Les examens cardiaques en tomographie par émission de positons

Cardiac positron emission tomography (PET) is yet considered as a reference imaging technique but remains poorly used in clinical practice. At the present time, the advantages of cardiac PET investigations are far to be evident, when compared with conventional tomoscintigraphy (SPECT), except for perfusion imaging in the obese and for viability assessment in case of very severe cardiac dysfunction. However, this situation might quickly move because of an enhanced availability of PET imaging, dramatic technical progresses and promising new tracers. In particular, the last-generation PET-cameras allow reaching spatial resolutions and detection sensitivities, which are now spectacularly higher than those from conventional SPECT imaging. In addition, the list mode recording allows the subsequent images reconstruction to be synchronized to cardiac cycle but also to respiratory cycle; and the quantifications of myocardial perfusion flow and of coronary flow reserve are now available in clinical routine. Furthermore, new tracers labelled with fluorine-18 are under development, especially for perfusion investigations, and kinetics properties of these new tracers are dramatically enhanced when compared with current perfusion SPECT tracers.     

Évaluation de la perfusion myocardique par TEP-TDM

For the past decade, PET and PET/CT have been widely studied for myocardial perfusion imaging. Several studies demonstrated the incremental value of PET for the diagnostic and prognostic assessment of patients with coronary artery disease. Moreover, PET allows for non-invasively quantifying myocardial blood flow and myocardial flow reserve, that both are recognized as surrogate marker of cardiac event free survival. By enabling the exploration of epicardial disease and the microvasculature, PET constitutes a unique tool to study pathophysiogical mechanisms leading to atherosclerosis genesis. The recent emergence of high-tech hybrid machines may even provide further incremental information about coronary function and morphology. By taking the best of each modality, a better assessment of patients with coronary artery disease is expected.     

New aspects of ICD therapy: from rhythm therapy to complex cardiac monitoring. Development of an implantable, ICD-assisted, intrathoracic 6-channel ECG for continuous monitoring of high infarct risk patients]

Implantable defibrillator systems (ICD) are therapy of choice for the treatment of life-threatening ventricular arrhythmias and in prevention of sudden cardiac death. In more than 80% of patients who receive an ICD, the underlying cardiac disease is a coronary heart disease. Since arrhythmogenic sudden cardiac death can be reliably prevented in these patients by the use of ICD technology, the cardiac prognosis for these patients is determined by the occurrence of myocardial ischemia and myocardial infarction, as well as from the heart failure which develops in consequence. An intrathoracic 6-channel ECG comparable to the standard surface ECG can be reconstructed by further technical development of the electrode configurations currently present in ICD systems. The importance of this development in early diagnosis of myocardial ischemias and myocardial infarction can hardly be adequately estimated at the moment. The chronic consequences of myocardial infarction can be completely prevented or at least greatly reduced by means of such diagnostics and inclusion of immediate initiation of effective, appropriate early therapeutic measures before more serious symptoms even occur. In the development and pilot studies thus far, it has been found that the intrathoracic 6-channel ECG which can be generated in the ICD is capable of reliably recognizing acute myocardial ischemia, irrespective of localization or extent earlier and better than the standard surface ECG. Continuous preventive ischemia monitoring using the implanted ICD thus appears possible in patients at risk of infarction.     

Cardiac PET-CT: advanced hybrid imaging for the detection of coronary artery disease

Hybrid imaging of positron emission tomography (PET) together with computed tomography (CT) is rapidly emerging. In cardiology, this new advanced hybrid imaging modality allows quantification of cardiac perfusion in combination with assessment of coronary anatomy within a single scanning session of less than 45 minutes. The near-simultaneous anatomical evaluation of coronary arteries using CT and corresponding functional status using PET provides a wealth of complementary information in patients who are being evaluated for (suspected) coronary artery disease, and could help guide clinical patient management in a novel manner. Clinical experience gained with this recently introduced advanced hybrid imaging tool, however, is still limited and its implementation into daily clinical practice remains largely unchartered territory. This review discusses principles of perfusion PET, its diagnostic accuracy, and potential clinical applications of cardiac PET-CT in patients with ischaemic heart disease. (Neth Heart J 2010;18:90–8.)     

