Effect of "Hot shot" on recovery after hypothermic ischemia in neonatal lamb heart

Background. Terminal warm blood cardioplegia, "Hot shot", is the method for providing an energy replenishment and/or early recovery of aerobic metabol ism without electromechanical activity at initial reperfusion. The mechanis m of beneficial effects of this "Hot Shot" is multifactorial. This study wa s designed to assess the effects of terminal warm blood cardioplegia by com paring with oxygenated terminal warm crystalloid cardioplegia. Methods, In Group HS-B, n=8 (oxygenated blood; 37 degreesC, Ht: 20%, K+ 20 mEq/1, pH 7.237, PO2 219 mmHg) and in Group HS-C, n=8 (bloodless oxygenated (5% CO2+95%O-2) crystalloid, 37 degreesC, K+ 20 mEq/1, pH 7.435, PO2 624 m mHg), terminal warm cardioplegia (20 ml/kg for 5 minutes) was studied in th e isolated blood perfused neonatal lamb heart following 2 hr of cardioplegi c ischemia.. Another eight hearts served as control without any kind of ter minal cardioplegia, After 60 min of reperfusion, LV function was measured. Coronary blood flow (CBF), oxy gen content, and oxygen consumption (MVO2) w ere measured and the oxygen extraction ratio was calculated in Group HS-B a nd HS-C during terminal cardioplegia and/or reperfusion, Results are given as % recovery of preischemic values. Results, HS-B as web as HS-C groups showed better functional recovery in ma ximum developed pressure (DP: 78.0 +/-8.3 in HS-B us 65.2 +/-9.2%; p=0.018) , maximum dp/dt (67.3 +/-6.2 in HS-B, 65.3 +/-7.4 in HS-C vs 55.8 +/-5.0%; p=0.003, p=0.02), DP V10 (87.1 +/-8.5 in HS-B us 67.2 +/-9.9%; p=0.0001), a nd peak dp/dt V10 (76.4 +/-7.6 in HS-B, 69.8 +/-8.1 in HS-C vs 58.6 +/-6.9 %; p=0.0001) than the control group. Between the HS-B and HS-C groups, HS-B showed better functional recovery in terms of DP V10 (p=0.01), Oxygen deli very of terminal cardioplegia was almost four times higher in HS-B group (9 0.4 +/- 17.7 us 18.7 +/-1.1 mcl/ml), contrarily, HS-C group showed four tim es higher oxygen extraction ratio compared to HS-B group (0.78 +/-0.06 vs 0 .18 +/- 011), thus oxygen consumption during hot shot was maintained at the same level in both groups. CBF in the control group was lower than that in the other groups at 60 min of reperfusion. Conclusions. Reperfusion with both terminal warm cardioplegia including blo od and oxygenated crystalloid cardioplegia resulted in better recovery of f unction and higher levels of CBF with slightly better function in terminal warm blood cardioplegia.