LAD Region Research Articles

Abstract Or106: DNA Double-stranded Breaks, a Hallmark of Aging, Defined at the Nucleotide Resolution, Are Increased and Associated with Transcription in the Cardiac Myocyte Genome in LMNA-Cardiomyopathy

Background: An intrinsic feature of gene transcription is the formation of DNA superhelices near the transcription bubble, which are resolved upon induction of transient double-stranded breaks (DSBs) by topoisomerases. Unrepaired DSBs are pathogenic as they lead to cell cycle arrest, senescence, inflammation, and organ dysfunction. Hypothesis and Aims: We posit that DSBs would be more prevalent at the genomic sites associated with gene expression. As Lamin-A (LMNA) regulates active transcription through Lamin associated domains (LADS) we predict for DSBs to be more common in non-LAD regions. The objectives were to identify and characterize genome-wide DSBs at the nucleotide resolution and determine the association of DSBs with transcription in cardiac myocytes. Methods: We identified the genome-wide DSBs in ~ 1 million cardiac myocytes per heart in 3 wild-type and 3 myocyte-specific LMNA-deficient ( Myh6-Cre:Lmna F/F ) mice by END-Sequencing, the LADs were defined in cardiac myocytes via LMNA CUT&RUN assay (N=5). Results: The prevalence of DSBs was 0.8% and 2.2% in the wild-type and Myh6-Cre:Lmna F/F myocytes, respectively. The END-Seq signals for 8 DSBs were enriched in the wild-type and 6,764 in Myh6-Cre:Lmna F/F myocytes, respectively (q<0.05). The DSBs were preferentially localized to the gene regions, transcription initiation sites, cardiac transcription factor motifs, and the G quadruplex forming structures. Because LMNA regulates transcription through the LADs, we defined the LADs in cardiac myocytes and found an average of 818 LADs per myocyte. LADs that were shared by at least three mice (N= 2,572) were considered constitutive LADs (cLADs), which comprised about a third of the mouse cardiac myocyte genomes. Transcript levels of the protein-coding genes located at the cLADs (N=3,975) were ~ 16-fold lower than those at the non-LAD regions (N=~17,778). The prevalence of DSBs was higher in the non-LAD as compared to the cLAD regions. Likewise, DSBs were more common in the loss-of LAD regions, defined as the juxtaposed genomic regions in the Myh6-Cre:Lmna F/F that corresponded to the LAD regions in the wild-type myocytes. Conclusions: To our knowledge, this is the first identification of DSBs, at the nucleotide resolution in the cardiovascular system. The prevalence of DSBs was higher in the genomic regions associated with transcription. Because transcription is pervasive, DSBs are expected to be common and pathogenic in various disease states and aging.

Rhythm matters: sinus and pace rhythm map significantly differ in endo/epicardial 3D electroanatomic mapping

Abstract Introduction Left ventricular substrate assessment utilizing ultra-high density multipolar catheters is frequently used to guide ablation procedures in patients with scar related ventricular tachycardia. However, 3D electroanatomic mapping is often performed during either sinus or paced rhythm. The effect of the modality (sinus vs. paced) used during mapping on substrate assessment remains elusive. Methods and Results We compared biventricular endo- and epicardial 3D high-density voltage and activation maps in sinus- and right ventricular-paced rhythm in domestic pigs. Data was acquired using a 20-polar mapping catheter with a cardiac tissue proximity filter based on catheter location and impedance measurements. Ventricular pacing (120 bmp) was performed with a permanent pacemaker electrode in right ventricular septal position, and high-density maps were acquired from the endo- and epicardium in sinus and paced rhythm (criterion for low voltage: <0.5 mV). Electroanatomical voltage and activation high-density (>6500 points per heart) mapping were performed with sufficient coverage in the right and left ventricles and the epicardium. The size of the low voltage area varied significantly between sinus and right ventricular-paced rhythm, particularly in epicardial mapping. In SR, the total low voltage was 7.2 ± 5.8%, while 11.1 ± 0.03% in paced rhythm. SR and paced maps revealed e.g. low voltage areas in the basal to apical anterior wall corresponding to the LAD regions, however, this was especially pronounced in sinus maps (e.g. pig 1: 64.2 cm²) compared to the paced rhythm map (e.g. pig 1: 32.8 cm²). Conclusion The extent of low voltage regions differed significantly in RV/LV, endo- and epicardially. Sinus maps showed the most accurate electrical representation of local voltage and corresponded correctly to local anatomical landmarks like e.g. the LAD with its surrounding epicardial fat tissue.3D biventricular epicardial voltage map

Abstract 18560: External Calcium Modification Technique to Recanalize a Balloon Uncrossable Chronic Coronary Total Occlusion

