Intrapericardial Delivery Enhances Cardiac Effects of Sotalol and Atenolol

Exploring the role of pericardial miRNAs and exosomes in modulating cardiac fibrosis

The potential of the pericardial space as a therapeutic delivery tool for cardiac fibrosis and heart failure (HF) treatment has yet to be elucidated. Recently, miRNAs and exosomes have been discovered to be present in human pericardial fluid (PF). Novel studies have shown characteristic human PF miRNA compositions associated with cardiac diseases and higher miRNA expressions in PF compared to peripheral blood. Five key studies found differentially expressed miRNAs in HF, angina pectoris, aortic stenosis, ventricular tachycardia, and congenital heart diseases with either atrial fibrillation or sinus rhythm. As miRNA-based therapeutics for cardiac fibrosis and HF showed promising results in several in vivo studies for multiple miRNAs, we hypothesize a potential role of miRNA-based therapeutics delivered through the pericardial cavity. This is underlined by the favorable results of the first phase 1b clinical trial in this emerging field. Presenting the first human miRNA antisense drug trial, inhibition of miR-132 by intravenous administration of a novel antisense oligonucleotide, CDR132L, established efficacy in reducing miR-132 in plasma samples in a dose-dependent manner. We screened the literature, provided an overview of the miRNAs and exosomes present in PF, and drew a connection to those miRNAs previously elucidated in cardiac fibrosis and HF. Further, we speculate about clinical implications and potential delivery methods.

An overview of human pericardial space and pericardial fluid

The pericardium is a double-layered fibro-serous sac that envelops the majority of the surface of the heart as well as the great vessels. Pericardial fluid is also contained within the pericardial space. Together, the pericardium and pericardial fluid contribute to a homeostatic environment that facilitates normal cardiac function. Different diseases and procedural interventions may disrupt this homeostatic space causing an imbalance in the composition of immune mediators or by mechanical stress. Inflammatory cells, cytokines, and chemokines are present in the pericardial space. How these specific mediators contribute to different diseases is the subject of debate and research. With the advent of highly specialized assays that can identify and quantify various mediators we can potentially establish specific and sensitive biomarkers that can be used to differentiate pathologies, and aid clinicians in improving clinical outcomes for patients.

Access routes, devices and guidance methods for intrapericardial delivery in cardiac conditions

Drug deposition into the intrapericardial space is favourable for achieving localised effects and targeted cardiac delivery owing to its proximity to the myocardium as well as facilitating optimised pharmacokinetic profiles and a reduction in systemic side effects. Access to the pericardium requires invasive procedures but the risks associated with this have been reduced with technological advances, such as combining transatrial and subxiphoid access with different guidance methods. A variety of introducer devices, ranging from needles to loop-catheters, have also been developed and validated in pre-clinical studies investigating intrapericardial delivery of therapeutic agents. Access techniques are generally well-tolerated, self-limiting and safe, although some rare complications associated with certain approaches have been reported. This review covers these access techniques and how they have been applied to the delivery of drugs, cells, and biologicals, demonstrating the potential of intrapericardial delivery for treatments in cardiac arrhythmia, vascular damage, and myocardial infarction.

Intrapericardial administration of anti-arrhythmic medications in patients with electrical storm

INTRODUCTION

Electrical storm (ES) is cardiac electrical instability characterized by recurrent episodes of ventricular tachyarrhythmias. ES is associated with increased mortality and morbidity, hence requires prompt intervention. Treatment of underlying etiology is of prime importance in termination of ES. Anti-arrhythmic medications serve as an adjunctive therapy in suppression of ES by reducing myocardial excitability. The anti-arrhythmic conventionally employed is amiodarone in combination with non-selective beta-blockers to reduce the adrenergic input to myocardium. However, anti-arrhythmics at increased concentrations can lead to adverse systemic effects including hemodynamic instability.

