Left atrial appendage occlusion and pulmonary vein isolation: interest of non-invasive imaging

A 67-year-old woman with paroxysmal atrial fibrillation (AF), not a candidate for anticoagulant therapy, underwent a combined procedure of pulmonary vein isolation (PVI) and occlusion of the left atrial appendage (LAA) with the Amplatzer cardiac plug prosthesis (AGA Medical Corporation, Plymouth, U.S.A.). After PVI, implantation of the Amplatzer cardiac plug was performed under transoesophageal echocardiography guidance after a complete evaluation of the LAA obtained by different imaging techniques. One month later, multidetector computed tomography and transoesophageal echocardiography confirmed proper position of the Amplatzer cardiac plug not interfering with the surrounding structures and the absence of complications resulting from either PVI or LAA closure.

Inhibition of the mTOR/p70S6K pathway is not involved in the insulin-sensitizing effect of AMPK on cardiac glucose uptake

The AMP-activated protein kinase (AMPK) is known to increase cardiac insulin sensitivity on glucose uptake. AMPK also inhibits the mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase (p70S6K) pathway. Once activated by insulin, mTOR/p70S6K phosphorylates insulin receptor substrate-1 (IRS-1) on serine residues, resulting in its inhibition and reduction of insulin signaling. AMPK was postulated to act on insulin by inhibiting this mTOR/p70S6K-mediated negative feedback loop. We tested this hypothesis in cardiomyocytes. The stimulation of glucose uptake by AMPK activators and insulin correlated with AMPK and protein kinase B (PKB/Akt) activation, respectively. Both treatments induced the phosphorylation of Akt substrate 160 (AS160) known to control glucose uptake. Together, insulin and AMPK activators acted synergistically to induce PKB/Akt overactivation, AS160 overphosphorylation, and glucose uptake overstimulation. This correlated with p70S6K inhibition and with a decrease in serine phosphorylation of IRS-1, indicating the inhibition of the negative feedback loop. We used the mTOR inhibitor rapamycin to confirm these results. Mimicking AMPK activators in the presence of insulin, rapamycin inhibited p70S6K and reduced IRS-1 phosphorylation on serine, resulting in the overphosphorylation of PKB/Akt and AS160. However, rapamycin did not enhance the insulin-induced stimulation of glucose uptake. In conclusion, although the insulin-sensitizing effect of AMPK on PKB/Akt is explained by the inhibition of the insulin-induced negative feedback loop, its effect on glucose uptake is independent of this mechanism. This disconnection revealed that the PKB/Akt/AS160 pathway does not seem to be the rate-limiting step in the control of glucose uptake under insulin treatment.

Iron overload in polytransfused patients without heart failure is associated with subclinical alterations of systolic left ventricular function using cardiovascular magnetic resonance tagging

BACKGROUND

It remains incompletely understood whether patients with transfusion related cardiac iron overload without signs of heart failure exhibit already subclinical alterations of systolic left ventricular (LV) dysfunction. Therefore we performed a comprehensive evaluation of systolic and diastolic cardiac function in such patients using tagged and phase-contrast CMR.

METHODS

19 patients requiring regular blood transfusions for chronic anemia and 8 healthy volunteers were investigated using cine, tagged, and phase-contrast and T2* CMR. LV ejection fraction, peak filling rate, end-systolic global midventricular systolic Eulerian radial thickening and shortening strains as well as left ventricular rotation and twist, mitral E and A wave velocity, and tissue e' wave and E/e' wave velocity ratio, as well as isovolumic relaxation time and E wave deceleration time were computed and compared to cardiac T2*.

RESULTS

Patients without significant iron overload (T2* > 20 ms, n = 9) had similar parameters of systolic and diastolic function as normal controls, whereas patients with severe iron overload (T2* < 10 ms, n = 5), had significant reduction of LV ejection fraction (54 ± 2% vs. 62 ± 6% and 65 ± 6% respectively p < 0.05), of end-systolic radial thickening (+6 ± 4% vs. +11 ± 2 and +11 ± 4% respectively p < 0.05) and of rotational twist (1.6 ± 0.2 degrees vs. 3.0 ± 1.2 and 3.5 ± 0.7 degrees respectively, p < 0.05) than patients without iron overload (T2* > 20 ms) or normal controls. Patients with moderate iron overload (T2* 10-20 ms, n = 5), had preserved ejection fraction (59 ± 6%, p = NS vs. pts. with T2* > 20 ms and controls), but showed reduced maximal LV rotational twist (1.8 ± 0.4 degrees). The magnitude of reduction of LV twist (r = 0.64, p < 0.001), of LV ejection fraction (r = 0.44, p < 0.001), of peak radial thickening (r = 0.58, p < 0.001) and of systolic (r = 0.50, p < 0.05) and diastolic twist and untwist rate (r = -0.53, p < 0.001) in patients were directly correlated to the logarithm of cardiac T2*.