Introduction: Despite improvements in equipment and techniques, uncrossable chronic total occlusion (CTO) coronary lesions remain challenging.Case: A 66-year-old male with typical angina and a history of failed CTO PCI was referred to our CTO tertiary center as he did not wish to undergo coronary artery bypass grafting. Transthoracic echocardiography revealed an ejection fraction of 45%, and cardiac MRI demonstrated viability in the LAD region. Coronary angiography revealed a long LAD CTO over 20 mm with heavy calcification (Figure 1a). The J-CTO score was calculated to be 4. The cap of the CTO was semi-ambiguous. The wire was advanced through the highly calcified lesion with the support of a microcatheter but the microcatheter and low-profile balloons were unable to be advanced despite backup with 7 French femoral access and an EBU catheter in place (Figure 1b) Upon failure on using Leopard crawl technique and grenadoplasty and with unfavorable side branch anatomy for STAR technique, cracking the calcification with a balloon advanced over a subintimal hydrophilic wire was considered. A fielder XT-A guidewire was advanced around the CTO lesion in the subintimal area (Figure 1c). A 2x12 mm balloon was inflated at 8 atm over the wire situated in the subintimal area in order the crack the calcification from outside. After extraluminal plaque modification, the wire and the balloon were withdrawn. A microcatheter was then able to be advanced with the support of an anchor balloon over the original true lumen wire (Figure 1d). Then the procedure was successfully completed with balloon dilatation and stent implantation (Figure 1e-f). Conclusion: External Calcium Modification technique which consists of plaque modification using a balloon in subintimal space (over an intentionally directed wire in subintima and around the calcium) and cracking the calcium from the outer vessel structure can be used as a last resort to overcome balloon uncrossable CTO lesions.

The preoperative myocardial perfusion and internal mammary artery graft blood flow relationship in patients with ischemic cardiomyopathy

Objective. The purpose of this study was to determine the association between preoperative myocardial perfusion data (obtained by SPECT) with transit time blood flow characteristics in left internal mammary artery (LIMA) to left anterior descending artery (LAD) grafts in patients with ischemic cardiomyopathy.Methods. The study group consisted of 57 patients with ischemic cardiomyopathy. Intraoperative transit-time flow measurement (TTFM) of LIMA-LAD grafts were performed in all patients. All patients were also examined with preoperative stress and rest myocardial perfusion SPECT with 99m Tc-MIBI. Anastomotic patency was considered satisfactory with a normal waveform of blood flow, diastolic-dominant blood filling, and a mean flow value greater than 11.5 ml/min.Results. All 57 patients with LIMA-LAD grafts were divided into two groups; those with graft satisfactory patency (n = 40) and those with unsatisfactory patency (n = 17) as determined by TTFM. We found differences among these groups in values of global summed rest score (20.7 ± 7.5 vs. 29.8 ± 4.0; p = 0.002), global total perfusion deficit (TPD) at rest (32.0 ± 11.4 vs. 43.0 ± 7.2; p = 0.01), and regional TPD at rest in the LAD territory (20.7 ± 7.5 vs. 29.8 ± 4.0; p = 0.002). Additionally, the flow characteristics were different in patients with and without surgical left ventricle reconstruction (Q (ml/min): 17 (11.5, 40.8) vs. 47 (25, 69.5), p = 0.013; PI: 3.9 (3.2, 7.4) vs. 2.4 (2.0, 3.6), p = 0.001; DF (%): 63.5 (44.5, 70.8) vs. 74 (66.0, 79.7), p = 0.019). TPD at rest was the best predictor of the LIMA-LAD graft satisfactory: area under curve = 0.771, cut-off value = 26.85 with 83.3% sensitivity and 78.1% specificity.Conclusions. Preoperative myocardial perfusion characteristics are associated with blood flow in LIMA-LAD graft in patients with ischemic cardiomyopathy. TPD at rest (assessed globally and in the LAD region) as well as global SRS value are potential predictors of early graft failure.

Clinical Utility of CT-based Attenuation-correction in Myocardial Perfusion SPECT Imaging.

We aimed to investigate and compare the role of computed tomography (CT)-based attenuation-corrected images (AC) with non-attenuation-corrected images (NAC) obtained by single-photon emission computed tomography/computed tomography (SPECT/CT) myocardial perfusion imaging (MPI). The data of 124 patients who were applied one-day stress-rest Tc-99m sestamibi SPECT/CT MPI and who had coronary angiography (CAG) results within ±3 months were retrospectively reviewed. AC and NAC images were visually evaluated by two nuclear medicine specialists in a consensus. CAG results were used as the reference standard. Specificity, sensitivity, and accuracy were calculated as 66%, 61%, 71%, 79% and 69%, 70% for AC and NAC imaging in the whole group, respectively. There was no statistically significant difference between AC and NAC images for specificity, sensitivity, and accuracy in the male and female subgroups. In the diagnosis of right coronary artery (RCA) disease, CT AC significantly increased the specificity from 87% to 96%. However, in the left anterior descending artery (LAD) region, the specificity was significantly reduced from 95% to 77%. CT-based AC did not significantly contribute to diagnostic performance for increased specificity for the RCA and reduced specificity in the LAD region. Therefore, AC images should always be evaluated side by side with NAC images to benefit from the different advantages of both techniques.

