Myocardial protection: efficacy of a novel magnesium-based cardioplegia (RS-C) compared to St Thomas' Hospital cardioplegic solution

Cardiac surgery patients now tend to be sicker with more severe disease; consequently, improved protection is important. We compared St Thomas' Hospital solution (STH2: hyperkalaemia and hypermagnesaemia) to a hypermagnesaemia-alone cardioplegia (RS-C) based on a novel non-phosphate buffered crystalloid solution (AqixRS-I). Isolated Langendorff-perfused rat hearts were used (function measured). Initial studies established optimal magnesium concentration as 25 mmol/l (LVDP recovery after 50 min at 37 degrees C global ischaemia (GI) for 16, 25, 35, 50 mmol/l magnesium vs. STH2 was 48+/-3, 50+/-2, 50+/-3, 30+/-3 and 51+/-2%, respectively). Contracture-related measurements (onset time, peak) for 25 mmol/l RS-C (32+/-1 min, 35+/-1 mmHg) compared favourable (P<0.05) to STH2 (26+/-1 min, 43+/-2 mmHg). LVDP recovery after a single 2-min cardioplegic infusion (with RS-C-25 or STH2) and 20, 30, 40 or 50 min GI was higher for RS-C-25 than STH2 after 20 min GI (81+/-1% vs. 74+/-1%; P<0.05]) but similar at other GI durations. Subsequent multi-infusion studies (60 min GI, 3x2 min infusions every 20 min) demonstrated significantly improved recovery with RS-C-25 vs. STH2 (LVDP: 73+/-2%, 44+/-1% P<0.001]; LVEDP: 9+/-2 mmHg, 45+/-2 mmHg P<0.001]). We conclude that single RS-C infusion with optimal 25 mmol/l magnesium improved protection after short (20 min) GI durations, or after multi-infusions during prolonged (60 min) GI durations. Magnesium-based cardioplegia may be a useful alternative to hyperkalaemic cardioplegia under certain specific conditions.