Cardia lymph in electrical ventricular fibrillation: an experimental study

The ebb and flow of cardiac lymphatics: a tidal wave of new discoveries

The heart is imbued with a vast lymphatic network that is responsible for fluid homeostasis and immune cell trafficking. Disturbances in the forces that regulate microvascular fluid movement can result in myocardial edema, which has profibrotic and proinflammatory consequences and contributes to cardiovascular dysfunction. This review explores the complex relationship between cardiac lymphatics, myocardial edema, and cardiac disease. It covers the revised paradigm of microvascular forces and fluid movement around the capillary as well as the arsenal of preclinical tools and animal models used to model myocardial edema and cardiac disease. Clinical studies of myocardial edema and their prognostic significance are examined in parallel to the recent elegant animal studies discerning the pathophysiological role and therapeutic potential of cardiac lymphatics in different cardiovascular disease models. This review highlights the outstanding questions of interest to both basic scientists and clinicians regarding the roles of cardiac lymphatics in health and disease.

IL-1β reduces cardiac lymphatic muscle contraction via COX-2 and PGE2 induction: Potential role in myocarditis

The role of lymphatic vessels in myocarditis is largely unknown, while it has been shown to play a key role in other inflammatory diseases. We aimed to investigate the role of lymphatic vessels in myocarditis using in vivo model induced with Theiler's murine encephalomyelitis virus (TMEV) and in vitro model with rat cardiac lymphatic muscle cells (RCLMC). In the TMEV model, we found that upregulation of a set of inflammatory mediator genes, including interleukin (IL)-1β, tumor necrosis factor (TNF)-αand COX-2 were associated with disease activity. Thus, using in vitro collagen gel contraction assays, we decided to clarify the role(s) of these mediators by testing contractility of RCLMC in response to IL-1β and TNF-α individually and in combination, in the presence or absence of: IL-1 receptor antagonist (Anakinra); cyclooxygenase (COX) inhibitors inhibitors (TFAP, diclofenac and DuP-697). IL-1β impaired RCLMC contractility dose-dependently, while co-incubation with both IL-1β and TNF-α exhibited synergistic effects in decreasing RCLMC contractility with increased COX-2 expression. Anakinra maintained RCLMC contractility; Anakinra blocked the mobilization of COX-2 induced by IL-1β with or without TNF-α. COX-2 inhibition blocked the IL-1β-mediated decrease in RCLMC contractility. Mechanistically, we found that IL-1β increased prostaglandin (PG) E₂ release dose-dependently, while Anakinra blocked IL-1β mediated PGE₂ release. Using prostaglandin E receptor 4 (EP4) receptor antagonist, we demonstrated that EP4 receptor blockade maintained RCLMC contractility following IL-1β exposure. Our results indicate that IL-1β reduces RCLMC contractility via COX-2/PGE₂ signaling with synergistic cooperation by TNF-α. These pathways may help provoke inflammatory mediator accumulation within the heart, driving progression from acute myocarditis into dilated cardiomyopathy.

Donor heart preservation in an empty beating state under mild hypothermia

BACKGROUND

Cardiac surgery during an empty beating heart state has proven to be beneficial in myocardial protection. Based on this, we hypothesized that maintaining this state for donor heart preservation would have the same efficacy and a prolonged preservation period.

METHODS

Part 1: 12 pigs were divided into two groups (n = 6 per group). Donor hearts were preserved in group A by perfusion with leukocyte-depleted blood in the beating state, and in group B, in the traditional hypothermic static state with University of Wisconsin solution. After 8 hours, myocardial samples were obtained to detect myocardial edema, adenosine triphosphate, and ultrastructure. Part 2: 12 donor-recipient swine pairs were randomly allocated to either beating heart preservation with perfusion (group C) or traditional static preservation (group D). Donor hearts were stored for 8 hours after isolation, followed by implantation into recipient animals. Implanted hearts recovered for 120 minutes in an empty and beating state followed by 30 minutes in a working state, after which cardiac function was measured.

RESULTS

After preservation, myocardial adenosine triphosphate levels in group A were significantly higher than in group B. However, myocardial water content was not significantly different between these two groups. The damage of myocardial ultrastructure in group A was slight compared with that of group B. The experimental transplant group C showed excellent heart function after implantation when compared with group D.