CONCLUSION

Multiple transfused patients with normal ejection fraction and without heart failure have subclinical alterations of systolic and diastolic LV function in direct relation to the severity of cardiac iron overload. Among all parameters, left ventricular twist is affected earliest, and has the highest correlation to log (T2*), suggesting that this parameter might be used to follow systolic left ventricular function in patients with iron overload.

Incidence, determinants, and prognostic impact of operative refusal or denial in octogenarians with severe aortic stenosis

BACKGROUND

Aortic stenosis (AS) is a common valve disease in octogenarians. Previous studies have shown that aortic valve replacement (AVR) is frequently not performed in these patients. This study investigated the incidence, determinants, and prognostic impact of AVR refusal or denial in these patients.

METHODS

Between 2000 and 2007, 163 octogenarians (mean age, 84 ± 3 years) with severe AS and an indication for operation according to guidelines were prospectively included in an echocardiographic registry. Among these, 97 underwent AVR, and 66 were treated conservatively.

RESULTS

Logistic regression analysis identified older age, a lower transaortic pressure gradient, a larger aortic valve area, and the presence of diabetes as independent predictors of AVR refusal or denial. Patients who underwent AVR had a 30-day mortality of 9%. Overall 5-year survival was 66% in AVR patients vs 31% in those treated conservatively (log rank p < 0.001 vs AVR). After adjustment for the propensity score, patients undergoing AVR still had a better outcome than conservatively treated patients (hazard ratio, 0.56; 95% confidence interval, 0.29 to 0.91; p = 0.022). In addition to the therapeutic decision, Cox regression analysis also identified low body weight, New York Heart Association class III/IV, and the logistic European System for Cardiac Operative Risk Evaluation as independent predictors of outcome in the overall series.

CONCLUSIONS

About 40% of octogenarians with severe AS and a definite indication for operation either refuse or are denied AVR. AVR refusal or denial has a profound impact on long-term prognosis, resulting in a twofold excess mortality, even after adjustment for the propensity score.

Magnetic resonance imaging evaluation of cerebral embolization during percutaneous aortic valve implantation: comparison of transfemoral and trans-apical approaches using Edwards Sapiens valve

OBJECTIVE

Cerebral embolization during trans-catheter aortic valve implantation (TAVI) has not been assessed clearly in the literature. Therefore, we compared the rate of cerebral embolisms with diffusion-weighted magnetic resonance imaging (DWI) in transfemoral (TF) and trans-apical (TA) approaches.

METHOD

Eighty patients benefited from TAVI between January 2008 and June 2010. Out of these, 35 were included in the study. Twenty-one were TF (group 1) and 14 TA (group 2). During the same period, 285 patients benefited from a conventional aortic valve surgery (aortic valve replacement (AVR)). Thirteen of these were also analyzed and considered as the control group (group 3). We systematically performed a DWI the day before the procedure and 48 h after. DWI studies were blindly analyzed by a neuroradiologist, and all patients had a clinical neurological assessment before and after the procedure, according the National Institutes of Health Stroke Scale (NIHSS).

RESULTS

Thirty-two patients in the TAVI group had new cerebral lesions: 19 in the TF group and 13 in the trans-apical group (p=NS). Mean number of embolic lesions per patient was 6.6 in group I and 6.0 in group II (p=NS). Mean volume of embolic lesions was 475.0 mm³ in group I and 2170.5 mm³ in group II (p=NS). In group III, one patient had one new cerebral lesion (p<0.05 vs TAVI) of 36.5 mm³ (p=NS vs TAVI). All patients were neurologically asymptomatic.

CONCLUSIONS

The incidence of silent cerebral embolic lesions after TAVI is significantly higher compared with the standard surgical AVR. The number of emboli is similar in the TF and TA groups but the volume tended to be higher in the TA group. However, there is no clinical impact of those lesions.

