Background: The recent development of accurate methods to measure two-dimensional strain during dobutamine stress echocardiography has reactivated the debate as to the respective value of myocardial perfusion versus myocardial function assessment in detecting coronary stenoses. The aim of our study was to compare the effects of progressive coronary constrictions on two-dimensional strain and myocardial contrast echocardiography parameters during stress conditions.Methods: Nine open-chest pigs were studied in the setting of various degrees of coronary constrictions. Two-dimensional strain and myocardial contrast echocardiography with Flash refilling sequence acquisitions were obtained at rest and during dobutamine infusion. Values of longitudinal strain (LS), circumferential strain (CS), radial strain (RS), and wall thickening, as well as myocardial perfusion parameter (A.b), were then calculated.Results: At rest, accuracy for detecting coronary stenosis was higher for CS, LS, and A.b (74%, 67%, and 69%, respectively) than for RS or wall thickening (62% and 64%, respectively). Dobutamine stress echocardiography increased the accuracy of A. b and LS to 77% and to 73%, respectively. Sensitivity during stress was higher for CS (93%) and A. b (77%), whereas specificity was higher for LS (89%) than for other parameters. Combined evaluations (CS+A.b, CS+LS, and LS+A.b) during dobutamine stress echocardiography improved both sensitivity and accuracy for detecting coronary stenosis.Conclusion: Quantitative evaluation of contraction by LS and CS analysis and perfusion (A. b) during stress echocardiography resulted in similar accuracy levels, whereas the radial component was less accurate. Maximal sensitivities and accuracies were obtained by combined evaluations during stress. (J Am Soc Echocardiogr 2010;23:95-103.)

This study analyzed the oxidant generation during ischemia-reperfusion protocols of Langendorff-perfused rat hearts, preconditioned with a mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) opener (i.e., diazoxide). The autofluorescence of mitochondrial flavoproteins, and that of the total NAD(P)H pool on the one hand and the fluorescence of dyes sensitive to H(2)O(2) or O(2)(*-) [i.e., the dihydrodichlorofluoroscein (H(2)DCF) and dihydroethidine (DHE), respectively] on the other, were noninvasively measured at the surface of the left ventricular wall by means of optic fibers. Isolated perfused rat hearts were subjected to an ischemia-reperfusion protocol. Opening mitoK(ATP) with diazoxide (100 microM) 1) improved the recovery of the rate-pressure product after reperfusion (72 +/- 2 vs. 16.8 +/- 2.5% of baseline value in control group, P < 0.01), and 2) attenuated the oxidant generation during both ischemic (-46 +/- 5% H(2)DCF oxidation and -40 +/- 3% DHE oxidation vs. control group, P < 0.01) and reperfusion (-26 +/- 2% H(2)DCF oxidation and -23 +/- 2% DHE oxidation vs. control group, P < 0.01) periods. All of these effects were abolished by coperfusion of 5-hydroxydecanoic acid (500 microM), a mitoK(ATP) blocker. During the preconditioning phase, diazoxide induced a transient, reversible, and 5-hydroxydecanoic acid-sensitive flavoprotein and H(2)DCF (but not DHE) oxidation. In conclusion, the diazoxide-mediated cardioprotection is supported by a moderate H(2)O(2) production during the preconditioning phase and a strong decrease in oxidant generation during the subsequent ischemic and reperfusion phases.