Abstract 11403: Systemic Administration of High Mobility Group Box 1 Fragment Improves Cardiac Functions via Activating Tissue Healing Pathway of Bone-Marrow Mesenchymal Stem Cell in a Porcine Ischemic Cardiomyopathy Model

Introduction : Regenerative therapy for heart failure (HF) points to bone marrow mesenchymal stem cell (BM-MSC) as a promising cell source. High mobility group box 1 (HMGB1) is a nuclear protein involved in tissue homeostasis. In this study, we developed an HMGB1 fragment containing a BM-MSC mobilization domain. Hypothesis: We hypothesize that the HMGB1 fragment improves cardiac function by activating a tissue healing pathway of BM-MSC within a porcine ischemic cardiomyopathy (ICM) model as a pre-clinical study. Methods: Gottingen mini pigs weighing 15-25 kg were used. An ICM model was generated by placing an ameroid constrictor ring (internal diameter; 3.5 mm) on the left anterior descending artery (LAD). After 4 weeks, either the HMGB1 fragment (HMGB1 group; 3 mg/kg, n=6) or normal saline (control group; n=5) was administered intravenously with one dose every 48 h for five times. We examined cardiac function before and 8 weeks post treatment through echocardiography, cardiac magnetic resonance imaging (cMRI) with late gadolinium enhancement (LGE), and a fluoroscopy-guided pressure wire study. Then, histological analysis was performed. Results: In echocardiography, ejection fraction significantly improved in the HMGB1 group compared with the control (+11.1% vs -4.8%, p=0.0003). cMRI with LGE demonstrated that the areas of damaged myocardium (core infarct zone + border zone) in the LAD region was reduced in the HMGB1 group compared with the control group (-11.9% vs +17.9%, p=0.0090). Coronary flow reserve (CFR) and resistive reserve ratio (RRR) were evaluated through pressure wire study; they improved in the HMGB1 group compared with the control group (ΔCFR; +0.38 vs +0.01, p=0.0249, ΔRRR; +0.42 vs +0.07, p=0.0275). Histological analysis showed that cardiomyocyte size (26.6 μm vs 38.0 μm, p=0.0339) and areas of fibrosis were smaller (9.8% vs 11.6%, p=0.1649), and the density of CD31-positive endothelial cells was higher (1033/mm 2 vs 640/mm 2 , p=0.0339) in the HMGB1 group than in the control group. Conclusions: Systemic administration of the HMGB1 fragment improved cardiac function, coronary flow reserve, and reduced cardiac fibrosis in an ICM model. This drug-induced activation of inner tissue repair and regeneration is a novel approach to treat HF.

Ischemia-reperfusion injury to coronary arteries: Comprehensive microscopic study after reperfused myocardial infarction

BackgroundCoronary arteries supply oxygen and nutrients to the heart. We evaluated the dynamics of microscopic damage throughout the ischemia-reperfusion process in the wall of coronary arteries following myocardial infarction (MI). MethodsIn a swine model of reperfused MI, animals were divided into one control and four MI groups: 90-min ischemia without reperfusion, or followed by one minute, one week or one month reperfusion. Left anterior descending (LAD; infarct-related artery) and control right coronary arteries (RCA) were isolated. Taking the balloon inflation region as a reference, we isolated the proximal and distal LAD areas, performing histological staining and immunohistochemistry. ResultsAlthough mild changes in tunica intima were observed during ischemia, an almost complete absence of endothelium, and abnormal breaks in the internal elastic layer were found post-revascularization. In tunica media, increased thickness was observed soon after reperfusion, whereas larger thickness, disorganized muscle cell distribution and edema were found one week after reperfusion. This damage was more pronounced in distal rather than proximal LAD, whereas no changes were detected in RCA. In the tunica adventitia, vasa vasorum density decayed during ischemia in both LAD regions, but was restored after one month. Leukocyte adhesion to the artery was observed post-revascularization, developing into a massive presence in the three layers one week post-reperfusion. ConclusionsIschemia-reperfusion can itself induce damage in the wall of the epicardial coronary artery, becoming more pronounced in the region distal to balloon inflation. Exploring these abnormalities will provide insight into the pathophysiology of coronary circulation and MI.

