Provide details of the patient \200\231s renal function, as this will enable appropriate precautions and consent to be taken in renal impairment if gadolinium contrast is to be administered. For obese patients, provide details of the patient \200\231s weight to assess whether the M RI table and scanner can safely accommodate the patient. In patients with suspected metallic foreign bodies in the eyes/orbits (absolute contraindication to MRI), arrange for orbital X-ray imaging to be undertaken befo re making the request if there is any doubt or the object has not been removed. Absolute contraindications to CMR \200 Pacemaker/implantable cardioverter de \201 brilla tor (ICD) or retained/ fractured pacing leads. Metallic foreign bodies in the eye/orbit. \200 Ferromagnetic cerebrovascular aneurysm cli ps. \200 Cochlear implants. \200 Insulin pumps. MAKING CMR REQUESTS 65 There is no documented harm from MRI in pregnancy. Nonetheless, adhering to the precautionary principle, it should be avoided, particularly in the \201 r st trimester, unless there is likely to be compelling clinical bene \201 t and the scan ca nnot be deferred. As a precaution, women who are breast-feeding should be advised to express and discard brea st milk for 24 hours after receiving gadolinium contrast media. 66 CHAPTER 1 Cardiac investigations CMR safety \200 Used with the appropriate precautions, CMR is a very safe diagnostic tech nique. However, the strong magnetic \201 elds employed, typically 1.5 T or 3 T can conver t any ferromagnetic object into a projectile with potentially lethal effect. All patients u ndergoing CMR examination should be screened for ferromagnetic implants, and equipment not speci \201 cally deemed MR safe , i.e. safe in all MRI environments, should be excluded. The radiofrequency pulses used as part of imaging can generate heating effects in wires or implants. Limb-to-limb skin contact can allow current loops to develop with thermal injury at the points of contact. Similar heating and burns can result from such apparently benign objects as standard ECG stickers. These must be removed from the patient prior to the scan, and monitoring carried out with carbon-based MR-safe stickers. In addition to the main magnetic \201 eld, gradient \201 elds are employed and switched on and off rapidly during imaging to generate various sequences and to allow spatial local ization of MR data. These generate very loud noise ( > 100 dB) and can cause hearing loss. All patients and anyone present in the scanner room should wear protective headphones or ea rplugs. Rapid gradient switching can also cause unpleasant peripheral nerve stimulation. Implanted prostheses \200 The precautions required depend on the material composition of the device and implant, and where doubt exists, the manufacturer should be consulted. Where no data exist to provide guidance, the risks and bene \201 ts of the scan must be careful ly weighed. For weakly ferromagnetic devices, a major concern is device/implant dislodgemen t. Particularly if the scan is not clinically urgent, it is generally recommended that scan s are deferred for 6 weeks after implantation to allow the healing process to take place an d ensure the device is adequately anchored. Coronary and vascular stents are generally only very weakly ferromagnetic. CMR studies can be performed safely in the majority of cases. Similarly, the majority of heart valve prostheses and annuloplasty rings have been labeled as MR safe. Ot hers have been deemed MR conditional , i.e. no hazard identi \201 ed under speci \201 c i maging conditions. The same applies to closure or occlusion devices, IVC \201 lters, or e mbolization coils. Sternal wires and epicardial pacing leads are safe; however, they can generate artifacts that hamper image interpretation. Pacemakers/automated ICDs (AICDs) \200 These pose potentially signi \201 cant hazards an d there have been reported deaths. In addition to device migration, radiofrequency (RF) heating in leads can result in cardiac injury. The magnetohydrodynamic effects of the strong \201 elds on the ECG can lead to inappropriate device behavior, and direct effects on device programming/res ponse can occur. New MR-safe pacemakers are now available, but currently CMR SAFETY 67 AICDs remain an absolute contraindication to CMR. Retained, particularly fractured device l eads pose a signi \201 cant theoretical safety risk and are regarded as an absolute contra indication to CMR. The need for a device should be carefully anticipated and, if indicated, CMR undertaken bef ore implantation if possible, as up to 75 % of such patients have or will develop an indica tion for CMR in their lifetime. Implantable loop recorders have been safely scanned and can be deemed MR conditional. They generate considerable artifact and, in theory, their performanc e can be in \202 uenced by strong magnetic \201 elds. They should therefore be