle, a movie composed of sequentially acquired sectors is created, demonstrating structura l motion, which can then be displayed on a monitor. Beam sweeping can be performed by mecha nical rotation of one or more crystals, or through the use of programmed \201 ring of a b ank of crystals (phased array). Sampling rates were previously dictated and limited by vide otape standards (e.g. PAL (phase alternating lines) or NTSC (National Television Standard C ommittee)) but, with digital capabilities appearing in some form on virtually all machines and replacing outdated tape technology, higher frame rates are possible. The availability of harmonic tissue imaging has substantially improved image resolution by eliminating artefactual \200\230noise \200\231. Low-level signals emanating from tissue an d comprising the \201 rst harmonic of the transmitted ultrasound are selectively sampled. In this way, extraneous re \202 ections such as reverberations are \201 ltered out, lea ving a cleaner image. Three-dimensional (3D) imaging (Fig. 1.3) While two-dimensional (2D) ECHO presents user-sel ected sector or tomographic information, 3D ECHO has the potential to provide a comprehensi ve evaluation of cardiac anatomy similar to that of more quantitatively mature technologies such as MRI or CT. Three-dimensional ECHO can be performed using the \200\230freehand \200\231 approach, in which mul- tiple 2D sectors are acquired from a probe that is positio nally mapped using a \200\230spark gap \200\231 or magnetic tracking system. Both image an d position data are stored for post-hoc 3D rendering. The development of rotational and, mo re recently, matrix array probes, coupled to powerful computer technology, has made post-ho c, 3D chamber reconstruction a reality, with accurate volumetric assessment. Most recently, real-time rendering of spatially limited cardiac segments has been made available. There a re considerable limitations, and it is currently available in limited form from various man ufacturers. TRANSTHORACIC ECHOCARDIOGRAPHY 13 Long axis Coronal Sagittal Transverse Short axis Right Left Fig. 1.2 The so-called \200\230anatomical position \200\231. The subject is upright and fa cing the observer. Any structure within the body can be described within the references of the three orthogonal planes \200\224 two in the long axis and the third in the short axis. Reprinted with permission from Anderson RH, Ho SY, Brecker SJ (2001). Anatomic basis of cr oss-sectional echocardiography. Heart 85 : 716 \200\22320. Long axis of body Long axis of heart 1/3 2/3 Fig. 1.3 The heart lies in the mediastinum with its own long axis tilted relative to the lo ng axis of the body. Appreciation of this discrepancy is important in the setting of cross- sectional echocardiography. Reprinted with permission from Anderson RH, Ho SY, Brecker SJ ( 2001). Anatomic basis of cross-sectional echocardiography. Heart 85 : 716 \200\22320. 14 CHAPTER 1 Cardiac investigations Transthoracic Doppler imaging Quanti \201 cation of object motion within the heart is perf ormed using Doppler-based technologies. In brief, the same equipment described earlier prop agates ultrasound, which is aimed at moving red blood cells or tissue. \200 The frequenci es of returning ultrasound are shifted upwards and downwards by cells traveling towards and away from the transducer, respectively. The frequency shift is proportional to an object \200\231s velocity. \200 The signal inte nsity is dependent on the number of cells moving at a particular velocity. Velocity information is depicted graphically as a spectral pattern over time (similar to th e M-mode display) or mapped to pixels as color overlaying the 2D or 3D image. The ECHO beam must be as parallel as possible to the target, with off-axis angulation by > 30 leading to signi \201 cant underestimation of velocities. Doppler is restricted in its ability to sample high velocities by the Nyquist limit , which is dependent on the sampling rate (the lower the frequency, the higher the evaluable veloc ity) and object depth (the deeper the object, the lower the sampling rate). When the freque ncy shift of moving objects (i.e. velocity) exceeds the Nyquist limit, aliasing occurs, pre cluding velocity assessment. Pulsed Doppler permits