Apport de l’IRM cardiaque à l’exploration des cardiopathies ischémiques

This article presents the current and future possibilities of the cardiac magnetic resonance imaging (MRI) in the ischemic heart disease. It is not an emergency technique, but is becoming an element of decision for an acute myocardial infarction. It makes it possible to visualize the extent of the myocardial lesions in post acute infarction, to appreciate functional recovery and to uncover a nonsymptomatic coronary stenosis or of atypical clinical presentation. The visualization of the coronary arteries in MRI is realizable, but remains experimentation field. The cardiac MRI place is to be defined by each medical team according to their diagram of ischemic heart disease follow-up.     

Myocardial ischemia--association with perioperative cardiac morbidity.

The development of ambulatory electrocardiographic recorders and analysers and the application of transesophageal echocardiography in the mid-1980''s enabled investigators to quantify and describe the occurrence of silent as well as symptomatic ischemia in the perioperative period. Several technical advances which have recently occurred in ECG monitoring include the use of miniaturized digital computing equipment to store and analyze data. In addition, real time ST-segment analysis has become widely available on multicomponent monitors in both the operating room and intensive care units. The incidence of perioperative myocardial ischemia depends on the patient population, the surgical procedure, and the monitoring technique used. Several studies in the early 1990''s have shown that cardiac morbidity in patients undergoing major, noncardiac surgery is best predicted by postoperative myocardial ischemia, rather than tradition preoperative clinical predictors. Long duration postoperative ischemia may be the factor most significantly associated with adverse cardiac outcome. Postoperative pain, physiological and emotional stress may all combine to cause tachycardia, hypertension, increase in cardiac output, and fluid shifts which, in high risk patients, might result in subendocardial ischemia and eventual myocardial infarction. If postoperative myocardial ischemia is the cause of late postoperative myocardial infarction in patients undergoing non-cardiac surgery, then treatment of postoperative myocardial ischemia should reduce morbidity. In addition, reducing pain and stress and avoiding postoperative hypoxemia might prevent postoperative myocardial ischemia and minimize the need for extensive preoperative cardiac evaluation.     

Nuclear cardiac imaging for the assessment of myocardial viability

An important aspect of the diagnostic and prognostic work-up of patients with ischaemic cardiomyopathy is the assessment of myocardial viability. Patients with left ventricular dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischaemia but at the same time benefit most from revascularisation. It is important to identify viable myocardium in these patients, and radionuclide myocardial scintigraphy is an excellent tool for this. Single-photon emission computed tomography perfusion scintigraphy (SPECT), whether using ²⁰¹thallium, ^99mTc-sestamibi, or ^99mTc- tetrofosmin, in stress and/or rest protocols, has consistently been shown to be an effective modality for identifying myocardial viability and guiding appropriate management.Metabolic and perfusion imaging with positron emission tomography radiotracers frequently adds additional information and is a powerful tool for predicting which patients will have an improved outcome from revascularisation. New techniques in the nuclear cardiology field, such as attenuation corrected SPECT, dual isotope simultaneous acquisition (DISA) SPECT and gated FDG PET are promising and will further improve the detection of myocardial viability. Also the combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and noninvasive coronary angiography to myocardial perfusion imaging and quantification.     

TEMP/TDM et TEP/TDM en cardiologie : quel avenir ?

Over the recent years, clinical cardiology has witnessed a rapid evolution of multi-slice computed tomography (CT), starting with 4-slice CT developing into the current state of the heart 64-slice CT technology. This technology permits non-invasive visualization of the coronaries with high precision. CT coronary angiography will likely play an important role in the diagnosis of coronary artery disease. Because not all coronary stenoses detected by CT angiography are flow limiting, the stress myocardial perfusion imaging data complement the CT information. The integration of nuclear imaging (SPECT or PET) and CT data provides a potential opportunity to delineate the anatomic extent and the physiologic severity of coronary artery disease. The objective of this article is to provide a critical view of the relative strengths and weaknesses of myocardial perfusion imaging and CT coronary angiography, which we hope will help elucidate the potential role of these modalities in the diagnosis and management algorithms of patients with known or suspected coronary artery disease.     