interroga ted before a scan is undertaken and again afterwards to clear the device buffers of any ina ppropriate artefactual data that may have accumulated during the scan. Gadolinium contrast media \200 The two principal risks of gadolinium contrast media are a naphylaxis to the gadolinium chelate or one of its excipients and nephrogenic systemic \201 brosis (NSF). MR contrast media are completely distinct from the iodinated contrast agents used in X-ray- based imaging, so allergy to one does not imply allergy to the other unless it is to a comm on excipient. \200 MR contrast media do not induce renal failure or contrast nephropathy; however, in patients with signi \201 cant renal impairment (estimated glomeru lar \201 ltration rate (eGFR) <30 mL/min/1.73 m 2 ), there is a risk of nephrogenic syste mic \201 brosis \200\224 a condition characterized by the development of dermal and mult i-organ \201 brosis, typically within days to weeks of contrast administration. 5 % of p atients experience a fulminant malignant course. It has only ever been reported in the context of renal impairment and is thought to be due to the release of free toxic Gd 3 + ions from their chelate. In th is context, cyclic gadolinium chelates appear to be signi \201 cantly safer than older lin ear agents. It is estimated to occur in 2.4 % of patients per study in the context of end-stage renal f ailure. In patients with an eGFR less than 30 L/min/ 1.73 m 2 , or in those who are on dial ysis, the risks and bene \201 ts of contrast administration should therefore be carefully weighed by both patient and physician. If contrast is to be administered, the lowest possib le effective dose should be given, and a cyclic gadolinium chelate should be employed. Pati ents who require renal replacement therapy should undergo haemodialysis immediately after t he scan. Caution should also be exercised in patients with any degree of renal impairment who are awaiting or who have recently had liver transplants, because of th e risk of hepatorenal syndrome. Unstable patients \200 Patients who are haemodynamically or otherwise unstable should not be taken into the scanner. There is limited scope for monitoring, and resuscitation equ ipment is not MR safe. Any patient requiring cardiopulmonary resuscitation (CPR) has to be transferred out of the scanner \201 rst. Together with limited access to the patient, the se constraints make CMR an impractical modality for the unstable patient. 68 CHAPTER 1 Cardiac investigations Cardiomyopathy assessment CMR has the unique ability in a single study to non-invasively, a ccurately, and reproducibly assess LV mass and wall thickness, LV and RV volumes, and myoca rdial perfusion, as well as the ability to detect myocardial \201 brosis and in \202 amm ation. It is therefore the modality of choice for the assessment and follow-up of patients with heart muscle disease. Dilated cardiomyopathy \200 Dilated cardiomyopathy is a disorder of heart muscle characte rized by LV and/or RV dilation and impairment of systolic function, in the absence of signi \201 cant coronary artery disease. The ability of CMR to accurately quantify biventricula r chamber volumes enables it to detect early LV dysfunction and dilatation, and its reprodu cibility facilitates serial follow-up and evaluation of response to treatment. CMR with del ayed hyperenhancement imaging may also allow the identi \201 cation of an ischaemic etiolo gy. Patients with a dilated cardiomyopathy and unobstructed coronaries demonstrate either no late gadolinium enhancement (60 % ) or evidence of mid-wall enhanceme nt correlating with mid-wall \201 brosis on histology (30 % ). A further 10 % demonstrate evidence of subendocardial hyperenhancement in a coronary distribution, which may represen t previous coronary thromboembolism, spasm, or thrombotic occlusion with spontaneous recana lization. Patients with obstructive coronary disease, however, have subendocardial late gadolinium enhancement. CMR may therefore potentially obviate the need for invasive coronary angiography in some patients, and in others disclose the signi \201 cance of any identi \201 ed coronary disease, enabling appropriate secondary prevention me asures to be instituted. The presence of mid-wall late gadolinium enhancement may be of independent prognostic signi \201 cance and identi \201 es a subgroup of patients at increased risk of all-cause mort ality and unplanned hospitalization. Imaging in the early phase after gadolinium allows the identi \201 cation of mural thrombu s, which may be encountered in severe LV dysfunction. Hypertrophic cardiomyopathy \200 Hypertrophic cardiomyopathy is an inherited disorder of the cardiac sarcomere characterized by the development of left ventricular hypertrophy in t he absence of any extrinsic physiological or pathophysiological stimulus. The multiplanar capabilities and high spatial resolution of CMR