accurate sampling of blood velocities averaged within a limited regi on of interest or \200\230sample volume \200\231. Transducer elements serve as both transm itters and receivers, permitting selective sampling of re \202 ected ultrasound and accura te range or spatial information. Pulsed Doppler spectral displays portray velocity vectors over time: \200 laminar \202 ow is found within normal vessels and chambers and characterized by a gradual increase in \202 ow velocities from the vessel wall to the ves sel center. laminar \202 ow is characterized by a narrow spectral trace representing a relatively discrete population of blood velocities. turbulent \202 ow occurs across stenotic or regurgitant ori \201 ces (valves, shunts, etc.), where high-pressure gradients lead to high red-cell kinetic energy and disor dered, high-velocity motion. turbulent \202 ow is graphically portrayed as spectral broadening. \200 aliasing often occurs with high-velocity jets, leading to \200\230wraparound \200\231 or the \200\230paint brush sign \200\231. Flow quantitation from pulsed Doppler Quantitation: pulsed Doppler spectral traces can provide important information regarding \202 ow quantitation or timing, e.g. assuming that sampling occurs at an ori \201 ce with a relatively \201 xed area over the cardiac cycle (e.g. the left ventricular out \202 ow tract) by integrating the time \200\223velocity spectral curve ( \200\230time \200\223velo city integral \200\231 or TVI), the area under the curve can be multiplied by the area of t he ori \201 ce (determined from 2D ECHO) and stroke volume determined. TRANSTHORACIC DOPPLER IMAGING 15 Continuous wave (CW) Doppler involves continuous transmission of ultrasound with one transd ucer element, while a second element serves as a receiver. Higher sampling rates are achiev ed and, consequently, higher velocities, as found in stenotic and regurgitant lesions, can be measured. CW Doppler does not permit ranging information to be acquired and all velociti es along a scan line are included in the spectral trace. CW Doppler can be performed with s tand-alone (Pedoff ) probes , where the operator determines sample location based on famili ar spectral patterns. Imaging CW Doppler permits beam steering. Transducer elements are shared for the purposes o f CW and intermittent 2D imaging. A virtual cur- sor positioned over the 2D image can be mo ved to guide and minimize off- axis sampling angulation. CW Doppler velocities are depicted as a \201 lled-in spectral tracing, since these represent sampling of all of the velocit ies in structures along the sampling cursor (or ultrasound beam). Blood cells traveling at the fastest velocities are represented at the outer edge of the spectral trace (peak) or da rkest line of the trace (modal) velocities. Color Doppler \202 ow imaging employs multigate pulsed Doppler to portray blood \202 ow overlying the 2D image. Information is used to detect regurgitant or stenotic lesions or s hunts, and qualitative assessment of velocities is possible using color maps. \200 Pixels are assigned a color based on user-con \201 gurable mapping parameters. Pixel color is ba sed on average velocity in the pixel region of interest. By convention, the BART color map system is used in all machines, with b lue colors representing \202 ow a way from the transducer and r ed color depicting \202 ow t owards the transducer (Fig. 1.4 ). The lighter the color, the higher the velocity. \200 Abnormal velocity distributions char acteristic of turbulence can be mapped, usually by including a green hue ( \200\230variance mapping \200\231). \200 Aliasing is depicted as a mix of colors or a \200\230mosaic \200\231 pattern. Tissue Doppler imaging (TDI) is used to assess low-velocity displacement of structures. A high-pass \201 lter excludes higher-frequency shifts caused by red-cell \202 ow, leaving only low-velocity shifts attributable to wall motion. \200 Mitral or t ricuspid annular motion can be tracked and correlates with systolic and relaxation performa nce of the associated ventricles. Regional wall motion can be assessed for displacement, which may be affected by overall cardiac motion or local tethering. Strain rate imaging can measure regional thickening and thinning, inde- pendent of the exte rnal in \202 uences described above, which in \202 uence tissue Doppler measurements. Wit h strain rate imaging, two sampling sites are simultaneously acquired and inter-sample disp lacement (strain) over time (strain rate) can be determined. 