Resistance to ventricular fibrillation predicted by the QRS/QTc - ratio in an intact rat model of hypothermia/rewarming

Background Accidental hypothermia is associated with increased risk for arrhythmias, including ventricular fibrillation and cardiac arrest. Recently QRS/QTc was proposed as an ECG-marker, where decreasing QRS/QTc ratio could predict ventricular arrhythmias in such patients. If reliable it should also predict nonappearance of arrhythmias, observed in species like rat that regularly tolerate prolonged hypothermia, during sustained sinus rhythm. Methods A rat model designed for studying cardiovascular function during cooling, 4 h experimental hypothermia (15 °C core temperature) and subsequent rewarming was used, and ECG recorded throughout the experimental protocol. Results No ventricular arrhythmias occured and there was no sign of a hypothermia-induced reduction of QRS/QTc values during moderate hypothermia. The ratio steadily increased throughout the entire cooling period and remained above normothermic baseline until rewarmed. Conclusion Different from the high incidence of hypothermia-induced ventricular arrhythmias in accidental hypothermia patients, where QRS/QTc ratio is decreased in moderate hypothermia, hypothermia and rewarming of rats is not associated with increased risk for ventricular fibrillation. This resistance to lethal hypothermia-induced arrhythmias was predicted by the QRS/QTc ratio.

Selective suppression of oral allergen-induced anaphylaxis by Allergin-1 on basophils in mice

Mast cells (MCs) play a critical role in oral allergen-induced anaphylaxis. However, the contribution of basophils to the anaphylaxis remains unclear. The inhibitory immunoreceptor Allergin-1 is highly expressed on MCs and basophils and inhibits FcεRI-mediated signaling in MCs. Here, we show that Allergin-1-deficient (Milr1−/−) mice developed more severe hypothermia, a higher mortality rate and a greater incidence of diarrhea than did wild-type (WT) mice in an oral ovalbumin (OVA)-induced food allergy model. MC-deficient Mas–TRECK mice, which had been reconstituted with either WT or Milr1−/− bone marrow-derived cultured MCs, did not develop hypothermia in this food allergy model. On the other hand, depletion of basophils by injection of anti-CD200R3 antibody rescued Milr1−/− mice from lethal hypothermia but not from diarrhea. In vitro analyses demonstrated that Allergin-1 inhibits IgE-dependent activation of both human and mouse basophils. Thus, Allergin-1 on basophils selectively suppresses oral allergen-induced anaphylaxis.