CONCLUSIONS

Our study reveals greater effects of donor heart preservation in a beating state rather than simply with hypothermic storage in University of Wisconsin solution.

Surgery for cardiac valves and aortic root without cardioplegic arrest ("beating heart"): experience with a new method of myocardial perfusion

Simultaneous antegrade/retrograde warm blood perfusion with a beating heart has not been previously reported as a mean of protecting hypertrophied hearts in cardiac valve and aortic root surgeries. Similarly, beating heart mitral valve surgery via the trans-septal approach with the aorta unclamped, is a novel technique. We, herein, report a series of 346 patients with a variety of cardiac pathologies who were operated upon utilizing a new modality of myocardial perfusion. Among this group of patients, there were 55 patients who were diagnosed with endocarditis of one or more valves. These patients were excluded from this series of patients. Mean age was 59 +/- 12, and there were 196 (67.3%) males and 95 (32.7%) females. There were six aortic root procedures, 90 mitral valve replacements (MVR), 46 mitral valve repairs, 20 MVR+ coronary artery bypass grafting (CABG), 28 tricuspid valve repairs, 106 aortic valve replacements (AVR), 17 AVR+CABG, and 8 AVR/MVR. Crude mortality for the group was 20 of 291 (6.8%). Intra-aortic balloon pump utilization at time of weaning from cardiopulmonary bypass was 6/291 (2.06%), and re-operation for bleeding was needed in 12 of 291 (4.1%) patients. Postoperative stroke occurred in 4 of 291 (1.3%) patients. In these patients, the clinical diagnosis of stroke was made prior to surgery. This initial experience with this new method of myocardial perfusion indicates that results are at least comparable, if not superior, to conventional techniques utilizing intermittent cold blood cardioplegia.

Keeping the heart empty and beating improves preservation of hypertrophied hearts for valve surgery

OBJECTIVE

This study was designed to determine whether keeping the heart empty and beating improved myocardial fluid homeostasis and energy metabolism of hypertrophied pig hearts in comparison with cardioplegic arrest.

METHODS

Twenty piglets underwent a 8-weeks (corrected) ascending aortic banding to induce left ventricular hypertrophy. Isolated hypertrophied hearts were divided into 4 groups (n = 5 in each group). Two groups underwent normothermic normokalemic simultaneous perfusion. The other 2 groups were subjected to normothermic hyperkalemic simultaneous perfusion and used as controls. Intramyocardial hydrostatic pressure was monitored with a microtip pressure transducer. Volumes of intracellular and extracellular compartments and myocardial energy metabolism were monitored by using phosphorus 31 magnetic resonance spectroscopy.

RESULTS

Normothermic normokalemic simultaneous perfusion (NNSP) maintained intramyocardial hydrostatic pressure at a significantly lower level (13.0 +/- 0.6 mm Hg) compared with normothermic hyperkalemic simultaneous perfusion (NHSP) (23.3 +/- 1.2 mm Hg) during a 90-minute preservation. NNSP maintained the normal volume of the intracellular compartment throughout the preservation period, whereas NHSP caused significant enlargement (to 123% +/- 6% of its normal volume) of the intracellular compartment. Expansion of the extracellular compartment during preservation was significantly less in the NNSP group (124% +/- 6%) than in the NHSP group (152% +/- 7%). NNSP maintained normal levels of phosphocreatine and adenosine triphosphate until coronary perfusion flow was reduced to 50% of the initial control level. No decrease in energy metabolites was observed in the NHSP group even when coronary perfusion flow was reduced to 10% of the initial control level.

CONCLUSIONS

Keeping the heart empty and beating improves myocardial fluid homeostasis for hypertrophied hearts relative to cardioplegic arrest. Its ability to maintain energy metabolism depends on the degree of coronary stenosis. This technique may be a promising protective strategy for hypertrophied hearts.

Myocardial fluid balance

Fluid accumulation in the cardiac interstitium or myocardial edema is a common manifestation of many clinical states. Specifically, cardiac surgery includes various interventions and pathophysiological conditions that cause or worsen myocardial edema including cardiopulmonary bypass and cardioplegic arrest. Myocardial edema should be a concern for clinicians as it has been demonstrated to produce cardiac dysfunction. This article will briefly discuss the factors governing myocardial fluid balance and review the evidence of myocardial edema in various pathological conditions. In particular, myocardial microvascular, interstitial, and lymphatic interactions relevant to the field of cardiac surgery will be emphasized.