Noninvasive unipolar electrogram T-wave upslope is an accurate marker of local refractoriness in explanted hearts with drug-induced repolarization dispersion

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): French National Research Agency Matthijs Cluitmans is supported by a Veni grant from the Netherlands Organization for Scientific Research Background The relationship between T-wave morphology in local unipolar electrograms (UEGs) as mapped with noninvasive electrocardiographic imaging (ECGI) and local repolarization time (RT) has not been validated in pronounced RT dispersion. Purpose To study the time of upslope of the T-wave (Tup) in epicardial UEGs mapped with ECGI as a marker of time of local refractoriness (trefr, a surrogate for RT) in intact hearts with RT dispersion. Methods Six pig hearts were Langendorff-perfused with selective perfusion of the LAD artery and submersed in a torso-shaped tank containing 256 electrodes on the torso surface (panel A). RT was prolonged in the non-LAD regions by infusing dofetilide (‘Dof’) and shortened in the LAD region using pinacidil (‘Pin’). Tup was determined in both invasive UEGs (recorded with epicardial electrodes) and in noninvasive UEGs (reconstructed with ECGI). Programmed stimulation was used to determine trefr, defined as the shortest coupling interval with capture. Both metrics were determined relative to the common pacing spike. Results In all six hearts, selective dofetilide and pinacidil infusion resulted in delayed trefr and Tup in the non-LAD region, and shortened invasive trefr and noninvasive Tup in the LAD region, respectively (panel B and C). Over all 59 observations, Tup showed high agreement with trefr (values close to line of identity, panel D) with strong correlation (r = 0.91). This finding was independent of T-wave polarity (positive, negative or biphasic). Conclusion The moment of steepest upslope of the T-wave in a noninvasively reconstructed UEG accurately reflects end of local refractoriness in intact hearts, in case of pronounced RT dispersion. Under these circumstances, when local RT is defined by moment of re-excitability (allowing to link it to conduction block and re-entry), ECGI T-wave upslope can be taken as a truthful marker for local RT. Abstract Figure. Results

Accuracy of global and regional longitudinal strain at peak of dobutamine stress echocardiography to detect significant coronary artery disease

Dobutamine stress echocardiography (DSE) is sensitive but subjective diagnostic tool to detect inducible ischemia. Nowadays, speckle tracking allows an objective quantification of regional wall function. We aimed to investigate the feasibility and accuracy of global (GLS) and regional longitudinal strain (RLS) during DSE to detect significant coronary stenosis (SCS). We conducted a prospective observational multicenter study including patients undergoing DSE for suspected SCS. 50 patients with positive DSE underwent coronary angiography. Besides visual regional wall motion score index (WMSI), GLS and RLS were determined at rest and at peak stress by Automated Function Imaging. DSE GLS feasibility was 96%. Among 35 patients with SCS, 12 patients were affected by multivessel disease, 18 had stenosis of left anterior descending artery (LAD), 18 of left circumflex (LCX) and 15 of right coronary artery (RCA). At peak stress, both GLS reduction (p = 0.037) and WMSI worsening (p = 0.04) showed significant agreement with coronary angiography for detecting SCS. When single lesion was considered, peak stress GLS and LAD RLS were lower in the obstructed LAD regions than in normo-perfused territories (17.4 ± 5.5 vs. 20.5 ± 4.4%, p = 0.03; 17.1 ± 7.6 vs. 21.6 ± 5.5%, p < 0.02, respectively). Furthermore, the addition of RLS to regional WMSI was able to improve accuracy in LAD SCS prediction (AUC 0.68, p = 0.037). Conversely, in presence of LCX or RCA SCS, LS was less accurate than WMSI at peak stress. In conclusion, DSE strain analysis is feasible and may improve prediction of LAD SCS, whereas regional WMSI assessment performs better in presence of SCS of LCX and RCA.

The effect of deep inspiration breath-hold technique on left anterior descending coronary artery and heart dose in left breast irradiation

PurposeTo determine the effect of the deep inspiration breath-hold (DIBH) technique on left anterior descending coronary artery (LAD) region and heart dose in left breast cancer irradiation.Materials and MethodsTwenty-five left breast cancer patients who previously received breast-conserving surgery underwent computed tomography (CT) simulation with both free-breathing (FB) and DIBH techniques and four radiation treatment plans. The plan comprised the following with both the FB and DIBH techniques: whole breast (WB), and WB with internal mammary lymph nodes (WB+IMNs). The prescription dose was 50 Gy in 25 fractions. The doses to the LAD region, heart and lungs were compared. Moreover, in-field maximum heart distance (maxHD) and breast volume were analyzed for correlations with the mean heart dose (MHD).ResultsIn the WB plan with DIBH vs. FB techniques, the mean radiation doses to the LAD region, MHD, and the left lung V20 were 11.48 Gy vs. 19.84 Gy (p < 0.0001), 2.95 Gy vs. 5.38 Gy (p < 0.0001), and 19.72% vs. 22.73% (p = 0.0045), respectively. In the WB+IMNs plan, the corresponding values were 23.88 Gy vs. 31.98 Gy (p < 0.0001), 6.43 Gy vs. 10.24 Gy (p < 0.0001), and 29.31% vs. 32.1% (p = 0.0009), respectively. MHD correlated with maxHD (r = 0.925) and breast volume (r = 0.6).ConclusionThe use of the DIBH technique in left breast cancer irradiation effectively reduces the radiation doses to the LAD region, heart and lungs. MHD is associated with maxHD and breast size.