provide a number of advanta ges over echocardiography. By avoiding oblique cuts, CMR avoids the overestimation of LV wa ll thickness that can occur with ECHO. CMR also allows the identi \201 cation of hypertrop hy at the LV apex and the anterolateral free wall, which may be missed on echocardiography. At the level of the basal anteroseptum, a common site for hypertrophy, it allows more accu rate differentiation of the LV septum from RV-septomarginal trabeculation, which is often o verestimated on echocardiography. CARDIOMYOPATHY ASSESSMENT 69 CMR enables the identi \201 cation of LVOT obstruction and systolic anterior motion of the mitral valve, and the assessment of associated posteriorly directed MR, although the higher temporal resolution of ECHO provides a distinct advantage in this s etting, especially with regard to assessing LVOT obstruction at rest and on exertion. CMR can also disclose the presence of accessory papillary muscles and chordae and help dete rmine their role in LVOT obstruction. This can be important to identify prior to considerat ion of invasive treatment. \200 CMR may identify areas of hypocontractility prior to the development of regional hypertrophy. It can also readily identify apical trabeculation, enabling apical hypertrophic cardiomyopathy (HCM) to be differentiated from apical LV non-compaction or end omyocardial \201 brosis, which may have similar appearances on ECHO. Uniquely, CMR can identify late gadolinium enhancement suggestive of \201 brosis. This is typically mid-wall in distribution and occurs in areas of hypertrophy. It may also be seen at the LV apex in the apical variant, and in variants with severe mid-ventricular thickeni ng, which can predispose to apical infarction and aneurysm 9 thrombus formation, neither of which can be readily visualized on ECHO. CMR can also accurately assess the extent and dis tribution of \201 brosis induced by alcohol septal ablation, and is therefore of use in e valuating the response to treatment. The extent of \201 brosis may correlate with a propensity to develop LV-systolic dysfunct ion and a more malignant natural history. CMR with adenosine stress perfusion imaging may identify areas of hypoperfusion that correlate with increased wall thickness. \200 CMR can be useful for di fferentiating sarcomeric HCM from phenocopies, the athlete \200\231s heart and cardiac amyloid. \200 Anderson \200\223Fabry \200\231s disease is an X-linked recessive disorder resulting from defective or absent lys osomal A -galactosidase-A. This can result in cardiac involvement with concentric LVH but a lso an asymmetric pattern. Approximately 50 % of patients with Anderson \200\223 Fabry \200 \231s disease exhibit mid-wall late gadolinium hyperenhancement, particularly con \201 ned to the basal inferolateral wall ( > 90 % of cases with cardiac involvement). The importanc e of identifying this is highlighted by the fact that 4 % of patients with suspected HCM tu rn out to have Anderson \200\223Fabry \200\231s disease and that enzyme- replacement therap y is now available to treat this multisystem condition. Hypertrophic cardiomyopathy remains the most common cause of sudden cardiac death in young people, and, in particular, athletes. The latter often pre sent with a degree of physiological hypertrophy, which can present a diagnostic challenge. However, LV wall thickness is rarely > 15 mm, indexed LV volumes in diastole tend to be inc reased in athletes engaged in dynamic exercise, and there should be no evidence of late gad olinium hyperenhancement. The absence of the latter or the presence of mild hypertrophy (wa ll thickness 12 \200\22315 mm) does not, however, exclude HCM, 70 CHAPTER 1 Cardiac investigations and, occasionally, repeat CMR imaging after at least 3 months of deconditioning may be requ ired. CMR may also aid differentiation between hypertensive LVH or HCM. Hypertrophy > 15 mm is unusual in hypertensive LVH. Levels above 20 mm are strongly suggestive of HCM. In addition, although hypertensive heart disease may be associated with increased LV interstitial \201 brosis, the patchy mid-wall late gadolinium enhancement o ften seen in HCM does not occur. CMR in HCM is therefore useful for diagnosis, differential diagnosis, follow-up, planning i nvasive treatment for LVOT obstruction, and identifying complications. In the future, quant i \201 cation of the degree of late gadolinium hyperenhancement may also provide prognosti c information. Arrhythmogenic RV cardiomyopathy \200 This is an inherited heart muscle disorder that pre dominantly but not exclusively affects the right ventricle, and that is characterized by \201 brofatty r eplacement of cardiomyocytes. CMR is an important modality for diagnostic evaluation, given its ability to precisely and accurately image the right ventricle and, through late gadolinium hyperenhancement imaging, identify areas of \201 brosis. \200 CMR features and