Cardiac Manifestation and Blood Catecholamine Levels during Succinylcholine‐Induced Stress of Malignant Hyperthermia Sensitive Pigs*

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Abstract
Fifteen crossbred pigs of Swedish Landrace and Yorkshire, about 6 months of age and susceptible to develop malignant hyperthermia (MH) when exposed to halothane, were subjected to stress provoked by the myorelaxant succinylcholine. The results were compared with those of 12 normal pigs. During the stress the halothane-sensitive (HS) pigs showed much higher levels of plasma noradrenaline and adrenaline and more severe ventricular arrhythmias than the controls. The degree of myocardial degeneration and necrosis being similar to catecholamine induced myocardial damage was significantly higher in the HS pigs than in the controls. The ultrastructural examination revealed three main types of changes in affected myocardial cells. One type of myocardial cell damage was characterized by various degree of hypercontraction, enlarged mitochondria with dense bodies and dilated sarcoplasmic reticulum. The other type showed mitochondria with tubular configuration whereas the third type of cell damage was characterized by almost normal mitochondria combined with a severe damage of the myofilaments. Three HS pigs which died within 30 min after stress showed signs of malignant hyperthermia. No signs of the disease were observed in the other 12 HS pigs.