P1404 Additional power of automated longitudinal strain during dobutamine stress echo for detecting inducible ischemia in left anterior descending artery stenosis

Abstract Background Dobutamine stress echo (DSE) is a sensitive but subjective test of inducible ischemia. Speckle tracking allows now a quantitative assessment of regional wall motion, even during DSE. Purpose To investigate the feasibility and accuracy of global and regional longitudinal strain during DSE to detect significant CAD. Methods This is a prospective, observational study, including 88 patients undergoing DSE for suspected CAD. Thirthy-three patients with negative DSE were excluded from analysis. The remaining 50 patients (82% males, mean age 66.3 ± 8.2 years) with positive DSE underwent subsequent invasive coronary angiography (CA). Besides visual regional wall motion score index (WMSI), global longitudinal strain (GLS) and regional longitudinal strain (RLS) were determined at rest, at peak stress and at early recovery by a dedicated software (Automated Function Imaging) incorporated in a quoad-screen of the echo machine and activated by automatic quantification. Obstructive CAD was defined as &amp;gt;70% stenosis or intermediate stenosis combined with fractional flow reserve &amp;lt;0.80. Results The feasibility of DES regional longitudinal strain was 100% (n = 50/50) in the pooled population. Fifteen patients did not show coronary stenosis whereas obstructive CAD was detected in 35 patients (12 with multi-vessel disease). Among these patients, 18 patients had left anterior descending artery (LAD) stenosis, 18 left circumflex coronary artery (LCX) stenosis and 15 right coronary artery (RCA) stenosis. GLS reduction at peak stress (k = 0.253, p = 0.037) and WMSI increase at peak stress (k = 0.217, p = 0.04) showed mild but significant agreement with CA for detecting significant coronary stenosis, whereas the agreement of GLS at recovery (k=-0.087, p = 0.518) was poor. When single lesion territory was considered, GLS at peak stress (17.4 ± 5.5 vs 20.5 ± 4.4%, p = 0.034) and LAD longitudinal strain (= average of 8 myocardial segments: middle and apical posterior septum, basal, middle and apical anterior septum, basal, middle and apical anterior wall) at peak stress showed significantly lower values in the obstructed LAD regions than the territories perfused by non-obstructed coronary arteries (17.1 ± 7.6 vs 21.6 ± 5.5% p = 0.021). Conversely, in presence of significant LCX or RCA stenosis, visual regional wall motion of LCX and RCA territories were higher at peak stress (WMSI LCX = 1.80 ± 0.65 in presence of LCX stenosis vs. 1.38 ± 0.44 in absence of stenosis, p &amp;lt; 0.01; WMSI RCA = 1.89 ± 0.52 in presence of RCA stenosis vs. 1.42 ± 0.42 in absence of stenosis, p = 0.002), but RLS at peak stress showed a trend to increase, without achieving the statistical significance (RLS RCA: p = 0.128, RLS LCX: p = 0.103). Conclusion AFI-based strain quantitative analysis appears to be highly feasible during DSE. It appears also to be more accurate than the visual wall motion for the detection of myocardial ischemia in presence of LAD while the accuracy is suboptimal in patients with LCX and RCA stenosis.

CoQ10 enhances PGC1\u03b1 and increases expression of mitochondrial antioxidant proteins in chronically ischemic swine myocardium

BackgroundExpression of mitochondrial proteins is reduced within hibernating myocardium (HM). It is unclear whether dietary supplementation with CoQ10 can increase expression of mitochondrial electron transport chain (ETC) and antioxidant proteins within this tissue. In a swine model of HM, we tested whether dietary administration of CoQ10 for four weeks enhances the expression of ETC and antioxidant proteins within the mitochondria via increased PGC1α signaling.Methods12 swine were instrumented with a fixed constrictor around the LAD artery to induce gradual stenosis. At three months, transthoracic ECHO was performed to confirm the presence of a wall motion abnormality in the anterior wall. Animals were then randomly assigned to receive daily dietary supplements of either CoQ10 (10 mg/kg/day) or placebo for four weeks. At this time, animals underwent a final ECHO and terminal procedure. Expression of nuclear-bound PGC1α (Western blots) and mitochondrial proteins (Tandem Mass Tag) were determined.ResultsMitochondrial and nuclear membranes were isolated from the LAD region. Nuclear-bound PGC1α levels were > 200-fold higher with administration of four weeks of CoQ10 treatment (p = 0.016). Expression of ETC proteins was increased in those animals that received CoQ10. Compared with mitochondria in the LAD region from placebo-treated pigs, CoQ10-treated pigs had higher levels of Complex I (p = 0.03), Complex IV (p = 0.04) and Complex V (p = 0.028) peptides.ConclusionsFour weeks of dietary CoQ10 in HM pigs enhances active, nuclear-bound PGC1α and increases the expression of ETC proteins within mitochondria of HM tissue.