Usefulness of B-type natriuretic peptide to predict outcome of patients treated by transcatheter aortic valve implantation

B-type natriuretic peptide (BNP) has been shown to predict outcomes after conventional aortic valve replacement. The aim of the present study was to investigate whether BNP also predicts the outcomes after transcatheter aortic valve implantation (TAVI). A total of 58 patients (36 men, age 84 ± 5 years) underwent TAVI in our institution for severe aortic stenosis (aortic valve area 0.6 ± 0.1 cm², mean gradient 41 ± 15 mm Hg) at high risk of surgery (logistic European System for Cardiac Operative Risk Evaluation 34 ± 17%). BNP was measured before and 24 hours after TAVI. The 30-day survival rate was 91%. Although the baseline clinical and hemodynamic characteristics were similar among the 30-day survivors (n = 53) and nonsurvivors (n = 5), the BNP levels were significantly lower in the 30-day survivors, at both baseline (463 ± 265 vs 1,067 ± 655 pg/ml; p = 0.005) and 24 hours after TAVI (488 ± 238 vs 1,632 ± 1,028 pg/ml; p <0.0001). The BNP levels were significantly greater in patients experiencing one major adverse event at 30 days. On multivariate analysis, only BNP levels (baseline value and change at 24 hours) were independent predictors of 30-day survival. Kaplan-Meier analysis showed that 30-day survival was significantly lower in patients with than in those without both a baseline BNP level >428 mg/dl (p = 0.04) and a significant BNP increase of >170 pg/ml at 24 hours after TAVI (p = 0.001). In conclusion, BNP is a strong predictor of 30-day outcomes after transcatheter aortic valve implantation, at both baseline and 24 hours after the procedure.

Urotensin II induction of adult cardiomyocytes hypertrophy involves the Akt/GSK-3beta signaling pathway

Urotensin II (UII) a potent vasoactive peptide is upregulated in the failing heart and promotes cardiomyocytes hypertrophy, in particular through mitogen-activated protein kinases. However, the regulation by UII of GSK-3beta, a recognized pivotal signaling element of cardiac hypertrophy has not yet been documented. We therefore investigated in adult cardiomyocytes, if UII phosphorylates GSK-3beta and Akt, one of its upstream regulators and stabilizes beta-catenin, a GSK-3beta dependent nuclear transcriptional co-activator. Primary cultures of adult rat cardiomyocytes were stimulated for 48h with UII. Cell size and protein/DNA contents were determined. Phosphorylated and total forms of Akt, GSK-3beta and the total amount of beta-catenin were quantified by western blot. The responses of cardiomyocytes to UII were also evaluated after pretreatment with the chemical phosphatidyl-inositol-3-kinase inhibitor, LY294002, and urantide, a competitive UII receptor antagonist. UII increased cell size and the protein/DNA ratio, consistent with a hypertrophic response. UII also increased phosphorylation of Akt and its downstream target GSK-3beta. beta-Catenin protein levels were increased. All of these effects of UII were prevented by LY294002, and urantide. The UII-induced adult cardiomyocytes hypertrophy involves the Akt/GSK-3beta signaling pathways and is accompanied by the stabilization of the beta-catenin. All these effects are abolished by competitive inhibition of the UII receptor, consistent with new therapeutic perspectives for heart failure treatment.

Effects of granulocyte-colony-stimulating factor on progenitor cell mobilization and heart perfusion and function in normal mice

BACKGROUND AIMS

Mobilization of stem cells and progenitor cells from the bone marrow (BM) into the peripheral blood (PB) by granulocyte-colony-stimulating factor (G-CSF) is being investigated for cardiac regeneration in ischemic heart disease. However, hematopoietic (HPC), mesenchymal (MPC) and endothelial (EPC) progenitor mobilization have not been optimized and the effect of G-CSF on myocardial perfusion and cardiac function in a normal heart has never been studied.

METHODS

Normal mice were injected daily for 1-10 days with subcutaneous recombinant human G-CSF. PB and BM were evaluated for HPC and EPC by flow cytometry and HPC and MPC by hematopoietic (CFU-GM) and mesenchymal (CFU-F) colony assays. Echocardiography, microSPECT imaging, cardiac catheterization and immunohistochemistry were performed in mice treated for 10 days.

