John M Power

Diabetes Australia, Victoria, Melbourne, Victoria, Australia

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Publications (47)198.16 Total impact

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    ABSTRACT: We have developed a percutaneous recirculation system (V-Vascular, V-V) to enable delivery of high levels of antibiotic to the limb in an isolated and targeted manner for the treatment of limb infection. Chronic and acute limb infections are relatively commonplace in a variety of wound types. Infection can become refractory to existing treatment strategies and can cause complications associated with wound healing, lead to amputation and even death. Gentamicin was delivered to the ovine hind limb (4 mg/kg) using the V-V system, a 'closed' recirculatory catheter system that draws blood from the venous system and returns it to the artery via an oxygenator, or via intra-venous (IV) infusion. Samples of muscle, bone and synovial fluid of the limb were collected at 30 and 60 min post administration of gentamicin. There was a significantly greater concentration of gentamicin observed in the bone and skeletal muscle of limbs receiving the antibiotic via V-V at 30 min post administration compared to IV delivery, (bone V-V 0.05 ± 0.04, I.V 0.004 ± 0.001 mg/L p<0.05; muscle V-V 0.005 ± 0.001, I.V 0.002 ± 0.0005 mg/L p<0.05) and bone and synovial fluid at 60 min post administration (bone V-V 0.06 ± 0.02, I.V 0.005 ± 0.001 mg/L p<0.05; synovial fluid V-V 34.58 ± 14.9, I.V 3.03 ± 0.59 mg/L p<0.05). These results suggest that the use of percutaneous recirculation is a safe and effective method for delivering a greater concentration of antibiotic to the limb without systemic implications.
    American Journal of Translational Research 01/2013; 5(1):47-52.
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    ABSTRACT: Down-regulation of sarcoplasmic reticulum calcium ATPase (SERCA2a) is a key molecular abnormality in heart failure (HF), which is not currently addressed by specific pharmacotherapy. We sought to evaluate, in detail, the impact of augmented SERCA2a expression on left ventricular (LV) mechanics in a large animal model of HF. Heart failure was induced in adult sheep by rapid pacing (180 b.p.m.) for 1 month, followed by delivery of adeno-associated virus (AAV) 2/1-SERCA, using a percutaneous, recirculating system for gene delivery over a 10 min period. Left ventricular mechanics was investigated by echocardiography and conductance catheter measurements in sheep receiving AAV2/1-SERCA2a after a further 4 weeks of pacing in comparison with untreated HF controls. Left ventricular function was significantly improved in the AAV2/1-SERCA2a-treated group, despite continued pacing, as measured by fractional shortening (delta absolute FS, control -4.2 ± 1.5% vs. treatment 4.4 ± 1.5%; P < 0.01) and conductance catheterization (delta Ees, control -1.22 ± 0.60 vs. treatment 0.65 ± 0.51; P < 0.05). Western blots showed an increase in SERCA protein in AAV2/1-SERCA2a-treated animals, and an analysis of gene delivery showed no evidence of regional myocardial heterogeneity in the distribution of AAV2/1-SERCA. In a large animal model, AAV2/1-mediated SERCA2a gene delivery using percutaneous, recirculating cardiac delivery leads to improved LV function.
    European Journal of Heart Failure 03/2011; 13(3):247-53. · 5.25 Impact Factor
  • D M Kaye, M J Byrne, J M Power
    Gene therapy 12/2009; 17(4):565-6. · 4.75 Impact Factor
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    ABSTRACT: Despite pharmacological advances for heart failure, morbidity and mortality remain unacceptably high. As a result, alternative approaches such as cell therapy have been suggested to hold potential promise. However, a major obstacle is the optimization of cell delivery to the heart. Therefore, we investigated the efficacy of a percutaneous recirculation system for the delivery of cells to the heart. Ovine fibroblasts were delivered to the ovine heart (3 x 10(7) cells) using the V-Focus system, a "closed" recirculatory system that draws blood from the coronary sinus and returns it to the coronary artery via an oxygenator, or intracoronary (IC) infusion, followed by a 2-hour recovery period. Animals were euthanized and cardiac tissue collected to determine presence of cells. There was a significant difference (P < 0.05) in the number of cells delivered to the heart by the V-Focus compared to direct coronary infusion for left ventricular freewall (V-Focus 1.39 +/- 0.63/mm(2), IC 0.11 +/- 0.06/mm(2)), septum (V-Focus 3.18 +/- 0.88/mm(2), IC 0.38 +/- 0.19/mm(2)), and right ventricle (V-Focus 0.46 +/- 0.23/mm(2), IC 0.05 +/- 0.04/mm(2)). These results suggest that potential therapeutic cells are optimally delivered to the large animal heart using the V-Focus cardiac delivery system in an ovine heart.
