Early reperfusion hemodynamics predict recovery in rat hearts: a potential approach towards evaluating cardiac grafts from non-heart-beating donors

Aims

Cardiac grafts from non-heartbeating donors (NHBDs) could significantly increase organ availability and reduce waiting-list mortality. Reluctance to exploit hearts from NHBDs arises from obligatory delays in procurement leading to periods of warm ischemia and possible subsequent contractile dysfunction. Means for early prediction of graft suitability prior to transplantation are thus required for development of heart transplantation programs with NHBDs.

Methods and Results

Hearts (n = 31) isolated from male Wistar rats were perfused with modified Krebs-Henseleit buffer aerobically for 20 min, followed by global, no-flow ischemia (32°C) for 30, 50, 55 or 60 min. Reperfusion was unloaded for 20 min, and then loaded, in working-mode, for 40 min. Left ventricular (LV) pressure was monitored using a micro-tip pressure catheter introduced via the mitral valve. Several hemodynamic parameters measured during early, unloaded reperfusion correlated significantly with LV work after 60 min reperfusion (p<0.001). Coronary flow and the production of lactate and lactate dehydrogenase (LDH) also correlated significantly with outcomes after 60 min reperfusion (p<0.05). Based on early reperfusion hemodynamic measures, a composite, weighted predictive parameter, incorporating heart rate (HR), developed pressure (DP) and end-diastolic pressure, was generated and evaluated against the HR-DP product after 60 min of reperfusion. Effective discriminating ability for this novel parameter was observed for four HR*DP cut-off values, particularly for ≥20 *10³ mmHg*beats*min⁻¹ (p<0.01).

Conclusion

Upon reperfusion of a NHBD heart, early evaluation, at the time of organ procurement, of cardiac hemodynamic parameters, as well as easily accessible markers of metabolism and necrosis seem to accurately predict subsequent contractile recovery and could thus potentially be of use in guiding the decision of accepting the ischemic heart for transplantation.

Electric pulses augment reporter gene expression in the beating heart

BACKGROUND

Gene therapy of the heart has been attempted in a number of clinical trials with the injection of naked DNA, although quantitative information on myocellular transfection rates is not available. The present study aimed to quantify the efficacy of electropulsing protocols that differ in pulse duration and number to stimulate transfection of cardiomyocytes and to determine the impact on myocardial integrity.

METHODS

Reporter plasmid for constitutive expression of green fluorescent protein (GFP) was injected into the left ventricle of beating hearts of adult, male Lewis rats. Four electrotransfer protocols consisting of repeated long pulses (8 × 20 ms), trains of short pulses (eight trains of either 60 or 80 × 100 µs) or their combination were compared with control procedures concerning the degree of GFP expression and the effect on infiltration, fibrosis and apoptosis.

RESULTS

All tested protocols produced GFP expression at the site of plasmid injection. Continuous pulses were most effective and increased the number of GFP-positive cardiomyocytes by more than 300-fold compared to plasmid injection alone (p < 0.05). Concomitantly, the incidence of macrophage infiltration, fibrosis and cell death was increased. Trains of short pulses reduced macrophage infiltration and fibrosis by four- and two-fold, respectively, although they were 20-fold less efficient in stimulating cardiomyocyte transfection. GFP expression co-related to delivered electric energy, infiltration and fibrosis, although not apoptosis.

CONCLUSIONS

The data imply that electropulsing of the myocardium promotes the overexpression of exogenous protein in mature cardiomyocytes in relation to an injury component. Fractionation of pulses is indicated as a option for sophisticated gene therapeutic approaches to the heart.

Long-term results after operations for active infective endocarditis in native and prosthetic valves

BACKGROUND

The objective of this study was to evaluate the midterm results of patients who underwent operations for active infective endocarditis.

METHODS

Within a 10-year period, 141 patients with active infective endocarditis received surgical therapy. We assessed outcome, freedom from reinfection, and freedom from reintervention. Prosthetic valve endocarditis was included in this series.

RESULTS

Surgical strategies included valve replacement with a tissue valve in 62% of patients and valve repair in 29% of patients. In 29% of patients, reconstruction of the aortomitral continuity, left ventricular outflow tract, or sinus of Valsalva was preferably performed with 1 or more bovine pericardial patches. In-hospital mortality was 11% and postoperative stroke rate was 7%. Multivariate logistic regression revealed multivalve involvement (p=0.052; odds ratio [OR], 5.84; 95% confidence interval [CI], 0.98-34.57), preoperative neurologic impairment (p=0.006; OR, 9.71; 95% CI, 1.92-49.09), and European system for cardiac operative risk evaluation (EuroSCORE) in quartiles (p=0.023; OR, 2.88; 95% CI, 1.15-7.17) to be independent predictors for in-hospital death. One-year and 5-year actuarial survival was 77% and 69%, respectively. One-year and 5-year actuarial freedom from reinfection was 100% and 90%, respectively. Freedom from reoperation at 5 years was 100%. Five-year survival was 74% for single-valve endocarditis and 46% for multivalve endocarditis (p<0.001). One-year freedom from reinfection was 100% for both single-valve and multivalve endocarditis; 5-year freedom from reinfection was 95% for single-valve endocarditis versus 67% for multivalve endocarditis (p=0.049).

