Geng-Hua Yi

PKA phosphorylation activates the calcium release channel (ryanodine receptor) in skeletal muscle: defective regulation in heart failure

The type 1 ryanodine receptor (RyR1) on the sarcoplasmic reticulum (SR) is the major calcium (Ca2+) release channel required for skeletal muscle excitation–contraction (EC) coupling. RyR1 function is modulated by proteins that bind to its large cytoplasmic scaffold domain, including the FK506 binding protein (FKBP12) and PKA. PKA is activated during sympathetic nervous system (SNS) stimulation. We show that PKA phosphorylation of RyR1 at Ser2843 activates the channel by releasing FKBP12. When FKB12 is bound to RyR1, it inhibits the channel by stabilizing its closed state. RyR1 in skeletal muscle from animals with heart failure (HF), a chronic hyperadrenergic state, were PKA hyperphosphorylated, depleted of FKBP12, and exhibited increased activity, suggesting that the channels are “leaky.” RyR1 PKA hyperphosphorylation correlated with impaired SR Ca2+ release and early fatigue in HF skeletal muscle. These findings identify a novel mechanism that regulates RyR1 function via PKA phosphorylation in response to SNS stimulation. PKA hyperphosphorylation of RyR1 may contribute to impaired skeletal muscle function in HF, suggesting that a generalized EC coupling myopathy may play a role in HF.

Bradycardic Therapy Improves Left Ventricular Function and Remodeling in Dogs with Coronary Embolization-Induced Chronic Heart Failure

Both β-adrenergic blockade and bradycardia may contribute to the therapeutic effect of β-blockers in chronic heart failure (CHF). This study tested the relative importance of bradycardia by comparing cilobradine (Cilo), a sinus node inhibitor, with a β-blocker, metoprolol (Meto), in an established canine model of CHF. Dogs were chronically instrumented for hemodynamic and left ventricular (LV) volume measurements. CHF was created by daily coronary embolization via a chronically implanted coronary (left anterior descending coronary artery) catheter. After establishment of CHF, control (n = 6), Meto (30 mg/day, n = 5), Cilo (low) (1 mg/kg/day, n = 5), or Cilo (high) (3 mg/kg/day, n = 5) was given orally for 12 weeks. Systemic hemodynamics, echocardiography, and pressure volume analysis were measured at baseline, at CHF, and 3 months after treatment in an awake state. Protein levels of cardiac sarcoplasmic reticulum calcium-ATPase (SERCA2a), ryanodine receptor (RyR2), and Na+-Ca2+ exchanger (NCX1) were measured by Western blot. RyR2 protein kinase A (PKA) phosphorylation was determined by back-phosphorylation. After 12 weeks, Meto and Cilo (high and low) produced similar bradycardic effects, accompanied by a significantly improved LV dP/dt versus control [Meto, 2602 ± 70; Cilo (low), 2517 ± 45; Cilo (high), 2579 ± 78; control, 1922 ± 115 mm Hg/s; p < 0.05]. Both Meto and Cilo (high) normalized protein levels of SERCA2a and NCX1 and reversed PKA hyperphosphorylation of RyR2, in contrast to controls. High-dose cilobradine effectively produced bradycardia and improved cardiac function after CHF, comparable with metoprolol. Restored protein levels of SERCA2a and improved function of RyR2 may be important mechanisms associated with cilobradine therapy.

Myoblast transfer in ischemic heart failure: effects on rhythm stability.

Skeletal myoblast (SM) implantation promotes recovery of myocardial function after ischemic injury. Clinical observations suggest an association of SM implantation and ventricular arrhythmias. Support for this link has been sought in animal studies, but none employing models of congestive heart failure. In a canine model of postinfarction congestive heart failure (CHF) we compared the frequency of rhythm disturbances using ambulatory electrocardiography monitoring following skeletal myoblast or saline (SAL) implantation. In 19 mongrel dogs ischemic injury and CHF were induced by intracoronary microsphere infusions. Direct intramyocardial injection of autologous skeletal myoblasts (ASM) (2.7–8.3 × 108 cells) or SAL controls was administered to 11 and 8 dogs, respectively. Serial echocardiography and 24-h ambulatory electrocardiography were recorded at baseline (after CHF induction) and at 4 weeks and at 8–10 weeks after injection. Comparisons between groups of left ventricular ejection fraction (LVEF) and the frequency of ventricular arrhythmias, supraventricular arrhythmias, and measures of heart rate variability (HRV) were made at each of the three time points. LVEF increased from 41 ± 6% to 47 ± 2% (p < 0.03) in the ASM group, and did not change (42 ± 6% to 40 ± 2%, p = ns) in SAL. After injection, no differences were seen in the number of dogs demonstrating ventricular tachycardia (n = 3 vs. n = 2, p = ns) or frequent PVCs (n = 3 vs. n = 3, p = ns) in the ASM versus SAL groups, respectively. Significant changes were observed in a time-domain measure of HRV, standard deviation of normal-to-normal RR interval (in ms: 4 weeks 174 ± 95 vs. 242 ± 19; 8 weeks 174 ± 78 vs. 276 ± 78, ASM vs. SAL), but not in other time domain parameters. In this canine model of ischemic CHF, ASM implantation did not result in a significant increase in ventricular arrhythmias compared to controls animals. The potential for ASM implantation to affect time–domain parameters of HRV merits further study.