    Journal of Interventional Cardiology 11/2009; 23(1):14-7. · 1.50 Impact Factor
  • Heart Lung and Circulation - HEART LUNG CIRC. 01/2009; 18.
  • Heart Lung and Circulation - HEART LUNG CIRC. 01/2009; 18.
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    ABSTRACT: Abnormal excitation-contraction coupling is a key pathophysiologic component of heart failure (HF), and at a molecular level reduced expression of the sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA2a) is a major contributor. Previous studies in small animals have suggested that restoration of SERCA function is beneficial in HF. Despite this promise, the means by which this information might be translated into potential clinical application remains uncertain. Using a recently established cardiac-directed recirculating method of gene delivery, we administered adeno-associated virus 2 (AAV2)/1SERCA2a to sheep with pacing-induced HF. We explored the effects of differing doses of AAV2/1SERCA2a (low 1 x 10(10) d.r.p.; medium 1 x 10(12) d.r.p. and high 1 x 10(13) d.r.p.) in conjunction with an intra-coronary delivery group (2.5 x 10(13) d.r.p.). At the end of the study, haemodynamic, echocardiographic, histopathologic and molecular biologic assessments were performed. Cardiac recirculation delivery of AAV2/1SERCA2a elicited a dose-dependent improvement in cardiac performance determined by left ventricular pressure analysis, (+d P/d t(max); low dose -220+/-70, P>0.05; medium dose 125+/-53, P<0.05; high dose 287+/-104, P<0.05) and echocardiographically (fractional shortening: low dose -3+/-2, P>0.05; medium dose 1+/-2, P>0.05; high dose 6.5+/-3.9, P<0.05). In addition to favourable haemodynamic effects, brain natriuretic peptide expression was reduced consistent with reversal of the HF molecular phenotype. In contrast, direct intra-coronary infusion did not elicit any effect on ventricular function. As such, AAV2/1SERCA2a elicits favourable functional and molecular actions when delivered in a mechanically targeted manner in an experimental model of HF. These observations lay a platform for potential clinical translation.
    Gene therapy 12/2008; 15(23):1550-7. · 4.75 Impact Factor
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    ABSTRACT: Atrial fibrillation (AF) is a common comorbidity in heart failure (HF) patients and is classically associated with acceleration in the rate of HF progression. The precise mechanism for this interaction is unclear, but comprises "bidirectional" aspects in which AF promotes HF and HF also increases the likelihood of AF. We therefore studied the relationship between AF in an ovine model of pacing-induced congestive HF, in an attempt to identify the mechanisms that underpin the apparent synergistic relationship between AF and HF. Sixteen adult sheep were paced at 190 beats/min for 21 days (HF). AF was induced in 8 of these animals at 14 days' pacing using programmed extrastimuli (HF + AF). Left ventricular hemodynamics and the pattern of cardiac neurohormonal activation, via coronary sinus (CS) sampling, were determined at rest and during submaximal exercise testing in both groups at 21 days and after AF reversion (by atrial defibrillation) at 21 days. CS norepinephrine (NE), endothelin (ET-1), and brain natriuretic peptide (BNP) levels were significantly increased in HF + AF animals, whereas LV end-diastolic pressure (EDP) and LV dP/dt max were significantly reduced compared with moderate HF alone. Cardioversion significantly reduced CS NE and BNP levels and improved contractility in AF + HF animals. In a further 6 animals, we explored the mechanism by which HF increases susceptibility to AF, with specific emphasis on the influence of functional mitral regurgitation. The elimination of MR in HF animals using a percutaneous mitral annular reduction device significantly decreased the inducibility of AF. AF induction significantly depresses left ventricular function and causes activation of myocardial neurohormones. In conjunction, the presence of functional MR increases susceptibility to AF and this may be attenuated by MR reduction by percutaneous mitral annular reduction.
