Myocardial viability

This article reviews various means to assess myocardial viability by imaging, and provides recommendations for current clinical practice. This article also discusses future directions in assessing myocardial viability.     

Myocardial viability assessment using nuclear imaging

Myocardial assessment continues to be an issue in patients with coronary artery disease and left ventricular dysfunction. Nuclear imaging has long played an important role in this field. In particular, PET imaging using 18F-fluorodeoxyglucose is regarded as the metabolic gold standard of tissue viability, which has been supported by a wide clinical experience. Viability assessment using SPECT techniques has gained more wide-spread clinical acceptance than PET, because it is more widely available at lower cost. Moreover, technical advances in SPECT technology such as gated-SPECT further improve the diagnostic accuracy of the test. However, other imaging techniques such as dobutamine echocardiography have recently emerged as competitors to nuclear imaging. It is also important to note that they sometimes may work in a complementary fashion to nuclear imaging, indicating that an appropriate use of these techniques may significantly improve their overall accuracy. In keeping these circumstances in mind, further efforts are necessary to further improve the diagnostic performance of nuclear imaging as a reliable viability test.     

Myocardial viability: Seeking relevance and redefinition

Conclusions  More than any other discipline, nuclear cardiology has contributed to understanding of myocardial viability, including the concepts of hibernation and stunning. It must be recognized, however, that these concepts are used as models to drive the process of scientific inquiry. These models may describe components of the pathophysiology of ventricular dysfunction in CAD. Integration of the models of hibernation and stunning may represent the next step toward a more complete understanding of how CAD causes ventricular dysfunction. As such, we are now poised to redirect the field of viability assessment. Although the development of improved instrumentation, new tracers, and better software are important, the areas of investigation that will have the most significant effect on cardiology as a whole are those that will elucidate the pathophysiologic components of LV dysfunction in CAD. The knowledge can then be applied to clinical processes such as viability assessment, with attention to how new techniques affect prognosis and cost of health care. The nuclear imaging community should strive to develop techniques that are complementary to “competing” technologies such as magnetic resonance imaging and echocardiography, providing incremental information. Significant contributions to these lines of investigation will require cooperative studies to achieve adequate statistical power, including collaboration with the PET community. With studies addressing both the pathophysiology and the impact on clinical outcomes of myocardial viability and its assessment, the nuclear cardiology community will have much to contribute to our understanding of CAD.     

Myocardial viability: What do we need?

Coronary revascularization in patients with chronic coronary heart disease (CHD) or acute myocardial infarction (AMI) is mainly based on factors such as coronary anatomy, ventricular function, accompanying diseases and the patient's biological age. Rest- or exercise-induced ischaemia should be proven before a bypass operation or percutaneous transluminal coronary angioplasty. Although a significant amount of ischaemic but still viable myocardium is a necessary condition for successful revascularization, the detection of viable myocardium is of major importance in a rather small subset of patients. These are patients with hibernating (or a combination of hibernating and stunned) myocardium in whom the aforementioned parameters do not yield an unequivocal result. Thallium-201 myocardial scintigraphy with re-injection or rest-redistricution is an established, proven and cost-effective way of detecting viable myocardium. Other methods such as positron emission tomography with different tracers or technetium-99m sestamibi SPET are discussed and compared to thallium-201 SPET. In conclusion, the detection of ischaemic but still viable myocardium is of importance in only a rather small subset of patients with CHD. In this context thallium-201 myocardial SPET is and still remains the method of choice. Correspondence to: H. Schoeder     

Cartilage viability after trochleoplasty

Trochleoplasty is an established and accepted technique for the treatment of patellar instability because of a missing trochlear groove. In this technique, a flap of cartilage over the trochlea is carefully removed and a new trochlear groove is created in the underlying bone before the cartilaginous flap is reattached with sutures. The mid-term clinical and radiological results of this operation are promising but no information about the viability of the reattached cartilage has been reported. To evaluate cartilage viability and quality after trochleoplasty and to verify the healing process, two osteochondral biopsies were harvested from three patients 6, 8, and 9 months after trochleoplasty. One cylinder was evaluated histologically to assess cartilage, calcified cartilage (cc), and subchondral bone quality, while the other one was examined by confocal microscopy to evaluate cell viability. The histological examination showed a normal matrix and cell distribution of the cartilage, while the cc showed lacunae ingrowing from the underlying bone. The subchondral bone showed normal lamellae and histology, and the healing of the flap. Confocal microscopy showed almost exclusively viable chondrocytes. This demonstration of non-injured cartilage at short-term follow-up together with promising clinical and radiological 2- and 5-year follow-up results indicate a potential promising outlook for the long term, as further chondral damage is not expected. So trochleoplasty can be seen as a primary intervention for patellar instability because of trochlear dysplasia as the risk for cartilage damage is low.     

