Pierre Melon

Relation Between Contractile Reserve and Positron Emission Tomographic Patterns of Perfusion and Glucose Utilization in Chronic Ischemic Left Ventricular Dysfunction: Implications for Identification of Myocardial Viability

OBJECTIVES This study sought to determine the incidence and extent of dobutamine-induced contractile reserve in myocardial regions characterized by classical and new positron emission tomographic (PET) patterns in patients with chronic ischemic left ventricular dysfunction. BACKGROUND PET is considered the most accurate method for assessment of myocardial viability, which is traditionally identified by perfusion-metabolism mismatch. METHODS In 23 patients, segmental wall thickening expressed by four echocardiographic scores at rest and during low dose (5 and 10 microg/kg body weight per min) dobutamine infusion and regional myocardial uptake of potassium-38 and fluorine-18 fluorodeoxyglucose (F-18 FDG) during glucose clamp were compared in 16 corresponding segments. RESULTS Of a total of 368 segments, data analysis focused on 214 (58%) dyssynergic segments at baseline. Contractile reserve was identified with increasing incidence according to the six following PET patterns: 1) diminished perfusion and moderate reduction of F-18 FDG uptake (3 [11%] of 28 segments); 2) proportional reduction of perfusion and F-18 FDG uptake (10 [23%] of 43 segments); 3) perfusion-metabolism mismatch (19 [46%] of 41 segments); 4) preserved perfusion but moderate reduction of F-18 FDG uptake (13 [46%] of 27 segments); 5) preserved perfusion and F-18 FDG uptake (37 [59%] of 63 segments) compared with our normal database; and 6) normal perfusion but absolute increased F-18 FDG uptake (8 [73%] of 11 segments). In the latter category, only 7 of 24 segments had normal rest function. In dyssynergic segments with F-18 FDG uptake > or = 50% supplied by vessels with > or = 75% stenosis, improvement in contractility during dobutamine correlated with the presence of collateral channels. CONCLUSIONS Myocardial regions with the traditional mismatch pattern of viability show contractile reserve in slightly < 50%. In segments with moderate reduction of F-18 FDG uptake, the contractile response to dobutamine is linked to the level of rest perfusion. Most segments with preserved perfusion and increased F-18 FDG uptake have impaired rest function, but contractile reserve is still present. These data suggest that in chronic ischemic left ventricular dysfunction, myocardial hibernation is a heterogeneous condition.

Fluorine-18-fluorodeoxyglucose positron emission tomography for preoperative parathyroid imaging in primary hyperparathyroidism

Fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging was performed in seven consecutive patients with primary hyperparathyroidism to preoperatively locate parathyroid adenomas. Foci of FDG accumulation corresponding to abnormal parathyroid tissue were observed in two out of nine surgically excised parathyroid adenomas. It was concluded that FDG PET imaging demonstrated a too low sensitivity for systematic preoperative detection and localization of parathyroid glands causing primary hyperparathyroidism.

Impact of contractile reserve on acute response to cardiac resynchronization therapy

BackgroundCardiac resynchronization therapy (CRT) provides benefit for congestive heart failure, but still 30% of patients failed to respond to such therapy. This lack of response may be due to the presence of significant amount of scar or fibrotic tissue at myocardial level. This study sought to investigate the potential impact of myocardial contractile reserve as assessed during exercise echocardiography on acute response following CRT implantation.MethodsFifty-one consecutive patients with heart failure (LV ejection fraction 27% ± 5%, 67% ischemic cardiomyopathy) underwent exercise Doppler echocardiography before CRT implantation to assess global contractile reserve (improvement in LV ejection fraction) and local contractile reserve in the region of the LV pacing lead (assessed by radial strain using speckle tracking analysis). Responders were defined by an increase in stroke volume ≥ 15% after CRT.ResultsCompared with nonresponders, responders (25 patients) showed a greater exercise-induced increase in LV ejection fraction, a higher degree of mitral regurgitation and a significant extent of LV dyssynchrony. The presence of contractile reserve was directly related to the acute increase in stroke volume (r = 0.48, p < 0.001). Baseline myocardial deformation as well as contractile reserve in the LV pacing lead region was greater in responders during exercise than in nonresponders (p < 0.0001).ConclusionThe present study showed that response to CRT largely depends not only on the extent of LV dyssynchrony and the severity of mitral regurgitation but also on the presence of contractile reserve.

