Rapid diminution of calcium in the myocardium by transfer to pericardial solutions. Myocardial dialysis.

A new method is described for the controlled and specific depletion of calcium from the vascularly perfused heart of experimental animals by means of dialysis, using a pericardial solution. A 30-40 ml isotonic phosphate buffer pH 7.3 with a low Ca2+ and high Mg2+ concentration (0.2 and 2.7 mM respectively) was inserted into the pericardial cavity of anaesthetized dogs and kept there for 10 or 60 min. The calcium content of the subendocardial and subepicardial halves of the left ventricular wall was similarly decreased to about 70% (P < 0.01) within 10 min and to 62% (P < 0.001) at 60 min, compared to that of hearts dialysed for 60 min in a standard solution of Ca2+ 1.2 mM and Mg2+ 1 mM. Calcium content of the myocardium dialysed with low Ca2+ and a standard Mg2+ solution decreased to only 75% (P < 0.01) at 60 min. Similar changes of calcium were measured in other parts of the heart. An increase in Ca2+ concentration in the pericardial solution was observed at the same time as a decrease in calcium in the myocardium. The increase in Ca2+ reached about 0.7 mM at 60 min, but decreased slightly, and finally, fell to 85% of pre-dialysis values at 60 min. It is concluded that this method of myocardial dialysis is effective in reducing myocardial calcium and is influenced by the duration of dialysis and the Mg2+ content of dialysate.

Distribution of lidocaine and digoxin in heart tissues and aorta following intrapericardial administration.

The distribution of lidocaine and digoxin in myocardial and aorta tissues of open chest anesthetized dogs was studied, following the administration of 30 ml phosphate buffer solution of the drugs in the pericardial cavity where it was kept for increasing time intervals. Transfer of lidocaine (15 or 30 mg) from the solution to myocardium was almost complete within 60 min, while only 50% of digoxin (2 or 50 micrograms) was removed, and this occurred during the first 30 min. Accordingly, the absorption rate of lidocaine by heart tissues increased with time up to 60 min while that of digoxin decreased with time. Absorption of digoxin by the atria and absorption of both drugs by intrapericardial aorta were higher than that of other heart tissues, between 20 and 60 min. At 30 and 60 min, lidocaine was evenly distributed across the LV wall while digoxin 50 micrograms was mainly concentrated subepicardially. On the contrary, i.v. administration of digoxin resulted in even distribution in the LV wall without preferential concentration in the atria. The uptake of both drugs by aorta was several times lower compared to heart tissues after i.v. administration. Drug concentrations in LV wall almost at therapeutic level, were derived from solution of low concentration of the drug in the pericardial cavity. It is concluded that intrapericardial administration of the drugs may be used when increased concentration of them is desired in specific areas of the heart and the aorta.