major Arrhythmogenic Right Ventri cular Myopathy (ARVC) Task Force criteria include severe RV dilatation and impairment of RV function with little or no LV involvement; localized RV aneurysm formation (akinetic or dyskinetic areas with diastolic bulging); and severe segmental dilatation of the RV. Mild global RV impairment or dilatation, mild RV segmental dilatation, and regional RV hypokinesia constitute minor ARVC Task Force criteria, which may be readily identi \201 ed by CMR. ARVC most commonly affects the RV apex, RVOT and subtricuspid region \200\224 the so-called triangle of dysplasia. > 60 % of patients exhibit late gadolinium enhancement of the RV. Approximately 20 % of patients may exhibit LV \201 brosis. LV involvement with wall-motion abnormalities but without signi \201 cant RV dysfunction is recognized. LV non-compaction cardiomyopathy \200 This cardiomyopathy results from the premature arre st in utero of the process of compaction of trabeculated or spongy myocardium in the LV. Th e normal process of compaction takes place from base to apex, from epicardium to endocardiu m, and from the septal to the lateral wall. The apex is therefore the most frequently involved segment, as this is the last region to c ompact. Traditionally, diagnosis has relied on echocardiography. However, due to near- \201 eld clutter and ECHO drop-out, the apex is poorly visualized with echocardiography. CM R is not subject to these limitations and can provide exquisitely detailed high-spatial-res olution images, facilitating diagnosis. The diagnosis is made if the ratio of non-compacted to compacted myocardium is > 2.3:1 in diastole. CARDIOMYOPATHY ASSESSMENT 71 By examining the LV early after the injection of gadolinium contrast, CMR also allows the d etection of LV thrombus, a major complication of LV non-compaction. Cardiac amyloid \200 Primary or AL amyloid clinically involves the heart in over 40 % of cases and is a major cause of death in such patients. Secondary or AA amyloid rarely involv es the heart. Hereditary amyloidosis, particularly due to amyloidogenic mutations in transt hyretin, frequently also involve the heart. In the older age group ( > 80 years), senile sy stemic amyloid is a signi \201 cant problem. CMR can play a signi \201 cant role in the d iagnosis of cardiac involvement. There is usually concentric thickening of the LV myocardium due to amyloid in \201 ltratio n (not hypertrophy as myocyte size is largely unaffected). A signi \201 cant proportion of patients may experience asymmetric hypertrophy, causing diagnostic confusion with HCM. In the later stages, there is systolic dysfunction with poor myocardial contraction. Commonly seen features such as bi-atrial enlargement and diastolic dysfunction are non-speci \201 c . Some patients may exhibit systolic anterior motion of the mitral valve 9 premature closur e of the aortic valve as in HCM. Unlike other modalities, CMR with gadolinium contrast can allow tissue characterization with high spatial resolution, and facilitate differential dia gnosis. CMR can reveal circumferential subendocardial to mid-wall late gadolinium enhancement in up to two-thirds of affected patients. As the septum has endocard ium on both sides, this can give rise to a characteristic zebra-stripe pattern of septal la te enhancement. The distribution of late enhancement is often in a non-coronary pattern, en abling differentiation from subendocardial myocardial infarction. In addition, the blood po ol can appear unusually dark. This is thought to be due to the avid uptake of gadolinium by the in \201 ltrated myocardium, together with more rapid washout from the blood pool. Oth er CMR features include thickening of the inter-atrial septum, RA free-wall and valve lea \202 ets, together with the consequences of signi \201 cant diastolic heart failure includ ing pericardial 9 pleural effusions and a dilated IVC. Sarcoid \200 Cardiac involvement can result in life-threatening ventricular arrhythmias, AV-conduction disease, and congestive cardiac failure. \200 CMR may reveal p atchy mid-myocardial or epicardial late gadolinium enhancement, papillary muscle involvemen t, or RV subendocardial or free-wall involvement. There may be a subendocardial or transmur al pattern of hyperenhancement, which may be confused with myocardial infarction, especiall y involving the anteroseptal and inferolateral walls. Identi \201 cation of RV involvement can help guide biopsies. T 2 -STIR (short tau inversion recovery) sequences can identify o edema, which may signify acute in \202 ammation and may be useful for identifying active d isease. The use of CMR increases the likelihood of diagnosing cardiac involvement over and above clinical criteria, but the diagnosis remains challenging. 