Identification of cardiac repercussions after intense and prolonged concentric isokinetic exercise in young sedentary people

Cardiopathies are the worlds leading cause of mortality and morbidity. Although rare, cardiovascular accidents can occur during intense and infrequent sporting activity, particularly among those who are unaware of their heart condition. The development of cardiospecific biochemical markers has led to a reconsideration of the role of biology in the diagnosis of cardiovascular illnesses. The aim of this study therefore was, through the use of cardiac biomarker assays, to highlight the impact of sustained physical effort in the form of intense and prolonged concentric isokinetic exercise and to research potential cardiovascular risks.

The role of early measurement of Nitrogen-13 ammonia uptake for predicting contractile recovery after acute myocardial infarction

Previous studies have shown that the maintenance of cell membrane integrity and metabolism requires the persistence of residual myocardial blood flow. The purpose of this study was to assess the role of N-13 ammonia positron emission tomographic (PET) imaging performed early after an acute myocardial infarction for predicting functional recovery. Seventeen patients with an acute myocardial infarction were included in the study. Thirteen received thrombolytic therapy, 2 underwent immediate angioplasty of the infarct-related artery and 2 were treated with heparin. N-13 ammonia imaging was performed 6 ± 2 days after the acute event and was followed by elective angioplasty in 13 patients. Using a 16-segment polar map display, regional N-13 ammonia uptake was expressed as a percentage of maximal segmental uptake and classified as normal (<63%), moderately reduced (63–50%) and severely reduced (<50% based on values of tracer uptake obtained from healthy subjects. By echocardiographic assessment of regional wall thickening within 96 hours and at 1 month after the infarct, we examined the relationship between blood flow and functional outcome of myocardial segments in the infarct-related area. Regional wall thickening was graded on a 4-point scale: normal (1), hypokinesia (2), akinesia (3) and dyskinesia (4). Of 77 dyssynergic segments at baseline echocardiographic study, 43 had normal flow, 15 moderately reduced flow and 19 severely reduced flow. Segments with N-13 ammonia uptake ≥ 50% demonstrated a significant improvement in wall thickening score at follow-up (p<0.001), whereas segments with N-13 ammonia uptake <50% showed no improvement in wall thickening scores (p<0.001). The proportion of segments improving contractility by at least 1 score was significantly higher in the group of segments with N-13 ammonia uptake >63%. The predictive value for defining functional recovery with segmental N-13 ammonia uptake >63% was 86%. The predictive value for absence of recovery (uptake <50%) was 54%. In conclusion, our data showed that early after an acute myocardial infarction N-13 ammonia imaging provides information regarding functional outcome.

Imaging of myocardial metabolism by positron emission tomography.

SummaryTracer techniques have provided new insight in cardiology by allowing noninvasive studies of myocardial perfusion, function, metabolism, and, more recently, ligandreceptor interaction. Positron emission tomography allows accurate quantification and the use of natural substrates labelled with 11C, 13N, or 15O.Myocardial metabolism is complex and utilizes a number of substrates, primarily fatty acids. Fatty acids utilization can be studied with 11C palmitate, while 14C acetate more selectively traces TCA cycle activity and reflects myocardial oxygen utilization. Glucose uptake can be traced using 18F deoxyglucose, a glucose analog that is a substrate for hexokinase but is not further metabolized. Flow and oxidative glucose metabolism are usually coupled, and thereby the uptake of FDG and perfusion tracers are usually similar. In myocardial ischemia, however, glucose utilization can persist due to anaerobic glycolysis, and its uptake is frequently enhanced. Clinical applications of the use of metabolic studies in patients with ischemic heart disease are presented.

Identification of viable myocardium : dobutamine echocardiography versus positron emission tomography

In patients with coronary artery disease, regional myocardial contractile dysfunction was assumed, until recently, to be due to myocardial infarction. However, clinical and experimental studies showed that viable myocardium may demonstrate prolonged alteration in contractility in two different myocardial states, termed stunning [1] and hibernation [2]. Stunning is a reversible form of postischemic contractile dysfunction that occurs when ischemia, sufficiently brief to allow cell viability, is relieved by restoration of blood flow. Despite reperfusion, there is a persistent wall motion abnormality and a gradual improvement in contractility. The duration of myocardial stunning is dependent on the duration of ischemia and recovery may require days to weeks in clinical settings [3,4].