16 CHAPTER 1 Cardiac investigations Calculations from Doppler measurements Valve gradients. The velocity of blood cells traveling across a narrow ori \201 ce is dire ctly proportional to the pressure gradient at that point in time. This relationship is appr oximated by the simpli \201 ed Bernoulli formula: Gradient (mmHg) = 4 V 2 (where V = peak Doppler velocity in m/s) In situations where there are high \202 ow velocities (e.g. aortic stenosis with high LVO T velocities), the \202 ow before the stenosis must be accounted for. Gradient (mmHg) = 4( V 2 2 \200\223 V 1 2 ) (where V 2 = velocity across the lesion and V 1 = pre-lesional velocity) Both peak and mean gradients can be determined, the latter by integrating the velocity spec tra over a cardiac cycle. Valve area (continuity equation). This is based upon the principle that \202 ow in the pr e-valve area (e.g. LVOT) = \202 ow across the valve. It is generally used for aortic sten osis quantitation, though it is applicable to other stenotic ori \201 ces as well. LVOT \202 ow = LVOT area \227 LVOT TVI by pulsed Doppler LVOT area = \200 (maximum LVOT diameter in PLA view) 2 Aortic valve \202 ow = aortic valve area \227 aortic valve TVI by CW Doppler As aortic valve \202 ow = LVOT \202 ow, Aortic valve area = LVOT TVI/aortic valve TVI \227 LVOT area PLA = parasternal long axis. (a) (b) Red Red Blue Red Fig. 1.4 Color Doppler (Red: toward \202 ow; Blue: away \202 ow). Reproduced with permi ssion from Shanewise JS. Journal of the American Society Echocardiography 1999; 12 :884 \200\223900. THE STANDARD TRANSTHORACIC ECHO 17 The standard transthoracic ECHO Most laboratories employ imaging protocols incorporating ac quisition of images from standard windows, resulting in standard views presented in a fairl y standard sequence. Image quality is maximized by avoiding pul- monary artifacts and rib r e \202 ections. Pulsed and color \202 ow Doppler are performed following 2D imaging in e ach view. Standard ECHO windows and views include: Left parasternal window \200 Long axis (PLA) (Fig. 1.5 ): left atrium, ventricle, proxima l ascending aorta, mitral and aortic valves, and right ventricle. Short axis (PSA) (Fig. 1.5 ): four levels \200\224 aortic valve/left atrial level: includes the tricuspid and pulmonic valves and pulmonary artery; mitral valve, papillary mu scle, and apex. \200 Right ventricular in \202 ow tract (RVIT). \200 Right ventricular out \202 ow tract (RVOT). Apical window \200 4 chamber (A4Ch) : atria, ventricles and AV valves, media, septal, and anterolateral LV walls. 5 chamber (A5Ch) : A4Ch angled anteriorly to the LVOT. \200 2 chamber (A2Ch) : anterior a nd inferior LV walls. \200 3 chamber/apical long axis (A3Ch) : apical version of PLA view with the anteroseptal, posterior walls, and LVOT. Suprasternal window (SS) : aortic arch. \200 Subcostal window (SC) : 4 chamber, short axi s, inferior vena cava. \200 Suprasternal window (optional): aortic arch and proximal desc ending thoracic aorta. Right parasternal window (optional): ascending aorta and CW Doppler of the aortic valve. Chamber evaluation \200 Chambers are routinely measured from M-mode tracings or, preferably, using digital calipers to perform point-to-point (PTP) assessment from 2D image s. Area tracings provide enhanced accuracy but are time-consuming. \200 Volumes are derived from 2D and PTP analysis using geometric modeling. The most common volumetric approaches include the modi \201 ed Simpson \200\231s biplane method of stacked disks, bullet and area \200\223length formulas. 3D volume assessment has been validated but the technology is immature and inappropriate fo r routine clinical assessment. Most clinical labs perform PTP measurements online. End-diastole is usually de \201 ned as the beginning of the QRS complex, and end-systolic measurements are performed at maximum LV contraction. 