72 CHAPTER 1 Cardiac investigations Myocarditis \200 Acute myocarditis is an important cause of acute heart failure, and in a proportion of patients can progress to a dilated cardiomyopathy or be complicated by sudde n cardiac death. Traditionally, diagnosis has relied upon endomyocardial biopsy; however, t his often fails to access affected areas of myocardium and therefore suffers from low sensi tivity and negative predictive value. CMR can identify and quantify regional or global ventricular dysfunction resulting from myocarditis. Changes in LV mass and volumes with resolution of myocardial oe dema can be detected by CMR. The in \202 ammatory process can involve the pericardium as p art of a myopericarditis in over 50 % of patients. CMR can detect the resultant pericardial effusions. T 2 -weighted sequences can reveal myocardial oedema. The T 2 -STIR sequence fu rther enhances the appearance of oedema by using inversion pulses to suppress the signal fr om fat and blood. Myocardial oedema and in \202 ammation cause expansion of the extracellular space. Gadolinium contrast rapidly diffuses into areas of cellular injury and in \202 ammation, and imaging in the early washout phase can reveal hyperenhancement, den oting capillary leak and hyperaemia. Imaging in the late phase can reveal hyperenhancement. This signi \201 es irreversible myocardial injury with replacement \201 brosis and is t ypically subepicardial to mid-wall in distribution, unlike that due to coronary disease, wh ich is classically subendocardial. The identi \201 cation of hyperenhancement in the early phase, and absence of such enhancement in the late phase denotes in \202 amed and threatened but pote ntially reversibly injured myocardium. CMR can be used to guide endomyocardial biopsy and i ncrease diagnostic yield. \200 CMR techniques have not been adequately validated with his tology, and the CMR criteria for diagnosis (Lake Louise criteria) are based on expert conse nsus, and, in the context of strong pre-test clinical suspicion, require two of: \200 reg ional or global increase in signal intensity in T 2 -weighted images. \200 increased glob al myocardial early gadolinium enhancement on T 1 -weighted images. the presence of one or more focal lesions on late gadolinium- enhanced T 1 -weighted images. The above criteria are estimated to have a diagnostic accuracy of 78 % . However, the CMR study should be repeated 1 \200\2232 weeks later if there is a strong clinical suspicion fo r myocarditis but none or only one of the above criteria have been ful \201 lled. Follow-u p scans may also be considered one month or more after diagnosis to assess for resolution a nd sequelae. Further reading Freidrich MG, Sechtem U, Schulz-Menger J, et al ( 2009 ). Cardiovascular ma gnetic resonance in myocarditis: a JACC White Paper. J Am Coll Cardiol 53 : 1475 \200\223 87 . ASSESSMENT OF CARDIAC IRON STATUS 73 Assessment of cardiac iron status \200 There is no physiological means by which excess ir on can be removed from the body. Patients with haemoglobinopathies such as B -thalassaemia major and sickle cell disease require repeated transfusions and can therefore develop iron overload. Levels of cardiac iron correlate poorly with traditional serum markers of iron status and a lso with liver iron loading as determined by biopsy. Prior to the introduction of CMR-based assessment of cardiac iron status, iron-overload cardiomyopathy was the leading cause of d eath in patients with transfusion-dependent anaemias. Although IV and oral chelation therap y exists, prior to the use of CMR there was no accurate way of predicting when to institute therapy and at what intensity. Both symptoms of heart failure and a decline in ejection fraction only develop at a very la te stage. Many patients with apparently effective chelation as assessed by traditional meth ods nonetheless succumb to iron-overload cardiomyopathy. Lysosomal deposits of microscopic iron particles (haemosiderin) in myocardium cause a short ening of T2 * (T2-star), a relaxation parameter or time constant for the decay in transvers e magnetization due to both spin \200\223spin de-phasing and inhomogeneity in the local mag netic \201 eld, the latter being heavily in \202 uenced by iron. T2 * can be measured in a single breath hold in a highly reproducible way. The normal value for T2 * is 37 5 ms , with values > 20 ms generally predicting absence of cardiac iron. Values below 20 ms are associated with progressively increasing iron loading and the development of overt contract ile dysfunction. A value of <10 ms has a 98 % sensitivity and 86 % speci \201 city for predicting the development of heart failure within 1 year; 47 % of patients with T2 * <6 ms develop heart failure within a year. The same technique can be used to assess liver iron s tores and has con \201 rmed that chelation therapy produces a more rapid clearance of hepa tic iron stores than cardiac iron. This allows the type, and duration of intensity of chelation therapy to be tailored to the patient \200\231s risk, and ef \201 cacy to be reproducibly and non-invasively monitored, transforming the outlook for these patients. Further reading Kirk P, Roughton M, Porter JB, et al ( 2009 ). Cardiac T2* magnetic resonan ce for prediction of cardiac complications in thalassemia major. Circulation 120 : 1961 \200\223 8 . 