Catheter-Based Endomyocardial Delivery of Mesenchymal Precursor Cells Using 3D Echo Guidance Improves Cardiac Function in a Chronic Myocardial Injury Ovine Model

The administration of bone marrow-derived stem cells may provide a new treatment option for patients with heart failure. Transcatheter cell injection may require multi-imaging modalities to optimize delivery. This study sought to evaluate whether endomyocardial injection of mesenchymal precursor cells (MPCs) could be guided by real-time 3D echocardiography (RT3DE) in treating chronic, postinfarction (MI) left ventricular (LV) dysfunction in sheep. Four weeks after induction of an anterior wall myocardial infarction in 39 sheep, allogeneic MPCs in doses of either 25 × 106 (n = 10), 75 × 106 (n = 9), or 225 × 106 (n = 10) cells or nonconditioned control media (n = 10) were administered intramyocardially into infarct and border zone areas using a catheter designed for combined fluoroscopic and RT3DE-guided injections. LV function was assessed before and after injection. Infarct dimension and vascular density were evaluated histologically. RT3DE-guided injection procedures were safe. Compared to controls, the highest dose MPC treatment led to increments in ejection fraction (3±3% in 225M MPCs vs. −5±4% in the control group, p < 0.01) and wall thickening in both infarct (4±4% in 225M MPCs vs. −3±6% in the control group, p = 0.02) and border zones (4±6% in 225M MPCs vs. −8±9% in the control group, p = 0.01). Histology analysis demonstrated significantly higher arteriole density in the infarct and border zones in the highest dose MPC-treated animals compared to the lower dose or control groups. Endomyocardial implantation of MPCs under RT3DE guidance was safe and without observed logistical obstacles. Significant increases in LV performance (ejection fraction and wall thickening) and neovascularization resulted from this technique, and so this technique has important implications for treating patients with postischemic LV dysfunction.

Prolonged effects of B-type natriuretic peptide infusion on cardiac remodeling after sustained myocardial injury

B-type natriuretic peptide (BNP) is an established first-line therapy for acute decompensated heart failure (HF), but its efficacy in preventing left ventricular (LV) remodeling after myocardial injury is unknown. The goal of this study was to evaluate the effects of BNP therapy on remodeling after ischemic injury in an awake canine model. Dogs were chronically instrumented for hemodynamics. Ischemia was created by daily coronary embolization (Embo; 3.1 x 10(4) beads/day) for 3 wk; 60 min after the first embolization, BNP (100 ng x kg(-1) x min(-1); n = 6) or saline (control; n = 6) was continuously infused via a left atrial catheter for 3 wk. Hemodynamics and echocardiography were performed in an awake state at baseline, 3 wk after Embo + BNP infusion, and 4 wk after stopping Embo + BNP infusion. End-systolic elastance (E(es)) and LV change in pressure over time (dP/dt) were preserved throughout Embo + BNP therapy versus control therapy (E(es): 3.76 +/- 1.01 vs. 1.41 +/- 0.16 mmHg/ml; LV dP/dt: 2,417 +/- 96 vs. 2,068 +/- 95 mmHg/s; both P < 0.05 vs. control). LV end-diastolic dimension was significantly smaller in BNP-treated dogs compared with control dogs (4.29 +/- 0.10 vs. 4.77 +/- 0.17 cm), and ejection fraction was maintained in treated dogs vs. control dogs (53 +/- 1% vs. 46 +/- 2%) (both P < 0.05 vs. control). Cyclooxygenase (COX)-2 expression in terminal LV tissue was significantly reduced after BNP therapy. Treatment with continuous infusion of BNP preserved LV geometry, improved systolic function, and prevented the progression of systolic HF after persistent ischemic injury.

The Role of Angiotensin II AT1 Receptor in the Maintenance of Hemodynamics in a Canine Model of Coronary Microembolization-Induced Heart Failure