Development of delineation for the left anterior descending coronary artery region in left breast cancer radiotherapy: An optimized organ at risk

Background and purposeThe left anterior descending coronary artery (LAD) and diagonal branches (DBs) are blurred on computed tomography (CT). We aimed to define the LAD region (LADR) with adequate inclusion of the LAD and DBs and contouring consistency. Methods and materialsThe LADR was defined using coronary CT angiograms. The inclusion ratio was used to assess the LAD and DBs inclusion by the LADR. Four radiation oncologists delineated the LAD and LADR, using contrast-enhanced CT of 15 patients undergoing left breast radiotherapy. The Sørensen–Dice similarity index (DSI), Jaccard similarity index (JSI), and Hausdorff distance (HD) were calculated to assess similarity. The mean dose (Dmean) and maximum dose (Dmax) to the LAD and LADR were calculated to compare consistency. Correlations were evaluated using Pearson’s correlation coefficient. ResultsThe inclusion ratio of the LAD by the LADR was 96%. The mean DSI, JSI, and HD values were respectively 27.9%, 16.7%, and 0.42mm for the LAD, and 83.1%, 73.0%, and 0.18mm for the LADR. The Dmean between the LAD and LADR were strongly correlated (r=0.93). ConclusionDelineation of the LADR significantly improved contouring similarity and consistency for dose reporting. This could optimize dose estimation for breast radiotherapy.

Magnetic resonance imaging assessment of cardiac function in a swine model of hibernating myocardium 3 months following bypass surgery

ObjectiveClinical studies demonstrate delayed recovery of hibernating myocardium (HM) following coronary artery bypass graft (CABG) surgery. Cardiac magnetic resonance (CMR) imaging is effective in identifying HM in clinical settings. Our animal model of HM shows partial but incomplete functional recovery 1 month following CABG using echocardiography. This study uses CMR imaging to determine completeness of recovery 3 months post-CABG. MethodsSwine (N = 12) underwent left anterior descending artery (LAD) 1.5-cm constrictor placement creating a territory of HM over 12 weeks. CMR at 12 weeks confirmed hibernation without infarction (N = 12). Off-pump left internal thoracic artery (LITA) to the LAD was performed in 9 animals. Three animals were killed as HM controls. CMR imaging was repeated in revascularized animals before death at 1 (n = 4) or 3 months (n = 5). CMR imaging was performed at baseline and with dobutamine infusion (5 μg/kg/min). ResultsTwelve weeks after constrictor placement, CMR imaging confirmed viability in LAD region and LAD stenosis in all animals. In HM, wall thickening is reduced at baseline but with contractile reserve present during dobutamine infusion. Following revascularization, CMR imaging confirmed patent LITA graft (n = 9). Analysis of baseline regional function shows incomplete recovery of HM following CABG, with reduced contractile reserve at both 1 and 3 months post-CABG. ConclusionsCMR imaging provides accurate spatial resolution of regional contractile function and confirms the presence of HM at 12 weeks following instrumentation of the LAD. Three months following CABG, partial recovery of HM with contractile reserve is present in the single LAD territory.

Pioglitazone increases PGC1-α signaling within chronically ischemic myocardium

The peroxisome proliferator-activated receptor (PPAR)-γ drug pioglitazone (PIO) has been shown to protect tissue against oxidant stress. In a swine model of chronic myocardial ischemia, we tested whether PIO increases PGC1-α signaling and the expression of mitochondrial antioxidant peptides. Eighteen pigs underwent a thoracotomy with placement of a fixed constrictor around the LAD artery. At 8 weeks, diet was supplemented with either PIO (3 mg/kg) or placebo for 4 weeks. Regional myocardial function and blood flow were determined at the time of the terminal study. PGC1-α expression was quantified from nuclear membranes by gels and respiration, oxidant stress markers and proteomics by iTRAQ were determined from isolated mitochondria. In the chronically ischemic LAD region, wall thickening from the PIO and control groups was 42 ± 6 and 45 ± 5 %, respectively (NS) with no intergroup differences in basal blood flow (0.72 ± 0.04 versus 0.74 ± 0.04 ml/min g, respectively; NS). In the PIO group, the expression of nuclear bound PGC1-α was higher (11.3 ± 2.6 versus 4.4 ± 1.4 AU; P < 0.05) and the content of mitochondrial antioxidant peptides including superoxide dismutase 2, aldose reductase, glutathione S-transferase and thioredoxin reductase were greater than controls. Although isolated mitochondria from the PIO group showed lower state 3 respiration (102 ± 13 versus 161 ± 22 nmol/min mg; P < 0.05), no differences in oxidant stress were noted by protein carbonyl (1.7 ± 0.7 versus 1.1 ± 0.1 nmol/mg). Chronic pioglitazone does not reduce regional myocardial blood flow or function in a swine model of chronic myocardial ischemia, but may have an important role in increasing expression of antioxidant proteins through PGC1-α signaling.