HYPOTHESIS

We hypothesize 1. The use of intravenous or oral anti-arrhythmic therapy for patients in electrical storm is limited by their toxicities and blood pressure lowering effect. Corollary 1. Injection of anti-arrhythmic medications into the pericardial space, an extra-vascular structure encasing the heart, provides an option for use of higher concentration of anti-arrhythmic while limiting systemic absorption. Corollary 2. The pericardial space has direct communication to the epicardium, the outer most layer of cardiac muscle, spatial proximity may allow for effective therapeutic options in electrical storm. We present experimental and clinical evidence in support of these hypothesis.

Technologies for intrapericardial delivery of therapeutics and cells

The pericardium, which surrounds the heart, provides a unique enclosed volume and a site for the delivery of agents to the heart and coronary arteries. While strategies for targeting the delivery of therapeutics to the heart are lacking, various technologies and nanodelivery approaches are emerging as promising methods for site specific delivery to increase therapeutic myocardial retention, efficacy, and bioactivity, while decreasing undesired systemic effects. Here, we provide a literature review of various approaches for intrapericardial delivery of agents. Emphasis is given to sustained delivery approaches (pumps and catheters) and localized release (patches, drug eluting stents, and support devices and meshes). Further, minimally invasive access techniques, pericardial access devices, pericardial washout and fluid analysis, as well as therapeutic and cell delivery vehicles are presented. Finally, several promising new therapeutic targets to treat heart diseases are highlighted.

Minimally Invasive Delivery of Hydrogel-Encapsulated Amiodarone to the Epicardium Reduces Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Although treatment options for AF exist, many patients cannot be maintained in normal sinus rhythm. Amiodarone is an effective medication for AF but has limited clinical utility because of off-target tissue toxicity.

METHODS

Here, we use a pig model of AF to test the efficacy of an amiodarone-containing polyethylene glycol-based hydrogel. The gel is placed directly on the atrial epicardium through the pericardial space in a minimally invasive procedure using a specially designed catheter.

RESULTS

Implantation of amiodarone-containing gel significantly reduced the duration of sustained AF at 21 and 28 days; inducibility of AF was reduced 14 and 21 days post-delivery. Off-target organ drug levels in the liver, lungs, thyroid, and fat were significantly reduced in animals treated with epicardial amiodarone gel compared with systemic controls in small-animal distribution studies.

CONCLUSIONS

The pericardium is an underutilized therapeutic site and may be a new treatment strategy for AF and other cardiovascular diseases.

Delivery of drugs, growth factors, genes and stem cells via intrapericardial, epicardial and intramyocardial routes for sustained local targeted therapy of myocardial disease

INTRODUCTION

Local myocardial delivery (LMD) of therapeutic agents is a promising strategy that aims to treat various myocardial pathologies. It is designed to deliver agents directly to the myocardium and minimize their extracardiac concentrations and side effects. LMD aims to enhance outcomes of existing therapies by broadening their therapeutic window and to utilize new agents that could not be otherwise be implemented systemically. Areas covered: This article provides a historical overview of six decades LMD evolution in terms of the approaches, including intrapericardial, epicardial, and intramyocardial delivery, and the wide array of classes of agents used to treat myocardial pathologies. We examines delivery of pharmaceutical compounds, targeted gene transfection and cell implantation techniques to produce therapeutic effects locally. We outline therapeutic indications, successes and failures as well as technical approaches for LMD. Expert opinion: While LMD is more complicated than conventional oral or intravenous administration, given recent advances in interventional cardiology, it is safe and may provide better therapeutic outcomes. LMD is complex as many factors impact pharmacokinetics and biologic result. The choice between routes of LMD is largely driven not only by the myocardial pathology but also by the nature and physicochemical properties of the therapeutic agents.

Testing the Efficacy of Pharmacological Agents in a Pericardial Target Delivery Model in the Swine