RESULTS

HPC and CFU-GM in PB peaked after 2 days, CFU-F after 4 days and EPC after 3 days. Thereafter, while HPC temporally decreased before showing a second peak, EPC remained detectable only at low levels. In BM, hematopoietic stem cells (HSC) and CFU-GM did not increase much overall but peaked twice on days 2 and 7. EPC (peak on day 7) production increased in the BM, but CFU-F formation declined considerably after day 2. G-CSF enhanced myocardial perfusion and vascularization but impaired hemodynamic performance of the heart through apparently increased ventricular wall rigidity.

CONCLUSIONS

G-CSF induces the mobilization of HPC, EPC and CFU-F progenitors in PB according to very different patterns, and has a significant impact on perfusion and function of the normal heart.

Activation of the cardiac mTOR/p70(S6K) pathway by leucine requires PDK1 and correlates with PRAS40 phosphorylation

Like insulin, leucine stimulates the mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase (p70(S6K)) axis in various organs. Insulin proceeds via the canonical association of phosphatidylinositol 3-kinase (PI3K), phosphoinositide-dependent protein kinase-1 (PDK1), and protein kinase B (PKB/Akt). The signaling involved in leucine effect, although known to implicate a PI3K mechanism independent of PKB/Akt, is more poorly understood. In this study, we investigated whether PDK1 could also participate in the events leading to mTOR/p70(S6K) activation in response to leucine in the heart. In wild-type hearts, both leucine and insulin increased p70(S6K) activity whereas, in contrast to insulin, leucine was unable to activate PKB/Akt. The changes in p70(S6K) activity induced by insulin and leucine correlated with changes in phosphorylation of Thr(389), the mTOR phosphorylation site on p70(S6K), and of Ser(2448) on mTOR, both related to mTOR activity. Leucine also triggered phosphorylation of the proline-rich Akt/PKB substrate of 40 kDa (PRAS40), a new pivotal mTOR regulator. In PDK1 knockout hearts, leucine, similarly to insulin, failed to induce the phosphorylation of mTOR and p70(S6K), leading to the absence of p70(S6K) activation. The loss of leucine effect in absence of PDK1 correlated with the lack of PRAS40 phosphorylation. Moreover, the introduction in PDK1 of the L155E mutation, which is known to preserve the insulin-induced and PKB/Akt-dependent phosphorylation of mTOR/p70(S6K), suppressed all leucine effects, including phosphorylation of mTOR, PRAS40, and p70(S6K). We conclude that the leucine-induced stimulation of the cardiac PRAS40/mTOR/p70(S6K) pathway requires PDK1 in a way that differs from that of insulin.

Myocardial injury induced by ultrasound-targeted microbubble destruction: evidence for the contribution of myocardial ischemia

Ultrasound-targeted microbubble destruction (UTMD) can cause left ventricular (LV) dysfunction and tissue alterations in rats when high ultrasound (US) energy and long duration of imaging are used. However, the mechanism underlying these alterations remains unclear. The aim of the present work was to investigate the possible role of ischemia in the pathogenesis of the UTMD-induced LV damages in rats. To address this issue, rat hearts were exposed in situ to perfluorocarbon-enhanced sonicated dextrose albumin (PESDA) and US at peak negative pressures of 0.6, 1.2 or 1.8 MPa for 1, 3, 9, 15 or 30 min. Blood pressure and electrocardiogram were continuously recorded during insonation. LV function was assessed before and immediately after US exposure, as well as at 24 h and 7 d. At each time point, groups of rats were euthanized and their hearts were harvested for morphologic analysis. Rats exposed to either PESDA alone or US alone showed no functional or morphologic abnormalities. By contrast, rats exposed to both PESDA and US exhibited transient LV dysfunction, transient ST-segment elevation, premature ventricular contractions, microvascular ruptures, contraction band necrosis and morphologic tissue damage. These bio-effects were spontaneously and completely reversible by one week, except in the groups exposed to the highest peak negative pressure for the longest duration, in which mild dysfunction persisted and interstitial fibrosis developed. In conclusion, simultaneous exposure of rat hearts to PESDA and US in vivo results in significant bio-effects that are similar to myocardial ischemia, including transient regional LV dysfunction, transient ST-segment elevation and myocyte contraction band necrosis.

NC100100, a new echo contrast agent for the assessment of myocardial perfusion--safety and comparison with technetium-99m sestamibi single-photon emission computed tomography in a randomized multicenter study

BACKGROUND AND HYPOTHESIS

Myocardial contrast echocardiography using second-generation agents has been proposed to study myocardial perfusion. A placebo-controlled, multicenter trial was conducted to evaluate the safety, optimal dose, and imaging mode for NC100100, a novel intravenous second-generation echo contrast agent, and to compare this technique with technetium-99m sestamibi (MIBI) single-photon emission computed tomography (SPECT).