Intrinsic defensive mechanisms in the heart: a potential novel approach to cardiac protection against ischemic injury

Despite recent advances in pharmacotherapy of coronary artery disease and interventional cardiology, the management of myocardial ischemia still remains a major challenge for basic scientists and clinical cardiologists. An urgent need to combat ischemic heart disease, its forms, such as infarction, and complications including sudden cardiac death led to the development of an alternative strategy of myocardial protection based on the exploitation of the heart's own intrinsic protective mechanisms. A new concept relies on the evidence that the heart is able to protect itself by way of adaptation, either short-term or long-term, to transient episodes of stress (e.g., ischemia, hypoxia, free oxygen radicals, heat stress, etc.) preceding sustained ischemia. Preconditioning by brief episodes of ischemia (ischemic preconditioning, IP) represents the most powerful cardioprotective phenomenon. Apart from the short-lasting protection afforded by classical IP or its delayed ("second window") phase, adaptation to long-lasting physiological stimuli or pathological processes is also known to increase myocardial resistance to ischemic injury. Although molecular mechanisms of cardiac adaptation conferring a higher ischemic tolerance still remain not sufficiently elucidated, multiple cascades of intracellular signalization are suggested to be involved in this process. Experimental studies led to the observations that pharmacological modulations at different levels of signal transduction might mimic protective effects of the adaptive phenomena and thus provide a safer way of inducing cardioprotection in humans.     

The percutaneous assessment of regional and acute coronary hot unstable plaques by thermographic evaluation (PARACHUTE) study: a prospective reproducibility and prognostic clinical study using thermography to predict future ischemic cardiac events

Intravascular thermography is currently being considered as a valuable tool in assessing macrophage-rich plaques. Since it is unknown what the prognostic value is of non-obstructive atherosclerotic plaques showing temperature heterogeneity, we designed the PARACHUTE study, a prospective, reproducibility, and prognostic clinical study using thermography in patients presenting with an unstable coronary syndrome. The primary endpoint of the study is the predictive value of temperature heterogeneity towards the occurrence of ischemic coronary events and hospitalization for ischemia and/or angina. The secondary endpoints are the predictive value of high-risk plaques associated with the development of future cardiac events, assessment of safety of the procedure, assessment of temperature reproducibility and heterogeneity in coronary arteries, as defined by the total thermal burden towards the occurrence of any cardiac event. Based on an event rate of death and myocardial infarction at 1 year of 10%, a sample size of 260 patients with presumed coronary artery disease, and positive troponin level who are scheduled to undergo an intervention will be included. All three main epicardiac vessels will undergo angiography and thermography at baseline after revascularization of the flow-limiting vessel. At 12 months, angiography of all vessels and thermography of the vessel with the highest thermographic burden will be performed. Independent core laboratories will assess outcomes and a clinical endpoint committee will assess clinical events.     

Thallium 201 Scintigraphy

The radioactive isotope thallium 201 behaves physiologically as a potassium analog, and when injected intravenously accumulates rapidly within the cells of many organs. Uptake of the isotope reflects both regional perfusion and sodium-potassium pump activity. The radionuclide emits 80 keV x-rays which are suitable for scintillation camera imaging.The main clinical application of ²⁰¹TI scintigraphy has been in myocardial imaging. Abnormal uptake of the isotope results in a cold spot on the myocardial image. In patients with coronary artery disease, the differentiation of ischemic and infarcted myocardium is made by comparing images obtained after injecting the radionuclide at the peak of a maximal exercise test with those obtained after injection at rest. Abnormalities due to ischemia usually are seen only on the stress image whereas fixed defects in both rest and stress studies usually indicate areas of infarction or scarring. Some investigators believe that redistribution images obtained four to six hours after stress injection (without administering further ²⁰¹TI) give the same information as a separate rest study. The sensitivity of stress imaging for detecting significant coronary disease is of the order of 80 percent to 95 percent, though computer processing of the images may be necessary to achieve the higher figure. The prediction of the extent of coronary disease from ²⁰¹TI images is less reliable. An abnormal ²⁰¹TI image is not entirely specific for coronary artery disease and the likelihood of an abnormal image being due to this diagnosis varies according to the clinical circumstances.The main clinical value of ²⁰¹TI myocardial imaging is likely to be in the noninvasive screening of patients with atypical chest pain or with ambiguous findings on stress electrocardiographic tests. It has also proved useful in studying patients with variant angina or following a coronary bypass operation. It is doubtful whether the technique is clinically helpful in most patients with suspected or established acute myocardial infarction.Imaging of organs other than the heart with ²⁰¹TI has received much less attention but has been reported in patients with peripheral vascular disease and various primary and secondary neoplasms.     

