Cardiac responses to the intrapericardial delivery of metoprolol: Targeted delivery compared to intravenous administration

Anti-arrhythmic drugs have narrow therapeutic ranges and typically can engender harmful side effects. The intrapericardial (IP) delivery of anti-arrhythmic agents proposes to achieve higher myocardial levels while minimizing plasma concentrations, thus diminishing systemic side effects. Furthermore, IP delivery enables concentrations at the target site to be more precisely controlled. Our study objective was to compare the relative cardiac effects of intrapericardial administration of metoprolol to standard intravenous (IV) delivery in a swine surgical model. In order to answer the question of how IP metoprolol affects sinus tachycardia, atrial electrophysiology, and pharmacokinetics compared with IV delivery, a medial sternotomy was performed on 21 swine that were divided into three groups: (1) After inducing sinus tachycardia, metoprolol boluses were delivered IP (n=4) or IV (n=4); (2) metoprolol was administered either IP (n=3) or IV (n=3) with saline controls (n=3), and electrophysiologic data were collected; (3) metoprolol levels were tracked both in the blood (IV, n=2) and pericardial (IP, n=2) fluid. After either IP or IV delivery of metoprolol, heart rates were lowered significantly to 70% and 73% of control rate, respectively. The therapeutic effect of IV-administered metoprolol was considerably reduced after 1 h but was sustained longer in the IP group. Additionally, ventricular contractility and mean arterial pressure parameters were significantly lower in IV-treated animals but were nearly unaffected in IP-treated animals. With IP administration, the elimination half-life of metoprolol in pericardial fluid was 14.4 min with negligible accumulations in the plasma, whereas with IV delivery, the elimination half-life in plasma was 11.1 min with negligible amounts found in the pericardial fluid. The targeted intrapericardial delivery of metoprolol effectively lowers heart rates for sustained periods of time, with minimal effect on either ventricular contractility or mean arterial pressure. We did not observe dramatic changes in induced atrial fibrillation times or refractory periods using this model.