74 CHAPTER 1 Cardiac investigations Ischaemia and viability assessment \200 Myocardial ischaemia can be detected using either gadolinium contrast- enhanced \201 rst-pass perfusion imaging with vasodilator stress, o r by the evaluation of wall motion under dobutamine stress, analogous to stress echocardiog raphy. Using coronary angiography as a gold standard, \201 rst- pass perfusion CMR has a sensitivity of 91 % and a speci \201 city of 81 % and compares favorably with nuclear SPEC T-based techniques. It is not subject to the attenuation artifacts experienced with SPECT a nd does not involve any ionizing radiation. It also has better spatial resolution and, anal ogous to PET, may allow quantitative assessment of perfusion, although this is cumbersome a nd currently only used in research settings. Vasodilator stress is achieved by infusing 140 mcg/kg/min of adenosine (3 mg/mL) until there is evidence of a haemodynamic response (typically 3 min), followed by rapid infusion of gadolinium contrast and rapid acquisition of short-axis slices at basal, mid-ventricular and apical level, as contrast enters the myocardium. The sequence requires a very long breath hold, but satisfactory images can be obtained with very gentle breathin g at the end of the longest breath hold managed. The use of adenosine to achieve vasodilator stress requires abstinence from caffeine-contai ning food and beverages (e.g. coffee, tea, chocolate, Coca-Cola, Red Bull) ideally for 24 h ours prior to testing. It is contraindicated by the presence of high-grade AV-conduction di sease or severe asthma. Forty-eight hours \200\231 abstinence from beta-blockers or rate-li miting calcium-channel antagonists is essential for dobutamine stress but not for vasodilat or stress-based protocols. Adenosine should not be co-administered with dipyridamole, as th e latter signi \201 cantly prolongs the half-life of adenosine and may indeed be used as a stress agent itself. Practical tip: for stress perfusion imaging, the patient requires two separate IV lines, on e large bore (18G or larger), to facilitate rapid con- trast bolus infusion and the other f or adenosine infusion. BP monitoring should be undertaken using the arm with the contrast l ine, otherwise BP measurements/cuff in \202 ation may interrupt adenosine infusion. A signi \201 cant limitation of MR-perfusion imaging at 1.5 T is the presence of dark-rim artifact, which may lower the speci \201 city for detecting subendocardial perfusion defec ts. Imaging at higher \201 eld strengths (3 T) affords higher contrast-to-noise ratio and also reduces the risk of this artifact, further improving diagnostic speci \201 city. Artifacts can often be identi \201 ed by examining rest perfusion images, and interpretati on can be further enhanced by examining images acquired in the late phase following gadolin ium enhancement. The latter technique detects \201 brosis and can further facilitate the differentiation of ischaemia from infarction. The limited space inside the scanner bore and the lack of MR-safe resuscitation equipment represent relative disadvantages of MR. Also, the magnetohydrodynam ic effects distort the ECG and make the use of ISCHAEMIA AND VIABILITY ASSESSMENT 75 ST-segment monitoring impossible. However, ST-change is a late stage in the ischaemic casca de, and rhythm monitoring, direct observation, and communication with the patient readily o bviate the need for this. \200 Despite these limitations, normal MR perfusion imaging aff ords > 99 % event-free survival at 3 years. Assessment of viability and hibernating myocardium \200 Over 60 % of patients with heart failure have ischaemic heart disease as the predominant cause. Viable myocardium can be de \201 ned as myocardium supplied by coronary arteries with \202 ow-limiting coronary disease that exhibits contractile dysfun ction in the absence of signi \201 cant scar tissue and therefore has potential for contra ctile recovery following successful revascularization. Hibernation is de \201 ned retrospe ctively by the presence of evidence of functional recovery of hypocontractile myocardium fo llowing revascularization. Successful revascularization of patients with signi \201 cant ( > 4 segments) ischaemic bu t viable myocardium appears to improve ejection fraction and prognosis proportionate to the degree of LV impairment, according to meta-analysis of outcome data from numerous retrospe ctive studies and registry data (prospective studies to assess this are under way and due t o report shortly). However, revascularization of patients without viable myocardium offers no apparent prognostic bene \201 t and may