Exploration par tomodensitométrie multidétecteur du cœur et des artères coronaires

Due to its excellent spatial and temporal resolution, multislice computerized tomography (MSCT) allows visualizing the heart and coronary arteries. Although the indications of MSCT did not reach a consensus level yet, some trends can be stated. The advantages and limitations of MSCT in cardiac exploration are summarized in this article. The indications are mainly based on the excellent negative predictive value of MSCT regarding coronary artery disease. Hence, patients at low to moderate risk of coronary artery disease (CAD) mostly benefit of the technique. MSCT can be an alternate examination in case of non feasible or non contributive stress test. MSCT is highly contributive in the ostial analysis, in detecting abnormal coronary implantation or course, in assessing a reimplanted artery or in analysing bypass grafts. MSCT remains limited in patients with heavily calcified coronary arteries, and in patients with stented distal arteries.     

Nouveautés en cardiologie nucléaire : une gamma caméra à semi-conducteurs dédiée à l’imagerie cardiaque

During the last few years, cardiac imaging made important breakthroughs thanks to the development of various techniques allowing the risk stratification of patients with coronary artery disease. The well-established single photon emission computed tomography (SPECT) as a myocardial imaging technique made an important progress with the recent improvement of high-speed volumic acquisition, using dedicated semi-conductor gamma camera. These cameras bring significant improvement to the image quality and the image acquisition time, which is now seven times lower. New type of artefacts is expected because of the geometry of detection, thus studies are still needed to assess the exact performance of this revolutionary technology.     

Effect of repeated episodes of reversible myocardial ischemia on myocardial blood flow and function in humans

Nine patients with coronary artery disease and normal left ventricular (LV) function underwent two episodes of dobutamine-induced ischemia to determine whether repeated episodes of ischemia lead to cumulative stunning. Positron emission tomography (PET) and oxygen 15-labeled H(2)O was used to assess myocardial blood flow (MBF) at baseline, peak stress, and after stress for each ischemic episode. Quantitative echocardiographic assessment of global ejection fraction (EF) and regional systolic function (SF) was performed at rest and regular intervals after dobutamine. SF was assessed for regions subtended by a coronary artery with a >70% diameter stenosis. Both EF and SF were more severely impaired 45 min after the second episode of stress compared with 45 min after the first (both P < 0.01), despite no difference in duration of the two dobutamine infusions or MBF at peak stress (1.72 vs. 1.69). After both episodes of ischemia, when LV function was impaired but subsequently recovered, MBF (1.15 +/- 0.39 and 1.20 +/- 0.43, respectively) was no different to baseline MBF (1.02 +/- 0.35), confirming that repeated episodes of dobutamine-induced ischemia lead to cumulative myocardial stunning.     

超声心动图评价冠状动脉慢血流现象的应用进展

摘要：冠状动脉慢血流现象(coronary slow flow phenomenon, CSFP)是通过冠状动脉血管造影(coronary angiography, CAG)发现的以冠状动脉内径正常或接近正常的血管远端造影剂显像延迟为特征的冠状动脉血管病变。多数患者心脏无器质性病变,但反复出现各种不同形式的心肌缺血症状,CSFP也可能引发如恶性心律失常、急性心肌梗死等严重的心脏不良事件,因此早期评估CSFP尤为重要。既往多种影像学检查手段价格昂贵、检查时间过长,并且后期随访及疗效评估困难,限制了这类检查在临床上的应用。传统的超声心动图指标难以反映早期心肌损伤,近年来各种超声心动图新技术检查在CSFP的定性、定量研究中都发挥了重要作用,其中斑点追踪成像技术(speckle tracking imaging,STI)更是在安全无创的基础上具有更高的准确性和敏感性。     

