Donor Left Ventricle Research Articles

Omecamtiv Mecarbil Modulation of Force Generation in Single Myofibrils from Human Cardiac Muscle

Omecamtiv mecarbil (OM) is a small molecule proved to enhance the function of the beta-myosin motor and presently used for the treatment of heart failure. Despite the positive outcomes of clinical trials, the mechanistic basis of its action is controversial and little is known of its functional impact in human cardiac sarcomeres. Here myofibrils from human donor left ventricle (frozen samples) have been used to study the effects of μmolar [OM] on isometric force in relaxing conditions (pCa 9) and at maximal (pCa 4.5) or half-maximal (pCa 5.75) calcium activation, both in control conditions (15°C, equimolar DMSO, contaminant [Pi] ∼ 170µM) or in presence of 5 mM [Pi]. In all conditions tested, OM increased isometric force with a complex dose-dependent effect peaking (about 40% increase) at 0.5 µM and never decreasing below control values. As already reported in human cardiac muscle (Swenson et al. 2017), OM strongly depressed the kinetics of force development up to 90% at 10 µM OM. Of note, OM was found to decrease the inhibition of force operated by Pi, in agreement with observations in rabbit slow-muscle (Governali et al. 2020), but the effect was modest and occurred at low (1-2 mM) [Pi]. At pCa 9 OM induced calcium-independent force development which approached the level of calcium activated tension at 10 µM OM. The kinetics of the calcium-independent force development at pCa 9 was very slow and dose-independent. The results support a role of OM in operating a complex perturbation of the thin/thick filament regulatory state as a result of its binding to myosin allosteric sites coupled to Pi release that favours the formation of strongly actin-bound motors. SilicoFCM EU H2020 grant agreement n. 777204.

A Simple Technique for a New Working Heterotopic Heart Transplantation Model in Rats

ObjectiveA new working model of heterotopic heart transplantation in rats was established using a simplified technique. Materials and methodsSprague-Dawley rats were used as donors and recipients. The donor left common carotid artery and left pulmonary artery were anastomosed to the recipient left renal artery and vein by a “sleeve and cuff” method, respectively. The donor left ventricle was blood volume loaded by anastomosing the left atrium to the recipient's abdominal aorta in end-to-side fashion. The characteristics of the donor heart were evaluated by palpating the abdominal wall of the rats. We examined the surgical success rate, changes in heart weight, and histology at 1 month after transplantation. ResultsThe model was attempted in 32 rats with the success rate of 93.7% (30/32); the 2 failed cases died due to postoperative bleeding. There was no significant difference in mean weight changes between the donor and native hearts at 1 month after transplantation (1.13 ± 0.13 g vs 1.09 ± 0.12 g, P = .244). The donor heart myocardium showed regularly shaped, unidirectional, healthy muscle similar to the native heart. ConclusionsThe technique was easily learned, allowing less recipient surgical stress. The hemodynamic performance appeared to be similar to the normal cardiac physiological situation, and thus may be more suitable for pre-clinical studies.

Establishment of a novel volume-loaded heterotopic heart transplantation model in rats

BackgroundNon–volume-loaded (NL) donor hearts in the heterotopic heart transplantation model in rats undergo atrophy and thrombus formation in graft cavities after transplantation. The present study aimed to establish a novel model with volume-loaded donor hearts. MethodsWe used Sprague-Dawley rats as donors and recipients. We established an NL model by anastomosing the donor ascending aorta and pulmonary artery end-to-side to the recipient abdominal aorta and inferior vena cava, respectively, and ligating the superior and inferior vena cava on the donor right atrium. The method of the volume-loaded (VL) model was the same as described above, except we performed an anastomosis of the donor left atrium to the recipient abdominal aorta to allow volume loading of the donor's left ventricle. We assessed the characteristics of the grafts by the surgical success rate, echocardiography, and histologic evaluation between the two models. ResultsEchocardiography showed that donor left ventricle in VL models was volume loaded and had normal systolic and diastolic function compared with the NL models. The mean weight of NL hearts was significantly less than that of VL hearts. Morphologic observation revealed that thrombus formation in donor heart cavities in NL model was significantly higher than that in the VL model. The area of cardiomyocytes per high-power field in the NL model was significantly lower than that in the VL model. ConclusionsWe provide a novel VL heterotopic heart transplantation model in rats, in which hemodynamic performance of grafts is close to the normal cardiac physiologic situation; thus, the novel model will be more suitable for clinical research.