Myocardial viability: assessment with three-dimensional MR imaging in pigs and patients

PURPOSE: To prospectively evaluate the correlation between a three-dimensional (3D) delayed enhancement magnetic resonance (MR) imaging sequence and a two-dimensional (2D) delayed enhancement MR imaging sequence for noninvasive assessment of myocardial viability in pigs and patients. MATERIALS AND METHODS: The pig and patient studies were approved by the responsible authorities, and patients gave written informed consent. MR imaging was performed by using a rapid 3D inversion-recovery balanced steady-state free precession sequence and a 2D segmented inversion-recovery fast low-angle shot sequence as the reference standard. Fourteen pigs with reperfused (n=7) or nonreperfused (n=7) myocardial infarction and 17 patients (13 men, four women; mean age, 64.9 years+/-8.6 [standard deviation]) suspected of having myocardial infarction were included. Linear regression analysis and Bland-Altman analysis were used to compare the infarction volumes. RESULTS: In 10 of the 14 pigs the induction of myocardial infarction was successful. In these pigs, altogether 81 segments with myocardial infarction were demonstrated by both MR sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 99.7%. The infarction volume determined by using 3D MR imaging (4.64 cm3+/-2.48) in the pigs highly correlated with that of 2D MR imaging (4.65 cm3+/-2.39, r=0.989, P<.001) and that of staining by using triphenyltetrazolium chloride (4.67 cm3+/-2.44, r=0.996, P<.001). Thirteen of the 17 patients examined showed myocardial infarction in 34 myocardial segments with both sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 98.6%. In the patients, the infarction volume determined with both sequences highly correlated (9.71 cm3+/-7.47 for the 3D sequence vs 10.01 cm3+/-8.04 for the 2D sequence, r=0.982, P<.001). The breath-hold time necessary for the 3D MR imaging (21.0+/-2.3 seconds) was significantly shorter than that for 2D MR imaging (188.3+/-20.2 seconds, P<.001). CONCLUSION: Myocardial infarction volumes obtained with the 3D MR imaging sequence are highly correlated and in good agreement with volumes obtained with the 2D MR imaging standard approach and reduced the acquisition time by a factor of nine.     

肾上腺髓质素对心肌梗死大鼠心肌重构的影响

目的探讨肾上腺髓质素(adrenomedullin,AM)对心肌梗死大鼠心肌重构的影响作用。方法采用结扎左冠状动脉前支制作大鼠心肌梗死模型,并将术后存活的40只大鼠随机分为(1)心肌梗死对照组,(2)0.05nmol.kg-1.d-1AM组,(3)0.1nmol.kg-1.d-1AM组,(4)1.0nmol.kg-1.d-1AM组;另设假手术组。各处理组每日皮下注射AM。4周后测量各组大鼠心脏重量指数(hear weighy index,HWI),左室重量指数(left ventricular weight index,LVWI),左室非梗死区羟脯氨酸含量。结果与假手术组比较,心肌梗死组HWI、LVWI,羟脯氨酸均明显增加(P<0.01);与心肌梗死组比较,不同剂量AM组上述指标均显著下降,并呈剂量依赖性(P<0.01)。结论AM可有效改善心肌梗死大鼠心肌重构现象。     

Myocardial tissue fraction--correction for partial volume effects and measure of tissue viability

We have compared two independent methods of correcting the systematic underestimation in measurements of myocardial radiotracer concentration due to wall motion and small transmural wall thickness in cardiac PET studies. The first technique was based on measurement of the tissue fraction by fitting 15O-labeled water dynamic PET data. The other technique involved the subtraction of the C15O-blood volume scan from the transmission data, producing an image of extravascular density. In normal myocardial regions, both values were observed to be about 60% of myocardial tissue density. The tissue fraction was approximately 10% larger than the extravascular density in normal tissue regions. The ratio of alpha/Dev indicates the proportion of the total extravascular tissue for a given ROI that is perfusable by water--independent of the partial volume effect. This ratio was confirmed to be the expected value in normal tissue regions but was reduced in regions of infarction. The use of 15O-water, C15O and transmission data may aid in the differentiation between perfusable and nonperfusable tissue in the infarcted myocardium.     