TWO BIOMARKERS FOR THE SCREENING OF CARDIAC RISK AMONG RUNNERS

Background Heart-type fatty acid-binding protein (H-FABP) is a low molecular weight protein involved in the intracellular uptake and buffering of long chain fatty in the myocardium. Troponin T is a component of the contractile apparatus of the striated musculature. Both are early markers for acute coronary syndrome. Objective The aim of our study was to compare the results obtained with the H-FABP and the highly sensitive cardiac troponins (hsTnT) and to test their cardiospecificity in healthy runners. Design Prospective, cohort study. Setting Amateur marathon runners. Patients 23 runners (marathon) were enrolled. Interventions We drowned blood samples at three times: just before (T0), just after (T1), and three hours after the end of the race (T3). Main outcome measurements H-FABP and hs-TnT were performed according to the manufacturers instructions. A linear regression was calculated to observe if there is any correlation between the two biomarkers. Values above the 95th percentile for H-FABP (2.5 ng/mL) and the 99th percentile for hsTnT (14 ng/L) were considered as positive. Results At T0, none of the subjects were positive for hsTnT but 35% were positive for H-FABP; at T1, 83% for hsTnT and 100% for H-FABP; at T3, 83% for hsTnT and 96% for H-FABP. At T0, the regression equation was H-FABP T0=3.9454–0.1001×hsTnT T0; at T1: H-FABP T1=51.838–1.7026×hsTnT T1; at T3: H-FABP T3=47.977–1.6193×hsTnT T3. No correlation was observed between the 2 biomarkers. Conclusion We observed a significant increase of H-FABP and hsTnT in runners. These markers are independent to each other. These values could biologically correspond to a heart ischemia. These biomarkers could be helpful for the screening of cardiac risk among runners.

Cardiac troponins and natriuretic peptides in runners: useful for cardiac risk screening ?

Background Cardiac troponins (cTn) are considered as the best biomarkers for detection of myocardial cell injury and NT-proBNP as the best for the cardiac insufficiency. Objective Our aim was to compare cTnT and NT-proBNP levels before and after the stress tests, in sportive subjects. Design Prospective, cohort study. Setting Amateur marathon runners and ultrarunners. Patients 28 subjects (26 men, 42.5±11 yrs) were enrolled. Interventions Subjects ran the Maasmarathon (42.195 kilometers) and 33 subjects (33 men, 45.7±9.3 yrs) ran the Ultratour of Liège (Belgium; 67 km). All subjects gave their informed consent. We took blood sample before (T0), just after (T1) and 3 hours after the race (T3). Main outcome measurements cTnT concentrations were measured by high sensitive methods (hsTnT, Roche Diagnostics) on heparin plasma. The NT-proBNP was also determined with the kit Roche on heparin plasma. All statistical analyses were performed using Medcalc version 8.1 for Windows. P-value <.01 was regarded as statistically significant. Results A significant difference between hsTnT concentrations at T0 and T1 (P<.001), and between T0 and T3 (P<.001) for NT-proBNP have been observed, but not between T1 and T3. This observation appeared only after a strenuous exercise. However, up to now this type of exercise is not reproducible easily in a laboratory. Moreover, nobody knows if these observations would have cardiac consequences at long terms. Conclusion Measurement of cardiac troponins by high sensitive methods allows detecting significant release of biomarkers from the heart during exercise. The value of NT-proBNP are also significant but less than TnThs. We think that the TnThs could be an interesting tool in the future to help sport medicine to detect risk of developing a cardiac problem in the future or a sudden death.

Use of a novel high-sensitivity troponin T, I and MPO, NT-proBNP assays to detect myocardial injury in patients with atrial fibrillation treated by direct-current cardioversion

Background: A fatty acid (FA) is a carboxilic acid with a long aliphatic chain, which is either saturated or unsaturated. Recently, the role of FA and particularly omega 3 and 6 has emerged as cardiovascular risk factor in the literature. The aim of our study was to establish reference value for these FA and to compare these results with data obtained in acute myocardial infarction (AMI) patients.1 Department of Clinical Chemistry of the University of Liege, Liege, Belgium 2 Department of Cardiology, CHU Sart-Tilman, Liege, Belgium 3 Department of Motricity Sciences of the University of Liege and CHU Sart-Tilman, Liege, Belgium Introduction: Novel high-sensitive cardiac troponin T (hsTnT) and I (TnI II) assays have the potential to detect myocardial injury with a higher sensitivity. The aim of the study was to assess the level of hsTnT and TnI II in patients with atrial fibrillation (AF) as compared to control and following direct current cardioversion. Levels of NT-proBNP, myeloperoxydase (MPO) and hs-CRP were concomitantly measured.