Experimental heterotopic heart transplantation without cardiopulmonary bypass: auxiliary support for the recipient heart

Background: Auxiliary cardiac support using heterotopic heart transplant is of considerable interest, but the outcome is not known. To investigate technical feasibility and the possibility of using auxiliary support from heterotopic heart transplantation without cardiopulmonary bypass, we evaluated hemodynamics including the pressure–volume relationship in experimental animals. Methods In heterotopic heart transplantation, we tailored the donor heart by removing the pulmonary and tricuspid valves, and by wide removal of the inter-atrial septum. Next, we anastomosed the descending aorta and left atrium of the donor heart to the descending aorta and left atrium of the recipient, without using cardiopulmonary bypass. Consequently, declamping the recipient’s descending aorta allowed the donor heart to fill with blood and to start beating. We performed hemodynamic assessments including the effects of adrenergic stimulation. We measured the pressure and volume relationship of the recipient heart by closing and opening inflow of the donor left atrium to change the pre-load of the donor left ventricle. Results The donor left ventricle produced a systolic blood pressure that was augmented by the recipient blood pressure and responded to adrenergic stimulation. When inflow of the donor left atrium was opened, the pressure–volume loop of the recipient heart shifted to the left and pressure–volume area decreased. Simultaneously, the mechanical efficiency and E max (the slope of the end-systolic pressure-volume relationship) of the recipient heart increased when inflow of the donor left atrium was opened. Conclusions This transplant model, without cardiopulmonary bypass, is feasible and can be applied to transplant investigations as a working heart model on the basis of the response of adrenergic stimulation. The increased pre-load of the donor left atrium from the recipient left atrium resulted in a recipient leftward shift of the pressure–volume relationship, suggesting that this transplant model with adequate pre-load acts as auxiliary assistance in the recipient intrathoracic cavity.

Postoperative hemodynamic improvement with paced linkage of the donor and recipient hearts following heterotopic cardiac transplantation

It has been shown that following heterotopic heart transplantation the recipient left ventricle ejects more effectively when it contracts out of phase with the donor left ventricle. However, this is rarely the situation, as the two hearts beat independently of one another and the denervated donor heart tends to beat faster than the recipient. In this study the hemodynamic effects of connecting the two hearts by an external temporary dual-chamber pacemaker were evaluated. The donor right ventricle was sensed and the recipient right atrium paced after a timed delay. The delay was adjusted so that recipient systole coincided with donor diastole. Eleven patients were studied in the first postoperative day. Pacing resulted in an improvement in cardiac output from 5.0 to 5.6 l/min (p = 0.003) and a reduction in pulmonary capillary wedge pressure from 16 to 12 mmHg (p = 0.0035). This was associated with a 35% reduction in inotrope requirements. It is concluded that sequential pacing of the two hearts is a useful adjunct to inotropic support in the postoperative period.

Working heart model of heterotopic heart-lung transplantation in rats

A technique for a working heart model of heterotopic heart-lung transplantation is described. The donor aorta and left pulmonary artery are anastomosed to the recipient's abdominal aorta in an end-to-side fashion. Arterial blood from the recipient's abdominal aorta enters the donor left heart via the donor left lung and is ejected into the donor ascending aorta by the transplanted left ventricle. With this model, the donor left ventricle performs work comparable to that of the native heart without hypoxia. This model is easily reproducible and can be applied to various studies, including long-term assessments of cardiac remodeling, long-term efficacy of cardiac preservation, and posttransplantation ventricular performance under more physiologic conditions. (J THORACCARDIOVASCSURG1994; 107:210-5)

Hemodynamic evaluation of heterotopic heart transplantation

To assess the relative contribution of native and donor hearts to total circulatory performance after heterotopic transplantation, we used cardiac catheterization to examine 10 patients. Left and right ventricular filling pressures significantly decreased by 41% and 36%, respectively, cardiac index increased by 25%, and pulmonary arteriolar resistance was reduced by 61%. Patients were subdivided into two groups according to the presence of one (group I) or two (group II) peaks on the aortic pressure curve. In group I, the donor left ventricle assumed total left ventricular work and 80% of right ventricular work. Because the native left ventricle could not generate enough pressure to open the aortic valve, its entire stroke volume was ejected into the common left atrium. In addition, in all four patients a native aortic regurgitation occurred in diastole and systole. In contrast, in group II, native left ventricular systolic pressure always exceeded aortic diastolic pressure. The donor left ventricle contributed 68% to systemic blood flow and the donor right ventricle 51% to pulmonary blood flow. Mild native aortic regurgitation was demonstrated in two patients only. Native left ventricular function deteriorated postoperatively in all patients (ejection fraction decreased from 0.22 +/- 0.09 to 0.14 +/- 0.08), but this deterioration was more marked in group I. Postoperative depression of native left ventricular function could not be ascribed to progression of coronary artery disease but was mainly due to reduced preload (competitive filling) and increased afterload. Thus in group I patients with more severe preoperative left ventricular dysfunction, the donor heart behaved like a total biventricular assist device. In contrast, in group II patients the donor heart acted like a partial biventricular assist device.