Experimental study of cardiac lymph dynamics and edema formation in ischemia/reperfusion injury--with reference to the effect of hyaluronidase

This study is designed to evaluate the effect of hyaluronidase on the canine myocardial edema derived from ischemia/reperfusion injury. The mongrel dog's heart received 90 minutes of ischemia under cardiopulmonary bypass consisting of 30 minutes of normothermia alone and 60 minutes of hypothermia with cardioplegic arrest. Reperfusion for 60 minutes was added thereafter. Two kinds of cardioplegic solution, 4 degrees C St. Thomas' Hospital solution with or without 3000 units/L of hyaluronidase, were prepared. The solution was given antegradely every 30 minutes during cardioplegic arrest. Cardiac lymph was collected continuously from the afferent duct of the cardiac lymph node by cannulation. Hyaluronidase in the cardioplegic solution increased cardiac lymph volume significantly and improved postischemic recovery of cardiac function. A high level of adenosine triphosphate was maintained at that time. The myocardial water content at the end of reperfusion revealed a minimum increase with hyaluronidase use. Active drainage of cardiac lymph by hyaluronidase alleviates the myocardial edema formation, thereby preserving cardiac function.

Augmenting cardiac contractility hastens myocardial edema resolution after cardiopulmonary bypass and cardioplegic arrest

Although myocardial edema is associated with cardiopulmonary bypass (CPB) and cardioplegic arrest (CPA), interventions to expedite edema removal have not been investigated. The primary mechanism for the removal of excess interstitial fluid in the heart is myocardial lymphatic drainage, but lymphatic function can be impaired by decreased contractility because of edema. The purpose of this study was to determine whether enhancing cardiac contractility would increase myocardial lymphatic function and hasten edema resolution after CPB. Sixteen dogs were subjected to CPB and 1 h of hypothermic CPA. After weaning from CPB, 10 dogs received an intravenous dobutamine infusion and 6 dogs received no inotropic support. We determined myocardial lymph driving pressure from the major cardiac lymphatic, myocardial water content by using microgravimetry, and the peak rate of left ventricular pressure increase (dP/dmax) by using micromanometry. Measurements were taken at baseline, during CPA, and 60 min after CPB. Compared with controls, dobutamine-treated dogs had an increased dP/dmax (P < 0.05), which was associated with higher lymph driving pressures (P < 0.05), resulting in lower myocardial water gain 1 h after CPB (P < 0.05). We conclude that the resolution of myocardial edema after CPB was hastened by dobutamine. Organized ventricular contraction and myocardial contractility seem to be important determinants of myocardial lymphatic function and myocardial edema removal. These findings suggest that the administration of inotropic drugs after CPB may hasten cardiac recovery.

IMPLICATIONS

Myocardial edema, which develops during cardiopulmonary bypass and cardioplegic arrest, contributes to cardiac dysfunction after heart surgery. This study demonstrated that enhancement of cardiac contractility by the administration of dobutamine after cardiopulmonary bypass and cardioplegic arrest was associated with increased myocardial lymphatic function and hastened edema resolution in dogs.

Active drainage of cardiac lymph in relation to reduction in size of myocardial infarction: an experimental study

Active drainage of cardiac lymph using hyaluronidase was attempted in dogs. The results were satisfactory and the ischemic myocardium was salvaged. The infarct risk area (I/R) ratio decreased after drainage. Regional myocardial ischemia and infarction were provided by means of ligature of the left coronary artery for 120 and 240 minutes respectively. Cardiac lymph was collected by conventional procedures. Enzymes released from the myocardium increased significantly in the cardiac lymph. The volume of cardiac lymph gradually increased after ligature of the coronary artery. Administration of hyaluronidase further increased the cardiac lymph flow and significantly decreased the I/R ratio as determined by triphenyl tetrazolium chloride (TTC) and methylene blue staining. Drainage of the cardiac lymph salvaged the ischemic myocardium. Reduction of interstitial edema and augmentation of cardiac lymph flow with the hyaluronidase prevented the development of the infarction. This is the first documentation of the effect of active drainage of cardiac lymph on the development of infarction through observation of the I/R ratio.