Objectives The aim of this study was to assess and validate 2-dimensional (2D) strain for the detection of ischemia during dobutamine stress echocardiography (DSE).Background Evaluation of abnormalities of left ventricular (LV) function from wall thickening during DSE is unsatisfactory and requires a high level of expertise.Methods In 10 open-chest anesthetized pigs, myocardial deformation was studied before and during dobutamine infusion, under control and ischemic conditions produced by various degrees of coronary artery constriction: 2 of nonflow-limiting stenoses (NFLS) of increasing severity reducing left anterior descending artery hyperemic flow by 40% and 70% and 2 flow-limiting stenoses (FLS) reducing resting coronary flow by 25% and 50%. Agreement between 2D strain echocardiography and sonomicrometry (reference method) was evaluated by linear regression and Bland-Altman analysis.Results Good correlation and agreement were observed between 2-dimensional strain and sonomicrometry at rest and during dobutamine infusion; longitudinal strain: r = 0.77, p < 0.001 and r = 0.80, p < 0.001; radial strain: r 0.57, p < 0.05 and r = 0.63, p < 0.05; and circumferential strain: r = 0.74, p < 0.001 and r = 0.58, p < 0.001. Circumferential and longitudinal strains in the risk area were significantly decreased at rest in the presence of FLS and during dobutamine infusion in the presence of NFLS. By contrast, radial strain was significantly decreased in the presence of severe FLS only during dobutamine infusion.Conclusions The 2D strain provides accurate assessment of LV regional function. Evaluation of circumferential and longitudinal strains during DSE has real potential for quantitative evaluation of LV deformation in the routine assessment of ischemia.

Background: Strain echocardiographic techniques have been developed in order to quantify myocardial contraction but are currently based on a transmural myocardial analysis whereas subendocardial (ENDO) and subepicardial (EPI) layers have different response to ischemia. Recent development in strain software enables to investigate simultaneously strain in 2 myocardial layers. Objectives: To assess and validate this new tool for the detection of ischemia during dobutamine stress echocardiography (DSE). Methods: In 6 open-chest anesthetized pigs, circumferential strain (CS) was studied before and during dobutamine infusion, in absence of coronary stenosis and in ischemic conditions produced by: 2 degrees of non flow-limiting stenoses reducing left anterior descending (LAD) artery hyperemic flow by 20% and then by 60% (NFLS20 and NFLS60), and 1 flow-limiting stenosis reducing resting LAD flow by 25% (FLS25). Agreement between CS echocardiography in ENDO and EPI layers in risk area (RA) and sonomicrometry was evaluated by linear regression and Bland-Altman analysis. CS in ENDO and EPI layers were studied in absence or coronary stenosis and in ischemic condition, in RA and in control area (CA). Results: Good correlations and agreements were observed between echocardiography and sonomicrometry at rest and during dobutamine : ENDO CS: r=0.66, P<0.001 and r=0.69, P<0.0001; EPI CS: r=0.65, P<0.01 and r=0.62, P<0.001. At rest, both ENDO and EPI CS in the RA were significantly decreased in the presence of FLS25. During dobutamine infusion, ENDO CS was significantly reduced in the presence of NFLS20 and EPI CS in the presence of NFLS60. Conclusions: Multilayer strain echocardiography provides accurate assessment of LV regional function. Evaluation of ENDO and EPI strains during DSE has real potential to improve detection of ischemia in clinical practice.

The aim of this study was to investigate the effects of HMR1098, a selective blocker of sarcolemmal ATP-sensitive potassium channel (sarcK(ATP)), in Langendorff-perfused rat hearts submitted to ischemia and reperfusion. The recovery of heart hemodynamic and mitochondrial function, studied on skinned fibers, was analyzed after 30-min global ischemia followed by 20-min reperfusion. Infarct size was quantified on a regional ischemia model after 2-h reperfusion. We report that the perfusion of 10 microM HMR1098 before ischemia, delays the onset of ischemic contracture, improves recovery of cardiac function upon reperfusion, preserves the mitochondrial architecture, and finally decreases infarct size. This HMR1098-induced cardioprotection is prevented by 1 mM 2-mercaptopropionylglycine, an antioxidant, and by 100 nM nifedipine, an L-type calcium channel blocker. Concomitantly, it is shown that HMR1098 perfusion induces (i) a transient and specific inhibition of the respiratory chain complex I and, (ii) an increase in the averaged intracellular calcium concentration probed by the in situ measurement of indo-1 fluorescence. Finally, all the beneficial effects of HMR1098 were strongly inhibited by 5-hydroxydecanoate and abolished by glibenclamide, two mitoK(ATP) blockers. This study demonstrates that the HMR1098-induced cardioprotection occurs indirectly through extracellular calcium influx, respiratory chain complex inhibition, reactive oxygen species production and mitoK(ATP) opening. Taken together, these data suggest that a functional interaction between sarcK(ATP) and mitoK(ATP) exists in isolated rat heart ischemia model, which is mediated by extracellular calcium influx.