Myocardial perfusion after marathon running

We investigated the effects of acute prolonged exercise (marathon running) on cardiac function and myocardial perfusion. Cardiac dimensions and function were measured in seven endurance-trained men using echocardiography before and repeatedly after marathon (42.2 km) running (at 10 min, 150 min, and 20 h). Myocardial perfusion and perfusion resistance were measured using positron emission tomography and 15O-H2O before and 85-115 min after running. Echocardiographic indices showed only mild and clinically non-significant changes in cardiac function after running. Rate-pressure-corrected basal myocardial perfusion (0.89+/-0.13 vs. 1.20+/-0.32 mL min(-1) g(-1), P=0.04) was increased after running. Also, adenosine-stimulated perfusion tended to be higher (3.67+/-0.81 vs. 4.47+/-0.52 mL min(-1) g(-1), P=0.12) and perfusion resistance during adenosine stimulation was significantly lower after running (26+/-6 vs. 18+/-3 mmHg min g mL(-1), P=0.03). Plasma free fatty acid (FFA) concentration was significantly increased after running. These results show that marathon running does not cause marked changes in cardiac function in healthy men. Basal perfusion was increased after exercise, probably reflecting changes in fuel preferences to increased use of FFAs. Strenuous exercise also seems to enhance coronary reactivity, which could thereby serve as a protective mechanism to vascular events after exercise.     

Assessment of myocardial viability after myocardial infarction

Conclusions  The data presented above suggest that assessment of myocardial viability after MI, particularly in those patients with severe LV dysfunction, is important for the identification of those with the highest risk, in whom revascularization can be of clinical benefit. There is growing and consistent evidence that patients with relatively large areas of dysfunctional but viable myocardium after MI have improved function, symptoms, and survival with prompt revascularization compared with medical therapy alone. Most importantly, long-term survival with revascularization in these patients is comparable with that achieved with cardiac transplantation. There are several methods available to the clinician with which to investigate the presence of tissue viability, and the evidence suggests that the scintigraphic approaches are the most sensitive. These observations suggest that noninvasive investigation of the amount of ischemic myocardium should be an important component of the diagnostic evaluation of patients with severe LV dysfunction after MI. This approach will likely enhance the often difficult process of selecting patients with poor cardiac function in whom revascularization will likely improve both the quality and quantity of life.     

Myocardial viability: breath-hold 3D MR imaging of delayed hyperenhancement with variable sampling in time

A method for visualizing myocardial infarction with a three-dimensional (3D) breath-hold gated acquisition was examined. By using variable sampling in time, whole heart coverage with a single volume acquisition was achieved in 24 heart beats. In a study of 35 patients, in whom 3D volume acquisition was compared with a two-dimensional (2D) acquisition, all regions of myocardial infarction were correctly identified at 3D examination. The mean imaging time for 12 section locations was 8.0 minutes +/- 3.0 with a 2D approach compared with 22 seconds +/- 4 with a 3D approach (P <.001). Advantages were also noted for infarct contrast-to-noise ratio: 60 +/- 37 for 3D versus 33 +/- 20 for 2D imaging (P <.001). No significant differences (P >.05) were noted at qualitative assessment of myocardial suppression, endocardial border visualization, respiratory and cardiac motion artifacts, or confidence of transmurality of the infarct.     