Role of NO in coronary and systemic vasodilation following cardiogenic reflexes

In acute experiments on anesthetized dogs under closed-chest conditions, we used the technique of double lumen catheterization of coronary vessels and peripheral vessel bed. We studied the role of endothelium-dependent relaxing factor/nitric oxide (EDRF/NO) in the development of parasympathetic coronary vasodilation after excitation of cardiac receptors. Under conditions of pharmacological stimulation of cardiac receptors of the left ventricle and short-lasting episodes of local myocardial ischemia, we also examined the effects of inhibition of NO synthesis on the development of cardiogenic depressor reflexes (hypotension and peripheral vasodilation). It was found that the reflex coronary dilatation following excitation of the cardiac (left ventricular) receptors significantly decreased after systemic NO synthase inhibition. Thus, NO production is one of the effector mechanisms of the development of coronary vessel dilatation; this conclusion is confirmed by changes in the dilatation level after blockade of this process with L-NNA (nitro-ω-L-arginine). We pioneered in demonstrating that after the blockade of NO synthesis peripheral vessel vasodilation decreases or disappeas altogether when cardiogenic reflexes are realized following pharmacological excitation of cardiac receptors with veratrine or catecholamine injections, and vasoconstrictor responses evoked by myocardial ischemia are significantly intensified. It is suggested that the influences of NO-dependent mechanisms exert a dual effect on sympathic control-mediated peripheral vasodilation during cardiogenic reflexes. Such mechanisms reduce central sympathetic tone and/or concurrently provide peripheral inhibition of neural sympathetic influences; in the latter case, NO-dependent cardiogenic reflexes play a crucial role in compensatory reactions after an injury to the heart.     

Use of a Hanging Weight System for Coronary Artery Occlusion in Mice

Murine studies of acute injury are an area of intense investigation, as knockout mice for different genes are becoming increasingly available ^1-38. Cardioprotection by ischemic preconditioning (IP) remains an area of intense investigation. To further elucidate its molecular basis, the use of knockout mouse studies is particularly important ^{7, 14, 30, 39}. Despite the fact that previous studies have already successfully performed cardiac ischemia and reperfusion in mice, this model is technically very challenging. Particularly, visual identification of the coronary artery, placement of the suture around the vessel and coronary occlusion by tying off the vessel with a supported knot is technically difficult. In addition, re-opening the knot for intermittent reperfusion of the coronary artery during IP without causing surgical trauma adds additional challenge. Moreover, if the knot is not tied down strong enough, inadvertent reperfusion due to imperfect occlusion of the coronary may affect the results. In fact, this can easily occur due to the movement of the beating heart.Based on potential problems associated with using a knotted coronary occlusion system, we adopted a previously published model of chronic cardiomyopathy based on a hanging weight system for intermittent coronary artery occlusion during IP ³⁹. In fact, coronary artery occlusion can thus be achieved without having to occlude the coronary by a knot. Moreover, reperfusion of the vessel can be easily achieved by supporting the hanging weights which are in a remote localization from cardiac tissues.We tested this system systematically, including variation of ischemia and reperfusion times, preconditioning regiments, body temperature and genetic backgrounds³⁹. In addition to infarct staining, we tested cardiac troponin I (cTnI) as a marker of myocardial infarction in this model. In fact, plasma levels of cTnI correlated with infarct sizes (R2=0.8). Finally, we could show in several studies that this technique yields highly reproducible infarct sizes during murine IP and myocardial infarction^{6, 8, 30, 40, 41}. Therefore, this technique may be helpful for researchers who pursue molecular mechanisms involved in cardioprotection by IP using a genetic approach in mice with targeted gene deletion. Further studies on cardiac IP using transgenic mice may consider this technique.     

Acquired hemophilia in a patient with myeloma.