CONCLUSIONS

Despite a high early mortality during the first year, surgical intervention for active infective endocarditis provided excellent results with regard to freedom from reinfection and reoperation. A strategy of extensive debridement, reconstruction of destroyed cardiac structures using xenopericardium, followed by valve replacement or repair is highly effective and shows favorable long-term outcomes.

Fine-tuning of substrate architecture and surface chemistry promotes muscle tissue development

Tissue engineering has been increasingly brought to the scientific spotlight in response to the tremendous demand for regeneration, restoration or substitution of skeletal or cardiac muscle after traumatic injury, tumour ablation or myocardial infarction. In vitro generation of a highly organized and contractile muscle tissue, however, crucially depends on an appropriate design of the cell culture substrate. The present work evaluated the impact of substrate properties, in particular morphology, chemical surface composition and mechanical properties, on muscle cell fate. To this end, aligned and randomly oriented micron (3.3±0.8 μm) or nano (237±98 nm) scaled fibrous poly(ε-caprolactone) non-wovens were processed by electrospinning. A nanometer-thick oxygen functional hydrocarbon coating was deposited by a radio frequency plasma process. C2C12 muscle cells were grown on pure and as-functionalized substrates and analysed for viability, proliferation, spatial orientation, differentiation and contractility. Cell orientation has been shown to depend strongly on substrate architecture, being most pronounced on micron-scaled parallel-oriented fibres. Oxygen functional hydrocarbons, representing stable, non-immunogenic surface groups, were identified as strong triggers for myotube differentiation. Accordingly, the highest myotube density (28±15% of total substrate area), sarcomeric striation and contractility were found on plasma-coated substrates. The current study highlights the manifold material characteristics to be addressed during the substrate design process and provides insight into processes to improve bio-interfaces.

Cardiovascular surgery in Marfan syndrome: implications of new molecular concepts in thoracic aortic disease

Acute dissection and rupture of aortic aneurysms comprise for 1–2% of all deaths in industrialized countries. Dilation of the aorta is caused by a multitude of mechanisms including inherited connective tissue disorders such as Marfan syndrome (MFS). MFS is one of the most common inherited connective tissue disorders affecting 1 in 5000 individuals. Although the phenotype of MFS can be quite variable, aneurysmal dilation of the aortic root and consecutive acute aortic dissection is the leading cause of death in this patient population. Over the past years it has been shown that a comprehensive understanding of this disorder provides greater understanding of vascular wall biology and identifies pathways relevant to aortic aneurysms and dissection in general. The current review discusses the surgical management of patients with MFS with a special emphasis on indications for surgery in this complex group of patients.

Proteome analysis in cardiovascular pathophysiology using Dahl rat model

Dahl salt-sensitive (DS) and salt-resistant (DR) inbred rat strains represent a well established animal model for cardiovascular research. Upon prolonged administration of high-salt-containing diet, DS rats develop systemic hypertension, and as a consequence they develop left ventricular hypertrophy, followed by heart failure. The aim of this work was to explore whether this animal model is suitable to identify biomarkers that characterize defined stages of cardiac pathophysiological conditions. The work had to be performed in two stages: in the first part proteomic differences that are attributable to the two separate rat lines (DS and DR) had to be established, and in the second part the process of development of heart failure due to feeding the rats with high-salt-containing diet has to be monitored. This work describes the results of the first stage, with the outcome of protein expression profiles of left ventricular tissues of DS and DR rats kept under low salt diet. Substantial extent of quantitative and qualitative expression differences between both strains of Dahl rats in heart tissue was detected. Using Principal Component Analysis, Linear Discriminant Analysis and other statistical means we have established sets of differentially expressed proteins, candidates for further molecular analysis of the heart failure mechanisms.

[Surgical treatment options in end-stage heart failure]

Despite significant improvements in pharmacological therapy heart failure is still one of the leading causes for death in the Western World. The gold standard treatment of end-stage heart failure remains cardiac transplantation, but there is a great excess of eligible candidates compared with the low number of suitable donor organs. The variety of surgical organ preserving treatment strategies has significantly increased during the last 20 years, intenting either to delay or even to prevent the need for cardiac transplantation. An individually tailored surgical concept should be considered as an alternative in any heart failure patient who has reached the limits of pharmacologic therapy. This article gives an overview about current and potential future therapeutic options in end-stage heart failure.