18 CHAPTER 1 Cardiac investigations The standard transthoracic ECHO: continued Pa RVOT RV Rcc Ao Ncc Lcc Ao LV LA RA LA Fig. 1.5 (a) Parasternal long axis view; (b) Parasternal short axis view (aortic level). Re produced with permission from Shanewise JS. Journal of the American Society Echocardiograph y 1999;12:884 \200\223900. Left atrium \200 Measure at ventricular end-systole (minimum LV chamber dimension). \200 Linear (anteroposterior) from PLA view at aortic cusp level (A4Ch). \200 Area (A4Ch) an d volume (preferably modi \201 ed Simpson \200\231s formula). Left ventricle \200 Measure at end-diastole and end-systole. \200 Linear from PLA at mi tral tips in end-diastole/systole. \200 Septal wall thickness from PLA at mitral tips in end-diastole. \200 Posterior wall thickness. \200 Volumes (modi \201 ed Simpson \200 \231s biplane method of disks). \200 Derived variables: fractional shortening : LVIDd \210\222LVIDs/LVIDs where LVID = LV internal diameter in diastole (d) and systole (s). ejection fraction (from 2D- or 3D-generated volumes or derived from M-mode (e.g. Teicholz formula)). mass : can be derived from M-mode measures (American Society of Echocardiography (ASE)-modi \201 ed Penn formula), 2D volumetric models, or 3D reconstr uction. M-mode mass calculations tend to over-quantify LV mass. Aortic root and ascending aorta Linear measurements from 2D PLA view or M-mode. The root is measured at cuspal level, and the aorta is measured at the sinotubular junction and 2 cm a bove this. THE STANDARD TRANSTHORACIC ECHO: CONTINUED 19 Right atrium \200 Area from 2D A4Ch view. \200 Inferior/superior and lateral/medial PTP measurements. Right ventricle \200 PTP measurements are exclusively used. \200 Irregularity of chambe r con \201 guration makes standardized quantitation dif \201 cult. Pulmonary artery PTP medial \200\223lateral measurement in PSA at aortic valve level. (a) (b) RV RV LV RA IVC (c) (d) RV LV Ao RA Pa LA Fig. 1.6 (a) Parasternal long-axis view (RV in \202 ow); (b) parasternal short-axis (mitra l valve level); (c) apical 4-chamber view; (d) suprasternal long axis. Ao = aorta; IVC = in ferior vena cava; Pa = pulmonary artery. Reproduced with permission from Shanewise JS. Jour nal of the American Society Echocardiography 1999;12:884 \200\223900. 20 CHAPTER 1 Cardiac investigations Assessment of wall motion Assessment is based upon review of multiple cuts as described ear lier. In general, abnormalities of LV regional function should be apparent in more than one view. Various labeling systems have been used but the American Heart Association (AHA) Car diac Imaging Committee 17-segment model is the standard convention: \200 basal (6): anter oseptal, anterior, anterolateral, posterolateral, inferior, inferoseptal. mid LV (6): same as above. \200 apical (5): anterior, lateral inferior, septal, and true apical. See Fig. 1.7. Regional functional assessment \200 Systolic function should be classi \201 ed as \200 \230normal \200\231, \200\230globaly hypokinetic \200\231, or demonstrating the presence o f \200\230regional wall motion abnormalities \200\231. \200 Global hypokinesis is consis tent with cardiomyopathy, either ischaemic or non-ischaemic. Some degree of regional variat ion may be present in non-ischaemic cardiomyopathy. The presence of distinct regional wall motion abnormalities with large areas of normal regi onal function is suggestive of underlying coronary artery disease. Evaluation should ideally be based on the degree of regional thickening as opposed to endoc ardial motion. Unfortunately, this is not always possible. Each regional segment can be quali \201 ed as: hyperkinetic. \200 normal. \200 hypokinetic. \200 akinetic. \200 dyskinetic. Wall motion quanti \201 cation, based on similar characteristics, may be prognostically useful, but is not useful in routine evaluation. Identi \201 cation of hyper-echogenic, thinned areas suggests the presence of scarring and should be mentioned in the evaluation. Scarred segments may demonstrate endocardial motion, without wall thickening, due to tethering by peripheral segments. ASSESSMENT OF WALL MOTION 21 Ant. Ivs (ANT. IVS) Ant ANT 15 2 1 16 5 Lat (Lat) Inf. Ivs (INF. IVS) Posterior Inf 17 3 4 15 18 7 6 18 19 6 1 12 10 8 20 9 14 4 9 15 18 1 6 21 12 12 11 22 13 13 14 3 8 16 3 4 2 5 8 7 9 19 10 14 12 13 11 22 Left anterior descending coronary artery Left circumflex coronary artery and right coronary artery Right coronary artery Left circumflex coronary artery Fig. 1.7 American Heart Association 17-segment model. From Swanton H (2003) Pocket Consulta nt: Cardiology . 