Sequentially paced heterotopic heart transplant in the left chest provides improved circulatory support for the failed left ventricle: A potential biologic bridge to orthotopic transplantation

Acute experimental transplantation of an allograft heart in a heterotopic position was performed in 14 sheep. The donor heart was implanted in the left side of the chest with left atrial, aortic, and pulmonary artery anastomoses. Hemodynamic studies were performed to evaluate the physiologic effects of the procedure, particularly when recipient left ventricular failure was produced by inflow and outflow obstruction. Pacing techniques were developed and tested to coordinate the rhythm of the two hearts either synchronously or sequentially with variable intervals between depolarization of the two hearts. Hemodynamic studies were performed to evaluate the rhythm that would most optimize the physiology. The cardiac index remained essentially unchanged when the dominant circulatory support was shifted from recipient left ventricle to donor left ventricle by producing recipient left ventricular failure (3.79 +/- 0.6 to 3.30 +/- 0.8, p = no significant difference). Consistent and reliable paced rhythms were achieved in each case. The cardiac index was significantly higher when the hearts were paced sequentially rather than synchronously (3.76 +/- 0.5 versus 3.29 +/- 0.5, p less than 0.04). Allograft donor hearts small in size or slightly inadequate otherwise, which may be unsuitable for orthotopic heart transplantation, may still be used heterotopically for short-term support. Their use would maximize the use of all donor organs and the survival of patients awaiting a suitable organ. Further, it may also be possible to use sequentially paced xenografts heterotopically for short-term left ventricular assistance as a bridge to orthotopic heart transplantation.

Noninvasive assessment of donor and native heart function after heterotopic heart transplantation

The contribution of the donor heart to total circulatory performance after heterotopic heart transplantation has been difficult to assess. First-pass nuclear angiocardiography and directional Doppler echocardiography were used to examine separately left and right ventricular function of the donor heart after heterotopic transplantation. A comparison was made between two patients, one with a low initial pulmonary vascular resistance and one with a high, relatively fixed pulmonary vascular resistance. In both cases, currently available noninvasive techniques allowed confirmation of the expectation that the donor left ventricle can function effectively as a left ventricular bypass. In neither case was recovery of the native heart demonstrated. The contribution of the donor right ventricle to total right ventricular output appeared to be dependent on the condition of the donor heart and on the pulmonary vascular resistance. In situations with a high pulmonary vascular resistance and end-stage right ventricular failure, it was concluded that the donor heart may not at first constitute an effective assist for the native right ventricle. Native right ventricular failure may then become a major factor influencing survival after heterotopic heart transplantation.

Changes in left ventricular mechanical and hemodynamic function during acute rejection of orthotopically transplanted hearts in dogs

During orthotopic cardiac transplantation in 10 nonimmunosuppressed dogs the donor left ventricle (LV) was equipped with endocardial piezoelectric crystals for direct ultrasound measurement of internal transverse diameter and an indwelling pressure transducer. Measurements made immediately postoperatively and then daily until death due to acute graft rejection included LV pressure and maximum dp/dt, end-diastolic and end-systolic internal diameters, the per cent shortening of diameter during systole, calculated ejection fraction, and the velocity of donor LV contraction. In addition, diastolic LV mechanics were characterized by the rate of filling, the prominence of the rapid filling phase of diastole, and the ratio of developed LV pressure to the increment in diameter during the total diastolic interval. Average survival was 6.2 (±0.8 S.E.) days. Developed LV pressure and maximum LV dp/dt remained within a normal range throughout the postoperative course except in three dogs studied immediately before death. Average end-diastolic diameter showed no significant changes throughout the postoperative interval, whereas end-systolic diameter decreased during postoperative recovery and then increased during rejection. The extent of diameter shortening during systole and calculated ejection fraction increased during recovery and fell during rejection. Indices of LV contraction velocity showed improvement after transplantation and then declined sharply during rejection. Changes in donor LV diastolic mechanics with advancing rejection suggested decreasing LV distensibility. These data indicate that the major functional components of acute cardiac allograft rejection responsible for hemodynamic deterioration consist of both impairment of ventricular contracile state and diminished ventricular compliance.