In vivo electroporation mediated gene delivery to the beating heart

Gene therapy may represent a promising alternative strategy for cardiac muscle regeneration. In vivo electroporation, a physical method of gene transfer, has recently evolved as an efficient method for gene transfer. In the current study, we investigated the efficiency and safety of a protocol involving in vivo electroporation for gene transfer to the beating heart. Adult male rats were anesthetised and the heart exposed through a left thoracotomy. Naked plasmid DNA was injected retrograde into the transiently occluded coronary sinus before the electric pulses were applied. Animals were sacrificed at specific time points and gene expression was detected. Results were compared to the group of animals where no electric pulses were applied. No post-procedure arrhythmia was observed. Left ventricular function was temporarily altered only in the group were high pulses were applied; CK-MB (Creatine kinase) and TNT (Troponin T) were also altered only in this group. Histology showed no signs of toxicity. Gene expression was highest at day one. Our results provide evidence that in vivo electroporation with an optimized protocol is a safe and effective tool for nonviral gene delivery to the beating heart. This method may be promising for clinical settings especially for perioperative gene delivery.

Absence of prosthesis-patient mismatch with the new generation of Edwards stented aortic bioprosthesis

Prosthesis-patient mismatch (PPM) remains a controversial issue with the most recent stented biological valves. We analyzed the incidence of PPM after implantation of the Carpentier-Edwards Perimount Magna Ease aortic valve (PMEAV) bioprosthesis and assessed the early clinical outcome. Two hundred and seventy consecutive patients who received a PMEAV bioprosthesis between January 2007 and July 2008 were analyzed. Pre-, peri- and postoperative data were assessed and echocardiographic as well as clinical follow-up was performed. Mean age was 72+/-9 years, 168 (62.2%) were males. Fifty-seven patients (21.1%) were below 65 years of age. Absence of PPM, corresponding to an indexed effective orifice area >0.85 cm(2)/m(2), was 99.5%. Observed in-hospital mortality was 2.2% (six patients), with a predicted mortality according to the additive EuroSCORE of 7.6+/-3.1%. At echocardiographic assessment after a mean follow-up period of 150+/-91 days, mean transvalvular gradient was 11.8+/-4.8 mmHg (all valve sizes). No paravalvular leakage was seen. Nine patients died during follow-up. The Carpentier-Edwards PMEAV bioprosthesis shows excellent hemodynamic performance. This valve can be implanted in all sizes with an incidence of severe PPM below 0.5%.

Transapical implantation of a novel self-expanding sutureless aortic valve prosthesis

BACKGROUND AND AIM OF THE STUDY

To date, transapical aortic valve implantation has required a balloon-expandable stented valve prosthesis. More recently, a novel self-expanding sutureless stented bovine pericardial prosthesis has been developed which allows rapid aortic valve replacement via an open transaortic approach in humans. The aim of this animal study was to develop a reliable protocol to facilitate the transapical implantation of this self-expanding valve in a porcine model.

METHODS

Off-pump transapical aortic valve implantation was performed through a left mini-thoracotomy using a bovine pericardial valve mounted on a self-expandable nitinol stent of size 21 mm and 23 mm in 11 pigs (average weight 60 kg). The crimped valve was introduced through the left ventricular apex using a flexible and steerable delivery sheath, using a three-step technique. Biplane fluoroscopy and transesophageal echocardiography were simultaneously used for guidance. Successful adjustment of alignment along three axes prior to deployment of the valve was accomplished in each animal. Deployments were performed during a period of rapid pacing.

RESULTS

All valves were successfully deployed and functioned normally following transapical removal of the delivery system. Paravalvular leak was documented in one case (9.1%) due to prosthetic misalignment. There was no evidence of valve migration. Correct anatomic seating was confirmed during post-procedure necropsy.

CONCLUSION

Successful transapical implantation of a novel self-expandable bovine pericardial valve was accomplished in 11 animals, without cardiopulmonary bypass. A flexible, steerable delivery system with a three-step release mechanism allowed precise positioning of the valve with a low rate of paravalvular leakage, and excellent device stability.

Heart valve sound of various mechanical composite grafts, and the impact on patients' quality of life

BACKGROUND AND AIM OF THE STUDY

The closing sounds of mechanical heart valves can be disturbing for patients and their closest relatives. Although some investigations into mechanical heart valve sounds have been performed, the particularities of the valve sound when it is attached to a vascular prosthesis to replace the aortic root and the ascending aorta has not been studied to date. The study aim was to compare the closing sounds of three various mechanical composite graft prostheses, and to analyze the impact of such sounds on the patients' quality of life.