indeed cause harm, because of the higher risks involved in the setting of signi \201 cant LV impairment. Late gadolinium enhancement CMR imaging allows the identi \201 cation of myocardial \201 brosis which. when due to ischaemia, extends from the subendocardium towards the epicardiu m. The technique, by virtue of its greater spatial resolution, is superior to both PET and SPECT at identifying \201 brosis. Viability is proportional to the transmurality of \201 brosis, with segments showing > 50 % \201 brosis being de \201 ned as non-viable. S peci \201 city can be improved by combining the technique with low-dose dobutamine stress CMR evaluation of wall-motion abnormalities. This is particularly helpful in patients with intermediate transmurality of infarction and may yield a sensitivity of 95 % and speci \201 city of 85 % when combined with late-enhancement imaging. \200 CMR has shown that, in the absence of \201 brosis, signi \201 cant functional recovery can take place even i n thinned (<5 mm) and remodeled myocardium that would traditionally have been regarded as n on-viable. Furthermore, the presence of late enhancement appears to be a powerful independe nt predictor of mortality. 76 CHAPTER 1 Cardiac investigations CMR in valvular heart disease \200 Doppler echocardiography remains the modality of choic e for the evaluation of valvular heart disease in the majority of circumstances, because of its highe r temporal resolution. CMR provides an alternative, however, where ECHO windows are challen ging or when there are contraindications to TOE or a marked discrepancy between ECHO data a nd the clinical picture. CMR is also useful where additional anatomical information is required, such as the dimensi ons of the aorta in a patient with bicuspid aortic valve disease or suspected coarctation o f the aorta, or where revascularization and valve repair are being planned and information about myocardial viability is needed. It is particularly useful for following up aortic reg urgitation secondary to aortic root disease where serial, accurate, and reproducible measur ements of root dimensions are needed. Phase-contrast \202 ow velocity mapping can enable determination of peak \202 ow veloci ties, estimation of valve gradients, and relatively accurate quanti \201 cation of regurgi tant fractions. Through-plane \202 ow maps are used to characterize \202 ow jets and fa cilitate accurate positioning for in-plane measurements of \202 ow velocity. Measurements can be taken in a single breath hold. The ability of CMR to accurately and directly quantify ventricular volumes allows the separ ate estimation of stroke volume and the calculation of interventricular stroke volume diffe rence, which is particularly useful for MR, where the combination of annular through- plane motion and the altering geometry of the valve plane itself make the accurate use of phase- contrast \202 ow velocity mapping dif \201 cult. CMR can be used to planimeter the aortic valve, allowing direct estimation of aortic valve area. In addition, root dimensions and aortic, iliac, and femora l arterial anatomy can be assessed, providing useful information where percutaneous aortic valve replacement is being considered. The multiplanar capability of CMR allows a stack of images to be taken through the mitral v alve to disclose the mechanism of MR and assess the suitability of lea \202 ets for repair . CMR allows the pulmonary valve and right ventricle to be imaged in exquisite detail and is invaluable for the precise evaluation of pulmonary regurgitation as well as pulmonary arter y anatomy in patients with tetralogy of Fallot and other congenital heart diseases with sig ni \201 cant right ventricular involvement. It also allows ready estimation of shunt fract ions, and thereby facilitates the evaluation of both intra- and extra-cardiac shunts. CMR FOR CONGENITAL HEART DISEASE 77 CMR for congenital heart disease \200 The lack of ionizing radiation (a particular concer n where serial evaluation is required in adolescents or young adults), a wide \201 eld of view, and the versatile multiplanar 2D and 3D imaging capability afforded by CMR make it the modality of choice for the evaluation and follow-up of patients with congenital heart disease. This is particularly true in those with complex anatomy, e.g. Fontan circulation, or after repeated surgical repairs where scar tissue can give rise to poor ECHO windows. The wide \201 eld of view allows visceroatrial situs and cardiac position to be readily assessed. Atrioventricular and ventriculoarterial concordance can also be eva luated. Accurate assessment of pulmonary and aortic \202 ows allows shunt ratios (Qp/Qs) to be readily calculated. Detailed visualization and \202 ow mapping of th e atrium and interatrial septum can enable assessment of ASD for percutaneous or surgical c losure, and ready identi \201 cation of anomalous pulmonary venous