It has been proposed that activation of the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) is part of signaling pathways triggering the cardioprotection afforded by ischemic preconditioning of the heart. This work was to analyze the mitochondrial function profile of Langendorff-perfused rat hearts during the different phases of various ischemia-reperfusion protocols. Specifically, skinned fibers of ischemic preconditioned hearts exhibit a decline in the succinate-supported respiration and complex II activity during ischemia, followed by a recovery during reperfusion. Meanwhile, the apparent affinity of respiration for ADP (which reflects the matrix volume expansion) is increased during preconditioning stimulus and, to a larger extent, during prolonged ischemia. This evolution pattern is mimicked by diazoxide and abolished by 5-hydroxydecanoate. It is concluded that opening the mitoK(ATP) channel mediates the preservation of mitochondrial structure-function via a mitochondrial matrix shrinkage and a reversible inactivation of complex II during prolonged ischemic insult.

Objectives: In normal hearts, the distribution of regional myocardial perfusion is altered by ventricular pacing. Little is known about the impact of ventricular pacing on regional myocardial perfusion in ischemic conditions. In this acute echocardiographic study, we compared the respective effects of right ventricular pacing (RVP), left ventricular pacing (LVP), and biventricular pacing (BVP) on regional perfusion in a swine model of graded ischemia.Methods and Results: Ventricular pacing leads were placed at the apex of the right ventricle and on the lateral wall of the left ventricle in nine open-chest pigs. Myocardial contrast echocardiography was successively performed during spontaneous rhythm (SR), RVP, LVP, and BVP in random order at baseline and during three stages of incremental ischemia (left anterior descending + circumflex). At baseline, RVP decreased myocardial perfusion of the septal and inferior walls compared to SR (P < 0.05), whereas LVP decreased perfusion of the lateral wall (P < 0.05). No significant differences were observed in regional perfusion during BVP compared to SR. In ischemic conditions, RVP worsened myocardial perfusion in the ischemic anterior wall as well as in the septal and inferior walls (P < 0.05), whereas both LVP and BVP did not alter perfusion in the ischemic area compared to SR.Conclusion: Compared to baseline, in ischemic conditions, RVP has a more pronounced detrimental impact on perfusion abnormalities. In contrast, BVP induced a significant improvement in local myocardial perfusion. Therefore, BVP could be preferred to RVP in patients with ischemic cardiomyopathy.

The intracellular mechanisms of regulation of energy fluxes and respiration in contracting heart cells were studied. For this, we investigated the workload dependencies of the rate of oxygen consumption and metabolic parameters in Langendorff-perfused isolated rat hearts.(31)P NMR spectroscopy was used to study the metabolic changes during transition from perfusion with glucose to that with pyruvate with and without active creatine kinase system. The experimental results showed that transition from perfusion with glucose to that with pyruvate increased the phosphocreatine content and stability of its level at increased workloads. Inhibition of creatine kinase reaction by 15-min infusion of iodoacetamide decreased the maximal developed tension and respiration rates by a factor of two.(31)P NMR data were analyzed by a mathematical model of compartmentalized energy transfer, which is independent from the restrictions of the classical concept of creatine kinase equilibrium. The analysis of experimental data by this model shows that metabolic stability-constant levels of phosphocreatine, ATP and inorganic phosphate-at increased energy fluxes is an inherent property of the compartmentalized system. This explains the observed substrate specificity by changes in mitochondrial membrane potential. The decreased maximal respiration rate and maximal work output of the heart with inhibited creatine kinase is well explained by the rise in myoplasmic ADP concentration. This activates the adenylate kinase reaction in the myofibrillar space and in the mitochondria to fulfil the energy transfer and signal transmission functions, usually performed by creatine kinase. The activity of this system, however, is not sufficient to maintain high enough energy fluxes. Therefore, there is a kinetic explanation for the decreased maximal respiration rate of the heart with inhibited creatine kinase: i.e. a kinetically induced switch from an efficient energy transfer pathway (PCr-CK system) to a non-efficient one (myokinase pathway) within the energy transfer network of the cell under conditions of low apparent affinity of mitochondria to ADP in vivo. This may result in a significant decrease in the thermodynamic affinity of compartmentalized ATPase systems and finally in heart failure.