METHODS

In a placebo-controlled, multicenter trial, 203 patients with myocardial infarction > 5 days and < 1 year previously underwent rest SPECT and MCE. Fundamental and harmonic imaging modes combined with continuous and electrocardiogram-- (ECG) triggered intermittent imaging were used. Six dose groups (0.030, 0.100, and 0.300 microliter particles/kg body weight for fundamental imaging; and 0.006, 0.030, and 0.150 microliter particles/kg body weight for harmonic imaging) were tested. A saline group was also included. Safety was followed for 72 h after contrast injection. Myocardial perfusion by MCE was compared with myocardial rest perfusion imaging using MIBI as a tracer.

RESULTS

NC100100 was well tolerated. No serious adverse events or deaths occurred. No clinically relevant changes in vital signs, laboratory parameters, and ECG recordings were noted. There was no significant difference between adverse events in the NC100100 (25.7%) and in the placebo group (17.9%, p = 0.3). Intermittent harmonic imaging using the intermediate dose was superior to all other modalities, allowing the assessment of perfusion in 76% of all segments. Eighty segments (96%) with normal perfusion by SPECT imaging also showed myocardial perfusion with MCE. However, a substantial percentage of segments (61-80%) with perfusion defects by SPECT imaging also showed opacification by MCE. This resulted in an overall agreement of 66-81% and a high specificity (80-96%), but in low sensitivity (20-39%) of MCE for the detection of perfusion defects.

CONCLUSION

NC100100 is safe in patients with myocardial infarction. Intermittent harmonic imaging with a dose of 0.03 microliter particles/kg body weight can be proposed as the best imaging protocol. Myocardial contrast echocardiography with NC 100100 provides perfusion information in approximately 76% of segments and results in myocardial opacification in the vast majority of segments with normal perfusion as assessed by SPECT. Although the discrepancies between MCE and SPECT with regard to the definition of perfusion defects requires further investigation, MCE with NC 100100 is a promising technique for the noninvasive assessment of myocardial perfusion.

Comparison between adenoviral and retroviral vectors for the transduction of the thymidine kinase PET reporter gene in rat mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a promising cell line for the treatment of ischemic heart disease. To evaluate the success of their transplantation into living animals, noninvasive imaging techniques that are able to track the distribution and fate of those cells would be useful. The aim of this study was to investigate the feasibility of infecting rat MSCs with adenoviruses and retroviruses carrying the herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene; to compare the level of transgene expression induced by the 2 viral vectors; to evaluate the effects of viral transduction on cell phenotype, viability, proliferation rates, and differentiation capabilities; and to test the possibility of noninvasively imaging transduced MSCs using 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (18F-FHBG) and small-animal PET after their transplantation into living rats.

METHODS

We infected rat bone marrow MSCs with adenoviruses carrying the HSV1 mutant tk (Ad-HSV1-sr39tk) PET reporter gene (PRG) or with a retroviral construct expressing the wild-type HSV1-tk PRG. The efficacy and intensity of HSV1-sr39tk and HSV1-tk gene expression were determined by a direct comparison of [8-3H]-penciclovir ([8-3H]-PCV) cell uptake in both infected MSC populations and noninfected control MSCs. Small-animal PET studies were performed on living rats after an intramuscular injection of infected MSCs. The MSCs either have been incubated in advance with 18F-FHBG or they were administered and 18F-FHBG was thereafter intravenously administered [corrected]

RESULTS

Both adenoviral and retroviral vectors can be used to introduce the tk PRG in MSCs. Neither adenovirus nor retrovirus infections significantly modify MSC phenotype, viability, proliferation, and differentiation capabilities. No significant 3H-PCV uptake was observed in noninfected MSCs. By contrast, after both adenoviral and retroviral infections, the infected MSC populations exhibited a similar, significantly higher, 3H-PCV accumulation. Small-animal PET images showed intense activity within the transplanted regions irrespective of the infected MSC population used.

CONCLUSION

Our results demonstrate the feasibility of infecting MSCs with adenoviruses and retroviruses expressing the HSV1-tk PRG and suggest that infected MSCs can be noninvasively imaged with 18F-FHBG and small-animal PET after their transplantation into living animals.