Three-hour preservation of the hypothermic globally ischemic heart with nifedipine.

We have previously shown that an intracellular-like crystalloid cardioplegic solution (ICS) provides superior protection to normothermic canine hearts subjected to 1 hour of global ischemia (GI) in comparison to a standard extracellular-type clinical cardioplegic solution (CPS). The addition of a calcium antagonist, nifedipine (N), to CPS was shown to be salutory. The new experiments used systemic hypothermia (25 degrees +/- 1 degrees C) and multidose (500 ml) cold (4 degrees C) CPS or ICS with and without N (200 to 400 micrograms/L) every 30 to 45 minutes during GI intervals of 3 hours at a resultant myocardial temperature of 10 degrees +/- 2 degrees C. The results show that after 3 hours of GI and 2 hours of observation stroke work index, (SWI) decreased to 50% +/- 10% of control for the CPS, ICS, and CPS + N groups. The ICS + N group had excellent preservation with left ventricular (LV) SWI and first derivatived left ventricular pressure (LV dP/dt) equal to the preischemic valve. Cardiac output was increased above control levels and responded normally to volume loading. Possible mechanisms of nifedipine and CPS interactions are discussed. It is concluded that a low sodium ICS containing N is highly efficacious for long ischemic intervals and that composition of the CPS strongly influences the effects of N on postischemic performance.