The purpose of this study was to determine whether Angiotensin II (Ang II) contributes to the regulation of resting hemodynamics via Ang II type 1 (AT1) receptors in awake dogs with coronary microembolization-induced heart failure. Six dogs were surgically instrumented for measurement of systemic hemodynamics and for coronary microembolization. The acute hemodynamic effects of a selective AT1-receptor antagonist, GR138950 (1 mg/kg, i.v.), were determined before and after congestive heart failure (CHF). GR138950 had no effects on hemodynamics before CHF Daily coronary microembolizations (through the previously implanted coronary catheter) resulted in CHF, as documented by hemodynamic measurements, a slight but significant increased Ang II plasma level (17.4 +/- 1.6 vs. 23 +/- 1.0 pg/ml; p < 0.05), and characteristic clinical signs of CHF. After CHF, GR138950 significantly increased left ventricular dP/dt(max) (LVdP/dt(max)) from 1,754 +/- 68 to 2,347 +/- 114 mm Hg/s and decreased LV systolic pressure (LVSP) from 118 +/- 5 to 101 +/- 7 mm Hg; meanwhile, heart rate (from 132 +/- 4 to 102 +/- 6 beats/min) and LV end-diastolic pressure (LVEDP; from 17 +/- 3 to 9 +/- 1.5 mm Hg) were significantly decreased. Mean arterial pressure (MAP) was not affected. The peak effects occurred 90 min after administration. Thus Ang II contributes significantly to resting hemodynamics via AT1 receptors in this CHF model; that is, the specific AT1 blocker inhibits the negative inotropic actions of Ang II in the CHF state.

Epicardial catheter-based ventricular reconstruction: a novel therapy for ischaemic heart failure with anteroapical aneurysm

OBJECTIVES Surgical ventricular reconstruction has been used to treat ischaemic cardiomyopathy with large akinetic or dyskinetic areas. However, application of this approach requires a sternotomy, cardiopulmonary bypass and a left ventriculotomy. This study assessed the feasibility and efficacy of minimally invasive, off-pump, epicardial catheter-based ventricular reconstruction (ECVR) in an anteroapical aneurysm ovine model. METHODS Left ventricular (LV) anteroapical myocardial infarction was induced percutaneously by coil embolization of the left anterior descending coronary artery. Eight weeks after infarction, via mini left thoracotomy and without cardiopulmonary bypass, ECVR was performed in six sheep. The scar was excluded by placing anchor pairs on the LV epicardial anterior wall and the right ventricular side of the interventricular septum under fluoroscopic guidance. LV performance was evaluated before, immediately after device implantation and after 6 weeks by echocardiography. Terminal histopathology was performed. RESULTS ECVR was completed expeditiously in all animals without complications. Parameters obtained 6 weeks after device implantation were compared with baseline (pre-device). End-systolic volume was decreased by 38% (25.6 ± 6.1 ml vs baseline 41.2 ± 7.2 ml, P = 0.02) with preservation of stroke volume. Ejection fraction was significantly increased by 13% (48.5 ± 7% vs baseline 35.8 ± 7%, P = 0.02). The circumferential strain in the anterior septum (-7.67 ± 5.12% vs baseline -0.96 ± 2.22%, P = 0.03) and anterior wall (-9.01 ± 3.51% vs baseline -4.15 ± 1.36%, P = 0.01) were significantly improved. The longitudinal strain in apex was reversed (-3.08 ± 1.53% vs baseline 3.09 ± 3.39%, P = 0.01). Histopathology showed full endocardial healing over the anchors with appreciable reduction of the chronic infarct in the LV. CONCLUSIONS ECVR without cardiopulmonary bypass is a less invasive alternative to current standard therapies, reverses LV remodelling and improves cardiac performance in an ovine model of anteroapical aneurysm.

First in vivo evaluation of a flexible self-apposing left atrial appendage closure device in the canine model.

Aimed to evaluate the feasibility of deployment and healing response of a novel transcatheter left atrial appendage (LAA) occlusion device in the canine model

Safety and feasibility of percutaneous delivery of a novel circulatory assist device (CircuLite® SYNERGY®) in the swine model.

AIMS To demonstrate the feasibility and safety of percutaneous delivery of the novel inflow cannula of the CircuLite® SYNERGY® pocket Micro-pump via transseptal access in the swine model. METHODS AND RESULTS After transseptal puncture, the inflow cannula system was advanced into the left atrium (LA) via the right external jugular vein and anchored onto the atrial septum under fluoroscopic and intracardiac echo guidance in 14 acute animals. Subsequently, chronic studies were performed to examine the long-term healing response to the cannula implantation with an artery-LA shunt (n=10) and overall safety of the Micro-pump components (n=6). Acute studies proved the concept of transcatheter delivery of the inflow cannula via superior venous access. The cannula tips were securely anchored in all chronic animals and appropriately endothelialised as early as two weeks. No thrombi or septal damage was observed. For the chronic pump group, device speed of 22,000 rpm (~2.0 L/min) was maintained without any adverse cardiac events. Plasma free haemoglobin assays confirmed the absence of clinically significant haemolysis. CONCLUSIONS The transcatheter delivery of the inflow cannula via superior venous access to the LA is feasible and safe. This percutaneous delivery presents a significantly less invasive alternative to deliver partial circulatory support devices.

Long‐term impact of balloon postdilatation on neointimal formation: An experimental comparative study between second‐generation self‐expanding versus balloon‐expandable stent technologies

Self‐expanding stents (SES) are reemerging as therapeutic alternatives to treat coronary artery disease. It has been proposed that SES can improve clinical outcomes by inducing less injury at implantation and achieving better vessel wall apposition. To date, little data exists comparing the vascular response to both methods of deployment in a controlled experimental setting.