Abstract 10277: Effect of CoQ10 on Contractile Reserve of Hibernating Swine Myocardium Following Bypass Surgery

Background: We have previously shown that the recovery of regional function and maximal oxygen consumption in a pig model of hibernating myocardium is incomplete at 4 weeks following bypass surgery (CABG). Because clinical studies suggest a beneficial effect of chronic administration of Coenzyme Q10 (CoQ10) in ischemic heart disease, we tested the benefit of this supplement on contractile reserve, using MRI. Methods: Twelve pigs underwent placement of a constrictor around the LAD artery and had reduced function by MRI at 12 weeks. They then underwent off-pump byass using a left internal mammary artery graft and were allowed to recover. Pigs were given daily dietary supplements of either CoQ10 (10 mg/kg/day) or placebo and restudied with MRI at 4 weeks post-CABG. Images were acquired prior to and following CABG with a 3.0-T scanner (Achieva, Philips Medical Systems, Andover MA, USA), with a 4-element phased array coil on the chest and EKG gating. Regional circumferential strain (EC) measures were determined at baseline and at the time of the final study post-CABG, during an infusion of low dose dobutamine. Immediately post-stress, blood samples were obtained for analysis of troponins. Results: One animal did not survive and comparisons are made between the Placebo (N=6) and CoQ10 (N=5) groups. At 12 weeks following instrumentation and just prior to CABG, strain in the LAD region of all animals was lower than the remote regions at rest (-14.27±0.65 versus -15.13±0.69 P&lt;0.05). At 4 weeks post-CABG, baseline strain in placebo and CoQ10 groups was -12.4±1.2 and -13.7±0.8 respectively (NS). In addition to no differences in basal function, there were no intergroup differences in either contractile reserve in the LAD region, as measured by circumferential strain, or cardiac troponin levels post-stress (Figure). In summary, in this model of chronic myocardial ischemia, daily supplementation with CoQ10 did not improve basal function or contractile reserve at 4 weeks following CABG.

Abstract 9825: Cardiac Strain in a Swine Model of Regional Hibernating Myocardium: Effects of Bypass Surgery on Contractile Reserve

Background: Clinical studies have suggested that functional recovery of hibernating myocardium may be delayed following coronary artery bypass graft (CABG) surgery. We have shown in a swine model of hibernating myocardium, that recovery of regional function and oxygen consumption during an infusion of high dose catecholamine is sub-maximal at 4-weeks following CABG. Using the same swine model of hibernating hearts along with MRI estimates of circumferential strain (ECC), we tested whether contractile reserve within hibernating myocardial regions during a low dose infusion of dobutamine improves post-CABG. Methods. Ten pigs underwent thoracotomy with placement of a constrictor around the LAD artery. At 12 weeks, MRI imaging was performed prior to CABG and repeated 4-weeks following off-pump revascularization with a left internal mammary artery graft to the LAD artery. MRI studies were performed at baseline and during an infusion of low dose dobutamine (5 μg/kg/min). Results: MRI studies prior to CABG showed that circumferential strain in the Hibernating (LAD) Region was lower than the Remote Region at rest (-14.5±0.7 versus -15.1±0.7 respectively; P&lt;0.05) and did not improve during dobutamine (-14.7±0.8 versus -16.7±0.8 respectively; P&lt;0.05). Following CABG, strain measurements in the hibernating LAD region remained lower than remote regions at rest, but improved during the same dose of dobutamine (Figure). Summary: Baseline function in hibernating myocardium does not fully recover at 4 weeks post-CABG but contractile reserve during an infusion of low dose dobutamine does improve compared with estimates of strain obtained prior to surgery. Future studies should address the time course of recovery of regional function post-CABG and test whether additional interventions might facilitate earlier recovery of contractile reserve.

Abstract 154: Allogeneic Cardiosphere-derived Cells From an Aged Donor Elicit Long-term Improvements in Left Ventricular Function and Myocyte Proliferation in a Mini-swine Model of Chronic Myocardial Ischemia

