How to avoid severe coronary vasoconstriction in potassium induced cardioplegia

The aim of this study was to investigate how high K⁺ concentrations can be safely used in cardioplegic solutions without causing severe coronary artery vasocontraction.

Twenty-four 50 kg pigs were used. The distal part of the left anterior descending coronary artery was cut into ring segments and transferred into organ baths with Krebs solution bubbled with 95% O₂ and 5% CO₂. K⁺ concentrations between 16 and 127 mM were used to induce vasocontractions at 37, 22, 15, and 8 °C. Mg²⁺ (0-20 mM) were used to attenuate K⁺ induced vasocontractions.

K⁺-Krebs solution 127 mM at 37 °C induced a strong, sustained vasocontraction defined as 100%. The contractions induced by 16, 23, 30 and 127 mM K⁺ were: 7.7, 38, 72 and 100% at 37 °C; 1.7, 7.4, 21 and 65% at 22 °C; 1, 6.6, 15 and 33% at 15 °C; 0.6, 2.1, 6 and 14% at 8 °C, respectively. Mg²⁺ reduced the K⁺-induced contraction at 37 °C in a concentration-dependent way and Mg²⁺ at 8 mM practically eliminated the risk for severe vasocontraction.

Hypothermia (8 °C) abolishes coronary contraction induced by K⁺-cardioplegic solutions. In normothermic cardioplegia 8 mM Mg²⁺ prevents vasoconstriction.