METHODS

Thirty patients who had undergone aortic root replacement were prospectively randomized into three groups, receiving either a Sorin, St. Jude Medical (SJM) or ATS mechanical composite graft. Valve sounds were recorded with microphones, and sound pressures at peak measured at three months after operation. Patients were interviewed at three and six months after surgery to assess subjective disturbance, using both an analog scale from 1 to 10 and a more detailed questionnaire.

RESULTS

Sound pressures at peak tended to be lower for the ATS than for the SJM and Sorin composite grafts (44.4 +/- 3.1 dB versus 47.8 +/- 3.1 dB and 46.6 +/- 6.0 dB; p = NS). The overall subjective disturbance with ATS valves scored significantly lower than the SJM and Sorin composite grafts (2.5 +/- 1.6 versus 4.1 +/- 1.7 and 4.6 +/- 2.2; p<0.05 after three months; and 2.6 +/- 1.2 versus 4.4 +/- 2.3 and 4.4 +/- 3.3; p<0.05 after six months). Scores for disturbance during daily activities, sleep disturbance and audibility to relatives were lowest for the ATS composite grafts.

CONCLUSION

The sound pressure of ATS composite grafts was slightly (p = NS) lower than that of SJM and Sorin composite grafts. Patients who received an ATS composite graft were significantly less disturbed by the valve noise than those with SJM and Sorin composite grafts.

Reactive oxygen species mediate functional differences in human radial and internal thoracic arteries from smokers

OBJECTIVE

Smoking not only increases the risk that coronary heart disease will develop but also morbidity and mortality in patients with known coronary atherosclerosis and after coronary artery bypass grafting. Excessive generation of reactive oxygen species (ROS) has been implicated as the final common pathway for the development of endothelial dysfunction in various cardiovascular risk factors. This study assessed the influence of smoking on two different human arteries routinely used as coronary artery bypass graft conduits.

METHODS

Isometric tension was recorded on discarded segments of human left internal thoracic artery (ITA) and the radial artery (RA) from smokers and nonsmokers.

RESULTS

The contractile response to endothelin-1 was significantly stronger in arteries from smokers than in those from nonsmokers. By contrast, endothelium-dependent relaxant responses to acetylcholine were attenuated in RA rings but enhanced in ITA rings from smokers. In additional experiments, 5-(&6)-chloromethyl-2'-7'-dichlorodihydro-fluorescein diacetate (DCDHF) was used to photochemically detect ROS by confocal imaging of intact ITA and RA. Enhanced production of ROS was induced by exposure of tissues to 28 degrees C. While during exposure to 28 degrees C, basal fluorescence emission was unchanged in ITA rings, it increased significantly in RA rings, indicating enhanced formation of ROS in this peripheral artery.

CONCLUSIONS

Data suggest that smoking induces endothelial dysfunction by increasing vascular ROS production. Different levels of endogenous antioxidant enzyme activities and the degree of atherosclerotic changes might modulate physiologic and pharmacologic vasoreactivity and be responsible for decreased graft patency of RA compared with ITA conduits, especially in active smokers.

The role of the sinuses of Valsalva in aortic root flow dynamics and aortic root surgery: evaluation by magnetic resonance imaging

BACKGROUND AND AIM OF THE STUDY

Combined replacement of the aortic valve and ascending aorta using a composite graft represents the standard treatment for dilated aortic root with concomitant structural damage of the aortic valve, especially when the aortic valve cannot be preserved. Unfortunately, hemodynamic changes associated with prosthetic replacement of the aortic root have not been fully elucidated. The study aim was to compare hemodynamics within the replaced aortic root using either a prosthetic vascular graft with bulges mimicking the sinuses of Valsalva and including a stented pericardial valve, or a straight xenopericardial conduit and a stentless porcine valve.

METHODS

Between July 2004 and March 2006, a total of 35 patients (mean age 65.2 years: range: 32-80 years) was enrolled into the present study. Aortic root replacement was performed in nine patients with a Valsalva graft (Gelweave Valsalva; Vascutek, Renfrewshire, UK) including a stented pericardial valve, and in 19 patients with a xenopericardial conduit containing a stentless porcine valve. All patients underwent postoperative magnetic resonance imaging (MRI). A control group of seven patients allowed for comparison with native aortic root hemodynamics.

RESULTS

Maximum flow-velocity above the aortic valve as one marker of compliance of the aortic root was slightly higher in patients with a Valsalva graft compared to native aortic roots (1.9 m/s versus 1.3 m/s, p = 0.001), but was significantly lower than in patients with the xenopericardial graft without neo-sinuses (1.3 m/s versus 2.4 m/s, p < 0.001).

CONCLUSION

The pre-shaped bulges in the prosthetic Valsalva graft effectively mimic the native sinuses of Valsalva, improve compliance of the aortic root, and result in a more physiologic flow pattern, as demonstrated by postoperative MRI.