5th ed, Oxford: Blackwell Publishing. 22 CHAPTER 1 Cardiac investigations Assessment of LV systolic function Global functional assessment \200 Ejection fraction es timation is usually performed qualitatively. Echocardiographers need to routinely \200\230recalibrate \200\231 their assessment abiliti es by comparing qualitative readings to more accurate quantitative modalities, such as MRI, radionuclide ventriculography, 3D or even quantitative 2D ECHO (see Table 1.1 ). 2D ECHO ejection fractions can be quanti \201 ed most ef \201 ciently on or of \202 ine by the: \200 Simpson \200\231s modi \201 ed biplane method of stacked disks : A4Ch and A2Ch LV traces are performed and the apex \200\223annulus length is divided int o a standard number of equal segments, the length of which serves as disc height. Cross-sec tional disc area is calculated from the elliptical formula ( \200 r 1 r 2 ) where r 1 and r 2 = the endocardial medial \200\223lateral dimension of each segment in the A4Ch and A2Ch views, respectively. cylinder hemi-ellipsoid model : volume is determined by measuring the LV endocardial area ( A ) on the PSA view at the papillary muscle level and the longest apex \200\223annulus length ( L ) in any apical view. Volume = 5/6 AL . Table 1.1 Assessment of left ventricular ejection fraction LV ejection fraction Qualitative assessment > 75 % Hyperdynamic 55 \200\22375 % Normal 40 \200\22354 % Mildy reduced 30 \200\22339 % Moderately reduced <30 % Severly reduced LV stroke volume : integration of LVOT spectra \227 LVOT area (derived from diameter in PLA view). Systemic output : LV stroke volume \227 heart rate. \200 Pulmonary stroke volume : integ ration of pulmonary artery spectral trace \227 pulmonary artery area (derived from systolic medial \200\223lateral dimension a t the level of Doppler sampling). \200 RV output : pulmonary stroke voume \227 heart rat e. \200 Pulmonic/systemic shunt ratio (Qp/Qs): pulmonary output/systemic output. Tissue Doppler of mitral and tricuspid annular motion. ASSESSMENT OF LV SYSTOLIC FUNCTION 23 Essential aspects of ECHO assessment in patients with impaired LV systolic function Anatomy \200 LV dimensions (systolic and end diastolic). \200 LV ejection fraction. \200 Reg ional wall motion abnormalities. Doppler characteristics \200 E:A ratio (grade according to Fig. 1.7 b Assessment of LV di astolic function, p. 27). \200 E deceleration time. \200 Estimate pulmonary artery (PA) systoli c (from tricuspid regurgitation (TR) jet). Estimate PA diastolic (from pulmonary regurgitation (PR) jet). \200 Estimate pulmonary ca pacitance (= stroke volume/(PAs \200\223 PAd pressures)). Implications for therapy \200 Mitral regurgitation at end diastole if AV delay too long. \200 Dys-synchrony (TDI septum/lateral annulus > 60 ms). 24 CHAPTER 1 Cardiac investigations Assessment of LV diastolic function Evaluation of LV diastolic function includes measuremen t of the various phases of diastole including isovolumic relaxation, early \201 lling, di astasis (atrioventricular pressure equilibration without LV \201 lling), and atrial systo le. These measures are generally age and heart-rate dependent, and affected by LV loading c onditions to variable degrees (see Fig. 1.8 ). Pulsed Doppler mitral in \202 ow: E wave (peak early diastolic velocity), A wave (peak atr ial systolic velocity), E/A ratio and transmitral deceleration time. The following should b e taken into account when assessing these parameters: \200 E/A ratio is particularly depe ndent on sample volume placement (annulus, mitral tips, etc.) and loading conditions. E/A ratio decreases with age, and assessment must be age-normalized. An E/A ratio <1.0 is c ommon among the elderly and often represents normal aging. increasing LV \201 lling pressures (e.g. in heart failure) lead to \200\230pseudonormalization \200\231 of the ratio, which often reverts to an abnormal patt ern following maneuvers to reduce LV preload (e.g. diuresis) or Valsalva maneuver. the deceleration time correlates somewhat with invasive measures of LV stiffness, whereas o ther measures largely re \202 ect LV relaxation.