    Journal of cardiac failure 06/2008; 14(4):320-6. · 3.25 Impact Factor
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    ABSTRACT: The purpose of this study was to develop a clinically applicable high-efficiency percutaneous means of therapeutic gene delivery to the failing heart. Substantial advances in the understanding of the cellular and molecular basis of heart failure (HF) have recently fostered interest in the potential utility of gene and cell therapy as novel therapeutic approaches. However, successful clinical translation is currently limited by the lack of safe, efficient, and selective delivery systems. We developed a novel percutaneous closed-loop recirculatory system that provides homogeneous myocardial delivery for gene transfer in the failing large animal heart. After 4 weeks' rapid pacing in adult sheep to induce HF, the animals were randomly allocated to receive either adenovirus expressing a pseudophosphorylated mutant (AdS16E) of phospholamban (PLN) or Ad-beta-galactosidase (AdLacZ). Two weeks after gene delivery, in the presence of continued pacing, left ventricular (LV) ejection fraction had significantly improved in the AdS16E-treated animals (27 +/- 3% to 50 +/- 4%; p < 0.001), whereas a further decline occurred in the AdLacZ group (34 +/- 4% to 27 +/- 3%; p < 0.05). In conjunction, AdS16E delivery resulted in significant reductions in LV filling pressures and end-diastolic diameter (both p < 0.05). In conjunction, AdS16E-treated animals showed significant improvement in the expression of PLN and Ca2+-adenosine triphosphatase activity. In separate animals, recirculating AdLacZ delivery was shown to achieve superior myocardial gene expression in contrast to intracoronary delivery and was associated with lower systemic expression. We report the development of a novel closed-loop system for cardiac gene therapy. Using this approach delivery of AdS16E reversed HF progression in a large animal HF model.
    Journal of the American College of Cardiology 08/2007; 50(3):253-60. · 14.09 Impact Factor
  • Heart Lung and Circulation - HEART LUNG CIRC. 01/2007; 16.
  • Heart Lung and Circulation - HEART LUNG CIRC. 01/2007; 16.
  • The Journal of extra-corporeal technology 04/2006; 38(1):51-2.
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    Melissa J. Byrne, David Kaye, John M. Power
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    ABSTRACT: Background: The development of targeted molecular therapy for the treatment of heart failure (HF) has lead to the development of a novel percutaneous recirculation technique, the V-Focus system. This study investigated its use to deliver adeno-associated vius mediated gene transfer of SR Ca2+ ATPase (AAV2/1SERCA2a) in an ovine model of tachycardia induced heart failure.Methods/Results: The V-Focus cardiac delivery system was used to deliver AAV2/1SERCA2a (5 × 1012 drp) in an ovine model of right ventricular pacing induced heart failure (HF), n = 6, six additional animals did not undergo therapy (control). Animals were continually paced for a further four weeks after delivery of AAV2/1SERCA2a at which time the animals were anaesthetised and an echocardiogram, left ventricular (LV) +dP/dtmax and LV tissue obtained. After four weeks of additional pacing there was a significant increase in both ejection fraction (EF; treatment 40.2 ± 4.6% vs control 27.8 ± 3.4%) and LV +dP/dtmax (treatment 1042 ± 178 vs control 893 ± 204) between animals receiving AAV2/1Serca2a and controls. There was minimal and no significant difference in degree of left ventricular fibrosis between the two groups (p>0.05).Conclusions: These results suggest that targeted molecular therapy using AAV2/1SERCA2a has successfully been applied in combination with the novel V-Focus delivery system in an animal model of tachycardia induced heart failure (HF) and has excellent potential for its treatment. The next valuable step will be to determine the dose-ranging efficacy of AAV2/1SERCA2a.
    Molecular Therapy 01/2006; 13. · 7.04 Impact Factor
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    ABSTRACT: In this study, we investigated for a potential mechanism by which atrial fibrillation (AF) might convey a worse prognosis in congestive heart failure (CHF). Specifically, we aimed to determine whether AF impaired cardiac sympathetic response to baroreceptor unloading in comparison to sinus rhythm (SR) in CHF. Eighteen CHF patients (ejection fraction 30+/-2%, age 59+/- 2 years), nine in SR and nine in AF, were enrolled. A right heart study and cardiac sympathetic tone assessment by coronary sinus catheter were performed at baseline and after 10 min of 20 degrees and 30 degrees of passive head up tilt (HUT). Filling pressures fell significantly during HUT in both SR and AF groups (AF, P=0.002; SR, P<0.001). The cardiac sympathetic response to HUT was significantly attenuated by AF compared with SR (P=0.014). In conjunction, right atrial appendages were collected from 23 cardiac surgery patients, 12 in SR and 11 in AF to investigate the presence of fibrosis. AF was associated with a significant increase in the collagen density (P=0.025). AF is associated with impaired cardiac sympathetic response to baroreceptor unloading compared with SR in CHF, possibly secondary to atrial fibrosis.