To date, many pharmacological agents used to treat or prevent arrhythmias in open-heart cases create undesired systemic side effects. For example, antiarrhythmic drugs administered intravenously can produce drops in systemic pressure in the already compromised cardiac patient. While performing open-heart procedures, surgeons will often either create a small port or form a pericardial cradle to create suitable fields for operation. This access yields opportunities for target pharmacological delivery (antiarrhythmic or ischemic preconditioning agents) directly to the myocardial tissue without undesired side effects. We have developed a swine model for testing pharmacological agents for target delivery within the pericardial fluid. While fully anesthetized, each animal was instrumented with a Swan-Ganz catheter as well as left and right ventricle pressure catheters, and pacing leads were placed in the right atrial appendage and the right ventricle. A medial sternotomy was then performed and a pericardial access cradle was created; a plunge pacing lead was placed in the left atrial appendage and a bipolar pacing lead was placed in the left ventricle. Utilizing a programmer and a cardiac mapping system, the refractory period of the atrioventricular node (AVN), atria and ventricles was determined. In addition, atrial fibrillation (AF) induction was produced utilizing a Grass stimulator and time in AF was observed. These measurements were performed prior to treatment, as well as 30 min and 60 min after pericardial treatment. Additional time points were added for selected studies. The heart was then cardiopleged and reanimated in a four chamber working mode. Pressure measurements and function were recorded for 1 hr after reanimation. This treatment strategy model allowed us to observe the effects of pharmacological agents that may decrease the incidence of cardiac arrhythmias and/or ischemic damage, during and after open-heart surgery.

Percutaneous microembolization of the left coronary artery to model ischemic heart disease in rats

Small animal models of myocardial infarction are used for a wide variety of research purposes, but common techniques for generating such models require thoracic surgeries that increase mortality risk and damage important structures, such as the pericardial sac. Here, we describe a technique for modeling myocardial infarction in rats by selective coronary microembolization, which has hitherto been described only in large animals. This technique selectively catheterizes the left coronary artery using a custom-made catheter that is introduced and precisely placed under fluoroscopic guidance. Microspheres are then injected through the catheter to cause embolization. This process creates multiple simultaneous micro-infarcts that resemble those from clinical embolization after a percutaneous coronary intervention. As this technique does not require thoracic surgery, a low attrition rate was expected and once it was optimized, this technique had a low mortality rate of just 14% during experimental application. This technique creates infarcts that appear small but are associated with transient ECG changes and a persistently lower ejection fraction after embolization. Microspheres are retained in the myocardial tissue and are visible by epifluorescent microscopy after histological staining and recognizable as a distinct speckle pattern in ultrasound images.

Myocardial drug distribution generated from local epicardial application: potential impact of cardiac capillary perfusion in a swine model using epinephrine

Prior studies in small mammals have shown that local epicardial application of inotropic compounds drives myocardial contractility without systemic side effects. Myocardial capillary blood flow, however, may be more significant in larger species than in small animals. We hypothesized that bulk perfusion in capillary beds of the large mammalian heart not only enhances drug distribution after local release, but also clears more drug from the tissue target than in small animals. Epicardial (EC) drug releasing systems were used to apply epinephrine to the anterior surface of the left heart of swine in either point-sourced or distributed configurations. Following local application or intravenous (IV) infusion at the same dose rates, hemodynamic responses, epinephrine levels in the coronary sinus and systemic circulation, and drug deposition across the ventricular wall, around the circumference and down the axis, were measured. EC delivery via point-source release generated transmural epinephrine gradients directly beneath the site of application extending into the middle third of the myocardial thickness. Gradients in drug deposition were also observed down the length of the heart and around the circumference toward the lateral wall, but not the interventricular septum. These gradients extended further than might be predicted from simple diffusion. The circumferential distribution following local epinephrine delivery from a distributed source to the entire anterior wall drove drug toward the inferior wall, further than with point-source release, but again, not to the septum. This augmented drug distribution away from the release source, down the axis of the left ventricle, and selectively toward the left heart follows the direction of capillary perfusion away from the anterior descending and circumflex arteries, suggesting a role for the coronary circulation in determining local drug deposition and clearance. The dominant role of the coronary vasculature is further suggested by the elevated drug levels in the coronary sinus effluent. Indeed, plasma levels, hemodynamic responses, and myocardial deposition remote from the point of release were similar following local EC or IV delivery. Therefore, the coronary vasculature shapes the pharmacokinetics of local myocardial delivery of small catecholamine drugs in large animal models. Optimal design of epicardial drug delivery systems must consider the underlying bulk capillary perfusion currents within the tissue to deliver drug to tissue targets and may favor therapeutic molecules with better potential retention in myocardial tissue.