drainage. Assessment of the effects of lesions on RV volumes and function may be critical for determining the natu re and timing of any surgical intervention. The origin and proximal course of coronary arteries can be delineated with whole-heart coro nary imaging sequences, allowing identi \201 cation of anomalous coronary arteries and de \201 nition of their course with respect to the aorta and pulmonary arteries. This can fac ilitate identi \201 cation of malignant courses and planning for surgical repair. CMR can also be used to assess the integrity of the proximal coronaries after Bentall repair for ao rtic root disease, the Ross procedure, and the arterial switch operation for transposition of the great arteries (TGA). This can also be combined with MR perfusion imaging to assess functional consequences. CMR is particularly adept at imaging the aorta and other great vessels. Patent ductus arter iosus (PDA) and associated anomalies are readily de \201 ned. Aortic coarctation can be co mprehensively assessed, including lesion severity and suitability for percutaneous treatmen t, or evaluation of re-coarctation or aneurysm formation following surgical repair. \200 The unrivaled clarity with which CMR images the RV, together with the functional informatio n it provides, makes it the ideal means for following up pulmonary regurgitation and RV fun ction in repaired tetralogy of Fallot. In recent years, the detection of right ventricular late gadolinium enhancement, signifying \201 brosis, has emerged as potentially prognostically important in patients with system ic right ventricles, e.g. transposition of great vessels treated by atrial redirection surg ery. CMR can therefore provide comprehensive evaluation of anatomy, ventricular function, v alve function, perfusion, and tissue characteristics in one non-invasive study. 78 CHAPTER 1 Cardiac investigations CMR for pericardial disease The ability of CMR to image in any plane with high spatial reso lution, and its tissue-characterizing ability, makes it the modality of choice for the asse ss- ment of pericardial disease. CMR can allow a detailed assessment of the pericardial ana tomy, detect the presence of active in \202 ammation, identify and often characterize peri cardial tumors and cysts, and help de \201 ne the haemodynamic consequences of pericardial disease. Pericarditis and pericardial effusions \200 In acute pericarditis, CMR with T 2 -STIR seq uences can often uniquely delineate areas of high signal in the pericardium, re \202 ectin g acute in \202 ammation. CMR can also reveal pericardial thickening, and the use of appro priate pre-pulses can facilitate the delineation of pericardium from surrounding fat or \202 uid. CMR is a particularly sensitive technique for the assessment of pericardial effusions. This can be readily accomplished with echocardiography; however, CMR can be helpful in the setting of loculated pericardial effusions; detecting pericardial haematoma; in those with poor ECHO windows; and in patients where neoplasia is suspected a nd information is required about surrounding tissues. CMR can be used to assess the sequelae of acute pericarditis. The administration of gadolinium can help to identify myocardial involvement, i.e. myoperic arditis, and, in the late phase, CMR can be used to diagnose constrictive pericarditis and to assess for surgery. Constrictive pericarditis \200 The pericardium is thickened and often low signal due to t he presence of \201 brotic tissue and calcium, which has poor water content. A pericardial t hickness > 4 mm should raise the index of suspicion for constriction. However, normal peric ardial thickness, i.e. 2 mm or less, does not exclude the condition. Other features that ma y be present include bi-atrial dilatation, engorgement of the IVC and hepatic veins, pleura l effusions, narrowing of the RV cavity, and reduction in the size of the AV groove. RV lon g-axis function, however, is often preserved in distinction to the situation with a restric tive cardiomyopathy. CMR tagging techniques can be used to identify \201 brous continuity between visceral and parietal pericardium. Real-time free-breathing cine sequences can be used to detect the haemodynamic effects of p ericardial constriction. The RV normally starts to \201 ll earlier than the LV. The const ricting pericardium prevents expansion of the RV that would normally accommodate this \201 lling. As a result, the interventricular septum is pushed from right to left in early diastole ( \200\230early septal bounce \200\231). Inspiration, by increasing RV \201 llin g, exacerbates the situation increasing left-ward septal movement in early diastole, partic ularly after the \201 rst heart beat following inspiration. These changes are not seen in restrictive cardiomyopathy. CMR FOR PERICARDIAL DISEASE 79 Pericardial defects \200 There may be partial or complete absence of the pericardium. Mos t