Myocardial scintigraphy--25 years after start

The development of myocardial scintigraphy (MS) reflects the clinical success of a representative procedure in nuclear medicine. Radiopharmaceuticals for visualizing vital and damaged myocardium and techniques (planar-qualitative, planar-quantitative, SPECT-qualitative-quantitative with comparative sensitivities) are briefly reviewed with the main focus on their clinical application in coronary (CHD) and noncoronary heart disease, where recent literature from the United States and Europe is considered. The limited value of MS for screening of CHD is outlined and its present and future role in detecting asymptomatic (silent) ischemia/infarction and symptomatic patients at professional risk is stressed. The present state of MS in coronary heart disease is discussed for single and multivessel disease, previous infarction, and risk stratification (myocardial washout, pulmonary uptake, ischemic dilation, absent heart sign), reflecting the importance of the procedure in exercise-induced ischemia as well as in ischemia at rest for prognostication of the natural and therapeutic course, i.e., therapy control (angioplasty, bypass, lysis, cardiac drugs). More marginal but upcoming clinical indications are mentioned, such as progressive systemic sclerosis, cardiac transplantation, pediatric cardiology, and problems of nephrology/urology. The "normal" values and the impact of digital radiology and of contrast cardiography are touched upon. Preliminary cases with 111In-antimyosin and 99mTc-Isonitriles are presented including correlative results between global ejection fraction determination according to gated 99mTc-isonitrile and conventional 99mTc-erythrocyte ventriculogram (r = 0.75; n = 10).     

DISA SPECT对心梗后骨髓干细胞移植心肌灌注和代谢的评价

目的:探讨DISASPECT在评价心肌梗死患者骨髓干细胞移植后心肌血流灌注和细胞代谢改变的价值。材料和方法:18例心肌梗死行骨髓干细胞移植治疗的患者在术前2周、术后3个月行DISA显像(18F-FDG心肌代谢显像和99Tcm-MIBI心肌灌注显像),其中4例在术后9个月再次进行复查。用目测法和半定量法分析图像。结果:①干细胞移植治疗前后99Tcm-MIBI显像和18F-FDG显像的F值分别为5.27±0.55、5.05±0.41与6.50±1.71、6.24±0.93,两者比较差异有统计学意义(P<0.05)。②18例中3例代谢靶心图面积治疗前后无明显变化,15例治疗后靶心图面积出现不同程度的恢复(83%),治疗后代谢恢复的面积占治疗前缺损面积的25.2%±4.8%。结论:心肌梗死行骨髓干细胞移植治疗后,心肌血流灌注与细胞代谢均有显著性差异;灌注结合代谢能较好地观察和评价心肌梗死行骨髓干细胞移植治疗后改善程度。     

Myocardial stress after competitive exercise in professional road cyclists

PURPOSE: Based on the determination of cardiac troponin (cTnT), brain natriuretic peptide (BNP), and echocardiographic measurements, recent investigations have reported myocardial damage and reversible cardiac dysfunction after prolonged endurance exercise in apparently healthy subjects. In the present study, we investigated the myocardial stress reaction in professional endurance athletes after strenuous competitive physical exercise. METHODS: Eleven highly trained male professional road cyclists (age 27 +/- 4 yr; .VO2peak 67 +/- 5 mL.kg-1.min-1; training workload 34,000 +/- 2,500 km.yr-1) were examined. The following parameters were determined before and after one stage of a 5-d professional cycling race: BNP, cTnT (third-generation assay that shows no cross reactivity with skeletal TnT), creatine kinase (CK), creatine kinase MB (CKMB), myoglobin (Myo), and urea. All participants were submitted to a careful cardiac examination including echocardiography and stress ECG. RESULTS: None of the athletes showed pathological findings in the cardiac examination. CK (P < 0.01), CKMB (P < 0.05), and Myo (P < 0.01) were increased after the race. Normal postexercise cTnT levels indicate that the increase in CK, CKMB, and Myo was of noncardiac origin. In contrast, BNP rose significantly from 47.5 +/- 37.5 to 75.3 +/- 55.3 pg.mL-1 (P < 0.01). Pre- and postexercise values of BNP as well as the individual exercise-induced increase in BNP were significantly correlated with age (R2 = 0.68, R2 = 0.66, and R2 = 0.58, respectively; P < 0.05). CONCLUSION: Strenuous endurance exercise in professional road cyclists does not result in structural myocardial damage. The rise in BNP in older athletes may reflect a reversible, mainly diastolic left ventricular dysfunction. This needs to be confirmed by larger trials including different intensities, sports, and age groups.     

Prediction of muscle viability after electrical burn necrosis.

In this preliminary study, Tc-99m MIBI, a muscle perfusion agent, was used to assess the viability of tissues in two patients with extensive high-tension electrical burns. This proved to be an easy and definitive diagnostic procedure and a practical solution to determining the level of amputation before surgery.