Objective: Virtually all large animal studies of cell-based therapy have employed young donor-recipient pairs. Since aging may impact the reparative ability of allogeneic cardiosphere-derived cells (CDCs), we tested whether CDCs from an aged donor promote functional repair of ischemic myocardium using a mini-swine model that enabled serial assessment of left ventricular (LV) function over an extended follow-up period. Methods: Immunosuppressed mini-swine (cyclosporine 100 mg/day) with a chronic (4-months) LAD stenosis were untreated (n=8) or received 20 million allogeneic aged CDCs (n=10). Cells were cultivated from a 9-year old mini-pig and infused into the 3 major coronary arteries under continuous flow (1 million cells/min). LV function was assessed by echocardiography at baseline and over a 3-month follow-up period, at which time histological assessment of myocyte morphometry, proliferation (Ki67), and cell retention (Y-FISH) was performed. Results: Wall thickening (WT) of the ischemic LAD region was impaired at baseline (LAD: 42.7 ± 2.1% vs. Remote: 81.4 ± 4.8%, p&lt;0.01) and not different between treatment groups. One month later, LAD WT improved in aged CDC-treated animals (from 41.0 ± 3.1 to 53.0 ± 1.7%, p=0.01) but remained depressed in untreated animals (from 45.1 ± 2.8% to 44.9 ± 2.6%, p=0.97). Extended follow-up revealed that LAD WT continued to improve, reaching 60.2 ± 1.6% (p=0.01) 3-months after CDC treatment. Histological analyses demonstrated morphometric changes consistent with myocyte regeneration, including an increase in myocyte nuclear density (1231 ± 34 vs. 1094 ± 34 nuclei/mm 2 , p=0.02) and reduction in myocyte diameter (13.9 ± 0.2 vs. 14.5 ± 0.3 μm, p=0.05). Increases in Ki67 + myocytes (468 ± 92 vs. 199 ± 32 nuclei/10 6 myocyte nuclei, p=0.02) and rare Y + cells in sex-mismatched recipients (0.5 ± 0.2 cells/cm 2 ) supported endogenous myocyte proliferation as the primary source of new myocytes. Conclusion: CDCs from an aged donor retain their reparative capacity to promote functional improvement and increase myocyte number following global intracoronary infusion. The progressive improvement in LV function 3-months after treatment with ongoing myocyte proliferation supports a long-lasting benefit after a single infusion.

Microcirculatory disorder hypothesis in Takotsubo cardiomyopathy

of patients with TC when compared with controls, with no difference observed between the two groups in other coronary arteries. Important conclusions from our study were: Takotsubo cardiomyopathy patients have an abnormal CTFC in the LAD territory suggesting disturbances in endothelial or microvascular function, and the preferential distribution of CTFC abnormality in LAD region may also plausibly explain why the apex of the heart is invariably affected in the apical ballooning syndrome [4–6]. Similar studies have been previously reported in literature and demonstrate abnormal TFC involving all three coronary arteries (and not LAD alone) depicting impaired multivessel (or diffuse) coronary microcirculation [3,7,8]. Furthermore these findings are reported either in the acute phase alone[7] or both the acute phase and follow-up [8]. These studies suggest that TFC can be utilized as a clinical indicator of myocardial perfusion and a useful diagnostic marker in assessing microvascular dysfunction in TC patients. From a pathophysiologic standpoint, microcirculatory disorder hypothesis (in combination with other mechanisms) is an important concept to recognize in evolution of Takotsubo cardiomyopathy.

Abstract 9912: Global Intracoronary Infusion of Allogeneic Atrial Cardiosphere-Derived Cells (CDCs) Stimulates Myocyte Regeneration and Reverses LV Remodeling in Miniature Swine With Chronic Myocardial Infarction

Background: Intracoronary infusion of autologous CDCs (icCDCs) into the infarct-related artery using the “stop flow” technique improves regional function in patients but global function remains unchanged. We tested the hypothesis that this reflects the inability to regress cellular hypertrophy and replace myocytes lost in remote remodeled regions that can be overcome by global intracoronary infusion of CDCs. Methods: Miniswine (n=10) were studied 8 weeks after chronic infarction was produced by LAD microembolization (1x10 6 microspheres, 45μm diameter). Ejection fraction decreased from 63 ± 2% at baseline to 31 ± 2% four weeks after infarction (p&lt;0.05 vs. baseline) and remained unchanged at 8 weeks (32 ± 2%, p-ns vs. 4 weeks). Allogeneic CDCs (20 x 10 6 CDCs, cyclosporine 100 mg/day) isolated from donor atrial biopsies were infused into the 3 major coronary distributions without interrupting flow. We assessed myocardial function (echo), myocyte proliferation (Ki67) and infarct size (TTC) in comparison to untreated controls. Regional myocyte regeneration was quantified by assessing myocyte nuclear density and size. Results: Infusing icCDCs into infarcted and remodeled remote myocardium increased regional function and ejection fraction (Table). icCDCs stimulated myocyte proliferation (Ki67) in LAD and remote regions by three-fold. As a result, myocyte number (nuclear density) increased by 35% and myocyte cell diameter decreased by 33% in both LAD and remote myocardium. The reduction in infarct volume after icCDCs was not significant. Conclusion: We conclude that global infusion of allogeneic icCDCs without “stop flow” 1.) stimulates myocyte proliferation throughout the LV and 2.) in a model of infarction, improves regional function with a substantial increase in left ventricular ejection fraction. Thus, allogeneic icCDCs may afford a widely available platform to reverse LV dysfunction in patients with chronic post infarction LV remodeling.