    European Heart Journal 12/2005; 26(23):2562-7. · 14.72 Impact Factor
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    ABSTRACT: To utilise an ovine model of tachycardia induced progressive dilated cardiomyopathy and heart failure to investigate the efficacy of passive ventricular constraint with the Acorn cardiac support device as a heart failure treatment. (a) Moderate heart failure was produced in 16 sheep by pacing for 3 weeks. Half were implanted and half sham implanted with the CSD. Pacing continued at a higher rate for an additional 3 weeks. Cardiac function was assessed by echocardiography and manometry. (b) Moderate heart failure was produced (as above) in 27 sheep, 9 were implanted with CSD, pacing was restarted for 4 weeks, the initial CSD implants were terminated and another 9 animals were CSD implanted (severe heart failure), pacing was restarted in the remaining 18 animals for an additional 4 weeks (total 12 weeks) and then all animals were terminated. Cardiac function was assessed using echocardiography and treadmill exercise testing. (a) After 6 weeks of rapid pacing CSD implant animals had significantly better cardiac function both when compared with pre implant values and with non-implanted animals at termination. (b) CSD implantation at both moderate and severe failure resulted in significant improvements in cardiac function both when compared with pre implant values and with non-implanted animals at termination. When compared to pre implant values the improvement was greatest in severe implant animals. In this ovine model of tachycardia induced progressive heart failure, CSD implantation in either moderate or severe heart failure resulted in improved cardiac function, reduced left ventricular volume and mitral regurgitation both when compared with function at time of implant and with non implanted control animals.
    Heart Failure Reviews 07/2005; 10(2):117-23. · 4.45 Impact Factor
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    ABSTRACT: Congestive heart failure (HF) is a leading cause of hospitalization, disability and death. Despite significant advances in pharmacotherapy, HF remains a progressive disorder with an unacceptably high mortality rate. While the molecular and cellular basis of the impairment of myocardial contractility has been determined in detail, current beneficial therapies for heart failure only act indirectly, by interfering with neurohormonal control of the heart. Accordingly, considerable attention has recently been directed at the identification of appropriate targets for gene therapy. In particular, studies directed at the excitation-contraction pathway of the heart have identified genes (particularly phospholamban and SERCA) that can be manipulated to improve contractility. As such, translation into clinical practice now requires the development of safe, minimally invasive methods that provide homogeneous delivery to the heart.We have developed a novel clinically-relevant, percutaneous system for the delivery of viral vectors to the myocardium, based upon an antegrade coronary arterial delivery system combined with recirculation of the coronary venous effluent via a membrane-pump oxygenator circuit. We have demonstrated the safe, reproducible, delivery of adeno-LacZ to the myocardium of both healthy normal sheep (n=15) and sheep with moderate to severe pacing induced heart failure (n=7). During 10-15 minutes recirculation, there was no evidence of compromise in myocardial function (as assessed by echocardiography and electrocardiographic monitoring). Similarly, there was no evidence of lactic acid accumulation in the recirculating blood (baseline vs 15 mins: 2.4 mmol/L vs 2.5 mmol/L). A homogeneous pattern of LacZ delivery was apparent by immunohistochemistry, 2 weeks after gene transfer and no evidence of tissue damage was evident on H+E staining. Of additional importance this 'closed-loop' recirculation system results in minimal systemic leakage (brain, kidney, liver and lung) of viral vector.
    Molecular Therapy 01/2005; 11. · 7.04 Impact Factor
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    ABSTRACT: Functional mitral valve regurgitation plays a key role in the symptomatic severity and progression of heart failure. In an ovine model of dilated cardiomyopathy, we examined the chronic functional consequences of mitral regurgitation reduction using a recently developed novel percutaneous mitral annular reduction (PMAR) device. Fourteen adult sheep were paced right ventricularly at 180 to 190 bpm for 5 weeks, leading to the development of moderate mitral valve regurgitation. After echocardiographic, hemodynamic, and neurohormonal analysis, 9 animals underwent PMAR. All animals were subsequently paced for another 28 days, and a final echocardiographic and hemodynamic study was conducted. Animals that had undergone PMAR showed significantly increased negative and positive dP/dt, whereas pulmonary capillary wedge pressure and mitral valve regurgitation were significantly reduced compared with those at device implant despite continued pacing. In conjunction, significant improvements in plasma norepinephrine and brain natriuretic peptide were apparent. The application of PMAR in animals with pacing-induced dilated cardiomyopathy and functional mitral valve regurgitation resulted in continued improvements in hemodynamic and neurohormonal parameters.
