Testing the Efficacy of Pharmacological Agents in a Pericardial Target Delivery Model in the Swine
Summary
We have developed a swine model for the target delivery of pharmacological agents within the pericardial space/fluid. Using this approach, the relative benefits of administered agents on induced atrial fibrillation, relative refractory periods and/or ischemic protection can be investigated.
Abstract
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.
Introduction
Currently in open-heart procedures, clinicians utilize antiarrhythmic and other treatment agents systemically. Yet, this can be problematic for many patients, especially those who are already clinically compromised. For example, intravenous treatments can result in systemic drops in blood pressure or renal dysfunction; further, they may create anesthesia management issues and/ or other long-term side effects.
Here we have created a model for testing the efficacy of administering pharmacological agents into the pericardial space. For example, this approach can be utilized for testing antiarrhythmic drugs, studying compounds that could increase cardiac function and/or promoting recovery of the myocardium after surgical procedures. There have been observed benefits to the target delivery of treatments into the pericardial space versus intravenous administration: e.g., our laboratory demonstrated that localized delivery of antiarrhythmic drugs, such as metoprolol, is protective against the incidence of arrhythmias while minimizing reductions in blood pressure 1. This target delivery strategy also provides the opportunity for administering higher focal concentrations while minimizing systemic levels. For example, high levels of intravenously delivered concentrations of fatty acids may result in hemolysis, but pericardial delivery minimizes this concern 2.
This study paradigm consists of three major objectives to determine the efficacy of pericardial delivered compounds: 1) in situ determination of refractory periods of the atrial ventricular node, the atria and ventricles, before treatment and 30 and 60 min post treatment; 2) the relative in situ AF burden before treatment and 30 and 60 min post treatment (additional timepoints were often added) 3) functional analysis of the heart after it has been reanimated 3 including hemodynamic monitoring, heart rate, heart metabolism (lactate and glucose) sampled from the coronary sinus, ejection fraction (EF%) and ventricular wall thickness (cm) monitored every 10 min post 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 or transplantation.
Protocol
Representative Results
Discussion
Here, we have demonstrated a unique approach for testing the potential efficacy of target delivered compounds into the pericardial space. This study paradigm can be utilized to test current market released pharmaceutical products or experimental compounds, thus providing direct translational applications to various clinical settings. Within this treatment strategy there are two major clinical applications for delivering pharmaceuticals to the pericardial space: 1) open-heart or minimally invasive cardiac surgical procedu…
Divulgations
The authors have nothing to disclose.
Acknowledgements
We would like to give a big thanks to the Visible Heart Laboratory staff and students that have helped with this project: Nate Menninga, Lars Mattison and Megan Schmidt.
Materials
| SelectSecure® 3830 lead | Medtronic | N/A | Pacing Lead |
| C304 Deflectable Catheter | Medtronic | N/A | Steerable catheter for placing leads |
| SelectSecure® 3830 lead | Medtronic | N/A | active fixation pacing leads |
| Grass S48 Stimulator | N/A | N/A | Electrical Stimulator |
| Premium 6500 Unipolar Pacing | N/A | Plunge pacing lead for LAA | |
| EnSite™ Cardiac Mapping | N/A | Electrophysiology mapping system | |
| CareLink Programer 2092 | Medtronic | N/A | programmer for pacing leads |
| GEM II ® pacemaker | Medtronic | N/A | pacemaker can |
| DLP ® Aortic Root Cannula | Medtronic | N/A | aortic root cannula for transplant |
| C-Arm Fluoroscopy | Ziehm | N/A | fluoroscopic imaging |
| Oscilliscope | Tektronix | N/A | |
| 11F Hemostasis introducer | SafeSheath | N/A | Hemostasis introducers |
| Swan-Ganz Catheter 8.0F | ICU Medical | N/A | thermal dilution catheter |
| Venogram balloon | Oscor | N/A | pressure monitoring |
| Ultraview SL | Spacelabs | N/A | EKG and blood pressure |
| s/5 Avance | General Electric | N/A | Anesthesia machine |
| Atrial 6492 – Unipolar Temporary Atrial Pacing Lead | Medtronic | N/A | temporary pacing lead |
| VIVID i | General Electric | 2D electrocardiography unit |
References
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