The generally accepted indications for stress testing in patients with coronary artery disease include confirming the diagnosis of angina, determining the limitation of activity caused by angina, assessing prognosis in patients with known coronary artery disease, assessing perioperative risk, and evaluating responses to therapy. In patients with a clinical scenario strongly suggestive of angina, testing is not necessary to diagnose coronary artery disease. The exercise treadmill-electrocardiogram test is the oldest and most extensively used stress test and can be reliably performed in patients who are clinically stable and who have an interpretable resting electrocardiogram. The addition of myocardial imaging agents such as thallium 201, technetium Tc 99m sestamibi, and technetium Tc 99m teboroxime increases the sensitivity and specificity for detecting coronary disease. Pharmacologic agents such as dipyridamole, adenosine, and dobutamine may be used in patients who cannot exercise adequately. Myocardial ischemia can also be evaluated by echocardiography, computed tomography, or magnetic resonance imaging, especially when additional information such as left ventricular and valvular function is desired. We review the indications for the noninvasive evaluation of coronary artery disease and the rationale for selecting a diagnostic test.     

Free fatty acid metabolism during myocardial ischemia and reperfusion

Long chain free fatty acids (FFA) are the preferred metabolic substrates of myocardium under aerobic conditions. However, under ischemic conditions long chain FFA have been shown to be harmful both clinically and experimentally. Serum levels of free fatty acids frequently are elevated in patients with myocardial ischemia. The proposed mechanisms of the detrimental effects of free fatty acids include: (1) accumulation of toxic intermediates of fatty acid metabolism, such as long chain acyl-CoA thioesters and long chain acylcarnitines, (2) inhibition of glucose utilization, particularly glycolysis, during ischemia and/or reperfusion, and (3) uncoupling of oxidative metabolism from electron transfer. The relative importance of these mechanisms remains controversial. The primary site of FFA-induced injury appears to be the sarcolemmal and intracellular membranes and their associated enzymes. Inhibitors of free fatty acid metabolism have been shown experimentally to decrease the size of myocardial infarction and lessen postischemic cardiac dysfunction in animal models of regional and global ischemia. The mechanism by which FFA inhibitors improve cardiac function in the postischemic heart is controversial. Whether the effects are dependent on decreased levels of long chain intermediates and/or enhancement of glucose utilization is under investigation. Manipulation of myocardial fatty acid metabolism may prove beneficial in the treatment of myocardial ischemia, particularly during situations of controlled ischemia and reperfusion, such as percutaneous transluminal coronary angioplasty and coronary artery bypass grafting. (Mol Cell Biochem 166: 85-94, 1997)     

Gender differences in detecting coronary artery disease with dipyridamole stress myocardial perfusion imaging using 99m-Tc sestamibi gated SPECT

There are some specifics in the presentation of coronary artery disease (CAD) in women compared with men that may cause diagnostic pitfalls. The accuracy of noninvasive diagnostic testing in women tends to be lower than that in men. Stress myocardial perfusion imaging with 99m-Tc sestamibi gated SPECT is an accurate technique for detecting CAD. Only a few studies have compared dipyridamole stress imaging according to gender. The aim of the study was to compare the diagnostic value of dipyridamole myocardial perfusion imaging with 99m-Tc sestamibi gated SPECT in detecting CAD among patients of both sexes. We studied 62 consecutive patients (38 men, 24 women) using 99m-Tc sestamibi gated SPECT and dipyridamole stress to detect CAD. All the patients also underwent coronary angiography. Overall regional sensitivity was significantly lower in women compared with men (71.4% vs. 92.7%, p=0.039). There were no significant differences for detecting CAD in individual coronary arteries, although regional sensitivity in all three vascular territories was higher in men compared to women. The lowest sensitivity in women was found in the LAD territory (66.6%). Overall regional specificity in men and women was similar and did not reach statistical significance (88.7% vs. 94.7%). Significantly lower specificity in men was found only in the RCA territory (79.1%), compared with that in women (100%). Our results confirmed that there are certain gender differences in the diagnostic performance of dipyridamole stress myocardial perfusion imaging with 99-Tc sestamibi gated SPECT which are assigned to the characteristics of the female population. However, the diagnostic accuracy is also quite high in women, which makes this technique efficient enough in detecting CAD among this population.