Re-excitation of the cardioplegic heart. A possible hazard in clinical cardioplegic arrest.

Clinical cardioplegic arrest may coincide with a washout of cardioplegic agents by varying amounts of extracoronary collateral blood flow. This may shorten the duration of electromechanical arrest. Furthermore, even in the absence of electromechanical cardiac activity, washout may influence the cardioprotective properties of cardioplegic methods. The present study was designed to quantify the effects of cardioplegic washout. In a standardized isolated paracorporeal dog heart model, the St. Thomas's Hospital solution (ST-CP) and the Bretschneider histidine buffered solution (B-CP) were compared under the condition of washout by arterial blood. An inverse relationship was found between the amount of blood flowing through the coronary system and the duration of electromechanical arrest. Flow rates compatible with a 100 min period of complete electromechanical arrest were less than 0.41 ml/100 gr heart weight . min in ST-CP arrest and less than 0.21 ml/100 gr . min in B-CP arrest. This would indicate a greater safety against washout-induced re-excitation in ST-CP arrest. Postarrest myocardial function after 2 hours of complete electromechanical arrest at 20 degrees C was distinctly influenced by washout with arterial blood (20 degrees C) even in the absence of cardiac activity. A 100-min period of 0.2 ml/100 gr . min blood flow during arrest improved postarrest recovery of left ventricular developed pressure by 10% (76% versus 66%) after ST-CP arrest. By contrast, after B-CP arrest at equal rates of washout, recovery was diminished by 20% (79% versus 99%). It is concluded, that ST-CP, as compared to B-CP, provides longer periods of electromechanical arrest under the same washout conditions. Whereas postarrest recovery in the B-CP group is clearly superior to ST-CP in totally ischemic hearts, i.e. in hearts without collateral blood supply (99% versus 66%), this advantage may vanish in the presence of cardioplegic washout.