title: Inducibility of ventricular fibrillation during mild therapeutic hypothermia: electrophysiological study in a swine model.
abstract: BACKGROUND
  Mild therapeutic hypothermia (MTH) is being used after cardiac arrest for its expected improvement in neurological outcome. Safety of MTH concerning inducibility of malignant arrhythmias has not been satisfactorily demonstrated. This study compares inducibility of ventricular fibrillation (VF) before and after induction of MTH in a whole body swine model and evaluates possible interaction with changing potassium plasma levels.
  
  
  METHODS
  The extracorporeal cooling was introduced in fully anesthetized swine (n = 6) to provide MTH. Inducibility of VF was studied by programmed ventricular stimulation three times in each animal under the following: during normothermia (NT), after reaching the core temperature of 32°C (HT) and after another 60 minutes of stable hypothermia (HT60). Inducibility of VF, effective refractory period of the ventricles (ERP), QTc interval and potassium plasma levels were measured.
  
  
  RESULTS
  Starting at normothermia of 38.7 (IQR 38.2; 39.8)°C, HT was achieved within 54 (39; 59) minutes and the core temperature was further maintained constant. Overall, the inducibility of VF was 100% (18/18 attempts) at NT, 83% (15/18) after reaching HT (P = 0.23) and 39% (7/18) at HT60 (P = 0.0001) using the same protocol. Similarly, ERP prolonged from 140 (130; 150) ms at NT to 206 (190; 220) ms when reaching HT (P < 0.001) and remained 206 (193; 220) ms at HT60. QTc interval was inversely proportional to the core temperature and extended from 376 (362; 395) at NT to 570 (545; 599) ms at HT. Potassium plasma level changed spontaneously: decreased during cooling from 4.1 (3.9; 4.8) to 3.7 (3.4; 4.1) mmol/L at HT (P < 0.01), then began to increase and returned to baseline level at HT60 (4.6 (4.4; 5.0) mmol/L, P = NS).
  
  
  CONCLUSIONS
  According to our swine model, MTH does not increase the risk of VF induction by ventricular pacing in healthy hearts. Moreover, when combined with normokalemia, MTH exerts an antiarrhythmic effect despite prolonged QTc interval.
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. jaroslav.kudlicka@vfn.cz.|3rd Department of Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. jaroslav.kudlicka@vfn.cz.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Kudlicka
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. mikulas.mlcek@staff.cuni.cz.
authors.forename: Mikulas
authors.initials: M
authors.lastname: Mlcek
authors.affiliation: 2nd Department of Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. jan.belohlavek@vfn.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Belohlavek
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. pavel.hala@homolka.cz.|Department of Cardiology, Na Homolce Hospital, Roentgenova 2/37, Prague 5, 150 30, Czech Republic. pavel.hala@homolka.cz.
authors.forename: Pavel
authors.initials: P
authors.lastname: Hala
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. stanislav.lacko78@googlemail.com.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Lacko
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. david.janak@vfn.cz.|2nd Department of Surgery, Cardiovascular Surgery, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. david.janak@vfn.cz.
authors.forename: David
authors.initials: D
authors.lastname: Janak
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. stepan.havranek@vfn.cz.|2nd Department of Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. stepan.havranek@vfn.cz.
authors.forename: Stepan
authors.initials: S
authors.lastname: Havranek
authors.affiliation: 3rd Department of Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. jan.malik@vfn.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Malik
authors.affiliation: 3rd Department of Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital, U Nemocnice 2, Prague 2, 128 00, Czech Republic. tomas.janota@vfn.cz.
authors.forename: Tomas
authors.initials: T
authors.lastname: Janota
authors.affiliation: Department of Cardiology, Na Homolce Hospital, Roentgenova 2/37, Prague 5, 150 30, Czech Republic. ostadal.petr@gmail.com.
authors.forename: Petr
authors.initials: P
authors.lastname: Ostadal
authors.affiliation: Department of Cardiology, Na Homolce Hospital, Roentgenova 2/37, Prague 5, 150 30, Czech Republic. petr.neuzil@homolka.cz.
authors.forename: Petr
authors.initials: P
authors.lastname: Neuzil
authors.affiliation: Department of Physiology, First Faculty of Medicine, Charles University in Prague, Albertov 5, Prague 2, 128 00, Czech Republic. otomar.kittnar@staff.cuni.cz.
authors.forename: Otomar
authors.initials: O
authors.lastname: Kittnar
mesh_terms: D000818:Animals; D001831:Body Temperature; D004195:Disease Models, Animal; D055724:Electrophysiological Phenomena; D015199:Extracorporeal Membrane Oxygenation; D005260:Female; D007036:Hypothermia, Induced / Q000009:adverse effects*; D016014:Linear Models; D011188:Potassium / Q000097:blood; D034421:Sus scrofa; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000097:blood / Q000209:etiology* / Q000503:physiopathology*
chemical_list: D011188:Potassium