We have compared the cardiotoxicity of 3 anthracyclines in a model of isolated perfused rat heart using the Langendorff technique. The contractile state and ventricular compliance were studied. Doxorubicin, epirubicin and pirarubicin were perfused at concentrations of 10(-6) and 10(-5) M during 70 min. The cardiac accumulation of the drugs was studied by HPLC. No significant alteration of cardiac functional parameters was observed at 10(-6) M. At 10(-5) M, epirubicin produced a significantly greater alteration of cardiac contractility than doxorubicin, whereas pirarubicin exerted first an inotropic effect followed by a recovery to initial values at the 60th min. Anthracycline accumulation in the heart was dose-dependent; epirubicin accumulated to a 30% greater extent than doxorubicin and pirarubicin heart concentrations were 4-5 times higher than those of doxorubicin at the end of the perfusion. These results suggest that doxorubicin and epirubicin have the same intrinsic cardiac toxicity, and that their distinct clinical cardiotoxicity must be explained by pharmacokinetic differences, whereas pirarubicin is much less cardiotoxic than the other anthracyclines because of different pharmacodynamic properties.

Digital imaging microscopy of fura-2 fluorescence has allowed us to assess the dynamic patterns of local Ca increase in newly isolated rat myocardial cells. Of the myocytes bathed in a saline solution (1.8 mM Ca2+, 37°C, pH 7.4), 10%–20% exhibited local spontaneous contractions. The resting intracellular free calcium concentration ([Ca2+]i) of these cells was 106±4nM versus 77±3 nM for non-contracting cells. The spontaneous contractile activity appeared to be closely related to internal spontaneous Ca waves that spread across the myoplasm (velocity ≈ 50 μm/s, maximal Ca amplitude=195±11nM) along the major axis of the cells. Precise topographical examination of Ca wave propagation indicated a refractory period for internal Ca release. The occurrence of both the generation and propagation of spontaneous Ca increases appeared to be closely dependent on the extent of Ca loading of the cells. Most of our observations were in accordance with the assumption that local Ca overload of the sarcoplasmic reticulum (SR) is the main parameter involved in the spontaneous Ca-release phenomena. Using the same approach, the increase in internal Ca evoked by KCl (50 mM) addition was investigated, and compared with that seen during spontaneous activity. Total [Ca2+]i increase induced by K+ depolarization involved three consecutive local Ca-release patterns: (a) a peripheral Ca enhancement that remained during the total [Ca2+]i increase, (b) subsequent transversal local Ca increases occurring in Z-line regions, (c) longitudinal local Ca increases. In addition, a weak heterogeneous Ca distribution was detected in both peripheral and central parts of resting cardiac cells. Thus, the total Ca increase seemed to result consecutively from a peripheral Ca pool, from junctional SR and from longitudinal structures (possibly longitudinal SR).

Während der letzten Jahre befaßte sich eine Anzahl von Studien mit den hämodynamischen Wirkungen der Nitrate [1,11]. Darin war insbesondere die Rede davon, daß Nitrate unmittelbar für das Gleichgewicht zwischen einem verminderten Sauerstoffbedarf und einem größeren Sauerstoffangebot verantwortlich sind, wodurch die myokardiale Kontraktilität verbessert wird. Diese Befunde wiesen darauf hin, daß Nitrate möglicherweise eine direkte Wirkung auf die Kontraktilität ausüben.

Recently, there have been a number of studies concerning the hemodynamic effects of nitrites [1, 11], which reported more particularly that nitrites are directly responsible for the balance between a reduction of oxygen demand and a greater oxygen supply, improving myocardial contractility. These findings suggested that nitrites may exert a probable direct effect on contractility.