    Circulation 12/2004; 110(19):3088-92. · 15.20 Impact Factor
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    ABSTRACT: Atrial fibrillation (AF) is the most common sustained arrhythmia. Its prevalence is increasing and accordingly, so is its burden on healthcare systems throughout the world. The pathophysiology of AF is complex and poorly understood, which of itself presents a major challenge to the management of this important condition. AF is associated with increased morbidity and mortality, particularly in patients with underlying left ventricular dysfunction. Once AF occurs, it is often difficult to 'cure' and as such, the major focus of therapy is currently divided essentially between a rate control strategy and a need to revert to and maintain sinus rhythm. Both approaches seek to minimise the associated symptoms and complications. Over the past two decades, numerous pharmacological approaches to the management of AF have been employed, many of which have been shown to be relatively ineffective or confounded by major complications. Accordingly, recent research and interest has focused on non-pharmacological electrophysiological therapies to either cure AF or improve symptoms. This review summarises the current approaches to the management AF and provides some new insights into emerging therapies for this common clinical problem.
    Expert Opinion on Pharmacotherapy 12/2003; 4(11):1889-99. · 2.86 Impact Factor
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    ABSTRACT: The Cox maze procedure has shown to be effective in treating atrial fibrillation. Radiofrequency ablation, with a similar objective, has been used as an adjunct to conventional cardiac surgery for the treatment of atrial fibrillation in more than 20 centers in Australia and New Zealand since March 2000. This is a report of those results. One hundred thirty-two patients in 20 centers underwent radiofrequency ablation as an adjunct to conventional cardiac surgery, with a standardized lesion set created with a flexible, 7-electrode, temperature-controlled probe (Cobra; EPTechnologies, San Jose, Calif). All data were entered into a central registry, with regular follow-up prompted by the registry cocoordinator. Each radiofrequency scar was made with standard parameters requiring 2 minutes of tissue coagulation at 80 degrees C to 85 degrees C. Patients undergoing mitral procedures had radiofrequency ablation performed in the left atrium endocardially. Patients undergoing aortic valve replacement or coronary artery bypass surgery underwent epicardial radiofrequency ablation of the left atrium. Epicardial radiofrequency ablation lesions on the right atrium were common to both groups of patients. Preoperatively, 75% of the patients had chronic atrial fibrillation, 21% had paroxysmal atrial fibrillation, and 4% had flutter. Surgical procedures performed included mitral valve procedure in 60%, coronary artery bypass grafting in 14%, aortic valve replacement in 7%, and coronary artery bypass grafting plus aortic valve replacement in 4%. There were no major complications related to the use of radiofrequency ablation. There were no soft tissue or cardiac perforations. Ten patients were defibrillated into sinus rhythm within 3 months postoperatively. The freedom from atrial fibrillation was 84% at 3 months, 90% at 6 months, and 100% at 12 months. All patients at 12 and 18 months' follow-up were in sinus rhythm. There were no thromboembolic complications. Surgical radiofrequency ablation can be performed safely as an adjunct to conventional cardiac surgery. A standardized lesion set created by using similar temperature settings can be adopted in multiple centers and might be effective in treating atrial fibrillation. Data collection through a central registry has helped in monitoring the effectiveness of this new technique in a scattered population.
    Journal of Thoracic and Cardiovascular Surgery 12/2003; 126(5):1357-66. · 3.53 Impact Factor

Publication Stats

805 Citations
198.16 Total Impact Points

Institutions

  • 2013
    • Diabetes Australia, Victoria
      Melbourne, Victoria, Australia
  • 2003–2011
    • Baker IDI Heart and Diabetes Institute
      • Heart Failure Research Group
      Melbourne, Victoria, Australia
    • Alfred Hospital
      Melbourne, Victoria, Australia
    • University of Chicago
      Chicago, Illinois, United States
  • 2007
    • University of Massachusetts Boston
      Boston, Massachusetts, United States
  • 2002
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
  • 1999–2002
    • University of Melbourne
      • Department of Medicine
      Melbourne, Victoria, Australia
  • 1993–2001
    • Austin Health
      • • Department of Cardiac Surgery
      • • Department of Cardiology
      Melbourne, Victoria, Australia